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In addition to the file `machine.md', a machine description includes a C header file conventionally given the name `machine.h'. This header file defines numerous macros that convey the information about the target machine that does not fit into the scheme of the `.md' file. The file `tm.h' should be a link to `machine.h'. The header file `config.h' includes `tm.h' and most compiler source files include `config.h'.
21.1 Controlling the Compilation Driver, `gcc' Controlling how the driver runs the compilation passes. 21.2 Run-time Target Specification Defining `-m' options like `-m68000' and `-m68020'. 21.3 Defining data structures for per-function information. 21.4 Storage Layout Defining sizes and alignments of data. 21.5 Layout of Source Language Data Types Defining sizes and properties of basic user data types. 21.6 Register Usage Naming and describing the hardware registers. 21.7 Register Classes Defining the classes of hardware registers. 21.8 Stack Layout and Calling Conventions Defining which way the stack grows and by how much. 21.9 Implementing the Varargs Macros Defining the varargs macros. 21.10 Trampolines for Nested Functions Code set up at run time to enter a nested function. 21.11 Implicit Calls to Library Routines Controlling how library routines are implicitly called. 21.12 Addressing Modes Defining addressing modes valid for memory operands. 21.13 Condition Code Status Defining how insns update the condition code. 21.14 Describing Relative Costs of Operations Defining relative costs of different operations. 21.15 Dividing the Output into Sections (Texts, Data, ...) Dividing storage into text, data, and other sections. 21.16 Position Independent Code Macros for position independent code. 21.17 Defining the Output Assembler Language Defining how to write insns and pseudo-ops to output. 21.18 Controlling Debugging Information Format Defining the format of debugging output. 21.19 Cross Compilation and Floating Point Handling floating point for cross-compilers. 21.20 Mode Switching Instructions Insertion of mode-switching instructions. 21.21 Miscellaneous Parameters Everything else.
You can control the compilation driver.
SWITCH_TAKES_ARG (char)
By default, this macro is defined as
DEFAULT_SWITCH_TAKES_ARG, which handles the standard options
properly. You need not define SWITCH_TAKES_ARG unless you
wish to add additional options which take arguments. Any redefinition
should call DEFAULT_SWITCH_TAKES_ARG and then check for
additional options.
WORD_SWITCH_TAKES_ARG (name)
SWITCH_TAKES_ARG is used for multi-character option names.
By default, this macro is defined as
DEFAULT_WORD_SWITCH_TAKES_ARG, which handles the standard options
properly. You need not define WORD_SWITCH_TAKES_ARG unless you
wish to add additional options which take arguments. Any redefinition
should call DEFAULT_WORD_SWITCH_TAKES_ARG and then check for
additional options.
SWITCH_CURTAILS_COMPILATION (char)
By default, this macro is defined as
DEFAULT_SWITCH_CURTAILS_COMPILATION, which handles the standard
options properly. You need not define
SWITCH_CURTAILS_COMPILATION unless you wish to add additional
options which affect the generation of an executable. Any redefinition
should call DEFAULT_SWITCH_CURTAILS_COMPILATION and then check
for additional options.
SWITCHES_NEED_SPACES
If this macro is not defined, the default value is "".
CPP_SPEC
Do not define this macro if it does not need to do anything.
CPLUSPLUS_CPP_SPEC
CPP_SPEC, but is used for C++, rather
than C. If you do not define this macro, then the value of
CPP_SPEC (if any) will be used instead.
NO_BUILTIN_SIZE_TYPE
__SIZE_TYPE__. The macro __SIZE_TYPE__ must then be defined
by CPP_SPEC instead.
This should be defined if SIZE_TYPE depends on target dependent flags
which are not accessible to the preprocessor. Otherwise, it should not
be defined.
NO_BUILTIN_PTRDIFF_TYPE
__PTRDIFF_TYPE__. The macro __PTRDIFF_TYPE__ must then be
defined by CPP_SPEC instead.
This should be defined if PTRDIFF_TYPE depends on target dependent flags
which are not accessible to the preprocessor. Otherwise, it should not
be defined.
NO_BUILTIN_WCHAR_TYPE
__WCHAR_TYPE__. The macro __WCHAR_TYPE__ must then be
defined by CPP_SPEC instead.
This should be defined if WCHAR_TYPE depends on target dependent flags
which are not accessible to the preprocessor. Otherwise, it should not
be defined.
NO_BUILTIN_WINT_TYPE
__WINT_TYPE__. The macro __WINT_TYPE__ must then be
defined by CPP_SPEC instead.
This should be defined if WINT_TYPE depends on target dependent flags
which are not accessible to the preprocessor. Otherwise, it should not
be defined.
SIGNED_CHAR_SPEC
char will be treated as
unsigned char by cc1.
Do not define this macro unless you need to override the default definition.
CC1_SPEC
cc1, cc1plus, f771, and the other language
front ends.
It can also specify how to translate options you give to GCC into options
for GCC to pass to front ends.
Do not define this macro if it does not need to do anything.
CC1PLUS_SPEC
cc1plus. It can also specify how to translate options you
give to GCC into options for GCC to pass to the cc1plus.
Do not define this macro if it does not need to do anything.
Note that everything defined in CC1_SPEC is already passed to
cc1plus so there is no need to duplicate the contents of
CC1_SPEC in CC1PLUS_SPEC.
ASM_SPEC
Do not define this macro if it does not need to do anything.
ASM_FINAL_SPEC
Do not define this macro if it does not need to do anything.
LINK_SPEC
Do not define this macro if it does not need to do anything.
LIB_SPEC
LINK_SPEC. The difference
between the two is that LIB_SPEC is used at the end of the
command given to the linker.
If this macro is not defined, a default is provided that loads the standard C library from the usual place. See `gcc.c'.
LIBGCC_SPEC
LIB_SPEC.
If this macro is not defined, the GCC driver provides a default that passes the string `-lgcc' to the linker.
STARTFILE_SPEC
LINK_SPEC. The
difference between the two is that STARTFILE_SPEC is used at
the very beginning of the command given to the linker.
If this macro is not defined, a default is provided that loads the standard C startup file from the usual place. See `gcc.c'.
ENDFILE_SPEC
LINK_SPEC. The
difference between the two is that ENDFILE_SPEC is used at
the very end of the command given to the linker.
Do not define this macro if it does not need to do anything.
THREAD_MODEL_SPEC
-v will print the thread model GCC was configured to use.
However, this doesn't work on platforms that are multilibbed on thread
models, such as AIX 4.3. On such platforms, define
THREAD_MODEL_SPEC such that it evaluates to a string without
blanks that names one of the recognized thread models. %*, the
default value of this macro, will expand to the value of
thread_file set in `config.gcc'.
EXTRA_SPECS
CC1_SPEC.
The definition should be an initializer for an array of structures, containing a string constant, that defines the specification name, and a string constant that provides the specification.
Do not define this macro if it does not need to do anything.
EXTRA_SPECS is useful when an architecture contains several
related targets, which have various ..._SPECS which are similar
to each other, and the maintainer would like one central place to keep
these definitions.
For example, the PowerPC System V.4 targets use EXTRA_SPECS to
define either _CALL_SYSV when the System V calling sequence is
used or _CALL_AIX when the older AIX-based calling sequence is
used.
The `config/rs6000/rs6000.h' target file defines:
#define EXTRA_SPECS \
{ "cpp_sysv_default", CPP_SYSV_DEFAULT },
#define CPP_SYS_DEFAULT ""
|
The `config/rs6000/sysv.h' target file defines:
#undef CPP_SPEC
#define CPP_SPEC \
"%{posix: -D_POSIX_SOURCE } \
%{mcall-sysv: -D_CALL_SYSV } %{mcall-aix: -D_CALL_AIX } \
%{!mcall-sysv: %{!mcall-aix: %(cpp_sysv_default) }} \
%{msoft-float: -D_SOFT_FLOAT} %{mcpu=403: -D_SOFT_FLOAT}"
#undef CPP_SYSV_DEFAULT
#define CPP_SYSV_DEFAULT "-D_CALL_SYSV"
|
while the `config/rs6000/eabiaix.h' target file defines
CPP_SYSV_DEFAULT as:
#undef CPP_SYSV_DEFAULT #define CPP_SYSV_DEFAULT "-D_CALL_AIX" |
LINK_LIBGCC_SPECIAL
LINK_LIBGCC_SPECIAL_1
LINK_LIBGCC_SPECIAL, except that it does
not affect `-L' options.
LINK_COMMAND_SPEC
LINK_ELIMINATE_DUPLICATE_LDIRECTORIES
MULTILIB_DEFAULTS
MULTILIB_OPTIONS.
Do not define this macro if MULTILIB_OPTIONS is not defined in
the target makefile fragment or if none of the options listed in
MULTILIB_OPTIONS are set by default.
See section 23.1 The Target Makefile Fragment.
RELATIVE_PREFIX_NOT_LINKDIR
gcc that it should only translate
a `-B' prefix into a `-L' linker option if the prefix
indicates an absolute file name.
STANDARD_EXEC_PREFIX
MD_EXEC_PREFIX
STANDARD_EXEC_PREFIX. MD_EXEC_PREFIX is not searched
when the `-b' option is used, or the compiler is built as a cross
compiler. If you define MD_EXEC_PREFIX, then be sure to add it
to the list of directories used to find the assembler in `configure.in'.
STANDARD_STARTFILE_PREFIX
MD_STARTFILE_PREFIX
MD_EXEC_PREFIX is not searched when the
`-b' option is used, or when the compiler is built as a cross
compiler.
MD_STARTFILE_PREFIX_1
INIT_ENVIRONMENT
putenv to
initialize the necessary environment variables.
LOCAL_INCLUDE_DIR
LOCAL_INCLUDE_DIR
comes before SYSTEM_INCLUDE_DIR in the search order.
Cross compilers do not use this macro and do not search either `/usr/local/include' or its replacement.
MODIFY_TARGET_NAME
For each switch, you can include a string to be appended to the first
part of the configuration name or a string to be deleted from the
configuration name, if present. The definition should be an initializer
for an array of structures. Each array element should have three
elements: the switch name (a string constant, including the initial
dash), one of the enumeration codes ADD or DELETE to
indicate whether the string should be inserted or deleted, and the string
to be inserted or deleted (a string constant).
For example, on a machine where `64' at the end of the configuration name denotes a 64-bit target and you want the `-32' and `-64' switches to select between 32- and 64-bit targets, you would code
#define MODIFY_TARGET_NAME \
{ { "-32", DELETE, "64"}, \
{"-64", ADD, "64"}}
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SYSTEM_INCLUDE_DIR
SYSTEM_INCLUDE_DIR comes before
STANDARD_INCLUDE_DIR in the search order.
Cross compilers do not use this macro and do not search the directory specified.
STANDARD_INCLUDE_DIR
Cross compilers do not use this macro and do not search either `/usr/include' or its replacement.
STANDARD_INCLUDE_COMPONENT
STANDARD_INCLUDE_DIR.
See INCLUDE_DEFAULTS, below, for the description of components.
If you do not define this macro, no component is used.
INCLUDE_DEFAULTS
GCC_INCLUDE_DIR, LOCAL_INCLUDE_DIR,
SYSTEM_INCLUDE_DIR, GPLUSPLUS_INCLUDE_DIR, and
STANDARD_INCLUDE_DIR. In addition, GPLUSPLUS_INCLUDE_DIR
and GCC_INCLUDE_DIR are defined automatically by `Makefile',
and specify private search areas for GCC. The directory
GPLUSPLUS_INCLUDE_DIR is used only for C++ programs.
The definition should be an initializer for an array of structures.
Each array element should have four elements: the directory name (a
string constant), the component name (also a string constant), a flag
for C++-only directories,
and a flag showing that the includes in the directory don't need to be
wrapped in extern `C' when compiling C++. Mark the end of
the array with a null element.
The component name denotes what GNU package the include file is part of, if any, in all upper-case letters. For example, it might be `GCC' or `BINUTILS'. If the package is part of a vendor-supplied operating system, code the component name as `0'.
For example, here is the definition used for VAX/VMS:
#define INCLUDE_DEFAULTS \
{ \
{ "GNU_GXX_INCLUDE:", "G++", 1, 1}, \
{ "GNU_CC_INCLUDE:", "GCC", 0, 0}, \
{ "SYS$SYSROOT:[SYSLIB.]", 0, 0, 0}, \
{ ".", 0, 0, 0}, \
{ 0, 0, 0, 0} \
}
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Here is the order of prefixes tried for exec files:
GCC_EXEC_PREFIX, if any.
COMPILER_PATH.
STANDARD_EXEC_PREFIX.
MD_EXEC_PREFIX, if any.
Here is the order of prefixes tried for startfiles:
GCC_EXEC_PREFIX, if any.
LIBRARY_PATH
(or port-specific name; native only, cross compilers do not use this).
STANDARD_EXEC_PREFIX.
MD_EXEC_PREFIX, if any.
MD_STARTFILE_PREFIX, if any.
STANDARD_STARTFILE_PREFIX.
Here are run-time target specifications.
CPP_PREDEFINES
In addition, a parallel set of macros are predefined, whose names are made by appending `__' at the beginning and at the end. These `__' macros are permitted by the ISO standard, so they are predefined regardless of whether `-ansi' or a `-std' option is specified.
For example, on the Sun, one can use the following value:
"-Dmc68000 -Dsun -Dunix" |
The result is to define the macros __mc68000__, __sun__
and __unix__ unconditionally, and the macros mc68000,
sun and unix provided `-ansi' is not specified.
extern int target_flags;
TARGET_...
TARGET_68020 that tests a bit in
target_flags.
Define a macro TARGET_featurename for each such option.
Its definition should test a bit in target_flags. It is
recommended that a helper macro TARGET_MASK_featurename
is defined for each bit-value to test, and used in
TARGET_featurename and TARGET_SWITCHES. For
example:
#define TARGET_MASK_68020 1 #define TARGET_68020 (target_flags & TARGET_MASK_68020) |
One place where these macros are used is in the condition-expressions
of instruction patterns. Note how TARGET_68020 appears
frequently in the 68000 machine description file, `m68k.md'.
Another place they are used is in the definitions of the other
macros in the `machine.h' file.
TARGET_SWITCHES
target_flags. Its definition is an initializer
with a subgrouping for each command option.
Each subgrouping contains a string constant, that defines the option
name, a number, which contains the bits to set in
target_flags, and a second string which is the description
displayed by `--help'. If the number is negative then the bits specified
by the number are cleared instead of being set. If the description
string is present but empty, then no help information will be displayed
for that option, but it will not count as an undocumented option. The
actual option name is made by appending `-m' to the specified name.
Non-empty description strings should be marked with N_(...) for
xgettext. In addition to the description for `--help',
more detailed documentation for each option should be added to
`invoke.texi'.
One of the subgroupings should have a null string. The number in
this grouping is the default value for target_flags. Any
target options act starting with that value.
Here is an example which defines `-m68000' and `-m68020' with opposite meanings, and picks the latter as the default:
#define TARGET_SWITCHES \
{ { "68020", TARGET_MASK_68020, "" }, \
{ "68000", -TARGET_MASK_68020, \
N_("Compile for the 68000") }, \
{ "", TARGET_MASK_68020, "" }}
|
TARGET_OPTIONS
TARGET_SWITCHES but defines names of command
options that have values. Its definition is an initializer with a
subgrouping for each command option.
Each subgrouping contains a string constant, that defines the fixed part
of the option name, the address of a variable, and a description string
(which should again be marked with N_(...)).
The variable, type char *, is set to the variable part of the
given option if the fixed part matches. The actual option name is made
by appending `-m' to the specified name. Again, each option should
also be documented in `invoke.texi'.
Here is an example which defines `-mshort-data-number'. If the
given option is `-mshort-data-512', the variable m88k_short_data
will be set to the string "512".
extern char *m88k_short_data;
#define TARGET_OPTIONS \
{ { "short-data-", &m88k_short_data, \
N_("Specify the size of the short data section") } }
|
TARGET_VERSION
stderr a string
describing the particular machine description choice. Every machine
description should define TARGET_VERSION. For example:
#ifdef MOTOROLA #define TARGET_VERSION \ fprintf (stderr, " (68k, Motorola syntax)"); #else #define TARGET_VERSION \ fprintf (stderr, " (68k, MIT syntax)"); #endif |
OVERRIDE_OPTIONS
OVERRIDE_OPTIONS to take account of this. This macro, if
defined, is executed once just after all the command options have been
parsed.
Don't use this macro to turn on various extra optimizations for
`-O'. That is what OPTIMIZATION_OPTIONS is for.
OPTIMIZATION_OPTIONS (level, size)
level is the optimization level specified; 2 if `-O2' is specified, 1 if `-O' is specified, and 0 if neither is specified.
size is nonzero if `-Os' is specified and zero otherwise.
You should not use this macro to change options that are not machine-specific. These should uniformly selected by the same optimization level on all supported machines. Use this macro to enable machine-specific optimizations.
Do not examine write_symbols in
this macro! The debugging options are not supposed to alter the
generated code.
CAN_DEBUG_WITHOUT_FP
If the target needs to store information on a per-function basis, GCC provides a macro and a couple of variables to allow this. Note, just using statics to store the information is a bad idea, since GCC supports nested functions, so you can be halfway through encoding one function when another one comes along.
GCC defines a data structure called struct function which
contains all of the data specific to an individual function. This
structure contains a field called machine whose type is
struct machine_function *, which can be used by targets to point
to their own specific data.
If a target needs per-function specific data it should define the type
struct machine_function and also the macro
INIT_EXPANDERS. This macro should be used to initialise some or
all of the function pointers init_machine_status,
free_machine_status and mark_machine_status. These
pointers are explained below.
One typical use of per-function, target specific data is to create an
RTX to hold the register containing the function's return address. This
RTX can then be used to implement the __builtin_return_address
function, for level 0.
Note--earlier implementations of GCC used a single data area to hold
all of the per-function information. Thus when processing of a nested
function began the old per-function data had to be pushed onto a
stack, and when the processing was finished, it had to be popped off the
stack. GCC used to provide function pointers called
save_machine_status and restore_machine_status to handle
the saving and restoring of the target specific information. Since the
single data area approach is no longer used, these pointers are no
longer supported.
The macro and function pointers are described below.
INIT_EXPANDERS
init_machine_status
void (*)(struct function *) function pointer. If this
pointer is non-NULL it will be called once per function, before function
compilation starts, in order to allow the target to perform any target
specific initialisation of the struct function structure. It is
intended that this would be used to initialise the machine of
that structure.
free_machine_status
void (*)(struct function *) function pointer. If this
pointer is non-NULL it will be called once per function, after the
function has been compiled, in order to allow any memory allocated
during the init_machine_status function call to be freed.
mark_machine_status
void (*)(struct function *) function pointer. If this
pointer is non-NULL it will be called once per function in order to mark
any data items in the struct machine_function structure which
need garbage collection.
Note that the definitions of the macros in this table which are sizes or
alignments measured in bits do not need to be constant. They can be C
expressions that refer to static variables, such as the target_flags.
See section 21.2 Run-time Target Specification.
BITS_BIG_ENDIAN
This macro does not affect the way structure fields are packed into
bytes or words; that is controlled by BYTES_BIG_ENDIAN.
BYTES_BIG_ENDIAN
WORDS_BIG_ENDIAN
LIBGCC2_WORDS_BIG_ENDIAN
WORDS_BIG_ENDIAN is not constant. This must be a
constant value with the same meaning as WORDS_BIG_ENDIAN, which will be
used only when compiling `libgcc2.c'. Typically the value will be set
based on preprocessor defines.
FLOAT_WORDS_BIG_ENDIAN
DFmode, XFmode or
TFmode floating point numbers are stored in memory with the word
containing the sign bit at the lowest address; otherwise define it to
have the value 0. This macro need not be a constant.
You need not define this macro if the ordering is the same as for multi-word integers.
BITS_PER_UNIT
BITS_PER_WORD
MAX_BITS_PER_WORD
BITS_PER_WORD. Otherwise, it is the constant value that is the
largest value that BITS_PER_WORD can have at run-time.
UNITS_PER_WORD
MIN_UNITS_PER_WORD
UNITS_PER_WORD. Otherwise, it is the constant value that is the
smallest value that UNITS_PER_WORD can have at run-time.
POINTER_SIZE
Pmode. If it is not equal to the width of Pmode,
you must define POINTERS_EXTEND_UNSIGNED.
POINTERS_EXTEND_UNSIGNED
POINTER_SIZE bits wide to Pmode are to
be zero-extended and zero if they are to be sign-extended.
You need not define this macro if the POINTER_SIZE is equal
to the width of Pmode.
PROMOTE_MODE (m, unsignedp, type)
On most RISC machines, which only have operations that operate on a full
register, define this macro to set m to word_mode if
m is an integer mode narrower than BITS_PER_WORD. In most
cases, only integer modes should be widened because wider-precision
floating-point operations are usually more expensive than their narrower
counterparts.
For most machines, the macro definition does not change unsignedp. However, some machines, have instructions that preferentially handle either signed or unsigned quantities of certain modes. For example, on the DEC Alpha, 32-bit loads from memory and 32-bit add instructions sign-extend the result to 64 bits. On such machines, set unsignedp according to which kind of extension is more efficient.
Do not define this macro if it would never modify m.
PROMOTE_FUNCTION_ARGS
PROMOTE_MODE
should also be done for outgoing function arguments.
PROMOTE_FUNCTION_RETURN
PROMOTE_MODE
should also be done for the return value of functions.
If this macro is defined, FUNCTION_VALUE must perform the same
promotions done by PROMOTE_MODE.
PROMOTE_FOR_CALL_ONLY
PROMOTE_MODE
should only be performed for outgoing function arguments or
function return values, as specified by PROMOTE_FUNCTION_ARGS
and PROMOTE_FUNCTION_RETURN, respectively.
PARM_BOUNDARY
STACK_BOUNDARY
PREFERRED_STACK_BOUNDARY is not defined.
PREFERRED_STACK_BOUNDARY
STACK_BOUNDARY is
also defined, this macro must evaluate to a value equal to or larger
than STACK_BOUNDARY.
FORCE_PREFERRED_STACK_BOUNDARY_IN_MAIN
PREFERRED_STACK_BOUNDARY is
not guaranteed by the runtime and we should emit code to align the stack
at the beginning of main.
If PUSH_ROUNDING is not defined, the stack will always be aligned
to the specified boundary. If PUSH_ROUNDING is defined and specifies
a less strict alignment than PREFERRED_STACK_BOUNDARY, the stack may
be momentarily unaligned while pushing arguments.
FUNCTION_BOUNDARY
BIGGEST_ALIGNMENT
MINIMUM_ATOMIC_ALIGNMENT
BITS_PER_UNIT, but may be larger
on machines that don't have byte or half-word store operations.
BIGGEST_FIELD_ALIGNMENT
BIGGEST_ALIGNMENT for
structure and union fields only, unless the field alignment has been set
by the __attribute__ ((aligned (n))) construct.
ADJUST_FIELD_ALIGN (field, computed)
BIGGEST_ALIGNMENT or
BIGGEST_FIELD_ALIGNMENT, if defined, for structure fields only.
MAX_OFILE_ALIGNMENT
__attribute__ ((aligned (n))) construct. If not defined,
the default value is BIGGEST_ALIGNMENT.
DATA_ALIGNMENT (type, basic-align)
If this macro is not defined, then basic-align is used.
One use of this macro is to increase alignment of medium-size data to
make it all fit in fewer cache lines. Another is to cause character
arrays to be word-aligned so that strcpy calls that copy
constants to character arrays can be done inline.
CONSTANT_ALIGNMENT (constant, basic-align)
If this macro is not defined, then basic-align is used.
The typical use of this macro is to increase alignment for string
constants to be word aligned so that strcpy calls that copy
constants can be done inline.
LOCAL_ALIGNMENT (type, basic-align)
If this macro is not defined, then basic-align is used.
One use of this macro is to increase alignment of medium-size data to make it all fit in fewer cache lines.
EMPTY_FIELD_BOUNDARY
int : 0;.
Note that PCC_BITFIELD_TYPE_MATTERS also affects the alignment
that results from an empty field.
STRUCTURE_SIZE_BOUNDARY
If you do not define this macro, the default is the same as
BITS_PER_UNIT.
STRICT_ALIGNMENT
PCC_BITFIELD_TYPE_MATTERS
The behavior is that the type written for a bit-field (int,
short, or other integer type) imposes an alignment for the
entire structure, as if the structure really did contain an ordinary
field of that type. In addition, the bit-field is placed within the
structure so that it would fit within such a field, not crossing a
boundary for it.
Thus, on most machines, a bit-field whose type is written as int
would not cross a four-byte boundary, and would force four-byte
alignment for the whole structure. (The alignment used may not be four
bytes; it is controlled by the other alignment parameters.)
If the macro is defined, its definition should be a C expression; a nonzero value for the expression enables this behavior.
Note that if this macro is not defined, or its value is zero, some bit-fields may cross more than one alignment boundary. The compiler can support such references if there are `insv', `extv', and `extzv' insns that can directly reference memory.
The other known way of making bit-fields work is to define
STRUCTURE_SIZE_BOUNDARY as large as BIGGEST_ALIGNMENT.
Then every structure can be accessed with fullwords.
Unless the machine has bit-field instructions or you define
STRUCTURE_SIZE_BOUNDARY that way, you must define
PCC_BITFIELD_TYPE_MATTERS to have a nonzero value.
If your aim is to make GCC use the same conventions for laying out bit-fields as are used by another compiler, here is how to investigate what the other compiler does. Compile and run this program:
struct foo1
{
char x;
char :0;
char y;
};
struct foo2
{
char x;
int :0;
char y;
};
main ()
{
printf ("Size of foo1 is %d\n",
sizeof (struct foo1));
printf ("Size of foo2 is %d\n",
sizeof (struct foo2));
exit (0);
}
|
If this prints 2 and 5, then the compiler's behavior is what you would
get from PCC_BITFIELD_TYPE_MATTERS.
BITFIELD_NBYTES_LIMITED
STRUCT_FORCE_BLK (field)
BLKMODE.
Normally, this is not needed. See the file `c4x.h' for an example of how to use this macro to prevent a structure having a floating point field from being accessed in an integer mode.
ROUND_TYPE_SIZE (type, computed, specified)
The default is to round computed up to a multiple of specified.
ROUND_TYPE_SIZE_UNIT (type, computed, specified)
ROUND_TYPE_SIZE, but sizes and alignments are
specified in units (bytes). If you define ROUND_TYPE_SIZE,
you must also define this macro and they must be defined consistently
with each other.
ROUND_TYPE_ALIGN (type, computed, specified)
The default is to use specified if it is larger; otherwise, use
the smaller of computed and BIGGEST_ALIGNMENT
MAX_FIXED_MODE_SIZE
GET_MODE_BITSIZE
(DImode) is assumed.
VECTOR_MODE_SUPPORTED_P(mode)
STACK_SAVEAREA_MODE (save_level)
enum machine_mode that
specifies the mode of the save area operand of a
save_stack_level named pattern (see section 20.8 Standard Pattern Names For Generation).
save_level is one of SAVE_BLOCK, SAVE_FUNCTION, or
SAVE_NONLOCAL and selects which of the three named patterns is
having its mode specified.
You need not define this macro if it always returns Pmode. You
would most commonly define this macro if the
save_stack_level patterns need to support both a 32- and a
64-bit mode.
STACK_SIZE_MODE
enum machine_mode that
specifies the mode of the size increment operand of an
allocate_stack named pattern (see section 20.8 Standard Pattern Names For Generation).
You need not define this macro if it always returns word_mode.
You would most commonly define this macro if the allocate_stack
pattern needs to support both a 32- and a 64-bit mode.
CHECK_FLOAT_VALUE (mode, value, overflow)
double) for mode mode. This means that you check whether
value fits within the possible range of values for mode
mode on this target machine. The mode mode is always
a mode of class MODE_FLOAT. overflow is nonzero if
the value is already known to be out of range.
If value is not valid or if overflow is nonzero, you should set overflow to 1 and then assign some valid value to value. Allowing an invalid value to go through the compiler can produce incorrect assembler code which may even cause Unix assemblers to crash.
This macro need not be defined if there is no work for it to do.
TARGET_FLOAT_FORMAT
IEEE_FLOAT_FORMAT
VAX_FLOAT_FORMAT
IBM_FLOAT_FORMAT
C4X_FLOAT_FORMAT
UNKNOWN_FLOAT_FORMAT
The value of this macro is compared with HOST_FLOAT_FORMAT
(see section 22. The Configuration File) to determine whether the target machine has the same
format as the host machine. If any other formats are actually in use on
supported machines, new codes should be defined for them.
The ordering of the component words of floating point values stored in
memory is controlled by FLOAT_WORDS_BIG_ENDIAN for the target
machine and HOST_FLOAT_WORDS_BIG_ENDIAN for the host.
DEFAULT_VTABLE_THUNKS
DEFAULT_VTABLE_THUNKS is 0, GCC uses the traditional
implementation by default. The "thunk" implementation is more efficient
(especially if you have provided an implementation of
ASM_OUTPUT_MI_THUNK, see 21.8.10 Function Entry and Exit), but is not binary
compatible with code compiled using the traditional implementation.
If you are writing a new port, define DEFAULT_VTABLE_THUNKS to 1.
If you do not define this macro, the default for `-fvtable-thunk' is 0.
These macros define the sizes and other characteristics of the standard basic data types used in programs being compiled. Unlike the macros in the previous section, these apply to specific features of C and related languages, rather than to fundamental aspects of storage layout.
INT_TYPE_SIZE
int on the
target machine. If you don't define this, the default is one word.
MAX_INT_TYPE_SIZE
int on the target
machine. If this is undefined, the default is INT_TYPE_SIZE.
Otherwise, it is the constant value that is the largest value that
INT_TYPE_SIZE can have at run-time. This is used in cpp.
SHORT_TYPE_SIZE
short on the
target machine. If you don't define this, the default is half a word.
(If this would be less than one storage unit, it is rounded up to one
unit.)
LONG_TYPE_SIZE
long on the
target machine. If you don't define this, the default is one word.
MAX_LONG_TYPE_SIZE
long on the
target machine. If this is undefined, the default is
LONG_TYPE_SIZE. Otherwise, it is the constant value that is the
largest value that LONG_TYPE_SIZE can have at run-time. This is
used in cpp.
LONG_LONG_TYPE_SIZE
long long on the
target machine. If you don't define this, the default is two
words. If you want to support GNU Ada on your machine, the value of this
macro must be at least 64.
CHAR_TYPE_SIZE
char on the
target machine. If you don't define this, the default is
BITS_PER_UNIT.
MAX_CHAR_TYPE_SIZE
char on the
target machine. If this is undefined, the default is
CHAR_TYPE_SIZE. Otherwise, it is the constant value that is the
largest value that CHAR_TYPE_SIZE can have at run-time. This is
used in cpp.
BOOL_TYPE_SIZE
bool on the
target machine. If you don't define this, the default is
CHAR_TYPE_SIZE.
FLOAT_TYPE_SIZE
float on the
target machine. If you don't define this, the default is one word.
DOUBLE_TYPE_SIZE
double on the
target machine. If you don't define this, the default is two
words.
LONG_DOUBLE_TYPE_SIZE
long double on
the target machine. If you don't define this, the default is two
words.
WIDEST_HARDWARE_FP_SIZE
LONG_DOUBLE_TYPE_SIZE.
If you do not define this macro, the value of LONG_DOUBLE_TYPE_SIZE
is the default.
DEFAULT_SIGNED_CHAR
char should be signed or unsigned by default. The user can
always override this default with the options `-fsigned-char'
and `-funsigned-char'.
DEFAULT_SHORT_ENUMS
enum type
only as many bytes as it takes to represent the range of possible values
of that type. A nonzero value means to do that; a zero value means all
enum types should be allocated like int.
If you don't define the macro, the default is 0.
SIZE_TYPE
size_t is defined using the
contents of the string.
The string can contain more than one keyword. If so, separate them with
spaces, and write first any length keyword, then unsigned if
appropriate, and finally int. The string must exactly match one
of the data type names defined in the function
init_decl_processing in the file `c-decl.c'. You may not
omit int or change the order--that would cause the compiler to
crash on startup.
If you don't define this macro, the default is "long unsigned
int".
PTRDIFF_TYPE
ptrdiff_t is defined using the contents of the string. See
SIZE_TYPE above for more information.
If you don't define this macro, the default is "long int".
WCHAR_TYPE
wchar_t is defined using
the contents of the string. See SIZE_TYPE above for more
information.
If you don't define this macro, the default is "int".
WCHAR_TYPE_SIZE
cpp, which cannot make use of
WCHAR_TYPE.
MAX_WCHAR_TYPE_SIZE
WCHAR_TYPE_SIZE. Otherwise, it is the constant value that is the
largest value that WCHAR_TYPE_SIZE can have at run-time. This is
used in cpp.
WINT_TYPE
printf and returned from
getwc. The typedef name wint_t is defined using the
contents of the string. See SIZE_TYPE above for more
information.
If you don't define this macro, the default is "unsigned int".
INTMAX_TYPE
intmax_t is defined using the contents of the
string. See SIZE_TYPE above for more information.
If you don't define this macro, the default is the first of
"int", "long int", or "long long int" that has as
much precision as long long int.
UINTMAX_TYPE
uintmax_t is defined using the contents
of the string. See SIZE_TYPE above for more information.
If you don't define this macro, the default is the first of
"unsigned int", "long unsigned int", or "long long
unsigned int" that has as much precision as long long unsigned
int.
OBJC_INT_SELECTORS
int.
If this macro is not defined, then selectors should have the type
struct objc_selector *.
OBJC_SELECTORS_WITHOUT_LABELS
On certain machines, it is important to have a separate label for each selector because this enables the linker to eliminate duplicate selectors.
TARGET_PTRMEMFUNC_VBIT_LOCATION
struct {
union {
void (*fn)();
ptrdiff_t vtable_index;
};
ptrdiff_t delta;
};
|
The C++ compiler must use one bit to indicate whether the function that
will be called through a pointer-to-member-function is virtual.
Normally, we assume that the low-order bit of a function pointer must
always be zero. Then, by ensuring that the vtable_index is odd, we can
distinguish which variant of the union is in use. But, on some
platforms function pointers can be odd, and so this doesn't work. In
that case, we use the low-order bit of the delta field, and shift
the remainder of the delta field to the left.
GCC will automatically make the right selection about where to store
this bit using the FUNCTION_BOUNDARY setting for your platform.
However, some platforms such as ARM/Thumb have FUNCTION_BOUNDARY
set such that functions always start at even addresses, but the lowest
bit of pointers to functions indicate whether the function at that
address is in ARM or Thumb mode. If this is the case of your
architecture, you should define this macro to
ptrmemfunc_vbit_in_delta.
In general, you should not have to define this macro. On architectures
in which function addresses are always even, according to
FUNCTION_BOUNDARY, GCC will automatically define this macro to
ptrmemfunc_vbit_in_pfn.
TARGET_BELL
TARGET_BS
TARGET_TAB
TARGET_NEWLINE
TARGET_VT
TARGET_FF
TARGET_CR
This section explains how to describe what registers the target machine has, and how (in general) they can be used.
The description of which registers a specific instruction can use is done with register classes; see 21.7 Register Classes. For information on using registers to access a stack frame, see 21.8.3 Registers That Address the Stack Frame. For passing values in registers, see 21.8.6 Passing Arguments in Registers. For returning values in registers, see 21.8.7 How Scalar Function Values Are Returned.
21.6.1 Basic Characteristics of Registers Number and kinds of registers. 21.6.2 Order of Allocation of Registers Order in which registers are allocated. 21.6.3 How Values Fit in Registers What kinds of values each reg can hold. 21.6.4 Handling Leaf Functions Renumbering registers for leaf functions. 21.6.5 Registers That Form a Stack Handling a register stack such as 80387.
Registers have various characteristics.
FIRST_PSEUDO_REGISTER
FIRST_PSEUDO_REGISTER-1; thus, the first
pseudo register's number really is assigned the number
FIRST_PSEUDO_REGISTER.
FIXED_REGISTERS
This information is expressed as a sequence of numbers, separated by commas and surrounded by braces. The nth number is 1 if register n is fixed, 0 otherwise.
The table initialized from this macro, and the table initialized by
the following one, may be overridden at run time either automatically,
by the actions of the macro CONDITIONAL_REGISTER_USAGE, or by
the user with the command options `-ffixed-reg',
`-fcall-used-reg' and `-fcall-saved-reg'.
CALL_USED_REGISTERS
FIXED_REGISTERS but has 1 for each register that is
clobbered (in general) by function calls as well as for fixed
registers. This macro therefore identifies the registers that are not
available for general allocation of values that must live across
function calls.
If a register has 0 in CALL_USED_REGISTERS, the compiler
automatically saves it on function entry and restores it on function
exit, if the register is used within the function.
HARD_REGNO_CALL_PART_CLOBBERED (regno, mode)
CONDITIONAL_REGISTER_USAGE
fixed_regs, call_used_regs, global_regs,
(these three are of type char []), reg_names (of type
const char * []) and reg_class_contents (of type
HARD_REG_SET).
Before the macro is called fixed_regs, call_used_regs
reg_class_contents and reg_names have been initialized
from FIXED_REGISTERS, CALL_USED_REGISTERS,
REG_CLASS_CONTENTS and REGISTER_NAMES, respectively,
global_regs has been cleared, and any `-ffixed-reg',
`-fcall-used-reg' and `-fcall-saved-reg' command
options have been applied.
This is necessary in case the fixed or call-clobbered registers depend on target flags.
You need not define this macro if it has no work to do.
If the usage of an entire class of registers depends on the target
flags, you may indicate this to GCC by using this macro to modify
fixed_regs and call_used_regs to 1 for each of the
registers in the classes which should not be used by GCC. Also define
the macro REG_CLASS_FROM_LETTER to return NO_REGS if it
is called with a letter for a class that shouldn't be used.
(However, if this class is not included in GENERAL_REGS and all
of the insn patterns whose constraints permit this class are
controlled by target switches, then GCC will automatically avoid using
these registers when the target switches are opposed to them.)
NON_SAVING_SETJMP
setjmp and related functions fail to save the registers, or that
longjmp fails to restore them. To compensate, the compiler
avoids putting variables in registers in functions that use
setjmp.
INCOMING_REGNO (out)
OUTGOING_REGNO (in)
LOCAL_REGNO (regno)
Registers are allocated in order.
REG_ALLOC_ORDER
If this macro is not defined, registers are used lowest numbered first (all else being equal).
One use of this macro is on machines where the highest numbered
registers must always be saved and the save-multiple-registers
instruction supports only sequences of consecutive registers. On such
machines, define REG_ALLOC_ORDER to be an initializer that lists
the highest numbered allocable register first.
ORDER_REGS_FOR_LOCAL_ALLOC
Store the desired register order in the array reg_alloc_order.
Element 0 should be the register to allocate first; element 1, the next
register; and so on.
The macro body should not assume anything about the contents of
reg_alloc_order before execution of the macro.
On most machines, it is not necessary to define this macro.
This section discusses the macros that describe which kinds of values (specifically, which machine modes) each register can hold, and how many consecutive registers are needed for a given mode.
HARD_REGNO_NREGS (regno, mode)
On a machine where all registers are exactly one word, a suitable definition of this macro is
#define HARD_REGNO_NREGS(REGNO, MODE) \
((GET_MODE_SIZE (MODE) + UNITS_PER_WORD - 1) \
/ UNITS_PER_WORD)
|
ALTER_HARD_SUBREG (tgt_mode, word, src_mode, regno)
(subreg:tgt_mode (reg:src_mode regno) word) |
This may be needed if the target machine has mixed sized big-endian registers, like Sparc v9.
HARD_REGNO_MODE_OK (regno, mode)
#define HARD_REGNO_MODE_OK(REGNO, MODE) 1 |
You need not include code to check for the numbers of fixed registers, because the allocation mechanism considers them to be always occupied.
On some machines, double-precision values must be kept in even/odd register pairs. You can implement that by defining this macro to reject odd register numbers for such modes.
The minimum requirement for a mode to be OK in a register is that the `movmode' instruction pattern support moves between the register and other hard register in the same class and that moving a value into the register and back out not alter it.
Since the same instruction used to move word_mode will work for
all narrower integer modes, it is not necessary on any machine for
HARD_REGNO_MODE_OK to distinguish between these modes, provided
you define patterns `movhi', etc., to take advantage of this. This
is useful because of the interaction between HARD_REGNO_MODE_OK
and MODES_TIEABLE_P; it is very desirable for all integer modes
to be tieable.
Many machines have special registers for floating point arithmetic. Often people assume that floating point machine modes are allowed only in floating point registers. This is not true. Any registers that can hold integers can safely hold a floating point machine mode, whether or not floating arithmetic can be done on it in those registers. Integer move instructions can be used to move the values.
On some machines, though, the converse is true: fixed-point machine
modes may not go in floating registers. This is true if the floating
registers normalize any value stored in them, because storing a
non-floating value there would garble it. In this case,
HARD_REGNO_MODE_OK should reject fixed-point machine modes in
floating registers. But if the floating registers do not automatically
normalize, if you can store any bit pattern in one and retrieve it
unchanged without a trap, then any machine mode may go in a floating
register, so you can define this macro to say so.
The primary significance of special floating registers is rather that
they are the registers acceptable in floating point arithmetic
instructions. However, this is of no concern to
HARD_REGNO_MODE_OK. You handle it by writing the proper
constraints for those instructions.
On some machines, the floating registers are especially slow to access,
so that it is better to store a value in a stack frame than in such a
register if floating point arithmetic is not being done. As long as the
floating registers are not in class GENERAL_REGS, they will not
be used unless some pattern's constraint asks for one.
MODES_TIEABLE_P (mode1, mode2)
If HARD_REGNO_MODE_OK (r, mode1) and
HARD_REGNO_MODE_OK (r, mode2) are always the same for
any r, then MODES_TIEABLE_P (mode1, mode2)
should be nonzero. If they differ for any r, you should define
this macro to return zero unless some other mechanism ensures the
accessibility of the value in a narrower mode.
You should define this macro to return nonzero in as many cases as possible since doing so will allow GCC to perform better register allocation.
AVOID_CCMODE_COPIES
CCmode
registers. You should only define this macro if support for copying to/from
CCmode is incomplete.
On some machines, a leaf function (i.e., one which makes no calls) can run more efficiently if it does not make its own register window. Often this means it is required to receive its arguments in the registers where they are passed by the caller, instead of the registers where they would normally arrive.
The special treatment for leaf functions generally applies only when other conditions are met; for example, often they may use only those registers for its own variables and temporaries. We use the term "leaf function" to mean a function that is suitable for this special handling, so that functions with no calls are not necessarily "leaf functions".
GCC assigns register numbers before it knows whether the function is suitable for leaf function treatment. So it needs to renumber the registers in order to output a leaf function. The following macros accomplish this.
LEAF_REGISTERS
If leaf function treatment involves renumbering the registers, then the registers marked here should be the ones before renumbering--those that GCC would ordinarily allocate. The registers which will actually be used in the assembler code, after renumbering, should not be marked with 1 in this vector.
Define this macro only if the target machine offers a way to optimize the treatment of leaf functions.
LEAF_REG_REMAP (regno)
If regno is a register number which should not appear in a leaf function before renumbering, then the expression should yield -1, which will cause the compiler to abort.
Define this macro only if the target machine offers a way to optimize the treatment of leaf functions, and registers need to be renumbered to do this.
Normally, FUNCTION_PROLOGUE and FUNCTION_EPILOGUE must
treat leaf functions specially. They can test the C variable
current_function_is_leaf which is nonzero for leaf functions.
current_function_is_leaf is set prior to local register allocation
and is valid for the remaining compiler passes. They can also test the C
variable current_function_uses_only_leaf_regs which is nonzero for
leaf functions which only use leaf registers.
current_function_uses_only_leaf_regs is valid after reload and is
only useful if LEAF_REGISTERS is defined.
There are special features to handle computers where some of the "registers" form a stack, as in the 80387 coprocessor for the 80386. Stack registers are normally written by pushing onto the stack, and are numbered relative to the top of the stack.
Currently, GCC can only handle one group of stack-like registers, and they must be consecutively numbered.
STACK_REGS
FIRST_STACK_REG
LAST_STACK_REG
On many machines, the numbered registers are not all equivalent. For example, certain registers may not be allowed for indexed addressing; certain registers may not be allowed in some instructions. These machine restrictions are described to the compiler using register classes.
You define a number of register classes, giving each one a name and saying which of the registers belong to it. Then you can specify register classes that are allowed as operands to particular instruction patterns.
In general, each register will belong to several classes. In fact, one
class must be named ALL_REGS and contain all the registers. Another
class must be named NO_REGS and contain no registers. Often the
union of two classes will be another class; however, this is not required.
One of the classes must be named GENERAL_REGS. There is nothing
terribly special about the name, but the operand constraint letters
`r' and `g' specify this class. If GENERAL_REGS is
the same as ALL_REGS, just define it as a macro which expands
to ALL_REGS.
Order the classes so that if class x is contained in class y then x has a lower class number than y.
The way classes other than GENERAL_REGS are specified in operand
constraints is through machine-dependent operand constraint letters.
You can define such letters to correspond to various classes, then use
them in operand constraints.
You should define a class for the union of two classes whenever some
instruction allows both classes. For example, if an instruction allows
either a floating point (coprocessor) register or a general register for a
certain operand, you should define a class FLOAT_OR_GENERAL_REGS
which includes both of them. Otherwise you will get suboptimal code.
You must also specify certain redundant information about the register classes: for each class, which classes contain it and which ones are contained in it; for each pair of classes, the largest class contained in their union.
When a value occupying several consecutive registers is expected in a
certain class, all the registers used must belong to that class.
Therefore, register classes cannot be used to enforce a requirement for
a register pair to start with an even-numbered register. The way to
specify this requirement is with HARD_REGNO_MODE_OK.
Register classes used for input-operands of bitwise-and or shift
instructions have a special requirement: each such class must have, for
each fixed-point machine mode, a subclass whose registers can transfer that
mode to or from memory. For example, on some machines, the operations for
single-byte values (QImode) are limited to certain registers. When
this is so, each register class that is used in a bitwise-and or shift
instruction must have a subclass consisting of registers from which
single-byte values can be loaded or stored. This is so that
PREFERRED_RELOAD_CLASS can always have a possible value to return.
enum reg_class
NO_REGS must be first. ALL_REGS
must be the last register class, followed by one more enumeral value,
LIM_REG_CLASSES, which is not a register class but rather
tells how many classes there are.
Each register class has a number, which is the value of casting
the class name to type int. The number serves as an index
in many of the tables described below.
N_REG_CLASSES
#define N_REG_CLASSES (int) LIM_REG_CLASSES |
REG_CLASS_NAMES
REG_CLASS_CONTENTS
mask & (1 << r) is 1.
When the machine has more than 32 registers, an integer does not suffice.
Then the integers are replaced by sub-initializers, braced groupings containing
several integers. Each sub-initializer must be suitable as an initializer
for the type HARD_REG_SET which is defined in `hard-reg-set.h'.
In this situation, the first integer in each sub-initializer corresponds to
registers 0 through 31, the second integer to registers 32 through 63, and
so on.
REGNO_REG_CLASS (regno)
BASE_REG_CLASS
INDEX_REG_CLASS
REG_CLASS_FROM_LETTER (char)
NO_REGS. The register letter `r',
corresponding to class GENERAL_REGS, will not be passed
to this macro; you do not need to handle it.
REGNO_OK_FOR_BASE_P (num)
REGNO_MODE_OK_FOR_BASE_P (num, mode)
REGNO_OK_FOR_BASE_P, except that
that expression may examine the mode of the memory reference in
mode. You should define this macro if the mode of the memory
reference affects whether a register may be used as a base register. If
you define this macro, the compiler will use it instead of
REGNO_OK_FOR_BASE_P.
REGNO_OK_FOR_INDEX_P (num)
The difference between an index register and a base register is that the index register may be scaled. If an address involves the sum of two registers, neither one of them scaled, then either one may be labeled the "base" and the other the "index"; but whichever labeling is used must fit the machine's constraints of which registers may serve in each capacity. The compiler will try both labelings, looking for one that is valid, and will reload one or both registers only if neither labeling works.
PREFERRED_RELOAD_CLASS (x, class)
#define PREFERRED_RELOAD_CLASS(X,CLASS) CLASS |
Sometimes returning a more restrictive class makes better code. For
example, on the 68000, when x is an integer constant that is in range
for a `moveq' instruction, the value of this macro is always
DATA_REGS as long as class includes the data registers.
Requiring a data register guarantees that a `moveq' will be used.
If x is a const_double, by returning NO_REGS
you can force x into a memory constant. This is useful on
certain machines where immediate floating values cannot be loaded into
certain kinds of registers.
PREFERRED_OUTPUT_RELOAD_CLASS (x, class)
PREFERRED_RELOAD_CLASS, but for output reloads instead of
input reloads. If you don't define this macro, the default is to use
class, unchanged.
LIMIT_RELOAD_CLASS (mode, class)
Unlike PREFERRED_RELOAD_CLASS, this macro should be used when
there are certain modes that simply can't go in certain reload classes.
The value is a register class; perhaps class, or perhaps another, smaller class.
Don't define this macro unless the target machine has limitations which require the macro to do something nontrivial.
SECONDARY_RELOAD_CLASS (class, mode, x)
SECONDARY_INPUT_RELOAD_CLASS (class, mode, x)
SECONDARY_OUTPUT_RELOAD_CLASS (class, mode, x)
You should define these macros to indicate to the reload phase that it may
need to allocate at least one register for a reload in addition to the
register to contain the data. Specifically, if copying x to a
register class in mode requires an intermediate register,
you should define SECONDARY_INPUT_RELOAD_CLASS to return the
largest register class all of whose registers can be used as
intermediate registers or scratch registers.
If copying a register class in mode to x requires an
intermediate or scratch register, SECONDARY_OUTPUT_RELOAD_CLASS
should be defined to return the largest register class required. If the
requirements for input and output reloads are the same, the macro
SECONDARY_RELOAD_CLASS should be used instead of defining both
macros identically.
The values returned by these macros are often GENERAL_REGS.
Return NO_REGS if no spare register is needed; i.e., if x
can be directly copied to or from a register of class in
mode without requiring a scratch register. Do not define this
macro if it would always return NO_REGS.
If a scratch register is required (either with or without an
intermediate register), you should define patterns for
`reload_inm' or `reload_outm', as required
(see section 20.8 Standard Pattern Names For Generation. These patterns, which will normally be
implemented with a define_expand, should be similar to the
`movm' patterns, except that operand 2 is the scratch
register.
Define constraints for the reload register and scratch register that contain a single register class. If the original reload register (whose class is class) can meet the constraint given in the pattern, the value returned by these macros is used for the class of the scratch register. Otherwise, two additional reload registers are required. Their classes are obtained from the constraints in the insn pattern.
x might be a pseudo-register or a subreg of a
pseudo-register, which could either be in a hard register or in memory.
Use true_regnum to find out; it will return -1 if the pseudo is
in memory and the hard register number if it is in a register.
These macros should not be used in the case where a particular class of
registers can only be copied to memory and not to another class of
registers. In that case, secondary reload registers are not needed and
would not be helpful. Instead, a stack location must be used to perform
the copy and the movm pattern should use memory as a
intermediate storage. This case often occurs between floating-point and
general registers.
SECONDARY_MEMORY_NEEDED (class1, class2, m)
Do not define this macro if its value would always be zero.
SECONDARY_MEMORY_NEEDED_RTX (mode)
SECONDARY_MEMORY_NEEDED is defined, the compiler
allocates a stack slot for a memory location needed for register copies.
If this macro is defined, the compiler instead uses the memory location
defined by this macro.
Do not define this macro if you do not define
SECONDARY_MEMORY_NEEDED.
SECONDARY_MEMORY_NEEDED_MODE (mode)
BITS_PER_WORD bits and performs the store and
load operations in a mode that many bits wide and whose class is the
same as that of mode.
This is right thing to do on most machines because it ensures that all bits of the register are copied and prevents accesses to the registers in a narrower mode, which some machines prohibit for floating-point registers.
However, this default behavior is not correct on some machines, such as the DEC Alpha, that store short integers in floating-point registers differently than in integer registers. On those machines, the default widening will not work correctly and you must define this macro to suppress that widening in some cases. See the file `alpha.h' for details.
Do not define this macro if you do not define
SECONDARY_MEMORY_NEEDED or if widening mode to a mode that
is BITS_PER_WORD bits wide is correct for your machine.
SMALL_REGISTER_CLASSES
Define SMALL_REGISTER_CLASSES to be an expression with a nonzero
value on these machines. When this macro has a nonzero value, the
compiler will try to minimize the lifetime of hard registers.
It is always safe to define this macro with a nonzero value, but if you unnecessarily define it, you will reduce the amount of optimizations that can be performed in some cases. If you do not define this macro with a nonzero value when it is required, the compiler will run out of spill registers and print a fatal error message. For most machines, you should not define this macro at all.
CLASS_LIKELY_SPILLED_P (class)
The default value of this macro returns 1 if class has exactly one register and zero otherwise. On most machines, this default should be used. Only define this macro to some other expression if pseudos allocated by `local-alloc.c' end up in memory because their hard registers were needed for spill registers. If this macro returns nonzero for those classes, those pseudos will only be allocated by `global.c', which knows how to reallocate the pseudo to another register. If there would not be another register available for reallocation, you should not change the definition of this macro since the only effect of such a definition would be to slow down register allocation.
CLASS_MAX_NREGS (class, mode)
This is closely related to the macro HARD_REGNO_NREGS. In fact,
the value of the macro CLASS_MAX_NREGS (class, mode)
should be the maximum value of HARD_REGNO_NREGS (regno,
mode) for all regno values in the class class.
This macro helps control the handling of multiple-word values in the reload pass.
CLASS_CANNOT_CHANGE_MODE
CLASS_CANNOT_CHANGE_MODE_P(from, to)
CLASS_CANNOT_CHANGE_MODE, the requested mode punning is invalid.
For the example, loading 32-bit integer or floating-point objects into
floating-point registers on the Alpha extends them to 64-bits.
Therefore loading a 64-bit object and then storing it as a 32-bit object
does not store the low-order 32-bits, as would be the case for a normal
register. Therefore, `alpha.h' defines CLASS_CANNOT_CHANGE_MODE
as FLOAT_REGS and CLASS_CANNOT_CHANGE_MODE_P restricts
mode changes to same-size modes.
Compare this to IA-64, which extends floating-point values to 82-bits,
and stores 64-bit integers in a different format than 64-bit doubles.
Therefore CLASS_CANNOT_CHANGE_MODE_P is always true.
Three other special macros describe which operands fit which constraint letters.
CONST_OK_FOR_LETTER_P (value, c)
CONST_DOUBLE_OK_FOR_LETTER_P (value, c)
const_double values
(`G' or `H').
If c is one of those letters, the expression should check that
value, an RTX of code const_double, is in the appropriate
range and return 1 if so, 0 otherwise. If c is not one of those
letters, the value should be 0 regardless of value.
const_double is used for all floating-point constants and for
DImode fixed-point constants. A given letter can accept either
or both kinds of values. It can use GET_MODE to distinguish
between these kinds.
EXTRA_CONSTRAINT (value, c)
REG_CLASS_FROM_LETTER
may be used. Normally this macro will not be defined.
If it is required for a particular target machine, it should return 1 if value corresponds to the operand type represented by the constraint letter c. If c is not defined as an extra constraint, the value returned should be 0 regardless of value.
For example, on the ROMP, load instructions cannot have their output in r0 if the memory reference contains a symbolic address. Constraint letter `Q' is defined as representing a memory address that does not contain a symbolic address. An alternative is specified with a `Q' constraint on the input and `r' on the output. The next alternative specifies `m' on the input and a register class that does not include r0 on the output.
This describes the stack layout and calling conventions.
Here is the basic stack layout.
STACK_GROWS_DOWNWARD
When we say, "define this macro if ...," it means that the
compiler checks this macro only with #ifdef so the precise
definition used does not matter.
FRAME_GROWS_DOWNWARD
ARGS_GROW_DOWNWARD
STARTING_FRAME_OFFSET
If FRAME_GROWS_DOWNWARD, find the next slot's offset by
subtracting the first slot's length from STARTING_FRAME_OFFSET.
Otherwise, it is found by adding the length of the first slot to the
value STARTING_FRAME_OFFSET.
STACK_POINTER_OFFSET
If ARGS_GROW_DOWNWARD, this is the offset to the location above
the first location at which outgoing arguments are placed.
FIRST_PARM_OFFSET (fundecl)
If ARGS_GROW_DOWNWARD, this is the offset to the location above
the first argument's address.
STACK_DYNAMIC_OFFSET (fundecl)
alloca.
The default value for this macro is STACK_POINTER_OFFSET plus the
length of the outgoing arguments. The default is correct for most
machines. See `function.c' for details.
DYNAMIC_CHAIN_ADDRESS (frameaddr)
If you don't define this macro, the default is to return the value of frameaddr---that is, the stack frame address is also the address of the stack word that points to the previous frame.
SETUP_FRAME_ADDRESSES
BUILTIN_SETJMP_FRAME_VALUE
setjmp buffer.
The default value, virtual_stack_vars_rtx, is correct for most
machines. One reason you may need to define this macro is if
hard_frame_pointer_rtx is the appropriate value on your machine.
RETURN_ADDR_RTX (count, frameaddr)
RETURN_ADDR_IN_PREVIOUS_FRAME is defined.
The value of the expression must always be the correct address when
count is zero, but may be NULL_RTX if there is not way to
determine the return address of other frames.
RETURN_ADDR_IN_PREVIOUS_FRAME
INCOMING_RETURN_ADDR_RTX
REG, indicating that the return
value is saved in `REG', or a MEM representing a location in
the stack.
You only need to define this macro if you want to support call frame debugging information like that provided by DWARF 2.
If this RTL is a REG, you should also define
DWARF_FRAME_RETURN_COLUMN to DWARF_FRAME_REGNUM (REGNO).
INCOMING_FRAME_SP_OFFSET
You only need to define this macro if you want to support call frame debugging information like that provided by DWARF 2.
ARG_POINTER_CFA_OFFSET (fundecl)
INCOMING_FRAME_SP_OFFSET. Which is unfortunately not usable
during virtual register instantiation.
The default value for this macro is FIRST_PARM_OFFSET (fundecl),
which is correct for most machines; in general, the arguments are found
immediately before the stack frame. Note that this is not the case on
some targets that save registers into the caller's frame, such as SPARC
and rs6000, and so such targets need to define this macro.
You only need to define this macro if the default is incorrect, and you want to support call frame debugging information like that provided by DWARF 2.
EH_RETURN_DATA_REGNO (N)
INVALID_REGNUM if fewer than
N registers are usable.
The exception handling library routines communicate with the exception handlers via a set of agreed upon registers. Ideally these registers should be call-clobbered; it is possible to use call-saved registers, but may negatively impact code size. The target must support at least 2 data registers, but should define 4 if there are enough free registers.
You must define this macro if you want to support call frame exception handling like that provided by DWARF 2.
EH_RETURN_STACKADJ_RTX
Typically this is a call-clobbered hard register that is otherwise untouched by the epilogue, but could also be a stack slot.
You must define this macro if you want to support call frame exception handling like that provided by DWARF 2.
EH_RETURN_HANDLER_RTX
Typically this is the location in the call frame at which the normal
return address is stored. For targets that return by popping an
address off the stack, this might be a memory address just below
the target call frame rather than inside the current call
frame. EH_RETURN_STACKADJ_RTX will have already been assigned,
so it may be used to calculate the location of the target call frame.
Some targets have more complex requirements than storing to an
address calculable during initial code generation. In that case
the eh_return instruction pattern should be used instead.
If you want to support call frame exception handling, you must
define either this macro or the eh_return instruction pattern.
ASM_PREFERRED_EH_DATA_FORMAT(code, global)
code is 0 for data, 1 for code labels, 2 for function pointers.
global is true if the symbol may be affected by dynamic relocations.
The macro should return a combination of the DW_EH_PE_* defines
as found in `dwarf2.h'.
If this macro is not defined, pointers will not be encoded but represented directly.
ASM_MAYBE_OUTPUT_ENCODED_ADDR_RTX(file, encoding, size, addr, done)
ASM_PREFERRED_EH_DATA_FORMAT.
Generic code takes care of pc-relative and indirect encodings; this must
be defined if the target uses text-relative or data-relative encodings.
This is a C statement that branches to done if the format was
handled. encoding is the format chosen, size is the number
of bytes that the format occupies, addr is the SYMBOL_REF
to be emitted.
SMALL_STACK
GCC will check that stack references are within the boundaries of the stack, if the `-fstack-check' is specified, in one of three ways:
STACK_CHECK_BUILTIN macro is nonzero, GCC
will assume that you have arranged for stack checking to be done at
appropriate places in the configuration files, e.g., in
FUNCTION_PROLOGUE. GCC will do not other special processing.
STACK_CHECK_BUILTIN is zero and you defined a named pattern
called check_stack in your `md' file, GCC will call that
pattern with one argument which is the address to compare the stack
value against. You must arrange for this pattern to report an error if
the stack pointer is out of range.
Normally, you will use the default values of these macros, so GCC will use the third approach.
STACK_CHECK_BUILTIN
STACK_CHECK_PROBE_INTERVAL
STACK_CHECK_PROBE_LOAD
STACK_CHECK_PROTECT
STACK_CHECK_MAX_FRAME_SIZE
STACK_CHECK_FIXED_FRAME_SIZE
STACK_CHECK_MAX_VAR_SIZE
This discusses registers that address the stack frame.
STACK_POINTER_REGNUM
FIXED_REGISTERS. On most machines,
the hardware determines which register this is.
FRAME_POINTER_REGNUM
HARD_FRAME_POINTER_REGNUM
FRAME_POINTER_REGNUM the number of a special, fixed register to
be used internally until the offset is known, and define
HARD_FRAME_POINTER_REGNUM to be the actual hard register number
used for the frame pointer.
You should define this macro only in the very rare circumstances when it
is not possible to calculate the offset between the frame pointer and
the automatic variables until after register allocation has been
completed. When this macro is defined, you must also indicate in your
definition of ELIMINABLE_REGS how to eliminate
FRAME_POINTER_REGNUM into either HARD_FRAME_POINTER_REGNUM
or STACK_POINTER_REGNUM.
Do not define this macro if it would be the same as
FRAME_POINTER_REGNUM.
ARG_POINTER_REGNUM
FIXED_REGISTERS, or arrange to be able to eliminate it
(see section 21.8.4 Eliminating Frame Pointer and Arg Pointer).
RETURN_ADDRESS_POINTER_REGNUM
ELIMINABLE_REGS into either the frame pointer or stack pointer.
Do not define this macro unless there is no other way to get the return address from the stack.
STATIC_CHAIN_REGNUM
STATIC_CHAIN_INCOMING_REGNUM
STATIC_CHAIN_INCOMING_REGNUM, while the register
number as seen by the calling function is STATIC_CHAIN_REGNUM. If
these registers are the same, STATIC_CHAIN_INCOMING_REGNUM need
not be defined.
The static chain register need not be a fixed register.
If the static chain is passed in memory, these macros should not be defined; instead, the next two macros should be defined.
STATIC_CHAIN
STATIC_CHAIN_INCOMING
mem expressions that denote where they are stored.
STATIC_CHAIN and STATIC_CHAIN_INCOMING give the locations
as seen by the calling and called functions, respectively. Often the former
will be at an offset from the stack pointer and the latter at an offset from
the frame pointer.
The variables stack_pointer_rtx, frame_pointer_rtx, and
arg_pointer_rtx will have been initialized prior to the use of these
macros and should be used to refer to those items.
If the static chain is passed in a register, the two previous macros should be defined instead.
This is about eliminating the frame pointer and arg pointer.
FRAME_POINTER_REQUIRED
The expression can in principle examine the current function and decide according to the facts, but on most machines the constant 0 or the constant 1 suffices. Use 0 when the machine allows code to be generated with no frame pointer, and doing so saves some time or space. Use 1 when there is no possible advantage to avoiding a frame pointer.
In certain cases, the compiler does not know how to produce valid code
without a frame pointer. The compiler recognizes those cases and
automatically gives the function a frame pointer regardless of what
FRAME_POINTER_REQUIRED says. You don't need to worry about
them.
In a function that does not require a frame pointer, the frame pointer
register can be allocated for ordinary usage, unless you mark it as a
fixed register. See FIXED_REGISTERS for more information.
INITIAL_FRAME_POINTER_OFFSET (depth-var)
get_frame_size () and the tables of
registers regs_ever_live and call_used_regs.
If ELIMINABLE_REGS is defined, this macro will be not be used and
need not be defined. Otherwise, it must be defined even if
FRAME_POINTER_REQUIRED is defined to always be true; in that
case, you may set depth-var to anything.
ELIMINABLE_REGS
The definition of this macro is a list of structure initializations, each of which specifies an original and replacement register.
On some machines, the position of the argument pointer is not known until the compilation is completed. In such a case, a separate hard register must be used for the argument pointer. This register can be eliminated by replacing it with either the frame pointer or the argument pointer, depending on whether or not the frame pointer has been eliminated.
In this case, you might specify:
#define ELIMINABLE_REGS \
{{ARG_POINTER_REGNUM, STACK_POINTER_REGNUM}, \
{ARG_POINTER_REGNUM, FRAME_POINTER_REGNUM}, \
{FRAME_POINTER_REGNUM, STACK_POINTER_REGNUM}}
|
Note that the elimination of the argument pointer with the stack pointer is specified first since that is the preferred elimination.
CAN_ELIMINATE (from-reg, to-reg)
ELIMINABLE_REGS
is defined, and will usually be the constant 1, since most of the cases
preventing register elimination are things that the compiler already
knows about.
INITIAL_ELIMINATION_OFFSET (from-reg, to-reg, offset-var)
INITIAL_FRAME_POINTER_OFFSET. It
specifies the initial difference between the specified pair of
registers. This macro must be defined if ELIMINABLE_REGS is
defined.
LONGJMP_RESTORE_FROM_STACK
longjmp function restores registers from
the stack frames, rather than from those saved specifically by
setjmp. Certain quantities must not be kept in registers across
a call to setjmp on such machines.
The macros in this section control how arguments are passed on the stack. See the following section for other macros that control passing certain arguments in registers.
PROMOTE_PROTOTYPES
int should
actually be passed as an int. In addition to avoiding
errors in certain cases of mismatch, it also makes for better
code on certain machines. If the macro is not defined in target
header files, it defaults to 0.
PUSH_ARGS
PUSH_ARGS is nonzero, PUSH_ROUNDING must be defined too.
On some machines, the definition
PUSH_ROUNDING (npushed)
On some machines, the definition
#define PUSH_ROUNDING(BYTES) (BYTES) |
will suffice. But on other machines, instructions that appear to push one byte actually push two bytes in an attempt to maintain alignment. Then the definition should be
#define PUSH_ROUNDING(BYTES) (((BYTES) + 1) & ~1) |
ACCUMULATE_OUTGOING_ARGS
current_function_outgoing_args_size. No space will be pushed
onto the stack for each call; instead, the function prologue should
increase the stack frame size by this amount.
Setting both PUSH_ARGS and ACCUMULATE_OUTGOING_ARGS
is not proper.
REG_PARM_STACK_SPACE (fndecl)
The value of this macro is the size, in bytes, of the area reserved for arguments passed in registers for the function represented by fndecl, which can be zero if GCC is calling a library function.
This space can be allocated by the caller, or be a part of the
machine-dependent stack frame: OUTGOING_REG_PARM_STACK_SPACE says
which.
MAYBE_REG_PARM_STACK_SPACE
FINAL_REG_PARM_STACK_SPACE (const_size, var_size)
The value of the first macro is the size, in bytes, of the area that we should initially assume would be reserved for arguments passed in registers.
The value of the second macro is the actual size, in bytes, of the area that will be reserved for arguments passed in registers. This takes two arguments: an integer representing the number of bytes of fixed sized arguments on the stack, and a tree representing the number of bytes of variable sized arguments on the stack.
When these macros are defined, REG_PARM_STACK_SPACE will only be
called for libcall functions, the current function, or for a function
being called when it is known that such stack space must be allocated.
In each case this value can be easily computed.
When deciding whether a called function needs such stack space, and how
much space to reserve, GCC uses these two macros instead of
REG_PARM_STACK_SPACE.
OUTGOING_REG_PARM_STACK_SPACE
If ACCUMULATE_OUTGOING_ARGS is defined, this macro controls
whether the space for these arguments counts in the value of
current_function_outgoing_args_size.
STACK_PARMS_IN_REG_PARM_AREA
REG_PARM_STACK_SPACE is defined, but the
stack parameters don't skip the area specified by it.
Normally, when a parameter is not passed in registers, it is placed on the
stack beyond the REG_PARM_STACK_SPACE area. Defining this macro
suppresses this behavior and causes the parameter to be passed on the
stack in its natural location.
RETURN_POPS_ARGS (fundecl, funtype, stack-size)
fundecl is a C variable whose value is a tree node that describes
the function in question. Normally it is a node of type
FUNCTION_DECL that describes the declaration of the function.
From this you can obtain the DECL_MACHINE_ATTRIBUTES of the function.
funtype is a C variable whose value is a tree node that
describes the function in question. Normally it is a node of type
FUNCTION_TYPE that describes the data type of the function.
From this it is possible to obtain the data types of the value and
arguments (if known).
When a call to a library function is being considered, fundecl will contain an identifier node for the library function. Thus, if you need to distinguish among various library functions, you can do so by their names. Note that "library function" in this context means a function used to perform arithmetic, whose name is known specially in the compiler and was not mentioned in the C code being compiled.
stack-size is the number of bytes of arguments passed on the stack. If a variable number of bytes is passed, it is zero, and argument popping will always be the responsibility of the calling function.
On the Vax, all functions always pop their arguments, so the definition
of this macro is stack-size. On the 68000, using the standard
calling convention, no functions pop their arguments, so the value of
the macro is always 0 in this case. But an alternative calling
convention is available in which functions that take a fixed number of
arguments pop them but other functions (such as printf) pop
nothing (the caller pops all). When this convention is in use,
funtype is examined to determine whether a function takes a fixed
number of arguments.
This section describes the macros which let you control how various types of arguments are passed in registers or how they are arranged in the stack.
FUNCTION_ARG (cum, mode, type, named)
The arguments are cum, which summarizes all the previous arguments; mode, the machine mode of the argument; type, the data type of the argument as a tree node or 0 if that is not known (which happens for C support library functions); and named, which is 1 for an ordinary argument and 0 for nameless arguments that correspond to `...' in the called function's prototype. type can be an incomplete type if a syntax error has previously occurred.
The value of the expression is usually either a reg RTX for the
hard register in which to pass the argument, or zero to pass the
argument on the stack.
For machines like the Vax and 68000, where normally all arguments are pushed, zero suffices as a definition.
The value of the expression can also be a parallel RTX. This is
used when an argument is passed in multiple locations. The mode of the
of the parallel should be the mode of the entire argument. The
parallel holds any number of expr_list pairs; each one
describes where part of the argument is passed. In each
expr_list the first operand must be a reg RTX for the hard
register in which to pass this part of the argument, and the mode of the
register RTX indicates how large this part of the argument is. The
second operand of the expr_list is a const_int which gives
the offset in bytes into the entire argument of where this part starts.
As a special exception the first expr_list in the parallel
RTX may have a first operand of zero. This indicates that the entire
argument is also stored on the stack.
The usual way to make the ISO library `stdarg.h' work on a machine
where some arguments are usually passed in registers, is to cause
nameless arguments to be passed on the stack instead. This is done
by making FUNCTION_ARG return 0 whenever named is 0.
You may use the macro MUST_PASS_IN_STACK (mode, type)
in the definition of this macro to determine if this argument is of a
type that must be passed in the stack. If REG_PARM_STACK_SPACE
is not defined and FUNCTION_ARG returns nonzero for such an
argument, the compiler will abort. If REG_PARM_STACK_SPACE is
defined, the argument will be computed in the stack and then loaded into
a register.
MUST_PASS_IN_STACK (mode, type)
FUNCTION_INCOMING_ARG (cum, mode, type, named)
For such machines, FUNCTION_ARG computes the register in which
the caller passes the value, and FUNCTION_INCOMING_ARG should
be defined in a similar fashion to tell the function being called
where the arguments will arrive.
If FUNCTION_INCOMING_ARG is not defined, FUNCTION_ARG
serves both purposes.
FUNCTION_ARG_PARTIAL_NREGS (cum, mode, type, named)
On some machines, certain arguments must be passed partially in
registers and partially in memory. On these machines, typically the
first n words of arguments are passed in registers, and the rest
on the stack. If a multi-word argument (a double or a
structure) crosses that boundary, its first few words must be passed
in registers and the rest must be pushed. This macro tells the
compiler when this occurs, and how many of the words should go in
registers.
FUNCTION_ARG for these arguments should return the first
register to be used by the caller for this argument; likewise
FUNCTION_INCOMING_ARG, for the called function.
FUNCTION_ARG_PASS_BY_REFERENCE (cum, mode, type, named)
On machines where REG_PARM_STACK_SPACE is not defined, a suitable
definition of this macro might be
#define FUNCTION_ARG_PASS_BY_REFERENCE\ (CUM, MODE, TYPE, NAMED) \ MUST_PASS_IN_STACK (MODE, TYPE) |
FUNCTION_ARG_CALLEE_COPIES (cum, mode, type, named)
FUNCTION_ARG_CALLEE_COPIES is defined and is
nonzero, the caller does not make a copy. Instead, it passes a pointer to the
"live" value. The called function must not modify this value. If it can be
determined that the value won't be modified, it need not make a copy;
otherwise a copy must be made.
CUMULATIVE_ARGS
FUNCTION_ARG and other related values. For some target machines,
the type int suffices and can hold the number of bytes of
argument so far.
There is no need to record in CUMULATIVE_ARGS anything about the
arguments that have been passed on the stack. The compiler has other
variables to keep track of that. For target machines on which all
arguments are passed on the stack, there is no need to store anything in
CUMULATIVE_ARGS; however, the data structure must exist and
should not be empty, so use int.
INIT_CUMULATIVE_ARGS (cum, fntype, libname, indirect)
CUMULATIVE_ARGS. The value of fntype is the tree node
for the data type of the function which will receive the args, or 0
if the args are to a compiler support library function. The value of
indirect is nonzero when processing an indirect call, for example
a call through a function pointer. The value of indirect is zero
for a call to an explicitly named function, a library function call, or when
INIT_CUMULATIVE_ARGS is used to find arguments for the function
being compiled.
When processing a call to a compiler support library function,
libname identifies which one. It is a symbol_ref rtx which
contains the name of the function, as a string. libname is 0 when
an ordinary C function call is being processed. Thus, each time this
macro is called, either libname or fntype is nonzero, but
never both of them at once.
INIT_CUMULATIVE_LIBCALL_ARGS (cum, mode, libname)
INIT_CUMULATIVE_ARGS but only used for outgoing libcalls,
it gets a MODE argument instead of fntype, that would be
NULL. indirect would always be zero, too. If this macro
is not defined, INIT_CUMULATIVE_ARGS (cum, NULL_RTX, libname,
0) is used instead.
INIT_CUMULATIVE_INCOMING_ARGS (cum, fntype, libname)
INIT_CUMULATIVE_ARGS but overrides it for the purposes of
finding the arguments for the function being compiled. If this macro is
undefined, INIT_CUMULATIVE_ARGS is used instead.
The value passed for libname is always 0, since library routines
with special calling conventions are never compiled with GCC. The
argument libname exists for symmetry with
INIT_CUMULATIVE_ARGS.
FUNCTION_ARG_ADVANCE (cum, mode, type, named)
FUNCTION_ARG, etc.
This macro need not do anything if the argument in question was passed on the stack. The compiler knows how to track the amount of stack space used for arguments without any special help.
FUNCTION_ARG_PADDING (mode, type)
enum direction: either upward to pad above the argument,
downward to pad below, or none to inhibit padding.
The amount of padding is always just enough to reach the next
multiple of FUNCTION_ARG_BOUNDARY; this macro does not control
it.
This macro has a default definition which is right for most systems.
For little-endian machines, the default is to pad upward. For
big-endian machines, the default is to pad downward for an argument of
constant size shorter than an int, and upward otherwise.
PAD_VARARGS_DOWN
PARM_BOUNDARY. If this macro is not defined, all such
arguments are padded down if BYTES_BIG_ENDIAN is true.
FUNCTION_ARG_BOUNDARY (mode, type)
PARM_BOUNDARY is used for all arguments.
FUNCTION_ARG_REGNO_P (regno)
LOAD_ARGS_REVERSED
This section discusses the macros that control returning scalars as values--values that can fit in registers.
TRADITIONAL_RETURN_FLOAT
float to convert the value to double.
FUNCTION_VALUE (valtype, func)
TYPE_MODE
(valtype) to get the machine mode used to represent that type.
On many machines, only the mode is relevant. (Actually, on most
machines, scalar values are returned in the same place regardless of
mode).
The value of the expression is usually a reg RTX for the hard
register where the return value is stored. The value can also be a
parallel RTX, if the return value is in multiple places. See
FUNCTION_ARG for an explanation of the parallel form.
If PROMOTE_FUNCTION_RETURN is defined, you must apply the same
promotion rules specified in PROMOTE_MODE if valtype is a
scalar type.
If the precise function being called is known, func is a tree
node (FUNCTION_DECL) for it; otherwise, func is a null
pointer. This makes it possible to use a different value-returning
convention for specific functions when all their calls are
known.
FUNCTION_VALUE is not used for return vales with aggregate data
types, because these are returned in another way. See
STRUCT_VALUE_REGNUM and related macros, below.
FUNCTION_OUTGOING_VALUE (valtype, func)
For such machines, FUNCTION_VALUE computes the register in which
the caller will see the value. FUNCTION_OUTGOING_VALUE should be
defined in a similar fashion to tell the function where to put the
value.
If FUNCTION_OUTGOING_VALUE is not defined,
FUNCTION_VALUE serves both purposes.
FUNCTION_OUTGOING_VALUE is not used for return vales with
aggregate data types, because these are returned in another way. See
STRUCT_VALUE_REGNUM and related macros, below.
LIBCALL_VALUE (mode)
FUNCTION_DECL) for it; otherwise, func is a null
pointer. This makes it possible to use a different value-returning
convention for specific functions when all their calls are
known.
Note that "library function" in this context means a compiler support routine, used to perform arithmetic, whose name is known specially by the compiler and was not mentioned in the C code being compiled.
The definition of LIBRARY_VALUE need not be concerned aggregate
data types, because none of the library functions returns such types.
FUNCTION_VALUE_REGNO_P (regno)
A register whose use for returning values is limited to serving as the
second of a pair (for a value of type double, say) need not be
recognized by this macro. So for most machines, this definition
suffices:
#define FUNCTION_VALUE_REGNO_P(N) ((N) == 0) |
If the machine has register windows, so that the caller and the called function use different registers for the return value, this macro should recognize only the caller's register numbers.
APPLY_RESULT_SIZE
FUNCTION_VALUE_REGNO_P for
saving and restoring an arbitrary return value.
When a function value's mode is BLKmode (and in some other
cases), the value is not returned according to FUNCTION_VALUE
(see section 21.8.7 How Scalar Function Values Are Returned). Instead, the caller passes the address of a
block of memory in which the value should be stored. This address
is called the structure value address.
This section describes how to control returning structure values in memory.
RETURN_IN_MEMORY (type)
tree, representing the data type of the value.
Note that values of mode BLKmode must be explicitly handled
by this macro. Also, the option `-fpcc-struct-return'
takes effect regardless of this macro. On most systems, it is
possible to leave the macro undefined; this causes a default
definition to be used, whose value is the constant 1 for BLKmode
values, and 0 otherwise.
Do not use this macro to indicate that structures and unions should always
be returned in memory. You should instead use DEFAULT_PCC_STRUCT_RETURN
to indicate this.
DEFAULT_PCC_STRUCT_RETURN
RETURN_IN_MEMORY macro.
If not defined, this defaults to the value 1.
STRUCT_VALUE_REGNUM
STRUCT_VALUE_REGNUM should be the number of that register.
STRUCT_VALUE
STRUCT_VALUE as an expression returning an RTX for the place
where the address is passed. If it returns 0, the address is passed as
an "invisible" first argument.
STRUCT_VALUE_INCOMING_REGNUM
If the incoming location of the structure value address is in a register, define this macro as the register number.
STRUCT_VALUE_INCOMING
STRUCT_VALUE_INCOMING as an expression for an RTX for where the
called function should find the value. If it should find the value on
the stack, define this to create a mem which refers to the frame
pointer. A definition of 0 means that the address is passed as an
"invisible" first argument.
PCC_STATIC_STRUCT_RETURN
Do not define this if the usual system convention is for the caller to pass an address to the subroutine.
This macro has effect in `-fpcc-struct-return' mode, but it does nothing when you use `-freg-struct-return' mode.
If you enable it, GCC can save registers around function calls. This makes it possible to use call-clobbered registers to hold variables that must live across calls.
DEFAULT_CALLER_SAVES
CALL_USED_REGISTERS has 1
for all registers. When defined, this macro enables `-fcaller-saves'
by default for all optimization levels. It has no effect for optimization
levels 2 and higher, where `-fcaller-saves' is the default.
CALLER_SAVE_PROFITABLE (refs, calls)
If you don't define this macro, a default is used which is good on most
machines: 4 * calls < refs.
HARD_REGNO_CALLER_SAVE_MODE (regno, nregs)
VOIDmode should be
returned. For most machines this macro need not be defined since GCC
will select the smallest suitable mode.
This section describes the macros that output function entry (prologue) and exit (epilogue) code.
FUNCTION_PROLOGUE (file, size)
The label for the beginning of the function need not be output by this macro. That has already been done when the macro is run.
To determine which registers to save, the macro can refer to the array
regs_ever_live: element r is nonzero if hard register
r is used anywhere within the function. This implies the function
prologue should save register r, provided it is not one of the
call-used registers. (FUNCTION_EPILOGUE must likewise use
regs_ever_live.)
On machines that have "register windows", the function entry code does not save on the stack the registers that are in the windows, even if they are supposed to be preserved by function calls; instead it takes appropriate steps to "push" the register stack, if any non-call-used registers are used in the function.
On machines where functions may or may not have frame-pointers, the
function entry code must vary accordingly; it must set up the frame
pointer if one is wanted, and not otherwise. To determine whether a
frame pointer is in wanted, the macro can refer to the variable
frame_pointer_needed. The variable's value will be 1 at run
time in a function that needs a frame pointer. See section 21.8.4 Eliminating Frame Pointer and Arg Pointer.
The function entry code is responsible for allocating any stack space
required for the function. This stack space consists of the regions
listed below. In most cases, these regions are allocated in the
order listed, with the last listed region closest to the top of the
stack (the lowest address if STACK_GROWS_DOWNWARD is defined, and
the highest address if it is not defined). You can use a different order
for a machine if doing so is more convenient or required for
compatibility reasons. Except in cases where required by standard
or by a debugger, there is no reason why the stack layout used by GCC
need agree with that used by other compilers for a machine.
current_function_pretend_args_size bytes of
uninitialized space just underneath the first argument arriving on the
stack. (This may not be at the very start of the allocated stack region
if the calling sequence has pushed anything else since pushing the stack
arguments. But usually, on such machines, nothing else has been pushed
yet, because the function prologue itself does all the pushing.) This
region is used on machines where an argument may be passed partly in
registers and partly in memory, and, in some cases to support the
features in <varargs.h> and <stdarg.h>.
ACCUMULATE_OUTGOING_ARGS is defined, a region of
current_function_outgoing_args_size bytes to be used for outgoing
argument lists of the function. See section 21.8.5 Passing Function Arguments on the Stack.
Normally, it is necessary for the macros FUNCTION_PROLOGUE and
FUNCTION_EPILOGUE to treat leaf functions specially. The C
variable current_function_is_leaf is nonzero for such a function.
EXIT_IGNORE_STACK
Note that this macro's value is relevant only for functions for which
frame pointers are maintained. It is never safe to delete a final
stack adjustment in a function that has no frame pointer, and the
compiler knows this regardless of EXIT_IGNORE_STACK.
EPILOGUE_USES (regno)
FUNCTION_EPILOGUE (file, size)
FUNCTION_PROLOGUE, and the
registers to restore are determined from regs_ever_live and
CALL_USED_REGISTERS in the same way.
On some machines, there is a single instruction that does all the work
of returning from the function. On these machines, give that
instruction the name `return' and do not define the macro
FUNCTION_EPILOGUE at all.
Do not define a pattern named `return' if you want the
FUNCTION_EPILOGUE to be used. If you want the target switches
to control whether return instructions or epilogues are used, define a
`return' pattern with a validity condition that tests the target
switches appropriately. If the `return' pattern's validity
condition is false, epilogues will be used.
On machines where functions may or may not have frame-pointers, the
function exit code must vary accordingly. Sometimes the code for these
two cases is completely different. To determine whether a frame pointer
is wanted, the macro can refer to the variable
frame_pointer_needed. The variable's value will be 1 when compiling
a function that needs a frame pointer.
Normally, FUNCTION_PROLOGUE and FUNCTION_EPILOGUE must
treat leaf functions specially. The C variable current_function_is_leaf
is nonzero for such a function. See section 21.6.4 Handling Leaf Functions.
On some machines, some functions pop their arguments on exit while others leave that for the caller to do. For example, the 68020 when given `-mrtd' pops arguments in functions that take a fixed number of arguments.
Your definition of the macro RETURN_POPS_ARGS decides which
functions pop their own arguments. FUNCTION_EPILOGUE needs to
know what was decided. The variable that is called
current_function_pops_args is the number of bytes of its
arguments that a function should pop. See section 21.8.7 How Scalar Function Values Are Returned.
DELAY_SLOTS_FOR_EPILOGUE
ELIGIBLE_FOR_EPILOGUE_DELAY (insn, n)
The argument n is an integer which identifies the delay slot now
being considered (since different slots may have different rules of
eligibility). It is never negative and is always less than the number
of epilogue delay slots (what DELAY_SLOTS_FOR_EPILOGUE returns).
If you reject a particular insn for a given delay slot, in principle, it
may be reconsidered for a subsequent delay slot. Also, other insns may
(at least in principle) be considered for the so far unfilled delay
slot.
The insns accepted to fill the epilogue delay slots are put in an RTL
list made with insn_list objects, stored in the variable
current_function_epilogue_delay_list. The insn for the first
delay slot comes first in the list. Your definition of the macro
FUNCTION_EPILOGUE should fill the delay slots by outputting the
insns in this list, usually by calling final_scan_insn.
You need not define this macro if you did not define
DELAY_SLOTS_FOR_EPILOGUE.
ASM_OUTPUT_MI_THUNK (file, thunk_fndecl, delta, function)
First, emit code to add the integer delta to the location that
contains the incoming first argument. Assume that this argument
contains a pointer, and is the one used to pass the this pointer
in C++. This is the incoming argument before the function prologue,
e.g. `%o0' on a sparc. The addition must preserve the values of
all other incoming arguments.
After the addition, emit code to jump to function, which is a
FUNCTION_DECL. This is a direct pure jump, not a call, and does
not touch the return address. Hence returning from FUNCTION will
return to whoever called the current `thunk'.
The effect must be as if function had been called directly with
the adjusted first argument. This macro is responsible for emitting all
of the code for a thunk function; FUNCTION_PROLOGUE and
FUNCTION_EPILOGUE are not invoked.
The thunk_fndecl is redundant. (delta and function have already been extracted from it.) It might possibly be useful on some targets, but probably not.
If you do not define this macro, the target-independent code in the C++ front end will generate a less efficient heavyweight thunk that calls function instead of jumping to it. The generic approach does not support varargs.
These macros will help you generate code for profiling.
FUNCTION_PROFILER (file, labelno)
mcount.
The details of how mcount expects to be called are determined by
your operating system environment, not by GCC. To figure them out,
compile a small program for profiling using the system's installed C
compiler and look at the assembler code that results.
Older implementations of mcount expect the address of a counter
variable to be loaded into some register. The name of this variable is
`LP' followed by the number labelno, so you would generate
the name using `LP%d' in a fprintf.
PROFILE_HOOK
mcount even the target does
not support profiling.
NO_PROFILE_COUNTERS
mcount subroutine on your system does
not need a counter variable allocated for each function. This is true
for almost all modern implementations. If you define this macro, you
must not use the labelno argument to FUNCTION_PROFILER.
PROFILE_BEFORE_PROLOGUE
FUNCTION_BLOCK_PROFILER (file, labelno)
profile_block_flag
distinguishes two profile modes.
profile_block_flag != 2
__bb_init_func once per
object module, passing it as its sole argument the address of a block
allocated in the object module.
The name of the block is a local symbol made with this statement:
ASM_GENERATE_INTERNAL_LABEL (buffer, "LPBX", 0); |
Of course, since you are writing the definition of
ASM_GENERATE_INTERNAL_LABEL as well as that of this macro, you
can take a short cut in the definition of this macro and use the name
that you know will result.
The first word of this block is a flag which will be nonzero if the
object module has already been initialized. So test this word first,
and do not call __bb_init_func if the flag is
nonzero. labelno contains a unique number which may be used to
generate a label as a branch destination when __bb_init_func
will not be called.
Described in assembler language, the code to be output looks like:
cmp (LPBX0),0 bne local_label parameter1 <- LPBX0 call __bb_init_func local_label: |
profile_block_flag == 2
__bb_init_trace_func
and pass two parameters to it. The first parameter is the same as
for __bb_init_func. The second parameter is the number of the
first basic block of the function as given by labelno. Note
that __bb_init_trace_func has to be called, even if the object
module has been initialized already.
Described in assembler language, the code to be output looks like:
parameter1 <- LPBX0 parameter2 <- labelno call __bb_init_trace_func |
BLOCK_PROFILER (file, blockno)
profile_block_flag distinguishes two profile modes.
profile_block_flag != 2
ASM_GENERATE_INTERNAL_LABEL (buffer, "LPBX", 2); |
Of course, since you are writing the definition of
ASM_GENERATE_INTERNAL_LABEL as well as that of this macro, you
can take a short cut in the definition of this macro and use the name
that you know will result.
Described in assembler language, the code to be output looks like:
inc (LPBX2+4*blockno) |
profile_block_flag == 2
__bb and
call the function __bb_trace_func, which will increment the
counter.
__bb consists of two words. In the first word, the current
basic block number, as given by blockno, has to be stored. In
the second word, the address of a block allocated in the object
module has to be stored. The address is given by the label created
with this statement:
ASM_GENERATE_INTERNAL_LABEL (buffer, "LPBX", 0); |
Described in assembler language, the code to be output looks like:
move blockno -> (__bb) move LPBX0 -> (__bb+4) call __bb_trace_func |
FUNCTION_BLOCK_PROFILER_EXIT (file)
__bb_trace_ret. The
assembler code should only be output
if the global compile flag profile_block_flag == 2. This
macro has to be used at every place where code for returning from
a function is generated (e.g. FUNCTION_EPILOGUE). Although
you have to write the definition of FUNCTION_EPILOGUE
as well, you have to define this macro to tell the compiler, that
the proper call to __bb_trace_ret is produced.
MACHINE_STATE_SAVE (id)
asm statement will be mostly likely needed to handle this
task. Local labels in the assembler code can be concatenated with the
string id, to obtain a unique label name.
Registers or condition codes clobbered by FUNCTION_PROLOGUE or
FUNCTION_EPILOGUE must be saved in the macros
FUNCTION_BLOCK_PROFILER, FUNCTION_BLOCK_PROFILER_EXIT and
BLOCK_PROFILER prior calling __bb_init_trace_func,
__bb_trace_ret and __bb_trace_func respectively.
MACHINE_STATE_RESTORE (id)
MACHINE_STATE_SAVE.
Registers or condition codes clobbered by FUNCTION_PROLOGUE or
FUNCTION_EPILOGUE must be restored in the macros
FUNCTION_BLOCK_PROFILER, FUNCTION_BLOCK_PROFILER_EXIT and
BLOCK_PROFILER after calling __bb_init_trace_func,
__bb_trace_ret and __bb_trace_func respectively.
BLOCK_PROFILER_CODE
TARGET_ALLOWS_PROFILING_WITHOUT_FRAME_POINTER
mcount routine provided by the GNU C Library finds the
address of the routine that called the routine that called mcount
by looking in the immediate caller's stack frame. If the immediate
caller has no frame pointer, this lookup will fail.
By default, GCC assumes that the target does allow profiling when the
frame pointer is omitted. This macro should be defined to a C
expression that evaluates to false if the target does not allow
profiling when the frame pointer is omitted.
By default if a function has a target specific attribute attached to it, it will not be inlined. This behaviour can be overridden if the target defines the `FUNCTION_ATTRIBUTE_INLINABLE_P' macro. This macro takes one argument, a `DECL' describing the function. It should return nonzero if the function can be inlined, otherwise it should return 0.
FUNCTION_OK_FOR_SIBCALL (decl)
It is not uncommon for limitations of calling conventions to prevent
tail calls to functions outside the current unit of translation, or
during PIC compilation. Use this macro to enforce these restrictions,
as the sibcall md pattern can not fail, or fall over to a
"normal" call.
GCC comes with an implementation of <varargs.h> and
<stdarg.h> that work without change on machines that pass arguments
on the stack. Other machines require their own implementations of
varargs, and the two machine independent header files must have
conditionals to include it.
ISO <stdarg.h> differs from traditional <varargs.h> mainly in
the calling convention for va_start. The traditional
implementation takes just one argument, which is the variable in which
to store the argument pointer. The ISO implementation of
va_start takes an additional second argument. The user is
supposed to write the last named argument of the function here.
However, va_start should not use this argument. The way to find
the end of the named arguments is with the built-in functions described
below.
__builtin_saveregs ()
va_start must use __builtin_saveregs, unless
you use SETUP_INCOMING_VARARGS (see below) instead.
On some machines, __builtin_saveregs is open-coded under the
control of the macro EXPAND_BUILTIN_SAVEREGS. On other machines,
it calls a routine written in assembler language, found in
`libgcc2.c'.
Code generated for the call to __builtin_saveregs appears at the
beginning of the function, as opposed to where the call to
__builtin_saveregs is written, regardless of what the code is.
This is because the registers must be saved before the function starts
to use them for its own purposes.
__builtin_args_info (category)
In general, a machine may have several categories of registers used for
arguments, each for a particular category of data types. (For example,
on some machines, floating-point registers are used for floating-point
arguments while other arguments are passed in the general registers.)
To make non-varargs functions use the proper calling convention, you
have defined the CUMULATIVE_ARGS data type to record how many
registers in each category have been used so far
__builtin_args_info accesses the same data structure of type
CUMULATIVE_ARGS after the ordinary argument layout is finished
with it, with category specifying which word to access. Thus, the
value indicates the first unused register in a given category.
Normally, you would use __builtin_args_info in the implementation
of va_start, accessing each category just once and storing the
value in the va_list object. This is because va_list will
have to update the values, and there is no way to alter the
values accessed by __builtin_args_info.
__builtin_next_arg (lastarg)
__builtin_args_info, for stack
arguments. It returns the address of the first anonymous stack
argument, as type void *. If ARGS_GROW_DOWNWARD, it
returns the address of the location above the first anonymous stack
argument. Use it in va_start to initialize the pointer for
fetching arguments from the stack. Also use it in va_start to
verify that the second parameter lastarg is the last named argument
of the current function.
__builtin_classify_type (object)
va_arg
has to embody these conventions. The easiest way to categorize the
specified data type is to use __builtin_classify_type together
with sizeof and __alignof__.
__builtin_classify_type ignores the value of object,
considering only its data type. It returns an integer describing what
kind of type that is--integer, floating, pointer, structure, and so on.
The file `typeclass.h' defines an enumeration that you can use to
interpret the values of __builtin_classify_type.
These machine description macros help implement varargs:
EXPAND_BUILTIN_SAVEREGS ()
__builtin_saveregs. This code will be moved to the
very beginning of the function, before any parameter access are made.
The return value of this function should be an RTX that contains the
value to use as the return of __builtin_saveregs.
SETUP_INCOMING_VARARGS (args_so_far, mode, type, pretend_args_size, second_time)
__builtin_saveregs and
defining the macro EXPAND_BUILTIN_SAVEREGS. Use it to store the
anonymous register arguments into the stack so that all the arguments
appear to have been passed consecutively on the stack. Once this is
done, you can use the standard implementation of varargs that works for
machines that pass all their arguments on the stack.
The argument args_so_far is the CUMULATIVE_ARGS data
structure, containing the values that are obtained after processing the
named arguments. The arguments mode and type describe the
last named argument--its machine mode and its data type as a tree node.
The macro implementation should do two things: first, push onto the
stack all the argument registers not used for the named
arguments, and second, store the size of the data thus pushed into the
int-valued variable whose name is supplied as the argument
pretend_args_size. The value that you store here will serve as
additional offset for setting up the stack frame.
Because you must generate code to push the anonymous arguments at
compile time without knowing their data types,
SETUP_INCOMING_VARARGS is only useful on machines that have just
a single category of argument register and use it uniformly for all data
types.
If the argument second_time is nonzero, it means that the
arguments of the function are being analyzed for the second time. This
happens for an inline function, which is not actually compiled until the
end of the source file. The macro SETUP_INCOMING_VARARGS should
not generate any instructions in this case.
STRICT_ARGUMENT_NAMING
This macro controls how the named argument to FUNCTION_ARG
is set for varargs and stdarg functions. If this macro returns a
nonzero value, the named argument is always true for named
arguments, and false for unnamed arguments. If it returns a value of
zero, but SETUP_INCOMING_VARARGS is defined, then all arguments
are treated as named. Otherwise, all named arguments except the last
are treated as named.
You need not define this macro if it always returns zero.
PRETEND_OUTGOING_VARARGS_NAMED
SETUP_INCOMING_VARARGS, but the other works like neither
SETUP_INCOMING_VARARGS nor STRICT_ARGUMENT_NAMING was
defined, then define this macro to return nonzero if
SETUP_INCOMING_VARARGS is used, zero otherwise.
Otherwise, you should not define this macro.
A trampoline is a small piece of code that is created at run time when the address of a nested function is taken. It normally resides on the stack, in the stack frame of the containing function. These macros tell GCC how to generate code to allocate and initialize a trampoline.
The instructions in the trampoline must do two things: load a constant address into the static chain register, and jump to the real address of the nested function. On CISC machines such as the m68k, this requires two instructions, a move immediate and a jump. Then the two addresses exist in the trampoline as word-long immediate operands. On RISC machines, it is often necessary to load each address into a register in two parts. Then pieces of each address form separate immediate operands.
The code generated to initialize the trampoline must store the variable parts--the static chain value and the function address--into the immediate operands of the instructions. On a CISC machine, this is simply a matter of copying each address to a memory reference at the proper offset from the start of the trampoline. On a RISC machine, it may be necessary to take out pieces of the address and store them separately.
TRAMPOLINE_TEMPLATE (file)
If you do not define this macro, it means no template is needed for the target. Do not define this macro on systems where the block move code to copy the trampoline into place would be larger than the code to generate it on the spot.
TRAMPOLINE_SECTION
TRAMPOLINE_SIZE
TRAMPOLINE_ALIGNMENT
If you don't define this macro, the value of BIGGEST_ALIGNMENT
is used for aligning trampolines.
INITIALIZE_TRAMPOLINE (addr, fnaddr, static_chain)
TRAMPOLINE_ADJUST_ADDRESS (addr)
INITIALIZE_TRAMPOLINE. In case the address to be
used for a function call should be different from the address in which
the template was stored, the different address should be assigned to
addr. If this macro is not defined, addr will be used for
function calls.
ALLOCATE_TRAMPOLINE (fp)
If this macro is not defined, by default the trampoline is allocated as
a stack slot. This default is right for most machines. The exceptions
are machines where it is impossible to execute instructions in the stack
area. On such machines, you may have to implement a separate stack,
using this macro in conjunction with FUNCTION_PROLOGUE and
FUNCTION_EPILOGUE.
fp points to a data structure, a struct function, which
describes the compilation status of the immediate containing function of
the function which the trampoline is for. Normally (when
ALLOCATE_TRAMPOLINE is not defined), the stack slot for the
trampoline is in the stack frame of this containing function. Other
allocation strategies probably must do something analogous with this
information.
Implementing trampolines is difficult on many machines because they have separate instruction and data caches. Writing into a stack location fails to clear the memory in the instruction cache, so when the program jumps to that location, it executes the old contents.
Here are two possible solutions. One is to clear the relevant parts of the instruction cache whenever a trampoline is set up. The other is to make all trampolines identical, by having them jump to a standard subroutine. The former technique makes trampoline execution faster; the latter makes initialization faster.
To clear the instruction cache when a trampoline is initialized, define the following macros which describe the shape of the cache.
INSN_CACHE_SIZE
INSN_CACHE_LINE_WIDTH
INSN_CACHE_DEPTH
Alternatively, if the machine has system calls or instructions to clear the instruction cache directly, you can define the following macro.
CLEAR_INSN_CACHE (beg, end)
INSN_CACHE_SIZE is defined, some generic code is generated to clear the
cache. The definition of this macro would typically be a series of
asm statements. Both beg and end are both pointer
expressions.
To use a standard subroutine, define the following macro. In addition, you must make sure that the instructions in a trampoline fill an entire cache line with identical instructions, or else ensure that the beginning of the trampoline code is always aligned at the same point in its cache line. Look in `m68k.h' as a guide.
TRANSFER_FROM_TRAMPOLINE
asm statements
which will be compiled with GCC. They go in a library function named
__transfer_from_trampoline.
If you need to avoid executing the ordinary prologue code of a compiled
C function when you jump to the subroutine, you can do so by placing a
special label of your own in the assembler code. Use one asm
statement to generate an assembler label, and another to make the label
global. Then trampolines can use that label to jump directly to your
special assembler code.
Here is an explanation of implicit calls to library routines.
MULSI3_LIBCALL
__mulsi3,
a function defined in `libgcc.a'.
DIVSI3_LIBCALL
__divsi3, a
function defined in `libgcc.a'.
UDIVSI3_LIBCALL
__udivsi3, a
function defined in `libgcc.a'.
MODSI3_LIBCALL
__modsi3, a function defined in `libgcc.a'.
UMODSI3_LIBCALL
__umodsi3, a function defined in `libgcc.a'.
MULDI3_LIBCALL
__muldi3,
a function defined in `libgcc.a'.
DIVDI3_LIBCALL
__divdi3, a
function defined in `libgcc.a'.
UDIVDI3_LIBCALL
__udivdi3, a
function defined in `libgcc.a'.
MODDI3_LIBCALL
__moddi3, a function defined in `libgcc.a'.
UMODDI3_LIBCALL
__umoddi3, a function defined in `libgcc.a'.
INIT_TARGET_OPTABS
init_optabs calls this macro after
initializing all the normal library routines.
FLOAT_LIB_COMPARE_RETURNS_BOOL
Most ports don't need to define this macro.
TARGET_EDOM
EDOM on the target machine, as a C integer constant
expression. If you don't define this macro, GCC does not attempt to
deposit the value of EDOM into errno directly. Look in
`/usr/include/errno.h' to find the value of EDOM on your
system.
If you do not define TARGET_EDOM, then compiled code reports
domain errors by calling the library function and letting it report the
error. If mathematical functions on your system use matherr when
there is an error, then you should leave TARGET_EDOM undefined so
that matherr is used normally.
GEN_ERRNO_RTX
errno. (On certain systems,
errno may not actually be a variable.) If you don't define this
macro, a reasonable default is used.
TARGET_MEM_FUNCTIONS
memcpy, memmove and
memset rather than the BSD functions bcopy and bzero.
LIBGCC_NEEDS_DOUBLE
float arguments cannot be passed to
library routines (so they must be converted to double). This
macro affects both how library calls are generated and how the library
routines in `libgcc1.c' accept their arguments. It is useful on
machines where floating and fixed point arguments are passed
differently, such as the i860.
FLOAT_ARG_TYPE
float. (By default, they use a union
of float and int.)
The obvious choice would be float---but that won't work with
traditional C compilers that expect all arguments declared as float
to arrive as double. To avoid this conversion, the library routines
ask for the value as some other type and then treat it as a float.
On some systems, no other type will work for this. For these systems,
you must use LIBGCC_NEEDS_DOUBLE instead, to force conversion of
the values double before they are passed.
FLOATIFY (passed-value)
float argument as a float instead of the type it was
passed as. The default is an expression which takes the float
field of the union.
FLOAT_VALUE_TYPE
float. (By default, they
use int.)
The obvious choice would be float---but that won't work with
traditional C compilers gratuitously convert values declared as
float into double.
INTIFY (float-value)
float-returning library routine should be packaged in order to
return it. These functions are actually declared to return type
FLOAT_VALUE_TYPE (normally int).
These values can't be returned as type float because traditional
C compilers would gratuitously convert the value to a double.
A local variable named intify is always available when the macro
INTIFY is used. It is a union of a float field named
f and a field named i whose type is
FLOAT_VALUE_TYPE or int.
If you don't define this macro, the default definition works by copying the value through that union.
nongcc_SI_type
SImode in the system's own C compiler.
You need not define this macro if that type is long int, as it usually
is.
nongcc_word_type
You need not define this macro if that type is long int, as it usually
is.
perform_...
float and double in the
library routines in `libgcc1.c'. See that file for a full list
of these macros and their arguments.
On most machines, you don't need to define any of these macros, because the C compiler that comes with the system takes care of doing them.
NEXT_OBJC_RUNTIME
The default calling convention passes just the object and the selector to the lookup function, which returns a pointer to the method.
This is about addressing modes.
HAVE_PRE_INCREMENT
HAVE_PRE_DECREMENT
HAVE_POST_INCREMENT
HAVE_POST_DECREMENT
HAVE_PRE_MODIFY_DISP
HAVE_POST_MODIFY_DISP
HAVE_PRE_MODIFY_REG
HAVE_POST_MODIFY_REG
CONSTANT_ADDRESS_P (x)
CONSTANT_P (x), but a few machines are more restrictive
in which constant addresses are supported.
CONSTANT_P accepts integer-values expressions whose values are
not explicitly known, such as symbol_ref, label_ref, and
high expressions and const arithmetic expressions, in
addition to const_int and const_double expressions.
MAX_REGS_PER_ADDRESS
GO_IF_LEGITIMATE_ADDRESS would ever
accept.
GO_IF_LEGITIMATE_ADDRESS (mode, x, label)
goto label;
executed if x (an RTX) is a legitimate memory address on the
target machine for a memory operand of mode mode.
It usually pays to define several simpler macros to serve as subroutines for this one. Otherwise it may be too complicated to understand.
This macro must exist in two variants: a strict variant and a non-strict one. The strict variant is used in the reload pass. It must be defined so that any pseudo-register that has not been allocated a hard register is considered a memory reference. In contexts where some kind of register is required, a pseudo-register with no hard register must be rejected.
The non-strict variant is used in other passes. It must be defined to accept all pseudo-registers in every context where some kind of register is required.
Compiler source files that want to use the strict variant of this
macro define the macro REG_OK_STRICT. You should use an
#ifdef REG_OK_STRICT conditional to define the strict variant
in that case and the non-strict variant otherwise.
Subroutines to check for acceptable registers for various purposes (one
for base registers, one for index registers, and so on) are typically
among the subroutines used to define GO_IF_LEGITIMATE_ADDRESS.
Then only these subroutine macros need have two variants; the higher
levels of macros may be the same whether strict or not.
Normally, constant addresses which are the sum of a symbol_ref
and an integer are stored inside a const RTX to mark them as
constant. Therefore, there is no need to recognize such sums
specifically as legitimate addresses. Normally you would simply
recognize any const as legitimate.
Usually PRINT_OPERAND_ADDRESS is not prepared to handle constant
sums that are not marked with const. It assumes that a naked
plus indicates indexing. If so, then you must reject such
naked constant sums as illegitimate addresses, so that none of them will
be given to PRINT_OPERAND_ADDRESS.
On some machines, whether a symbolic address is legitimate depends on
the section that the address refers to. On these machines, define the
macro ENCODE_SECTION_INFO to store the information into the
symbol_ref, and then check for it here. When you see a
const, you will have to look inside it to find the
symbol_ref in order to determine the section. See section 21.17 Defining the Output Assembler Language.
The best way to modify the name string is by adding text to the
beginning, with suitable punctuation to prevent any ambiguity. Allocate
the new name in saveable_obstack. You will have to modify
ASM_OUTPUT_LABELREF to remove and decode the added text and
output the name accordingly, and define STRIP_NAME_ENCODING to
access the original name string.
You can check the information stored here into the symbol_ref in
the definitions of the macros GO_IF_LEGITIMATE_ADDRESS and
PRINT_OPERAND_ADDRESS.
REG_OK_FOR_BASE_P (x)
reg
RTX) is valid for use as a base register. For hard registers, it
should always accept those which the hardware permits and reject the
others. Whether the macro accepts or rejects pseudo registers must be
controlled by REG_OK_STRICT as described above. This usually
requires two variant definitions, of which REG_OK_STRICT
controls the one actually used.
REG_MODE_OK_FOR_BASE_P (x, mode)
REG_OK_FOR_BASE_P, except that
that expression may examine the mode of the memory reference in
mode. You should define this macro if the mode of the memory
reference affects whether a register may be used as a base register. If
you define this macro, the compiler will use it instead of
REG_OK_FOR_BASE_P.
REG_OK_FOR_INDEX_P (x)
reg
RTX) is valid for use as an index register.
The difference between an index register and a base register is that the index register may be scaled. If an address involves the sum of two registers, neither one of them scaled, then either one may be labeled the "base" and the other the "index"; but whichever labeling is used must fit the machine's constraints of which registers may serve in each capacity. The compiler will try both labelings, looking for one that is valid, and will reload one or both registers only if neither labeling works.
FIND_BASE_TERM (x)
It is always safe for this macro to not be defined. It exists so that alias analysis can understand machine-dependent addresses.
The typical use of this macro is to handle addresses containing a label_ref or symbol_ref within an UNSPEC.
LEGITIMIZE_ADDRESS (x, oldx, mode, win)
GO_IF_LEGITIMATE_ADDRESS (mode, x, win); |
to avoid further processing if the address has become legitimate.
x will always be the result of a call to break_out_memory_refs,
and oldx will be the operand that was given to that function to produce
x.
The code generated by this macro should not alter the substructure of x. If it transforms x into a more legitimate form, it should assign x (which will always be a C variable) a new value.
It is not necessary for this macro to come up with a legitimate address. The compiler has standard ways of doing so in all cases. In fact, it is safe for this macro to do nothing. But often a machine-dependent strategy can generate better code.
LEGITIMIZE_RELOAD_ADDRESS (x, mode, opnum, type, ind_levels, win)
For example, on the i386, it is sometimes possible to use a single
reload register instead of two by reloading a sum of two pseudo
registers into a register. On the other hand, for number of RISC
processors offsets are limited so that often an intermediate address
needs to be generated in order to address a stack slot. By defining
LEGITIMIZE_RELOAD_ADDRESS appropriately, the intermediate addresses
generated for adjacent some stack slots can be made identical, and thus
be shared.
Note: This macro should be used with caution. It is necessary to know something of how reload works in order to effectively use this, and it is quite easy to produce macros that build in too much knowledge of reload internals.
Note: This macro must be able to reload an address created by a previous invocation of this macro. If it fails to handle such addresses then the compiler may generate incorrect code or abort.
The macro definition should use push_reload to indicate parts that
need reloading; opnum, type and ind_levels are usually
suitable to be passed unaltered to push_reload.
The code generated by this macro must not alter the substructure of
x. If it transforms x into a more legitimate form, it
should assign x (which will always be a C variable) a new value.
This also applies to parts that you change indirectly by calling
push_reload.
The macro definition may use strict_memory_address_p to test if
the address has become legitimate.
If you want to change only a part of x, one standard way of doing
this is to use copy_rtx. Note, however, that is unshares only a
single level of rtl. Thus, if the part to be changed is not at the
top level, you'll need to replace first the top level.
It is not necessary for this macro to come up with a legitimate
address; but often a machine-dependent strategy can generate better code.
GO_IF_MODE_DEPENDENT_ADDRESS (addr, label)
goto
label; executed if memory address x (an RTX) can have
different meanings depending on the machine mode of the memory
reference it is used for or if the address is valid for some modes
but not others.
Autoincrement and autodecrement addresses typically have mode-dependent effects because the amount of the increment or decrement is the size of the operand being addressed. Some machines have other mode-dependent addresses. Many RISC machines have no mode-dependent addresses.
You may assume that addr is a valid address for the machine.
LEGITIMATE_CONSTANT_P (x)
CONSTANT_P, so you need not check this. In fact,
`1' is a suitable definition for this macro on machines where
anything CONSTANT_P is valid.
This describes the condition code status.
The file `conditions.h' defines a variable cc_status to
describe how the condition code was computed (in case the interpretation of
the condition code depends on the instruction that it was set by). This
variable contains the RTL expressions on which the condition code is
currently based, and several standard flags.
Sometimes additional machine-specific flags must be defined in the machine
description header file. It can also add additional machine-specific
information by defining CC_STATUS_MDEP.
CC_STATUS_MDEP
mdep
component of cc_status. It defaults to int.
This macro is not used on machines that do not use cc0.
CC_STATUS_MDEP_INIT
mdep field to "empty".
The default definition does nothing, since most machines don't use
the field anyway. If you want to use the field, you should probably
define this macro to initialize it.
This macro is not used on machines that do not use cc0.
NOTICE_UPDATE_CC (exp, insn)
cc_status
appropriately for an insn insn whose body is exp. It is
this macro's responsibility to recognize insns that set the condition
code as a byproduct of other activity as well as those that explicitly
set (cc0).
This macro is not used on machines that do not use cc0.
If there are insns that do not set the condition code but do alter
other machine registers, this macro must check to see whether they
invalidate the expressions that the condition code is recorded as
reflecting. For example, on the 68000, insns that store in address
registers do not set the condition code, which means that usually
NOTICE_UPDATE_CC can leave cc_status unaltered for such
insns. But suppose that the previous insn set the condition code
based on location `a4@(102)' and the current insn stores a new
value in `a4'. Although the condition code is not changed by
this, it will no longer be true that it reflects the contents of
`a4@(102)'. Therefore, NOTICE_UPDATE_CC must alter
cc_status in this case to say that nothing is known about the
condition code value.
The definition of NOTICE_UPDATE_CC must be prepared to deal
with the results of peephole optimization: insns whose patterns are
parallel RTXs containing various reg, mem or
constants which are just the operands. The RTL structure of these
insns is not sufficient to indicate what the insns actually do. What
NOTICE_UPDATE_CC should do when it sees one is just to run
CC_STATUS_INIT.
A possible definition of NOTICE_UPDATE_CC is to call a function
that looks at an attribute (see section 20.17 Instruction Attributes) named, for example,
`cc'. This avoids having detailed information about patterns in
two places, the `md' file and in NOTICE_UPDATE_CC.
EXTRA_CC_MODES
CC separated by white space. CC takes
two arguments. The first is the enumeration name of the mode, which
should begin with `CC' and end with `mode'. The second is a C
string giving the printable name of the mode; it should be the same as
the first argument, but with the trailing `mode' removed.
You should only define this macro if additional modes are required.
A sample definition of EXTRA_CC_MODES is:
#define EXTRA_CC_MODES \
CC(CC_NOOVmode, "CC_NOOV") \
CC(CCFPmode, "CCFP") \
CC(CCFPEmode, "CCFPE")
|
SELECT_CC_MODE (op, x, y)
MODE_CC to be used when comparison
operation code op is applied to rtx x and y. For
example, on the Sparc, SELECT_CC_MODE is defined as (see
see section 20.11 Defining Jump Instruction Patterns for a description of the reason for this
definition)
#define SELECT_CC_MODE(OP,X,Y) \
(GET_MODE_CLASS (GET_MODE (X)) == MODE_FLOAT \
? ((OP == EQ || OP == NE) ? CCFPmode : CCFPEmode) \
: ((GET_CODE (X) == PLUS || GET_CODE (X) == MINUS \
|| GET_CODE (X) == NEG) \
? CC_NOOVmode : CCmode))
|
You need not define this macro if EXTRA_CC_MODES is not defined.
CANONICALIZE_COMPARISON (code, op0, op1)
GT comparison, but you can use an LT
comparison instead and swap the order of the operands.
On such machines, define this macro to be a C statement to do any required conversions. code is the initial comparison code and op0 and op1 are the left and right operands of the comparison, respectively. You should modify code, op0, and op1 as required.
GCC will not assume that the comparison resulting from this macro is valid but will see if the resulting insn matches a pattern in the `md' file.
You need not define this macro if it would never change the comparison code or operands.
REVERSIBLE_CC_MODE (mode)
SELECT_CC_MODE
can ever return mode for a floating-point inequality comparison,
then REVERSIBLE_CC_MODE (mode) must be zero.
You need not define this macro if it would always returns zero or if the
floating-point format is anything other than IEEE_FLOAT_FORMAT.
For example, here is the definition used on the Sparc, where floating-point
inequality comparisons are always given CCFPEmode:
#define REVERSIBLE_CC_MODE(MODE) ((MODE) != CCFPEmode) |
A C expression whose value is reversed condition code of the code for
comparison done in CC_MODE mode. The macro is used only in case
REVERSIBLE_CC_MODE (mode) is nonzero. Define this macro in case
machine has some non-standard way how to reverse certain conditionals. For
instance in case all floating point conditions are non-trapping, compiler may
freely convert unordered compares to ordered one. Then definition may look
like:
#define REVERSE_CONDITION(CODE, MODE) \
((MODE) != CCFPmode ? reverse_condition (CODE) \
: reverse_condition_maybe_unordered (CODE))
|
These macros let you describe the relative speed of various operations on the target machine.
CONST_COSTS (x, code, outer_code)
switch statement that describes the relative costs
of constant RTL expressions. It must contain case labels for
expression codes const_int, const, symbol_ref,
label_ref and const_double. Each case must ultimately
reach a return statement to return the relative cost of the use
of that kind of constant value in an expression. The cost may depend on
the precise value of the constant, which is available for examination in
x, and the rtx code of the expression in which it is contained,
found in outer_code.
code is the expression code--redundant, since it can be
obtained with GET_CODE (x).
RTX_COSTS (x, code, outer_code)
CONST_COSTS but applies to nonconstant RTL expressions.
This can be used, for example, to indicate how costly a multiply
instruction is. In writing this macro, you can use the construct
COSTS_N_INSNS (n) to specify a cost equal to n fast
instructions. outer_code is the code of the expression in which
x is contained.
This macro is optional; do not define it if the default cost assumptions are adequate for the target machine.
DEFAULT_RTX_COSTS (x, code, outer_code)
RTX_COSTS or CONST_COSTS macros. This eliminates the need
to put case labels into the macro, but the code, or any functions it
calls, must assume that the RTL in x could be of any type that has
not already been handled. The arguments are the same as for
RTX_COSTS, and the macro should execute a return statement giving
the cost of any RTL expressions that it can handle. The default cost
calculation is used for any RTL for which this macro does not return a
value.
This macro is optional; do not define it if the default cost assumptions are adequate for the target machine.
ADDRESS_COST (address)
CONST_COSTS values.
For most CISC machines, the default cost is a good approximation of the true cost of the addressing mode. However, on RISC machines, all instructions normally have the same length and execution time. Hence all addresses will have equal costs.
In cases where more than one form of an address is known, the form with the lowest cost will be used. If multiple forms have the same, lowest, cost, the one that is the most complex will be used.
For example, suppose an address that is equal to the sum of a register and a constant is used twice in the same basic block. When this macro is not defined, the address will be computed in a register and memory references will be indirect through that register. On machines where the cost of the addressing mode containing the sum is no higher than that of a simple indirect reference, this will produce an additional instruction and possibly require an additional register. Proper specification of this macro eliminates this overhead for such machines.
Similar use of this macro is made in strength reduction of loops.
address need not be valid as an address. In such a case, the cost is not relevant and can be any value; invalid addresses need not be assigned a different cost.
On machines where an address involving more than one register is as
cheap as an address computation involving only one register, defining
ADDRESS_COST to reflect this can cause two registers to be live
over a region of code where only one would have been if
ADDRESS_COST were not defined in that manner. This effect should
be considered in the definition of this macro. Equivalent costs should
probably only be given to addresses with different numbers of registers
on machines with lots of registers.
This macro will normally either not be defined or be defined as a constant.
REGISTER_MOVE_COST (mode, from, to)
GENERAL_REGS. A
value of 2 is the default; other values are interpreted relative to
that.
It is not required that the cost always equal 2 when from is the same as to; on some machines it is expensive to move between registers if they are not general registers.
If reload sees an insn consisting of a single set between two
hard registers, and if REGISTER_MOVE_COST applied to their
classes returns a value of 2, reload does not check to ensure that the
constraints of the insn are met. Setting a cost of other than 2 will
allow reload to verify that the constraints are met. You should do this
if the `movm' pattern's constraints do not allow such copying.
MEMORY_MOVE_COST (mode, class, in)
REGISTER_MOVE_COST. If moving between
registers and memory is more expensive than between two registers, you
should define this macro to express the relative cost.
If you do not define this macro, GCC uses a default cost of 4 plus the cost of copying via a secondary reload register, if one is needed. If your machine requires a secondary reload register to copy between memory and a register of class but the reload mechanism is more complex than copying via an intermediate, define this macro to reflect the actual cost of the move.
GCC defines the function memory_move_secondary_cost if
secondary reloads are needed. It computes the costs due to copying via
a secondary register. If your machine copies from memory using a
secondary register in the conventional way but the default base value of
4 is not correct for your machine, define this macro to add some other
value to the result of that function. The arguments to that function
are the same as to this macro.
BRANCH_COST
Here are additional macros which do not specify precise relative costs, but only that certain actions are more expensive than GCC would ordinarily expect.
SLOW_BYTE_ACCESS
char or a short) is no
faster than accessing a word of memory, i.e., if such access
require more than one instruction or if there is no difference in cost
between byte and (aligned) word loads.
When this macro is not defined, the compiler will access a field by finding the smallest containing object; when it is defined, a fullword load will be used if alignment permits. Unless bytes accesses are faster than word accesses, using word accesses is preferable since it may eliminate subsequent memory access if subsequent accesses occur to other fields in the same word of the structure, but to different bytes.
SLOW_ZERO_EXTEND
char or short
to an int) can be done faster if the destination is a register
that is known to be zero.
If you define this macro, you must have instruction patterns that recognize RTL structures like this:
(set (strict_low_part (subreg:QI (reg:SI ...) 0)) ...) |
and likewise for HImode.
SLOW_UNALIGNED_ACCESS (mode, alignment)
When this macro is nonzero, the compiler will act as if
STRICT_ALIGNMENT were nonzero when generating code for block
moves. This can cause significantly more instructions to be produced.
Therefore, do not set this macro nonzero if unaligned accesses only add a
cycle or two to the time for a memory access.
If the value of this macro is always zero, it need not be defined. If
this macro is defined, it should produce a nonzero value when
STRICT_ALIGNMENT is nonzero.
DONT_REDUCE_ADDR
MOVE_RATIO
Note that on machines where the corresponding move insn is a
define_expand that emits a sequence of insns, this macro counts
the number of such sequences.
If you don't define this, a reasonable default is used.
MOVE_BY_PIECES_P (size, alignment)
move_by_pieces will be used to
copy a chunk of memory, or whether some other block move mechanism
will be used. Defaults to 1 if move_by_pieces_ninsns returns less
than MOVE_RATIO.
MOVE_MAX_PIECES
move_by_pieces to determine the largest unit
a load or store used to copy memory is. Defaults to MOVE_MAX.
USE_LOAD_POST_INCREMENT (mode)
HAVE_POST_INCREMENT.
USE_LOAD_POST_DECREMENT (mode)
HAVE_POST_DECREMENT.
USE_LOAD_PRE_INCREMENT (mode)
HAVE_PRE_INCREMENT.
USE_LOAD_PRE_DECREMENT (mode)
HAVE_PRE_DECREMENT.
USE_STORE_POST_INCREMENT (mode)
HAVE_POST_INCREMENT.
USE_STORE_POST_DECREMENT (mode)
HAVE_POST_DECREMENT.
USE_STORE_PRE_INCREMENT (mode)
HAVE_PRE_INCREMENT.
USE_STORE_PRE_DECREMENT (mode)
HAVE_PRE_DECREMENT.
NO_FUNCTION_CSE
NO_RECURSIVE_FUNCTION_CSE
ADJUST_COST (insn, link, dep_insn, cost)
ADJUST_PRIORITY (insn)
INSN_PRIORITY(insn). Reduce the priority
to execute the insn earlier, increase the priority to execute
insn later. Do not define this macro if you do not need to
adjust the scheduling priorities of insns.
An object file is divided into sections containing different types of data. In the most common case, there are three sections: the text section, which holds instructions and read-only data; the data section, which holds initialized writable data; and the bss section, which holds uninitialized data. Some systems have other kinds of sections.
The compiler must tell the assembler when to switch sections. These macros control what commands to output to tell the assembler this. You can also define additional sections.
TEXT_SECTION_ASM_OP
"\t.text" is right.
DATA_SECTION_ASM_OP
"\t.data" is right.
SHARED_SECTION_ASM_OP
DATA_SECTION_ASM_OP will be used.
BSS_SECTION_ASM_OP
ASM_OUTPUT_BSS nor ASM_OUTPUT_ALIGNED_BSS are defined,
uninitialized global data will be output in the data section if
`-fno-common' is passed, otherwise ASM_OUTPUT_COMMON will be
used.
SHARED_BSS_SECTION_ASM_OP
BSS_SECTION_ASM_OP is, the latter will be used.
INIT_SECTION_ASM_OP
FINI_SECTION_ASM_OP
CRT_CALL_STATIC_FUNCTION
INIT_SECTION_ASM_OP or FINI_SECTION_ASM_OP to calls to
initialization and finalization functions from the init and fini
sections. By default, this macro is a simple function call. Some
ports need hand-crafted assembly code to avoid dependencies on
registers initialized in the function prologue or to ensure that
constant pools don't end up too far way in the text section.
EXTRA_SECTIONS
in_text and in_data. You need not define this macro
on a system with no other sections (that GCC needs to use).
EXTRA_SECTION_FUNCTIONS
text_section and
data_section, for your additional sections. Do not define this
macro if you do not define EXTRA_SECTIONS.
READONLY_DATA_SECTION
data_section or a function defined in EXTRA_SECTIONS) that
switches to the section to be used for read-only items.
If these items should be placed in the text section, this macro should not be defined.
SELECT_SECTION (exp, reloc)
VAR_DECL node or a constant of some sort. reloc
indicates whether the initial value of exp requires link-time
relocations. Select the section by calling text_section or one
of the alternatives for other sections.
Do not define this macro if you put all read-only variables and constants in the read-only data section (usually the text section).
SELECT_RTX_SECTION (mode, rtx)
const_int rtx. Select the section by
calling text_section or one of the alternatives for other
sections.
Do not define this macro if you put all constants in the read-only data section.
JUMP_TABLES_IN_TEXT_SECTION
tablejump insns) should be output in the text
section, along with the assembler instructions. Otherwise, the
readonly data section is used.
This macro is irrelevant if there is no separate readonly data section.
ENCODE_SECTION_INFO (decl)
The macro definition, if any, is executed immediately after the rtl for
decl has been created and stored in DECL_RTL (decl).
The value of the rtl will be a mem whose address is a
symbol_ref.
The usual thing for this macro to do is to record a flag in the
symbol_ref (such as SYMBOL_REF_FLAG) or to store a
modified name string in the symbol_ref (if one bit is not enough
information).
STRIP_NAME_ENCODING (var, sym_name)
ENCODE_SECTION_INFO alters the symbol's name string.
UNIQUE_SECTION_P (decl)
UNIQUE_SECTION (decl, reloc)
STRING_CST node, and assign it to `DECL_SECTION_NAME (decl)'.
reloc indicates whether the initial value of exp requires
link-time relocations. If you do not define this macro, GCC will use
the symbol name prefixed by `.' as the section name. Note - this
macro can now be called for uninitialised data items as well as
initialised data and functions.
This section describes macros that help implement generation of position
independent code. Simply defining these macros is not enough to
generate valid PIC; you must also add support to the macros
GO_IF_LEGITIMATE_ADDRESS and PRINT_OPERAND_ADDRESS, as
well as LEGITIMIZE_ADDRESS. You must modify the definition of
`movsi' to do something appropriate when the source operand
contains a symbolic address. You may also need to alter the handling of
switch statements so that they use relative addresses.
PIC_OFFSET_TABLE_REGNUM
PIC_OFFSET_TABLE_REG_CALL_CLOBBERED
PIC_OFFSET_TABLE_REGNUM is clobbered by calls. Do not define
this macro if PIC_OFFSET_TABLE_REGNUM is not defined.
FINALIZE_PIC
The FINALIZE_PIC macro serves as a hook to emit these special
codes once the function is being compiled into assembly code, but not
before. (It is not done before, because in the case of compiling an
inline function, it would lead to multiple PIC prologues being
included in functions which used inline functions and were compiled to
assembly language.)
LEGITIMATE_PIC_OPERAND_P (x)
CONSTANT_P, so you need not
check this. You can also assume flag_pic is true, so you need not
check it either. You need not define this macro if all constants
(including SYMBOL_REF) can be immediate operands when generating
position independent code.
This section describes macros whose principal purpose is to describe how to write instructions in assembler language--rather than what the instructions do.
21.17.1 The Overall Framework of an Assembler File Structural information for the assembler file. 21.17.2 Output of Data Output of constants (numbers, strings, addresses). 21.17.3 Output of Uninitialized Variables Output of uninitialized variables. 21.17.4 Output and Generation of Labels Output and generation of labels. 21.17.5 How Initialization Functions Are Handled General principles of initialization and termination routines. 21.17.6 Macros Controlling Initialization Routines Specific macros that control the handling of initialization and termination routines. 21.17.7 Output of Assembler Instructions Output of actual instructions. 21.17.8 Output of Dispatch Tables Output of jump tables. 21.17.9 Assembler Commands for Exception Regions Output of exception region code. 21.17.10 Assembler Commands for Alignment Pseudo ops for alignment and skipping data.
This describes the overall framework of an assembler file.
ASM_FILE_START (stream)
Normally this macro is defined to output a line containing `#NO_APP', which is a comment that has no effect on most assemblers but tells the GNU assembler that it can save time by not checking for certain assembler constructs.
On systems that use SDB, it is necessary to output certain commands; see `attasm.h'.
ASM_FILE_END (stream)
If this macro is not defined, the default is to output nothing special at the end of the file. Most systems don't require any definition.
On systems that use SDB, it is necessary to output certain commands; see `attasm.h'.
ASM_COMMENT_START
ASM_APP_ON
asm
statement or group of consecutive ones. Normally this is
"#APP", which is a comment that has no effect on most
assemblers but tells the GNU assembler that it must check the lines
that follow for all valid assembler constructs.
ASM_APP_OFF
asm
statement or group of consecutive ones. Normally this is
"#NO_APP", which tells the GNU assembler to resume making the
time-saving assumptions that are valid for ordinary compiler output.
ASM_OUTPUT_SOURCE_FILENAME (stream, name)
This macro need not be defined if the standard form of output for the file format in use is appropriate.
OUTPUT_QUOTED_STRING (stream, string)
output_quoted_string
in your config files, GCC will only call it to output filenames to
the assembler source. So you can use it to canonicalize the format
of the filename using this macro.
ASM_OUTPUT_SOURCE_LINE (stream, line)
This macro need not be defined if the standard form of debugging information for the debugger in use is appropriate.
ASM_OUTPUT_IDENT (stream, string)
ASM_OUTPUT_SECTION_NAME (stream, decl, name, reloc)
FUNCTION_DECL, a
VAR_DECL or NULL_TREE. reloc
indicates whether the initial value of exp requires link-time
relocations. The string given by name will always be the
canonical version stored in the global stringpool.
Some target formats do not support arbitrary sections. Do not define this macro in such cases.
At present this macro is only used to support section attributes. When this macro is undefined, section attributes are disabled.
OBJC_PROLOGUE
This describes data output.
ASM_OUTPUT_LONG_DOUBLE (stream, value)
ASM_OUTPUT_DOUBLE (stream, value)
ASM_OUTPUT_FLOAT (stream, value)
ASM_OUTPUT_THREE_QUARTER_FLOAT (stream, value)
ASM_OUTPUT_SHORT_FLOAT (stream, value)
ASM_OUTPUT_BYTE_FLOAT (stream, value)
TFmode,
DFmode, SFmode, TQFmode, HFmode, or
QFmode, respectively, whose value is value. value
will be a C expression of type REAL_VALUE_TYPE. Macros such as
REAL_VALUE_TO_TARGET_DOUBLE are useful for writing these
definitions.
ASM_OUTPUT_QUADRUPLE_INT (stream, exp)
ASM_OUTPUT_DOUBLE_INT (stream, exp)
ASM_OUTPUT_INT (stream, exp)
ASM_OUTPUT_SHORT (stream, exp)
ASM_OUTPUT_CHAR (stream, exp)
For sizes larger than UNITS_PER_WORD, if the action of a macro
would be identical to repeatedly calling the macro corresponding to
a size of UNITS_PER_WORD, once for each word, you need not define
the macro.
OUTPUT_ADDR_CONST_EXTRA (stream, x, fail)
output_addr_const can't deal with, and output assembly code to
stream corresponding to the pattern x. This may be used to
allow machine-dependent UNSPECs to appear within constants.
If OUTPUT_ADDR_CONST_EXTRA fails to recognize a pattern, it must
goto fail, so that a standard error message is printed. If it
prints an error message itself, by calling, for example,
output_operand_lossage, it may just complete normally.
ASM_OUTPUT_BYTE (stream, value)
ASM_BYTE_OP
"\t.byte\t".
ASM_OUTPUT_ASCII (stream, ptr, len)
char * and len a C expression of type int.
If the assembler has a .ascii pseudo-op as found in the
Berkeley Unix assembler, do not define the macro
ASM_OUTPUT_ASCII.
CONSTANT_POOL_BEFORE_FUNCTION
ASM_OUTPUT_POOL_PROLOGUE (file, funname, fundecl, size)
If no constant-pool prefix is required, the usual case, this macro need not be defined.
ASM_OUTPUT_SPECIAL_POOL_ENTRY (file, x, mode, align, labelno, jumpto)
The argument file is the standard I/O stream to output the assembler code on. x is the RTL expression for the constant to output, and mode is the machine mode (in case x is a `const_int'). align is the required alignment for the value x; you should output an assembler directive to force this much alignment.
The argument labelno is a number to use in an internal label for the address of this pool entry. The definition of this macro is responsible for outputting the label definition at the proper place. Here is how to do this:
ASM_OUTPUT_INTERNAL_LABEL (file, "LC", labelno); |
When you output a pool entry specially, you should end with a
goto to the label jumpto. This will prevent the same pool
entry from being output a second time in the usual manner.
You need not define this macro if it would do nothing.
CONSTANT_AFTER_FUNCTION_P (exp)
tree, should be output after the code for a
function. The compiler will normally output all constants before the
function; you need not define this macro if this is OK.
ASM_OUTPUT_POOL_EPILOGUE (file funname fundecl size)
If no constant-pool epilogue is required, the usual case, you need not define this macro.
IS_ASM_LOGICAL_LINE_SEPARATOR (C)
If you do not define this macro, the default is that only the character `;' is treated as a logical line separator.
ASM_OPEN_PAREN
ASM_CLOSE_PAREN
#define ASM_OPEN_PAREN "("
#define ASM_CLOSE_PAREN ")"
|
These macros are provided by `real.h' for writing the definitions
of ASM_OUTPUT_DOUBLE and the like:
REAL_VALUE_TO_TARGET_SINGLE (x, l)
REAL_VALUE_TO_TARGET_DOUBLE (x, l)
REAL_VALUE_TO_TARGET_LONG_DOUBLE (x, l)
REAL_VALUE_TYPE, to the target's
floating point representation, and store its bit pattern in the array of
long int whose address is l. The number of elements in the
output array is determined by the size of the desired target floating
point data type: 32 bits of it go in each long int array
element. Each array element holds 32 bits of the result, even if
long int is wider than 32 bits on the host machine.
The array element values are designed so that you can print them out
using fprintf in the order they should appear in the target
machine's memory.
REAL_VALUE_TO_DECIMAL (x, format, string)
REAL_VALUE_TYPE, to a
decimal number and stores it as a string into string.
You must pass, as string, the address of a long enough block
of space to hold the result.
The argument format is a printf-specification that serves
as a suggestion for how to format the output string.
Each of the macros in this section is used to do the whole job of outputting a single uninitialized variable.
ASM_OUTPUT_COMMON (stream, name, size, rounded)
Use the expression assemble_name (stream, name) to
output the name itself; before and after that, output the additional
assembler syntax for defining the name, and a newline.
This macro controls how the assembler definitions of uninitialized common global variables are output.
ASM_OUTPUT_ALIGNED_COMMON (stream, name, size, alignment)
ASM_OUTPUT_COMMON except takes the required alignment as a
separate, explicit argument. If you define this macro, it is used in
place of ASM_OUTPUT_COMMON, and gives you more flexibility in
handling the required alignment of the variable. The alignment is specified
as the number of bits.
ASM_OUTPUT_ALIGNED_DECL_COMMON (stream, decl, name, size, alignment)
ASM_OUTPUT_ALIGNED_COMMON except that decl of the
variable to be output, if there is one, or NULL_TREE if there
is no corresponding variable. If you define this macro, GCC will use it
in place of both ASM_OUTPUT_COMMON and
ASM_OUTPUT_ALIGNED_COMMON. Define this macro when you need to see
the variable's decl in order to chose what to output.
ASM_OUTPUT_SHARED_COMMON (stream, name, size, rounded)
ASM_OUTPUT_COMMON, except that it
is used when name is shared. If not defined, ASM_OUTPUT_COMMON
will be used.
ASM_OUTPUT_BSS (stream, decl, name, size, rounded)
Try to use function asm_output_bss defined in `varasm.c' when
defining this macro. If unable, use the expression
assemble_name (stream, name) to output the name itself;
before and after that, output the additional assembler syntax for defining
the name, and a newline.
This macro controls how the assembler definitions of uninitialized global
variables are output. This macro exists to properly support languages like
C++ which do not have common data. However, this macro currently
is not defined for all targets. If this macro and
ASM_OUTPUT_ALIGNED_BSS are not defined then ASM_OUTPUT_COMMON
or ASM_OUTPUT_ALIGNED_COMMON or
ASM_OUTPUT_ALIGNED_DECL_COMMON is used.
ASM_OUTPUT_ALIGNED_BSS (stream, decl, name, size, alignment)
ASM_OUTPUT_BSS except takes the required alignment as a
separate, explicit argument. If you define this macro, it is used in
place of ASM_OUTPUT_BSS, and gives you more flexibility in
handling the required alignment of the variable. The alignment is specified
as the number of bits.
Try to use function asm_output_aligned_bss defined in file
`varasm.c' when defining this macro.
ASM_OUTPUT_SHARED_BSS (stream, decl, name, size, rounded)
ASM_OUTPUT_BSS, except that it
is used when name is shared. If not defined, ASM_OUTPUT_BSS
will be used.
ASM_OUTPUT_LOCAL (stream, name, size, rounded)
Use the expression assemble_name (stream, name) to
output the name itself; before and after that, output the additional
assembler syntax for defining the name, and a newline.
This macro controls how the assembler definitions of uninitialized static variables are output.
ASM_OUTPUT_ALIGNED_LOCAL (stream, name, size, alignment)
ASM_OUTPUT_LOCAL except takes the required alignment as a
separate, explicit argument. If you define this macro, it is used in
place of ASM_OUTPUT_LOCAL, and gives you more flexibility in
handling the required alignment of the variable. The alignment is specified
as the number of bits.
ASM_OUTPUT_ALIGNED_DECL_LOCAL (stream, decl, name, size, alignment)
ASM_OUTPUT_ALIGNED_DECL except that decl of the
variable to be output, if there is one, or NULL_TREE if there
is no corresponding variable. If you define this macro, GCC will use it
in place of both ASM_OUTPUT_DECL and
ASM_OUTPUT_ALIGNED_DECL. Define this macro when you need to see
the variable's decl in order to chose what to output.
ASM_OUTPUT_SHARED_LOCAL (stream, name, size, rounded)
ASM_OUTPUT_LOCAL, except that it
is used when name is shared. If not defined, ASM_OUTPUT_LOCAL
will be used.
This is about outputting labels.
ASM_OUTPUT_LABEL (stream, name)
assemble_name (stream, name) to
output the name itself; before and after that, output the additional
assembler syntax for defining the name, and a newline.
ASM_DECLARE_FUNCTION_NAME (stream, name, decl)
ASM_OUTPUT_LABEL). The argument decl is the
FUNCTION_DECL tree node representing the function.
If this macro is not defined, then the function name is defined in the
usual manner as a label (by means of ASM_OUTPUT_LABEL).
ASM_DECLARE_FUNCTION_SIZE (stream, name, decl)
FUNCTION_DECL tree node
representing the function.
If this macro is not defined, then the function size is not defined.
ASM_DECLARE_OBJECT_NAME (stream, name, decl)
ASM_OUTPUT_LABEL). The argument
decl is the VAR_DECL tree node representing the variable.
If this macro is not defined, then the variable name is defined in the
usual manner as a label (by means of ASM_OUTPUT_LABEL).
ASM_DECLARE_REGISTER_GLOBAL (stream, decl, regno, name)
If you don't define this macro, that is equivalent to defining it to do nothing.
ASM_FINISH_DECLARE_OBJECT (stream, decl, toplevel, atend)
If you don't define this macro, that is equivalent to defining it to do nothing.
ASM_GLOBALIZE_LABEL (stream, name)
assemble_name (stream, name) to output the name
itself; before and after that, output the additional assembler syntax
for making that name global, and a newline.
ASM_WEAKEN_LABEL
assemble_name (stream, name) to output the name
itself; before and after that, output the additional assembler syntax
for making that name weak, and a newline.
If you don't define this macro, GCC will not support weak
symbols and you should not define the SUPPORTS_WEAK macro.
SUPPORTS_WEAK
If you don't define this macro, `defaults.h' provides a default
definition. If ASM_WEAKEN_LABEL is defined, the default
definition is `1'; otherwise, it is `0'. Define this macro if
you want to control weak symbol support with a compiler flag such as
`-melf'.
MAKE_DECL_ONE_ONLY
SUPPORTS_ONE_ONLY
If you don't define this macro, `varasm.c' provides a default
definition. If MAKE_DECL_ONE_ONLY is defined, the default
definition is `1'; otherwise, it is `0'. Define this macro if
you want to control one-only symbol support with a compiler flag, or if
setting the DECL_ONE_ONLY flag is enough to mark a declaration to
be emitted as one-only.
ASM_OUTPUT_EXTERNAL (stream, decl, name)
This macro need not be defined if it does not need to output anything. The GNU assembler and most Unix assemblers don't require anything.
ASM_OUTPUT_EXTERNAL_LIBCALL (stream, symref)
rtx and
is a symbol_ref.
This macro need not be defined if it does not need to output anything. The GNU assembler and most Unix assemblers don't require anything.
ASM_OUTPUT_LABELREF (stream, name)
assemble_name.
ASM_OUTPUT_SYMBOL_REF (stream, sym)
SYMBOL_REF sym. If not defined, assemble_output
will be used to output the name of the symbol. This macro may be used
to modify the way a symbol is referenced depending on information
encoded by ENCODE_SECTION_INFO.
ASM_OUTPUT_INTERNAL_LABEL (stream, prefix, num)
It is absolutely essential that these labels be distinct from the labels used for user-level functions and variables. Otherwise, certain programs will have name conflicts with internal labels.
It is desirable to exclude internal labels from the symbol table of the object file. Most assemblers have a naming convention for labels that should be excluded; on many systems, the letter `L' at the beginning of a label has this effect. You should find out what convention your system uses, and follow it.
The usual definition of this macro is as follows:
fprintf (stream, "L%s%d:\n", prefix, num) |
ASM_OUTPUT_DEBUG_LABEL (stream, prefix, num)
If this macro is not defined, then ASM_OUTPUT_INTERNAL_LABEL will be
used.
ASM_OUTPUT_ALTERNATE_LABEL_NAME (stream, string)
The default definition of this macro is as follows:
fprintf (stream, "%s:\n", LABEL_ALTERNATE_NAME (INSN)) |
ASM_GENERATE_INTERNAL_LABEL (string, prefix, num)
This string, when output subsequently by assemble_name, should
produce the output that ASM_OUTPUT_INTERNAL_LABEL would produce
with the same prefix and num.
If the string begins with `*', then assemble_name will
output the rest of the string unchanged. It is often convenient for
ASM_GENERATE_INTERNAL_LABEL to use `*' in this way. If the
string doesn't start with `*', then ASM_OUTPUT_LABELREF gets
to output the string, and may change it. (Of course,
ASM_OUTPUT_LABELREF is also part of your machine description, so
you should know what it does on your machine.)
ASM_FORMAT_PRIVATE_NAME (outvar, name, number)
char *) a newly allocated string made from the string
name and the number number, with some suitable punctuation
added. Use alloca to get space for the string.
The string will be used as an argument to ASM_OUTPUT_LABELREF to
produce an assembler label for an internal static variable whose name is
name. Therefore, the string must be such as to result in valid
assembler code. The argument number is different each time this
macro is executed; it prevents conflicts between similarly-named
internal static variables in different scopes.
Ideally this string should not be a valid C identifier, to prevent any conflict with the user's own symbols. Most assemblers allow periods or percent signs in assembler symbols; putting at least one of these between the name and the number will suffice.
ASM_OUTPUT_DEF (stream, name, value)
If SET_ASM_OP is defined, a default definition is provided which is
correct for most systems.
ASM_OUTPUT_DEF_FROM_DECLS (stream, decl_of_name, decl_of_value)
ASM_OUTPUT_DEFINE_LABEL_DIFFERENCE_SYMBOL (stream, symbol, high, low)
If SET_ASM_OP is defined, a default definition is provided which is
correct for most systems.
ASM_OUTPUT_WEAK_ALIAS (stream, name, value)
NULL, it defines name as
an undefined weak symbol.
Define this macro if the target only supports weak aliases; define
ASM_OUTPUT_DEF instead if possible.
OBJC_GEN_METHOD_LABEL (buf, is_inst, class_name, cat_name, sel_name)
The default name is a unique method number followed by the name of the class (e.g. `_1_Foo'). For methods in categories, the name of the category is also included in the assembler name (e.g. `_1_Foo_Bar').
These names are safe on most systems, but make debugging difficult since the method's selector is not present in the name. Therefore, particular systems define other ways of computing names.
buf is an expression of type char * which gives you a
buffer in which to store the name; its length is as long as
class_name, cat_name and sel_name put together, plus
50 characters extra.
The argument is_inst specifies whether the method is an instance
method or a class method; class_name is the name of the class;
cat_name is the name of the category (or NULL if the method is not
in a category); and sel_name is the name of the selector.
On systems where the assembler can handle quoted names, you can use this macro to provide more human-readable names.
The compiled code for certain languages includes constructors
(also called initialization routines)---functions to initialize
data in the program when the program is started. These functions need
to be called before the program is "started"---that is to say, before
main is called.
Compiling some languages generates destructors (also called termination routines) that should be called when the program terminates.
To make the initialization and termination functions work, the compiler must output something in the assembler code to cause those functions to be called at the appropriate time. When you port the compiler to a new system, you need to specify how to do this.
There are two major ways that GCC currently supports the execution of initialization and termination functions. Each way has two variants. Much of the structure is common to all four variations.
The linker must build two lists of these functions--a list of
initialization functions, called __CTOR_LIST__, and a list of
termination functions, called __DTOR_LIST__.
Each list always begins with an ignored function pointer (which may hold 0, -1, or a count of the function pointers after it, depending on the environment). This is followed by a series of zero or more function pointers to constructors (or destructors), followed by a function pointer containing zero.
Depending on the operating system and its executable file format, either `crtstuff.c' or `libgcc2.c' traverses these lists at startup time and exit time. Constructors are called in reverse order of the list; destructors in forward order.
The best way to handle static constructors works only for object file formats which provide arbitrarily-named sections. A section is set aside for a list of constructors, and another for a list of destructors. Traditionally these are called `.ctors' and `.dtors'. Each object file that defines an initialization function also puts a word in the constructor section to point to that function. The linker accumulates all these words into one contiguous `.ctors' section. Termination functions are handled similarly.
To use this method, you need appropriate definitions of the macros
ASM_OUTPUT_CONSTRUCTOR and ASM_OUTPUT_DESTRUCTOR. Usually
you can get them by including `svr4.h'.
When arbitrary sections are available, there are two variants, depending
upon how the code in `crtstuff.c' is called. On systems that
support an init section which is executed at program startup,
parts of `crtstuff.c' are compiled into that section. The
program is linked by the gcc driver like this:
ld -o output_file crtbegin.o ... crtend.o -lgcc |
The head of a function (__do_global_ctors) appears in the init
section of `crtbegin.o'; the remainder of the function appears in
the init section of `crtend.o'. The linker will pull these two
parts of the section together, making a whole function. If any of the
user's object files linked into the middle of it contribute code, then that
code will be executed as part of the body of __do_global_ctors.
To use this variant, you must define the INIT_SECTION_ASM_OP
macro properly.
If no init section is available, do not define
INIT_SECTION_ASM_OP. Then __do_global_ctors is built into
the text section like all other functions, and resides in
`libgcc.a'. When GCC compiles any function called main, it
inserts a procedure call to __main as the first executable code
after the function prologue. The __main function, also defined
in `libgcc2.c', simply calls `__do_global_ctors'.
In file formats that don't support arbitrary sections, there are again
two variants. In the simplest variant, the GNU linker (GNU ld)
and an `a.out' format must be used. In this case,
ASM_OUTPUT_CONSTRUCTOR is defined to produce a .stabs
entry of type `N_SETT', referencing the name __CTOR_LIST__,
and with the address of the void function containing the initialization
code as its value. The GNU linker recognizes this as a request to add
the value to a "set"; the values are accumulated, and are eventually
placed in the executable as a vector in the format described above, with
a leading (ignored) count and a trailing zero element.
ASM_OUTPUT_DESTRUCTOR is handled similarly. Since no init
section is available, the absence of INIT_SECTION_ASM_OP causes
the compilation of main to call __main as above, starting
the initialization process.
The last variant uses neither arbitrary sections nor the GNU linker.
This is preferable when you want to do dynamic linking and when using
file formats which the GNU linker does not support, such as `ECOFF'. In
this case, ASM_OUTPUT_CONSTRUCTOR does not produce an
N_SETT symbol; initialization and termination functions are
recognized simply by their names. This requires an extra program in the
linkage step, called collect2. This program pretends to be the
linker, for use with GCC; it does its job by running the ordinary
linker, but also arranges to include the vectors of initialization and
termination functions. These functions are called via __main as
described above.
Choosing among these configuration options has been simplified by a set of operating-system-dependent files in the `config' subdirectory. These files define all of the relevant parameters. Usually it is sufficient to include one into your specific machine-dependent configuration file. These files are:
The following section describes the specific macros that control and customize the handling of initialization and termination functions.
Here are the macros that control how the compiler handles initialization and termination functions:
INIT_SECTION_ASM_OP
HAS_INIT_SECTION
main will not call __main as described above.
This macro should be defined for systems that control the contents of the
init section on a symbol-by-symbol basis, such as OSF/1, and should not
be defined explicitly for systems that support
INIT_SECTION_ASM_OP.
LD_INIT_SWITCH
LD_FINI_SWITCH
INVOKE__main
main will call __main despite the presence of
INIT_SECTION_ASM_OP. This macro should be defined for systems
where the init section is not actually run automatically, but is still
useful for collecting the lists of constructors and destructors.
SUPPORTS_INIT_PRIORITY
init_priority attribute is supported and the
compiler should emit instructions to control the order of initialization
of objects. If zero, the compiler will issue an error message upon
encountering an init_priority attribute.
ASM_OUTPUT_CONSTRUCTOR (stream, name)
Assume that name is the name of a C function generated
automatically by the compiler. This function takes no arguments. Use
the function assemble_name to output the name name; this
performs any system-specific syntactic transformations such as adding an
underscore.
If you don't define this macro, nothing special is output to arrange to
call the function. This is correct when the function will be called in
some other manner--for example, by means of the collect2 program,
which looks through the symbol table to find these functions by their
names.
ASM_OUTPUT_DESTRUCTOR (stream, name)
ASM_OUTPUT_CONSTRUCTOR but used for termination
functions rather than initialization functions.
When ASM_OUTPUT_CONSTRUCTOR and ASM_OUTPUT_DESTRUCTOR are
defined, the initialization routine generated for the generated object
file will have static linkage.
If your system uses collect2 as the means of processing
constructors, then that program normally uses nm to scan an
object file for constructor functions to be called. On such systems you
must not define ASM_OUTPUT_CONSTRUCTOR and ASM_OUTPUT_DESTRUCTOR
as the object file's initialization routine must have global scope.
On certain kinds of systems, you can define these macros to make
collect2 work faster (and, in some cases, make it work at all):
OBJECT_FORMAT_COFF
collect2 can assume this format and scan
object files directly for dynamic constructor/destructor functions.
OBJECT_FORMAT_ROSE
collect2 can assume this format and scan object files directly
for dynamic constructor/destructor functions.
These macros are effective only in a native compiler; collect2 as
part of a cross compiler always uses nm for the target machine.
REAL_NM_FILE_NAME
nm. The default is to search the path normally for
nm.
If your system supports shared libraries and has a program to list the dynamic dependencies of a given library or executable, you can define these macros to enable support for running initialization and termination functions in shared libraries:
LDD_SUFFIX
"ldd" under SunOS 4.
PARSE_LDD_OUTPUT (ptr)
LDD_SUFFIX. ptr is a variable
of type char * that points to the beginning of a line of output
from LDD_SUFFIX. If the line lists a dynamic dependency, the
code must advance ptr to the beginning of the filename on that
line. Otherwise, it must set ptr to NULL.
This describes assembler instruction output.
REGISTER_NAMES
ADDITIONAL_REGISTER_NAMES
asm option in declarations to refer
to registers using alternate names.
ASM_OUTPUT_OPCODE (stream, ptr)
The definition is a C statement or statements which output an
assembler instruction opcode to the stdio stream stream. The
macro-operand ptr is a variable of type char * which
points to the opcode name in its "internal" form--the form that is
written in the machine description. The definition should output the
opcode name to stream, performing any translation you desire, and
increment the variable ptr to point at the end of the opcode
so that it will not be output twice.
In fact, your macro definition may process less than the entire opcode name, or more than the opcode name; but if you want to process text that includes `%'-sequences to substitute operands, you must take care of the substitution yourself. Just be sure to increment ptr over whatever text should not be output normally.
If you need to look at the operand values, they can be found as the
elements of recog_operand.
If the macro definition does nothing, the instruction is output in the usual way.
FINAL_PRESCAN_INSN (insn, opvec, noperands)
Here the argument opvec is the vector containing the operands extracted from insn, and noperands is the number of elements of the vector which contain meaningful data for this insn. The contents of this vector are what will be used to convert the insn template into assembler code, so you can change the assembler output by changing the contents of the vector.
This macro is useful when various assembler syntaxes share a single file of instruction patterns; by defining this macro differently, you can cause a large class of instructions to be output differently (such as with rearranged operands). Naturally, variations in assembler syntax affecting individual insn patterns ought to be handled by writing conditional output routines in those patterns.
If this macro is not defined, it is equivalent to a null statement.
FINAL_PRESCAN_LABEL
FINAL_PRESCAN_INSN will be called on each
CODE_LABEL. In that case, opvec will be a null pointer and
noperands will be zero.
PRINT_OPERAND (stream, x, code)
code is a value that can be used to specify one of several ways of printing the operand. It is used when identical operands must be printed differently depending on the context. code comes from the `%' specification that was used to request printing of the operand. If the specification was just `%digit' then code is 0; if the specification was `%ltr digit' then code is the ASCII code for ltr.
If x is a register, this macro should print the register's name.
The names can be found in an array reg_names whose type is
char *[]. reg_names is initialized from
REGISTER_NAMES.
When the machine description has a specification `%punct' (a `%' followed by a punctuation character), this macro is called with a null pointer for x and the punctuation character for code.
PRINT_OPERAND_PUNCT_VALID_P (code)
PRINT_OPERAND macro. If
PRINT_OPERAND_PUNCT_VALID_P is not defined, it means that no
punctuation characters (except for the standard one, `%') are used
in this way.
PRINT_OPERAND_ADDRESS (stream, x)
On some machines, the syntax for a symbolic address depends on the
section that the address refers to. On these machines, define the macro
ENCODE_SECTION_INFO to store the information into the
symbol_ref, and then check for it here. See section 21.17 Defining the Output Assembler Language.
DBR_OUTPUT_SEQEND(file)
dbr_sequence_length to
determine the number of slots filled in a sequence (zero if not
currently outputting a sequence), to decide how many no-ops to output,
or whatever.
Don't define this macro if it has nothing to do, but it is helpful in reading assembly output if the extent of the delay sequence is made explicit (e.g. with white space).
Note that output routines for instructions with delay slots must be
prepared to deal with not being output as part of a sequence
(i.e. when the scheduling pass is not run, or when no slot fillers could be
found.) The variable final_sequence is null when not
processing a sequence, otherwise it contains the sequence rtx
being output.
REGISTER_PREFIX
LOCAL_LABEL_PREFIX
USER_LABEL_PREFIX
IMMEDIATE_PREFIX
asm_fprintf (see
`final.c'). These are useful when a single `md' file must
support multiple assembler formats. In that case, the various `tm.h'
files can define these macros differently.
ASM_FPRINTF_EXTENSIONS(file, argptr, format)
case
statements which will be parsed inside the switch statement of
the asm_fprintf function. This allows targets to define extra
printf formats which may useful when generating their assembler
statements. Note that upper case letters are reserved for future
generic extensions to asm_fprintf, and so are not available to target
specific code. The output file is given by the parameter file.
The varargs input pointer is argptr and the rest of the format
string, starting the character after the one that is being switched
upon, is pointed to by format.
ASSEMBLER_DIALECT
If this macro is defined, you may use constructs of the form
`{option0|option1|option2...}' in the output
templates of patterns (see section 20.5 Output Templates and Operand Substitution) or in the first argument
of asm_fprintf. This construct outputs `option0',
`option1' or `option2', etc., if the value of
ASSEMBLER_DIALECT is zero, one or two, etc. Any special
characters within these strings retain their usual meaning.
If you do not define this macro, the characters `{', `|' and
`}' do not have any special meaning when used in templates or
operands to asm_fprintf.
Define the macros REGISTER_PREFIX, LOCAL_LABEL_PREFIX,
USER_LABEL_PREFIX and IMMEDIATE_PREFIX if you can express
the variations in assembler language syntax with that mechanism. Define
ASSEMBLER_DIALECT and use the `{option0|option1}' syntax
if the syntax variant are larger and involve such things as different
opcodes or operand order.
ASM_OUTPUT_REG_PUSH (stream, regno)
ASM_OUTPUT_REG_POP (stream, regno)
This concerns dispatch tables.
ASM_OUTPUT_ADDR_DIFF_ELT (stream, body, value, rel)
ASM_OUTPUT_INTERNAL_LABEL, and they must be printed in the same
way here. For example,
fprintf (stream, "\t.word L%d-L%d\n",
value, rel)
|
You must provide this macro on machines where the addresses in a
dispatch table are relative to the table's own address. If defined, GCC
will also use this macro on all machines when producing PIC.
body is the body of the ADDR_DIFF_VEC; it is provided so that the
mode and flags can be read.
ASM_OUTPUT_ADDR_VEC_ELT (stream, value)
The definition should be a C statement to output to the stdio stream
stream an assembler pseudo-instruction to generate a reference to
a label. value is the number of an internal label whose
definition is output using ASM_OUTPUT_INTERNAL_LABEL.
For example,
fprintf (stream, "\t.word L%d\n", value) |
ASM_OUTPUT_CASE_LABEL (stream, prefix, num, table)
ASM_OUTPUT_INTERNAL_LABEL; the fourth argument is the
jump-table which follows (a jump_insn containing an
addr_vec or addr_diff_vec).
This feature is used on system V to output a swbeg statement
for the table.
If this macro is not defined, these labels are output with
ASM_OUTPUT_INTERNAL_LABEL.
ASM_OUTPUT_CASE_END (stream, num, table)
If this macro is not defined, nothing special is output at the end of the jump-table.
This describes commands marking the start and the end of an exception region.
ASM_OUTPUT_EH_REGION_BEG ()
This macro need not be defined on most platforms.
ASM_OUTPUT_EH_REGION_END ()
This macro need not be defined on most platforms.
EXCEPTION_SECTION ()
.gcc_except_table on machines that support named
sections via ASM_OUTPUT_SECTION_NAME, otherwise if `-fpic'
or `-fPIC' is in effect, the data_section, otherwise the
readonly_data_section.
EH_FRAME_SECTION_ASM_OP
You should define this symbol if your target supports DWARF 2 frame unwind information and the default definition does not work.
OMIT_EH_TABLE ()
This macro need not be defined on most platforms.
EH_TABLE_LOOKUP ()
This macro need not be defined on most platforms.
DOESNT_NEED_UNWINDER
MASK_RETURN_ADDR
RETURN_ADDR_RTX, so
that it does not contain any extraneous set bits in it.
DWARF2_UNWIND_INFO
If this macro is defined to 1, the DWARF 2 unwinder will be the default
exception handling mechanism; otherwise, setjmp/longjmp will be used by
default.
If this macro is defined to anything, the DWARF 2 unwinder will be used
instead of inline unwinders and __unwind_function in the non-setjmp case.
DWARF_CIE_DATA_ALIGNMENT
UNITS_PER_WORD. The definition should be the negative minimum
alignment if STACK_GROWS_DOWNWARD is defined, and the positive
minimum alignment otherwise. See section 21.18.5 Macros for SDB and DWARF Output. Only applicable if
the target supports DWARF 2 frame unwind information.
This describes commands for alignment.
LABEL_ALIGN_AFTER_BARRIER (label)
BARRIER.
This macro need not be defined if you don't want any special alignment to be done at such a time. Most machine descriptions do not currently define the macro.
Unless it's necessary to inspect the label parameter, it is better
to set the variable align_jumps in the target's
OVERRIDE_OPTIONS. Otherwise, you should try to honour the user's
selection in align_jumps in a LABEL_ALIGN_AFTER_BARRIER
implementation.
LABEL_ALIGN_AFTER_BARRIER_MAX_SKIP
LABEL_ALIGN_AFTER_BARRIER. This works only if
ASM_OUTPUT_MAX_SKIP_ALIGN is defined.
LOOP_ALIGN (label)
NOTE_INSN_LOOP_BEG note.
This macro need not be defined if you don't want any special alignment to be done at such a time. Most machine descriptions do not currently define the macro.
Unless it's necessary to inspect the label parameter, it is better
to set the variable align_loops in the target's
OVERRIDE_OPTIONS. Otherwise, you should try to honour the user's
selection in align_loops in a LOOP_ALIGN implementation.
LOOP_ALIGN_MAX_SKIP
LOOP_ALIGN.
This works only if ASM_OUTPUT_MAX_SKIP_ALIGN is defined.
LABEL_ALIGN (label)
LABEL_ALIGN_AFTER_BARRIER / LOOP_ALIGN specify a different alignment,
the maximum of the specified values is used.
Unless it's necessary to inspect the label parameter, it is better
to set the variable align_labels in the target's
OVERRIDE_OPTIONS. Otherwise, you should try to honour the user's
selection in align_labels in a LABEL_ALIGN implementation.
LABEL_ALIGN_MAX_SKIP
LABEL_ALIGN.
This works only if ASM_OUTPUT_MAX_SKIP_ALIGN is defined.
ASM_OUTPUT_SKIP (stream, nbytes)
int.
ASM_NO_SKIP_IN_TEXT
ASM_OUTPUT_SKIP should not be used in the
text section because it fails to put zeros in the bytes that are skipped.
This is true on many Unix systems, where the pseudo--op to skip bytes
produces no-op instructions rather than zeros when used in the text
section.
ASM_OUTPUT_ALIGN (stream, power)
int.
ASM_OUTPUT_MAX_SKIP_ALIGN (stream, power, max_skip)
int.
This describes how to specify debugging information.
21.18.1 Macros Affecting All Debugging Formats Macros that affect all debugging formats uniformly. 21.18.2 Specific Options for DBX Output Macros enabling specific options in DBX format. 21.18.3 Open-Ended Hooks for DBX Format Hook macros for varying DBX format. 21.18.4 File Names in DBX Format Macros controlling output of file names in DBX format. 21.18.5 Macros for SDB and DWARF Output Macros for SDB (COFF) and DWARF formats.
These macros affect all debugging formats.
DBX_REGISTER_NUMBER (regno)
If two registers have consecutive numbers inside GCC, and they can be
used as a pair to hold a multiword value, then they must have
consecutive numbers after renumbering with DBX_REGISTER_NUMBER.
Otherwise, debuggers will be unable to access such a pair, because they
expect register pairs to be consecutive in their own numbering scheme.
If you find yourself defining DBX_REGISTER_NUMBER in way that
does not preserve register pairs, then what you must do instead is
redefine the actual register numbering scheme.
DEBUGGER_AUTO_OFFSET (x)
DEBUGGER_ARG_OFFSET (offset, x)
PREFERRED_DEBUGGING_TYPE
DBX_DEBUG,
SDB_DEBUG, DWARF_DEBUG, DWARF2_DEBUG, and
XCOFF_DEBUG.
When the user specifies `-ggdb', GCC normally also uses the
value of this macro to select the debugging output format, but with two
exceptions. If DWARF2_DEBUGGING_INFO is defined and
LINKER_DOES_NOT_WORK_WITH_DWARF2 is not defined, GCC uses the
value DWARF2_DEBUG. Otherwise, if DBX_DEBUGGING_INFO is
defined, GCC uses DBX_DEBUG.
The value of this macro only affects the default debugging output; the user can always get a specific type of output by using `-gstabs', `-gcoff', `-gdwarf-1', `-gdwarf-2', or `-gxcoff'.
These are specific options for DBX output.
DBX_DEBUGGING_INFO
XCOFF_DEBUGGING_INFO
DEFAULT_GDB_EXTENSIONS
DEBUG_SYMS_TEXT
.stabs commands should be output while
in the text section.
ASM_STABS_OP
"\t.stabs\t" to define an ordinary debugging symbol.
If you don't define this macro, "\t.stabs\t" is used. This macro
applies only to DBX debugging information format.
ASM_STABD_OP
"\t.stabd\t" to define a debugging symbol whose
value is the current location. If you don't define this macro,
"\t.stabd\t" is used. This macro applies only to DBX debugging
information format.
ASM_STABN_OP
"\t.stabn\t" to define a debugging symbol with no
name. If you don't define this macro, "\t.stabn\t" is used. This
macro applies only to DBX debugging information format.
DBX_NO_XREFS
DBX_CONTIN_LENGTH
.stabs directives) when it
exceeds a certain length (by default, 80 characters). On some
operating systems, DBX requires this splitting; on others, splitting
must not be done. You can inhibit splitting by defining this macro
with the value zero. You can override the default splitting-length by
defining this macro as an expression for the length you desire.
DBX_CONTIN_CHAR
.stabs string when a continuation follows. To use
a different character instead, define this macro as a character
constant for the character you want to use. Do not define this macro
if backslash is correct for your system.
DBX_STATIC_STAB_DATA_SECTION
DBX_TYPE_DECL_STABS_CODE
.stabs directive
for a typedef. The default is N_LSYM.
DBX_STATIC_CONST_VAR_CODE
.stabs directive
for a static variable located in the text section. DBX format does not
provide any "right" way to do this. The default is N_FUN.
DBX_REGPARM_STABS_CODE
.stabs directive
for a parameter passed in registers. DBX format does not provide any
"right" way to do this. The default is N_RSYM.
DBX_REGPARM_STABS_LETTER
'P'.
DBX_MEMPARM_STABS_LETTER
'p'.
DBX_FUNCTION_FIRST
DBX_LBRAC_FIRST
N_LBRAC symbol for a block should
precede the debugging information for variables and functions defined in
that block. Normally, in DBX format, the N_LBRAC symbol comes
first.
DBX_BLOCKS_FUNCTION_RELATIVE
N_LBRAC or N_RBRAC) should be relative to the start
of the enclosing function. Normally, GCC uses an absolute address.
DBX_USE_BINCL
N_BINCL and
N_EINCL stabs for included header files, as on Sun systems. This
macro also directs GCC to output a type number as a pair of a file
number and a type number within the file. Normally, GCC does not
generate N_BINCL or N_EINCL stabs, and it outputs a single
number for a type number.
These are hooks for DBX format.
DBX_OUTPUT_LBRAC (stream, name)
assemble_name) whose value is the address where the scope begins.
DBX_OUTPUT_RBRAC (stream, name)
DBX_OUTPUT_LBRAC, but for the end of a scope level.
DBX_OUTPUT_ENUM (stream, type)
DBX_OUTPUT_FUNCTION_END (stream, function)
FUNCTION_DECL node for
the function.
DBX_OUTPUT_STANDARD_TYPES (syms)
tree which is a chain of all the predefined
global symbols, including names of data types.
Normally, DBX output starts with definitions of the types for integers and characters, followed by all the other predefined types of the particular language in no particular order.
On some machines, it is necessary to output different particular types
first. To do this, define DBX_OUTPUT_STANDARD_TYPES to output
those symbols in the necessary order. Any predefined types that you
don't explicitly output will be output afterward in no particular order.
Be careful not to define this macro so that it works only for C. There are no global variables to access most of the built-in types, because another language may have another set of types. The way to output a particular type is to look through syms to see if you can find it. Here is an example:
{
tree decl;
for (decl = syms; decl; decl = TREE_CHAIN (decl))
if (!strcmp (IDENTIFIER_POINTER (DECL_NAME (decl)),
"long int"))
dbxout_symbol (decl);
...
}
|
This does nothing if the expected type does not exist.
See the function init_decl_processing in `c-decl.c' to find
the names to use for all the built-in C types.
Here is another way of finding a particular type:
{
tree decl;
for (decl = syms; decl; decl = TREE_CHAIN (decl))
if (TREE_CODE (decl) == TYPE_DECL
&& (TREE_CODE (TREE_TYPE (decl))
== INTEGER_CST)
&& TYPE_PRECISION (TREE_TYPE (decl)) == 16
&& TYPE_UNSIGNED (TREE_TYPE (decl)))
/* This must be |
NO_DBX_FUNCTION_END
.stabs "",N_FUN,,0,0,Lscope-function-1 gdb dbx extension construct.
On those machines, define this macro to turn this feature off without
disturbing the rest of the gdb extensions.
This describes file names in DBX format.
DBX_WORKING_DIRECTORY
Note that the working directory is always recorded if GDB extensions are enabled.
DBX_OUTPUT_MAIN_SOURCE_FILENAME (stream, name)
This macro need not be defined if the standard form of output for DBX debugging information is appropriate.
DBX_OUTPUT_MAIN_SOURCE_DIRECTORY (stream, name)
This macro need not be defined if the standard form of output for DBX debugging information is appropriate.
DBX_OUTPUT_MAIN_SOURCE_FILE_END (stream, name)
If you don't define this macro, nothing special is output at the end of compilation, which is correct for most machines.
DBX_OUTPUT_SOURCE_FILENAME (stream, name)
This macro need not be defined if the standard form of output for DBX debugging information is appropriate.
Here are macros for SDB and DWARF output.
SDB_DEBUGGING_INFO
DWARF_DEBUGGING_INFO
DWARF2_DEBUGGING_INFO
To support optional call frame debugging information, you must also
define INCOMING_RETURN_ADDR_RTX and either set
RTX_FRAME_RELATED_P on the prologue insns if you use RTL for the
prologue, or call dwarf2out_def_cfa and dwarf2out_reg_save
as appropriate from FUNCTION_PROLOGUE if you don't.
DWARF2_FRAME_INFO
DWARF2_UNWIND_INFO
(see section 21.17.9 Assembler Commands for Exception Regions is nonzero, GCC will output this
information not matter how you define DWARF2_FRAME_INFO.
LINKER_DOES_NOT_WORK_WITH_DWARF2
PREFERRED_DEBUGGING_TYPE macro for more details.
DWARF2_GENERATE_TEXT_SECTION_LABEL
DWARF2_ASM_LINE_DEBUG_INFO
PUT_SDB_...
SDB_DELIM
PUT_SDB_op macros if this is the only change
required.
SDB_GENERATE_FAKE
SDB_ALLOW_UNKNOWN_REFERENCES
SDB_ALLOW_FORWARD_REFERENCES
While all modern machines use 2's complement representation for integers, there are a variety of representations for floating point numbers. This means that in a cross-compiler the representation of floating point numbers in the compiled program may be different from that used in the machine doing the compilation.
Because different representation systems may offer different amounts of
range and precision, the cross compiler cannot safely use the host
machine's floating point arithmetic. Therefore, floating point constants
must be represented in the target machine's format. This means that the
cross compiler cannot use atof to parse a floating point constant;
it must have its own special routine to use instead. Also, constant
folding must emulate the target machine's arithmetic (or must not be done
at all).
The macros in the following table should be defined only if you are cross compiling between different floating point formats.
Otherwise, don't define them. Then default definitions will be set up which
use double as the data type, == to test for equality, etc.
You don't need to worry about how many times you use an operand of any of these macros. The compiler never uses operands which have side effects.
REAL_VALUE_TYPE
struct containing an array of int.
REAL_VALUES_EQUAL (x, y)
REAL_VALUE_TYPE.
REAL_VALUES_LESS (x, y)
REAL_VALUE_TYPE and
interpreted as floating point numbers in the target machine's
representation.
REAL_VALUE_LDEXP (x, scale)
ldexp, but using the target machine's floating point
representation. Both x and the value of the expression have
type REAL_VALUE_TYPE. The second argument, scale, is an
integer.
REAL_VALUE_FIX (x)
REAL_VALUE_TYPE.
REAL_VALUE_UNSIGNED_FIX (x)
REAL_VALUE_TYPE.
REAL_VALUE_RNDZINT (x)
REAL_VALUE_TYPE,
and so does the value.
REAL_VALUE_UNSIGNED_RNDZINT (x)
REAL_VALUE_TYPE, and so does the value.
REAL_VALUE_ATOF (string, mode)
char *, into a floating point number in the target machine's
representation for mode mode. The value has type
REAL_VALUE_TYPE.
REAL_INFINITY
REAL_VALUE_ISINF (x)
int.
By default, this is defined to call isinf.
REAL_VALUE_ISNAN (x)
int. By default, this is defined to call isnan.
Define the following additional macros if you want to make floating point constant folding work while cross compiling. If you don't define them, cross compilation is still possible, but constant folding will not happen for floating point values.
REAL_ARITHMETIC (output, code, x, y)
REAL_VALUE_TYPE in the target machine's representation, to
produce a result of the same type and representation which is stored
in output (which will be a variable).
The operation to be performed is specified by code, a tree code
which will always be one of the following: PLUS_EXPR,
MINUS_EXPR, MULT_EXPR, RDIV_EXPR,
MAX_EXPR, MIN_EXPR.
The expansion of this macro is responsible for checking for overflow.
If overflow happens, the macro expansion should execute the statement
return 0;, which indicates the inability to perform the
arithmetic operation requested.
REAL_VALUE_NEGATE (x)
REAL_VALUE_TYPE and are in the target machine's
floating point representation.
There is no way for this macro to report overflow, since overflow can't happen in the negation operation.
REAL_VALUE_TRUNCATE (mode, x)
Both x and the value of the expression are in the target machine's
floating point representation and have type REAL_VALUE_TYPE.
However, the value should have an appropriate bit pattern to be output
properly as a floating constant whose precision accords with mode
mode.
There is no way for this macro to report overflow.
REAL_VALUE_TO_INT (low, high, x)
REAL_VALUE_FROM_INT (x, low, high, mode)
REAL_VALUE_TYPE.
OPTIMIZE_MODE_SWITCHING (entity)
For an example, the SH4 can perform both single and double precision
floating point operations, but to perform a single precision operation,
the FPSCR PR bit has to be cleared, while for a double precision
operation, this bit has to be set. Changing the PR bit requires a general
purpose register as a scratch register, hence these FPSCR sets have to
be inserted before reload, i.e. you can't put this into instruction emitting
or MACHINE_DEPENDENT_REORG.
You can have multiple entities that are mode-switched, and select at run time
which entities actually need it. OPTIMIZE_MODE_SWITCHING should
return nonzero for any entity that needs mode-switching.
If you define this macro, you also have to define
NUM_MODES_FOR_MODE_SWITCHING, MODE_NEEDED,
MODE_PRIORITY_TO_MODE and EMIT_MODE_SET.
NORMAL_MODE is optional.
NUM_MODES_FOR_MODE_SWITCHING
OPTIMIZE_MODE_SWITCHING, you have to define this as
initializer for an array of integers. Each initializer element
N refers to an entity that needs mode switching, and specifies the number
of different modes that might need to be set for this entity.
The position of the initializer in the initializer - starting counting at
zero - determines the integer that is used to refer to the mode-switched
entity in question.
In macros that take mode arguments / yield a mode result, modes are
represented as numbers 0 ... N - 1. N is used to specify that no mode
switch is needed / supplied.
MODE_NEEDED (entity, insn)
OPTIMIZE_MODE_SWITCHING is defined, you must define this macro to
return an integer value not larger than the corresponding element in
NUM_MODES_FOR_MODE_SWITCHING, to denote the mode that entity must
be switched into prior to the execution of insn.
NORMAL_MODE (entity)
MODE_PRIORITY_TO_MODE (entity, n)
NUM_MODES_FOR_MODE_SWITCHING[entity] - 1 the
lowest. The value of the macro should be an integer designating a mode
for entity. For any fixed entity, mode_priority_to_mode
(entity, n) shall be a bijection in 0 ...
num_modes_for_mode_switching[entity] - 1.
EMIT_MODE_SET (entity, mode, hard_regs_live)
Here are several miscellaneous parameters.
PREDICATE_CODES
#define PREDICATE_CODES \
{"gen_reg_rtx_operand", {SUBREG, REG}}, \
{"reg_or_short_cint_operand", {SUBREG, REG, CONST_INT}},
|
Defining this macro does not affect the generated code (however, incorrect definitions that omit an rtl code that may be matched by the predicate can cause the compiler to malfunction). Instead, it allows the table built by `genrecog' to be more compact and efficient, thus speeding up the compiler. The most important predicates to include in the list specified by this macro are those used in the most insn patterns.
For each predicate function named in PREDICATE_CODES, a
declaration will be generated in `insn-codes.h'.
SPECIAL_MODE_PREDICATES
match_operand without a mode; if the operand predicate is
listed in SPECIAL_MODE_PREDICATES, the warning will be
suppressed.
Here is an example from the IA-32 port (ext_register_operand
specially checks for HImode or SImode in preparation
for a byte extraction from %ah etc.).
#define SPECIAL_MODE_PREDICATES \ "ext_register_operand", |
CASE_VECTOR_MODE
CASE_VECTOR_SHORTEN_MODE (min_offset, max_offset, body)
addr_diff_vec
when the minimum and maximum offset are known. If you define this,
it enables extra code in branch shortening to deal with addr_diff_vec.
To make this work, you also have to define INSN_ALIGN and
make the alignment for addr_diff_vec explicit.
The body argument is provided so that the offset_unsigned and scale
flags can be updated.
CASE_VECTOR_PC_RELATIVE
CASE_DROPS_THROUGH
case insn when the index
value is out of range. This means the specified default-label is
actually ignored by the case insn proper.
CASE_VALUES_THRESHOLD
casesi instruction and
five otherwise. This is best for most machines.
WORD_REGISTER_OPERATIONS
LOAD_EXTEND_OP (mode)
SIGN_EXTEND for values
of mode for which the
insn sign-extends, ZERO_EXTEND for which it zero-extends, and
NIL for other modes.
This macro is not called with mode non-integral or with a width
greater than or equal to BITS_PER_WORD, so you may return any
value in this case. Do not define this macro if it would always return
NIL. On machines where this macro is defined, you will normally
define it as the constant SIGN_EXTEND or ZERO_EXTEND.
SHORT_IMMEDIATES_SIGN_EXTEND
IMPLICIT_FIX_EXPR
FIX_ROUND_EXPR is used.
FIXUNS_TRUNC_LIKE_FIX_TRUNC
EASY_DIV_EXPR
TRUNC_DIV_EXPR, FLOOR_DIV_EXPR, CEIL_DIV_EXPR or
ROUND_DIV_EXPR. These four division operators differ in how
they round the result to an integer. EASY_DIV_EXPR is used
when it is permissible to use any of those kinds of division and the
choice should be made on the basis of efficiency.
MOVE_MAX
MAX_MOVE_MAX
MOVE_MAX. Otherwise, it is the
constant value that is the largest value that MOVE_MAX can have
at run-time.
SHIFT_COUNT_TRUNCATED
SHIFT_COUNT_TRUNCATED
also enables deletion of truncations of the values that serve as
arguments to bit-field instructions.
If both types of instructions truncate the count (for shifts) and position (for bit-field operations), or if no variable-position bit-field instructions exist, you should define this macro.
However, on some machines, such as the 80386 and the 680x0, truncation
only applies to shift operations and not the (real or pretended)
bit-field operations. Define SHIFT_COUNT_TRUNCATED to be zero on
such machines. Instead, add patterns to the `md' file that include
the implied truncation of the shift instructions.
You need not define this macro if it would always have the value of zero.
TRULY_NOOP_TRUNCATION (outprec, inprec)
On many machines, this expression can be 1.
When TRULY_NOOP_TRUNCATION returns 1 for a pair of sizes for
modes for which MODES_TIEABLE_P is 0, suboptimal code can result.
If this is the case, making TRULY_NOOP_TRUNCATION return 0 in
such cases may improve things.
STORE_FLAG_VALUE
MODE_INT mode.
A value of 1 or -1 means that the instruction implementing the
comparison operator returns exactly 1 or -1 when the comparison is true
and 0 when the comparison is false. Otherwise, the value indicates
which bits of the result are guaranteed to be 1 when the comparison is
true. This value is interpreted in the mode of the comparison
operation, which is given by the mode of the first operand in the
`scond' pattern. Either the low bit or the sign bit of
STORE_FLAG_VALUE be on. Presently, only those bits are used by
the compiler.
If STORE_FLAG_VALUE is neither 1 or -1, the compiler will
generate code that depends only on the specified bits. It can also
replace comparison operators with equivalent operations if they cause
the required bits to be set, even if the remaining bits are undefined.
For example, on a machine whose comparison operators return an
SImode value and where STORE_FLAG_VALUE is defined as
`0x80000000', saying that just the sign bit is relevant, the
expression
(ne:SI (and:SI x (const_int power-of-2)) (const_int 0)) |
can be converted to
(ashift:SI x (const_int n)) |
where n is the appropriate shift count to move the bit being tested into the sign bit.
There is no way to describe a machine that always sets the low-order bit for a true value, but does not guarantee the value of any other bits, but we do not know of any machine that has such an instruction. If you are trying to port GCC to such a machine, include an instruction to perform a logical-and of the result with 1 in the pattern for the comparison operators and let us know (see section How to Report Bugs).
Often, a machine will have multiple instructions that obtain a value
from a comparison (or the condition codes). Here are rules to guide the
choice of value for STORE_FLAG_VALUE, and hence the instructions
to be used:
STORE_FLAG_VALUE. It is more efficient for the compiler to
"normalize" the value (convert it to, e.g., 1 or 0) than for the
comparison operators to do so because there may be opportunities to
combine the normalization with other operations.
Many machines can produce both the value chosen for
STORE_FLAG_VALUE and its negation in the same number of
instructions. On those machines, you should also define a pattern for
those cases, e.g., one matching
(set A (neg:m (ne:m B C))) |
Some machines can also perform and or plus operations on
condition code values with less instructions than the corresponding
`scond' insn followed by and or plus. On those
machines, define the appropriate patterns. Use the names incscc
and decscc, respectively, for the patterns which perform
plus or minus operations on condition code values. See
`rs6000.md' for some examples. The GNU Superoptizer can be used to
find such instruction sequences on other machines.
You need not define STORE_FLAG_VALUE if the machine has no store-flag
instructions.
FLOAT_STORE_FLAG_VALUE (mode)
REAL_VALUE_TYPE value that is
returned when comparison operators with floating-point results are true.
Define this macro on machine that have comparison operations that return
floating-point values. If there are no such operations, do not define
this macro.
Pmode
SImode on 32-bit machine or DImode on 64-bit machines.
On some machines you must define this to be one of the partial integer
modes, such as PSImode.
The width of Pmode must be at least as large as the value of
POINTER_SIZE. If it is not equal, you must define the macro
POINTERS_EXTEND_UNSIGNED to specify how pointers are extended
to Pmode.
FUNCTION_MODE
call RTL expressions. On most machines this
should be QImode.
INTEGRATE_THRESHOLD (decl)
FUNCTION_DECL node.
The default definition of this macro is 64 plus 8 times the number of arguments that the function accepts. Some people think a larger threshold should be used on RISC machines.
SCCS_DIRECTIVE
#sccs directives
and print no error message.
NO_IMPLICIT_EXTERN_C
HANDLE_PRAGMA (getc, ungetc, name)
REGISTER_TARGET_PRAGMAS instead.
REGISTER_TARGET_PRAGMAS (pfile)
cpp_register_pragma and/or cpp_register_pragma_space
functions. The pfile argument is the first argument to supply to
these functions. The macro may also do setup required for the pragmas.
The primary reason to define this macro is to provide compatibility with other compilers for the same target. In general, we discourage definition of target-specific pragmas for GCC.
If the pragma can be implemented by attributes then the macro `INSERT_ATTRIBUTES' might be a useful one to define as well.
Preprocessor macros that appear on pragma lines are not expanded. All `#pragma' directives that do not match any registered pragma are silently ignored, unless the user specifies `-Wunknown-pragmas'.
Each call to cpp_register_pragma establishes one pragma. The
callback routine will be called when the preprocessor encounters a
pragma of the form
#pragma [space] name ... |
space must have been the subject of a previous call to
cpp_register_pragma_space, or else be a null pointer. The
callback routine receives pfile as its first argument, but must
not use it for anything (this may change in the future). It may read
any text after the name by making calls to c_lex. Text
which is not read by the callback will be silently ignored.
Note that both space and name are case sensitive.
For an example use of this routine, see `c4x.h' and the callback routines defined in `c4x.c'.
Note that the use of c_lex is specific to the C and C++
compilers. It will not work in the Java or Fortran compilers, or any
other language compilers for that matter. Thus if c_lex is going
to be called from target-specific code, it must only be done so when
building the C and C++ compilers. This can be done by defining the
variables c_target_objs and cxx_target_objs in the
target entry in the `config.gcc' file. These variables should name
the target-specific, language-specific object file which contains the
code that uses c_lex. Note it will also be necessary to add a
rule to the makefile fragment pointed to by tmake_file that shows
how to build this object file.
cpp_register_pragma. For
example, pragmas defined by the C standard are in the `STDC'
namespace, and pragmas specific to GCC are in the `GCC' namespace.
For an example use of this routine in a target header, see `v850.h'.
HANDLE_SYSV_PRAGMA
The pack pragma specifies the maximum alignment (in bytes) of fields
within a structure, in much the same way as the `__aligned__' and
`__packed__' __attribute__s do. A pack value of zero resets
the behaviour to the default.
The weak pragma only works if SUPPORTS_WEAK and
ASM_WEAKEN_LABEL are defined. If enabled it allows the creation
of specifically named weak labels, optionally with a value.
HANDLE_PRAGMA_PACK_PUSH_POP
__attribute__s do. A
pack value of zero resets the behaviour to the default. Successive
invocations of this pragma cause the previous values to be stacked, so
that invocations of `#pragma pack(pop)' will return to the previous
value.
VALID_MACHINE_DECL_ATTRIBUTE (decl, attributes, identifier, args)
VALID_MACHINE_TYPE_ATTRIBUTE (type, attributes, identifier, args)
COMP_TYPE_ATTRIBUTES (type1, type2)
SET_DEFAULT_TYPE_ATTRIBUTES (type)
MERGE_MACHINE_TYPE_ATTRIBUTES (type1, type2)
MERGE_MACHINE_DECL_ATTRIBUTES (olddecl, newdecl)
INSERT_ATTRIBUTES (node, attr_ptr, prefix_ptr)
SET_DEFAULT_DECL_ATTRIBUTES (decl, attributes)
DOLLARS_IN_IDENTIFIERS
NO_DOLLAR_IN_LABEL
NO_DOT_IN_LABEL
DEFAULT_MAIN_RETURN
main
function to return a standard "success" value by default (if no other
value is explicitly returned).
The definition should be a C statement (sans semicolon) to generate the
appropriate rtl instructions. It is used only when compiling the end of
main.
NEED_ATEXIT
atexit
from the ISO C standard. If this macro is defined, a default definition
will be provided to support C++. If ON_EXIT is not defined,
a default exit function will also be provided.
ON_EXIT
exit. For instance, SunOS 4 has
a similar on_exit library function.
The definition should be a functional macro which can be used just like
the atexit function.
EXIT_BODY
exit function needs to do something
besides calling an external function _cleanup before
terminating with _exit. The EXIT_BODY macro is
only needed if NEED_ATEXIT is defined and ON_EXIT is not
defined.
INSN_SETS_ARE_DELAYED (insn)
jump_insn or an insn; GCC knows that
every call_insn has this behavior. On machines where some insn
or jump_insn is really a function call and hence has this behavior,
you should define this macro.
You need not define this macro if it would always return zero.
INSN_REFERENCES_ARE_DELAYED (insn)
jump_insn or an insn. On machines where
some insn or jump_insn is really a function call and its operands
are registers whose use is actually in the subroutine it calls, you should
define this macro. Doing so allows the delay slot scheduler to move
instructions which copy arguments into the argument registers into the delay
slot of insn.
You need not define this macro if it would always return zero.
MACHINE_DEPENDENT_REORG (insn)
MULTIPLE_SYMBOL_SPACES
MD_ASM_CLOBBERS (clobbers)
STRING_CST trees for
any hard regs the port wishes to automatically clobber for all asms.
ISSUE_RATE
MD_SCHED_INIT (file, verbose, max_ready)
MD_SCHED_FINISH (file, verbose)
MD_SCHED_REORDER (file, verbose, ready, n_ready, clock, can_issue_more)
issue_rate. See also `MD_SCHED_REORDER2'.
MD_SCHED_REORDER2 (file, verbose, ready, n_ready, clock, can_issue_more)
MD_SCHED_VARIABLE_ISSUE (file, verbose, insn, more)
MAX_INTEGER_COMPUTATION_MODE
You need only define this macro if the target holds values larger than
word_mode in general purpose registers. Most targets should not define
this macro.
MATH_LIBRARY
You need only define this macro if the default of `"-lm"' is wrong.
LIBRARY_PATH_ENV
You need only define this macro if the default of `"LIBRARY_PATH"' is wrong.
TARGET_HAS_F_SETLKW
TARGET_HAS_F_SETLKW will enable the test coverage code
to use file locking when exiting a program, which avoids race conditions
if the program has forked.
MAX_CONDITIONAL_EXECUTE
A C expression for the maximum number of instructions to execute via
conditional execution instructions instead of a branch. A value of
BRANCH_COST+1 is the default if the machine does not use cc0, and
1 if it does use cc0.
IFCVT_MODIFY_TESTS
TRUE_EXPR, and
FALSE_EXPR for use in converting insns in TEST_BB,
THEN_BB, ELSE_BB, and JOIN_BB basic blocks to
conditional execution. Set either TRUE_EXPR or FALSE_EXPR
to a null pointer if the tests cannot be converted.
IFCVT_MODIFY_INSN
PATTERN of an INSN that is to
be converted to conditional execution format.
IFCVT_MODIFY_FINAL
TEST_BB, THEN_BB, ELSE_BB, and JOIN_BB.
IFCVT_MODIFY_CANCEL
TEST_BB, THEN_BB, ELSE_BB, and JOIN_BB.
MD_INIT_BUILTINS
Machine specific built-in functions can be useful to expand special machine instructions that would otherwise not normally be generated because they have no equivalent in the source language (for example, SIMD vector instructions or prefetch instructions).
To create a built-in function, call the function builtin_function
which is defined by the language front end. You can use any type nodes set
up by build_common_tree_nodes and build_common_tree_nodes_2;
only language front ends that use these two functions will use
`MD_INIT_BUILTINS'.
MD_EXPAND_BUILTIN(exp, target, subtarget, mode, ignore)
Expand a call to a machine specific built-in function that was set up by `MD_INIT_BUILTINS'. exp is the expression for the function call; the result should go to target if that is convenient, and have mode mode if that is convenient. subtarget may be used as the target for computing one of exp's operands. ignore is nonzero if the value is to be ignored. This macro should return the result of the call to the built-in function.
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