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17.2 Controlling the Compilation Driver, gcc

You can control the compilation driver.

— Macro: 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.

— Macro: 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.

— Macro: 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.

— Macro: 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 "".

— Macro: 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" }
— Macro: DRIVER_SELF_SPECS

A list of specs for the driver itself. It should be a suitable initializer for an array of strings, with no surrounding braces.

The driver applies these specs to its own command line between loading default specs files (but not command-line specified ones) and choosing the multilib directory or running any subcommands. It applies them in the order given, so each spec can depend on the options added by earlier ones. It is also possible to remove options using `%<option' in the usual way.

This macro can be useful when a port has several interdependent target options. It provides a way of standardizing the command line so that the other specs are easier to write.

Do not define this macro if it does not need to do anything.

— Macro: OPTION_DEFAULT_SPECS

A list of specs used to support configure-time default options (i.e. --with options) in the driver. It should be a suitable initializer for an array of structures, each containing two strings, without the outermost pair of surrounding braces.

The first item in the pair is the name of the default. This must match the code in config.gcc for the target. The second item is a spec to apply if a default with this name was specified. The string `%(VALUE)' in the spec will be replaced by the value of the default everywhere it occurs.

The driver will apply these specs to its own command line between loading default specs files and processing DRIVER_SELF_SPECS, using the same mechanism as DRIVER_SELF_SPECS.

Do not define this macro if it does not need to do anything.

— Macro: 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.

— Macro: 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.

— Macro: 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.

— Macro: 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.

— Macro: 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.

— Macro: 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.

— Macro: AS_NEEDS_DASH_FOR_PIPED_INPUT

Define this macro, with no value, if the driver should give the assembler an argument consisting of a single dash, -, to instruct it to read from its standard input (which will be a pipe connected to the output of the compiler proper). This argument is given after any -o option specifying the name of the output file.

If you do not define this macro, the assembler is assumed to read its standard input if given no non-option arguments. If your assembler cannot read standard input at all, use a `%{pipe:%e}' construct; see mips.h for instance.

— Macro: 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.

— Macro: 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.

— Macro: 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.

— Macro: REAL_LIBGCC_SPEC

By default, if ENABLE_SHARED_LIBGCC is defined, the LIBGCC_SPEC is not directly used by the driver program but is instead modified to refer to different versions of libgcc.a depending on the values of the command line flags -static, -shared, -static-libgcc, and -shared-libgcc. On targets where these modifications are inappropriate, define REAL_LIBGCC_SPEC instead. REAL_LIBGCC_SPEC tells the driver how to place a reference to libgcc on the link command line, but, unlike LIBGCC_SPEC, it is used unmodified.

— Macro: USE_LD_AS_NEEDED

A macro that controls the modifications to LIBGCC_SPEC mentioned in REAL_LIBGCC_SPEC. If nonzero, a spec will be generated that uses –as-needed and the shared libgcc in place of the static exception handler library, when linking without any of -static, -static-libgcc, or -shared-libgcc.

— Macro: LINK_EH_SPEC

If defined, this C string constant is added to LINK_SPEC. When USE_LD_AS_NEEDED is zero or undefined, it also affects the modifications to LIBGCC_SPEC mentioned in REAL_LIBGCC_SPEC.

— Macro: 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.

— Macro: 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.

— Macro: 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.

— Macro: SYSROOT_SUFFIX_SPEC

Define this macro to add a suffix to the target sysroot when GCC is configured with a sysroot. This will cause GCC to search for usr/lib, et al, within sysroot+suffix.

— Macro: SYSROOT_HEADERS_SUFFIX_SPEC

Define this macro to add a headers_suffix to the target sysroot when GCC is configured with a sysroot. This will cause GCC to pass the updated sysroot+headers_suffix to CPP, causing it to search for usr/include, et al, within sysroot+headers_suffix.

— Macro: 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-sysv: %(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"
— Macro: 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.

— Macro: LINK_GCC_C_SEQUENCE_SPEC

The sequence in which libgcc and libc are specified to the linker. By default this is %G %L %G.

— Macro: 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.

— Macro: 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.

— Macro: 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. See Target Fragment.

— Macro: 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.

— Macro: 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.

— Macro: STANDARD_STARTFILE_PREFIX

Define this macro as a C string constant if you wish to override the standard choice of libdir as the default prefix to try when searching for startup files such as crt0.o. STANDARD_STARTFILE_PREFIX is not searched when the compiler is built as a cross compiler.

— Macro: STANDARD_STARTFILE_PREFIX_1

Define this macro as a C string constant if you wish to override the standard choice of /lib as a prefix to try after the default prefix when searching for startup files such as crt0.o. STANDARD_STARTFILE_PREFIX_1 is not searched when the compiler is built as a cross compiler.

— Macro: STANDARD_STARTFILE_PREFIX_2

Define this macro as a C string constant if you wish to override the standard choice of /lib as yet another prefix to try after the default prefix when searching for startup files such as crt0.o. STANDARD_STARTFILE_PREFIX_2 is not searched when the compiler is built as a cross compiler.

— Macro: 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.

— Macro: 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.

— Macro: 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.

— Macro: 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.

— Macro: MODIFY_TARGET_NAME

Define this macro if you wish 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"}}
— Macro: 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.

— Macro: 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 ignore this macro and do not search either /usr/include or its replacement.

— Macro: 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.

— Macro: 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 uppercase 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 or, if GCC_EXEC_PREFIX is not set and the compiler has not been installed in the configure-time prefix, the location in which the compiler has actually been installed.
  3. The directories specified by the environment variable COMPILER_PATH.
  4. The macro STANDARD_EXEC_PREFIX, if the compiler has been installed in the configured-time prefix.
  5. The location /usr/libexec/gcc/, but only if this is a native compiler.
  6. The location /usr/lib/gcc/, but only if this is a native compiler.
  7. The macro MD_EXEC_PREFIX, if defined, but only if this is a native compiler.

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 or its automatically determined value based on the installed toolchain location.
  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, but only if the toolchain is installed in the configured prefix or this is a native compiler.
  5. The location /usr/lib/gcc/, but only if this is a native compiler.
  6. The macro MD_EXEC_PREFIX, if defined, but only if this is a native compiler.
  7. The macro MD_STARTFILE_PREFIX, if defined, but only if this is a native compiler, or we have a target system root.
  8. The macro MD_STARTFILE_PREFIX_1, if defined, but only if this is a native compiler, or we have a target system root.
  9. The macro STANDARD_STARTFILE_PREFIX, with any sysroot modifications. If this path is relative it will be prefixed by GCC_EXEC_PREFIX and the machine suffix or STANDARD_EXEC_PREFIX and the machine suffix.
  10. The macro STANDARD_STARTFILE_PREFIX_1, but only if this is a native compiler, or we have a target system root. The default for this macro is /lib/.
  11. The macro STANDARD_STARTFILE_PREFIX_2, but only if this is a native compiler, or we have a target system root. The default for this macro is /usr/lib/.