This is doc/gccint.info, produced by makeinfo version 4.5 from doc/gccint.texi. INFO-DIR-SECTION Programming START-INFO-DIR-ENTRY * gccint: (gccint). Internals of the GNU Compiler Collection. END-INFO-DIR-ENTRY This file documents the internals of the GNU compilers. Published by the Free Software Foundation 59 Temple Place - Suite 330 Boston, MA 02111-1307 USA Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002 Free Software Foundation, Inc. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.1 or any later version published by the Free Software Foundation; with the Invariant Sections being "GNU General Public License" and "Funding Free Software", the Front-Cover texts being (a) (see below), and with the Back-Cover Texts being (b) (see below). A copy of the license is included in the section entitled "GNU Free Documentation License". (a) The FSF's Front-Cover Text is: A GNU Manual (b) The FSF's Back-Cover Text is: You have freedom to copy and modify this GNU Manual, like GNU software. Copies published by the Free Software Foundation raise funds for GNU development.  File: gccint.info, Node: Driver, Next: Run-time Target, Prev: Target Structure, Up: Target Macros Controlling the Compilation Driver, `gcc' ========================================= You can control the compilation driver. `SWITCH_TAKES_ARG (CHAR)' A C expression which determines whether the option `-CHAR' takes arguments. The value should be the number of arguments that option takes-zero, for many options. 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)' A C expression which determines whether the option `-NAME' takes arguments. The value should be the number of arguments that option takes-zero, for many options. This macro rather than `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)' A C expression which determines whether the option `-CHAR' stops compilation before the generation of an executable. The value is boolean, nonzero if the option does stop an executable from being generated, zero otherwise. 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' A string-valued C expression which enumerates the options for which the linker needs a space between the option and its argument. If this macro is not defined, the default value is `""'. `TARGET_OPTION_TRANSLATE_TABLE' If defined, a list of pairs of strings, the first of which is a potential command line target to the `gcc' driver program, and the second of which is a space-separated (tabs and other whitespace are not supported) list of options with which to replace the first option. The target defining this list is responsible for assuring that the results are valid. Replacement options may not be the `--opt' style, they must be the `-opt' style. It is the intention of this macro to provide a mechanism for substitution that affects the multilibs chosen, such as one option that enables many options, some of which select multilibs. Example nonsensical definition, where `-malt-abi', `-EB', and `-mspoo' cause different multilibs to be chosen: #define TARGET_OPTION_TRANSLATE_TABLE \ { "-fast", "-march=fast-foo -malt-abi -I/usr/fast-foo" }, \ { "-compat", "-EB -malign=4 -mspoo" } `CPP_SPEC' A C string constant that tells the GCC driver program options to pass to CPP. It can also specify how to translate options you give to GCC into options for GCC to pass to the CPP. Do not define this macro if it does not need to do anything. `CPLUSPLUS_CPP_SPEC' This macro is just like `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' If this macro is defined, the preprocessor will not define the built-in macro `__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' If this macro is defined, the preprocessor will not define the built-in macro `__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' If this macro is defined, the preprocessor will not define the built-in macro `__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' If this macro is defined, the preprocessor will not define the built-in macro `__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. `CC1_SPEC' A C string constant that tells the GCC driver program options to pass to `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' A C string constant that tells the GCC driver program options to pass to `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' A C string constant that tells the GCC driver program options to pass to the assembler. It can also specify how to translate options you give to GCC into options for GCC to pass to the assembler. See the file `sun3.h' for an example of this. Do not define this macro if it does not need to do anything. `ASM_FINAL_SPEC' A C string constant that tells the GCC driver program how to run any programs which cleanup after the normal assembler. Normally, this is not needed. See the file `mips.h' for an example of this. Do not define this macro if it does not need to do anything. `LINK_SPEC' A C string constant that tells the GCC driver program options to pass to the linker. It can also specify how to translate options you give to GCC into options for GCC to pass to the linker. Do not define this macro if it does not need to do anything. `LIB_SPEC' Another C string constant used much like `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' Another C string constant that tells the GCC driver program how and when to place a reference to `libgcc.a' into the linker command line. This constant is placed both before and after the value of `LIB_SPEC'. If this macro is not defined, the GCC driver provides a default that passes the string `-lgcc' to the linker. `STARTFILE_SPEC' Another C string constant used much like `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' Another C string constant used much like `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' GCC `-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' Define this macro to provide additional specifications to put in the `specs' file that can be used in various specifications like `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' Define this macro if the driver program should find the library `libgcc.a' itself and should not pass `-L' options to the linker. If you do not define this macro, the driver program will pass the argument `-lgcc' to tell the linker to do the search and will pass `-L' options to it. `LINK_LIBGCC_SPECIAL_1' Define this macro if the driver program should find the library `libgcc.a'. If you do not define this macro, the driver program will pass the argument `-lgcc' to tell the linker to do the search. This macro is similar to `LINK_LIBGCC_SPECIAL', except that it does not affect `-L' options. `LINK_GCC_C_SEQUENCE_SPEC' The sequence in which libgcc and libc are specified to the linker. By default this is `%G %L %G'. `LINK_COMMAND_SPEC' A C string constant giving the complete command line need to execute the linker. When you do this, you will need to update your port each time a change is made to the link command line within `gcc.c'. Therefore, define this macro only if you need to completely redefine the command line for invoking the linker and there is no other way to accomplish the effect you need. Overriding this macro may be avoidable by overriding `LINK_GCC_C_SEQUENCE_SPEC' instead. `LINK_ELIMINATE_DUPLICATE_LDIRECTORIES' A nonzero value causes `collect2' to remove duplicate `-LDIRECTORY' search directories from linking commands. Do not give it a nonzero value if removing duplicate search directories changes the linker's semantics. `MULTILIB_DEFAULTS' Define this macro as a C expression for the initializer of an array of string to tell the driver program which options are defaults for this target and thus do not need to be handled specially when using `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. *Note Target Fragment::. `RELATIVE_PREFIX_NOT_LINKDIR' Define this macro to tell `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' Define this macro as a C string constant if you wish to override the standard choice of `/usr/local/lib/gcc-lib/' as the default prefix to try when searching for the executable files of the compiler. `MD_EXEC_PREFIX' If defined, this macro is an additional prefix to try after `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' Define this macro as a C string constant if you wish to override the standard choice of `/usr/local/lib/' as the default prefix to try when searching for startup files such as `crt0.o'. `MD_STARTFILE_PREFIX' If defined, this macro supplies an additional prefix to try after the standard prefixes. `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' If defined, this macro supplies yet another prefix to try after the standard prefixes. It is not searched when the `-b' option is used, or when the compiler is built as a cross compiler. `INIT_ENVIRONMENT' Define this macro as a C string constant if you wish to set environment variables for programs called by the driver, such as the assembler and loader. The driver passes the value of this macro to `putenv' to initialize the necessary environment variables. `LOCAL_INCLUDE_DIR' Define this macro as a C string constant if you wish to override the standard choice of `/usr/local/include' as the default prefix to try when searching for local header files. `LOCAL_INCLUDE_DIR' comes before `SYSTEM_INCLUDE_DIR' in the search order. Cross compilers do not search either `/usr/local/include' or its replacement. `MODIFY_TARGET_NAME' Define this macro if you with to define command-line switches that modify the default 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"}} `SYSTEM_INCLUDE_DIR' Define this macro as a C string constant if you wish to specify a system-specific directory to search for header files before the standard directory. `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' Define this macro as a C string constant if you wish to override the standard choice of `/usr/include' as the default prefix to try when searching for header files. Cross compilers do not use this macro and do not search either `/usr/include' or its replacement. `STANDARD_INCLUDE_COMPONENT' The "component" corresponding to `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' Define this macro if you wish to override the entire default search path for include files. For a native compiler, the default search path usually consists of `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} \ } Here is the order of prefixes tried for exec files: 1. Any prefixes specified by the user with `-B'. 2. The environment variable `GCC_EXEC_PREFIX', if any. 3. The directories specified by the environment variable `COMPILER_PATH'. 4. The macro `STANDARD_EXEC_PREFIX'. 5. `/usr/lib/gcc/'. 6. The macro `MD_EXEC_PREFIX', if any. Here is the order of prefixes tried for startfiles: 1. Any prefixes specified by the user with `-B'. 2. The environment variable `GCC_EXEC_PREFIX', if any. 3. The directories specified by the environment variable `LIBRARY_PATH' (or port-specific name; native only, cross compilers do not use this). 4. The macro `STANDARD_EXEC_PREFIX'. 5. `/usr/lib/gcc/'. 6. The macro `MD_EXEC_PREFIX', if any. 7. The macro `MD_STARTFILE_PREFIX', if any. 8. The macro `STANDARD_STARTFILE_PREFIX'. 9. `/lib/'. 10. `/usr/lib/'.  File: gccint.info, Node: Run-time Target, Next: Per-Function Data, Prev: Driver, Up: Target Macros Run-time Target Specification ============================= Here are run-time target specifications. `CPP_PREDEFINES' Define this to be a string constant containing `-D' options to define the predefined macros that identify this machine and system. These macros will be predefined unless the `-ansi' option (or a `-std' option for strict ISO C conformance) is specified. 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;' This declaration should be present. `TARGET_...' This series of macros is to allow compiler command arguments to enable or disable the use of optional features of the target machine. For example, one machine description serves both the 68000 and the 68020; a command argument tells the compiler whether it should use 68020-only instructions or not. This command argument works by means of a macro `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' This macro defines names of command options to set and clear bits in `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'. Please do not mark empty strings because the empty string is reserved by GNU gettext. `gettext("")' returns the header entry of the message catalog with meta information, not the empty string. 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' This macro is similar to `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. Non-empty description strings should be marked with `N_(...)' for `xgettext'. Please do not mark empty strings because the empty string is reserved by GNU gettext. `gettext("")' returns the header entry of the message catalog with meta information, not the empty string. 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' This macro is a C statement to print on `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' Sometimes certain combinations of command options do not make sense on a particular target machine. You can define a macro `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)' Some machines may desire to change what optimizations are performed for various optimization levels. This macro, if defined, is executed once just after the optimization level is determined and before the remainder of the command options have been parsed. Values set in this macro are used as the default values for the other command line options. 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' Define this macro if debugging can be performed even without a frame pointer. If this macro is defined, GCC will turn on the `-fomit-frame-pointer' option whenever `-O' is specified.  File: gccint.info, Node: Per-Function Data, Next: Storage Layout, Prev: Run-time Target, Up: Target Macros Defining data structures for per-function information. ====================================================== 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 initialize 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' Macro called to initialize any target specific information. This macro is called once per function, before generation of any RTL has begun. The intention of this macro is to allow the initialization of the function pointers below. `init_machine_status' This is a `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 initialization of the `struct function' structure. It is intended that this would be used to initialize the `machine' of that structure. `free_machine_status' This is a `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' This is a `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.  File: gccint.info, Node: Storage Layout, Next: Type Layout, Prev: Per-Function Data, Up: Target Macros Storage Layout ============== 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'. *Note Run-time Target::. `BITS_BIG_ENDIAN' Define this macro to have the value 1 if the most significant bit in a byte has the lowest number; otherwise define it to have the value zero. This means that bit-field instructions count from the most significant bit. If the machine has no bit-field instructions, then this must still be defined, but it doesn't matter which value it is defined to. This macro need not be a constant. 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' Define this macro to have the value 1 if the most significant byte in a word has the lowest number. This macro need not be a constant. `WORDS_BIG_ENDIAN' Define this macro to have the value 1 if, in a multiword object, the most significant word has the lowest number. This applies to both memory locations and registers; GCC fundamentally assumes that the order of words in memory is the same as the order in registers. This macro need not be a constant. `LIBGCC2_WORDS_BIG_ENDIAN' Define this macro if `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' Define this macro to have the value 1 if `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' Define this macro to be the number of bits in an addressable storage unit (byte); normally 8. `BITS_PER_WORD' Number of bits in a word; normally 32. `MAX_BITS_PER_WORD' Maximum number of bits in a word. If this is undefined, the default is `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' Number of storage units in a word; normally 4. `MIN_UNITS_PER_WORD' Minimum number of units in a word. If this is undefined, the default is `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' Width of a pointer, in bits. You must specify a value no wider than the width of `Pmode'. If it is not equal to the width of `Pmode', you must define `POINTERS_EXTEND_UNSIGNED'. `POINTERS_EXTEND_UNSIGNED' A C expression whose value is greater than zero if pointers that need to be extended from being `POINTER_SIZE' bits wide to `Pmode' are to be zero-extended and zero if they are to be sign-extended. If the value is less then zero then there must be an "ptr_extend" instruction that extends a pointer from `POINTER_SIZE' to `Pmode'. You need not define this macro if the `POINTER_SIZE' is equal to the width of `Pmode'. `PROMOTE_MODE (M, UNSIGNEDP, TYPE)' A macro to update M and UNSIGNEDP when an object whose type is TYPE and which has the specified mode and signedness is to be stored in a register. This macro is only called when TYPE is a scalar 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' Define this macro if the promotion described by `PROMOTE_MODE' should also be done for outgoing function arguments. `PROMOTE_FUNCTION_RETURN' Define this macro if the promotion described by `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' Define this macro if the promotion described by `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' Normal alignment required for function parameters on the stack, in bits. All stack parameters receive at least this much alignment regardless of data type. On most machines, this is the same as the size of an integer. `STACK_BOUNDARY' Define this macro to the minimum alignment enforced by hardware for the stack pointer on this machine. The definition is a C expression for the desired alignment (measured in bits). This value is used as a default if `PREFERRED_STACK_BOUNDARY' is not defined. On most machines, this should be the same as `PARM_BOUNDARY'. `PREFERRED_STACK_BOUNDARY' Define this macro if you wish to preserve a certain alignment for the stack pointer, greater than what the hardware enforces. The definition is a C expression for the desired alignment (measured in bits). This macro must evaluate to a value equal to or larger than `STACK_BOUNDARY'. `FORCE_PREFERRED_STACK_BOUNDARY_IN_MAIN' A C expression that evaluates true if `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' Alignment required for a function entry point, in bits. `BIGGEST_ALIGNMENT' Biggest alignment that any data type can require on this machine, in bits. `MINIMUM_ATOMIC_ALIGNMENT' If defined, the smallest alignment, in bits, that can be given to an object that can be referenced in one operation, without disturbing any nearby object. Normally, this is `BITS_PER_UNIT', but may be larger on machines that don't have byte or half-word store operations. `BIGGEST_FIELD_ALIGNMENT' Biggest alignment that any structure or union field can require on this machine, in bits. If defined, this overrides `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)' An expression for the alignment of a structure field FIELD if the alignment computed in the usual way (including applying of `BIGGEST_ALIGNMENT' and `BIGGEST_FIELD_ALIGNMENT' to the alignment) is COMPUTED. It overrides alignment only if the field alignment has not been set by the `__attribute__ ((aligned (N)))' construct. `MAX_OFILE_ALIGNMENT' Biggest alignment supported by the object file format of this machine. Use this macro to limit the alignment which can be specified using the `__attribute__ ((aligned (N)))' construct. If not defined, the default value is `BIGGEST_ALIGNMENT'. `DATA_ALIGNMENT (TYPE, BASIC-ALIGN)' If defined, a C expression to compute the alignment for a variable in the static store. TYPE is the data type, and BASIC-ALIGN is the alignment that the object would ordinarily have. The value of this macro is used instead of that alignment to align the object. 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 defined, a C expression to compute the alignment given to a constant that is being placed in memory. CONSTANT is the constant and BASIC-ALIGN is the alignment that the object would ordinarily have. The value of this macro is used instead of that alignment to align the object. 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 defined, a C expression to compute the alignment for a variable in the local store. TYPE is the data type, and BASIC-ALIGN is the alignment that the object would ordinarily have. The value of this macro is used instead of that alignment to align the object. 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' Alignment in bits to be given to a structure bit-field that follows an empty field such as `int : 0;'. Note that `PCC_BITFIELD_TYPE_MATTERS' also affects the alignment that results from an empty field. `STRUCTURE_SIZE_BOUNDARY' Number of bits which any structure or union's size must be a multiple of. Each structure or union's size is rounded up to a multiple of this. If you do not define this macro, the default is the same as `BITS_PER_UNIT'. `STRICT_ALIGNMENT' Define this macro to be the value 1 if instructions will fail to work if given data not on the nominal alignment. If instructions will merely go slower in that case, define this macro as 0. `PCC_BITFIELD_TYPE_MATTERS' Define this if you wish to imitate the way many other C compilers handle alignment of bit-fields and the structures that contain them. 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' Like `PCC_BITFIELD_TYPE_MATTERS' except that its effect is limited to aligning a bit-field within the structure. `MEMBER_TYPE_FORCES_BLK (FIELD)' Return 1 if a structure or array containing FIELD should be accessed using `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)' Define this macro as an expression for the overall size of a type (given by TYPE as a tree node) when the size computed in the usual way is COMPUTED and the alignment is SPECIFIED. The default is to round COMPUTED up to a multiple of SPECIFIED. `ROUND_TYPE_SIZE_UNIT (TYPE, COMPUTED, SPECIFIED)' Similar to `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)' Define this macro as an expression for the alignment of a type (given by TYPE as a tree node) if the alignment computed in the usual way is COMPUTED and the alignment explicitly specified was SPECIFIED. The default is to use SPECIFIED if it is larger; otherwise, use the smaller of COMPUTED and `BIGGEST_ALIGNMENT' `MAX_FIXED_MODE_SIZE' An integer expression for the size in bits of the largest integer machine mode that should actually be used. All integer machine modes of this size or smaller can be used for structures and unions with the appropriate sizes. If this macro is undefined, `GET_MODE_BITSIZE (DImode)' is assumed. `VECTOR_MODE_SUPPORTED_P(MODE)' Define this macro to be nonzero if the port is prepared to handle insns involving vector mode MODE. At the very least, it must have move patterns for this mode. `STACK_SAVEAREA_MODE (SAVE_LEVEL)' If defined, an expression of type `enum machine_mode' that specifies the mode of the save area operand of a `save_stack_LEVEL' named pattern (*note Standard Names::). 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' If defined, an expression of type `enum machine_mode' that specifies the mode of the size increment operand of an `allocate_stack' named pattern (*note Standard Names::). 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)' A C statement to validate the value VALUE (of type `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' A code distinguishing the floating point format of the target machine. There are five defined values: `IEEE_FLOAT_FORMAT' This code indicates IEEE floating point. It is the default; there is no need to define this macro when the format is IEEE. `VAX_FLOAT_FORMAT' This code indicates the "D float" format used on the VAX. `IBM_FLOAT_FORMAT' This code indicates the format used on the IBM System/370. `C4X_FLOAT_FORMAT' This code indicates the format used on the TMS320C3x/C4x. `UNKNOWN_FLOAT_FORMAT' This code indicates any other format. The value of this macro is compared with `HOST_FLOAT_FORMAT', which is defined by the `configure' script, 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'. - Target Hook: bool TARGET_MS_BITFIELD_LAYOUT_P (tree RECORD_TYPE) This target hook returns `true' if bit-fields in the given RECORD_TYPE are to be laid out following the rules of Microsoft Visual C/C++, namely: (i) a bit-field won't share the same storage unit with the previous bit-field if their underlying types have different sizes, and the bit-field will be aligned to the highest alignment of the underlying types of itself and of the previous bit-field; (ii) a zero-sized bit-field will affect the alignment of the whole enclosing structure, even if it is unnamed; except that (iii) a zero-sized bit-field will be disregarded unless it follows another bit-field of non-zero size. If this hook returns `true', other macros that control bit-field layout are ignored.