nimum size of buffers (i.e. arrays) that will receive
          stack smashing protection when `-fstack-protection' is used.

    `max-jump-thread-duplication-stmts'
          Maximum number of statements allowed in a block that needs to
          be duplicated when threading jumps.

    `max-fields-for-field-sensitive'
          Maximum number of fields in a structure we will treat in a
          field sensitive manner during pointer analysis.  The default
          is zero for -O0, and -O1 and 100 for -Os, -O2, and -O3.

    `prefetch-latency'
          Estimate on average number of instructions that are executed
          before prefetch finishes.  The distance we prefetch ahead is
          proportional to this constant.  Increasing this number may
          also lead to less streams being prefetched (see
          `simultaneous-prefetches').

    `simultaneous-prefetches'
          Maximum number of prefetches that can run at the same time.

    `l1-cache-line-size'
          The size of cache line in L1 cache, in bytes.

    `l1-cache-size'
          The size of L1 cache, in kilobytes.

    `l2-cache-size'
          The size of L2 cache, in kilobytes.

    `use-canonical-types'
          Whether the compiler should use the "canonical" type system.
          By default, this should always be 1, which uses a more
          efficient internal mechanism for comparing types in C++ and
          Objective-C++.  However, if bugs in the canonical type system
          are causing compilation failures, set this value to 0 to
          disable canonical types.

    `max-partial-antic-length'
          Maximum length of the partial antic set computed during the
          tree partial redundancy elimination optimization
          (`-ftree-pre') when optimizing at `-O3' and above.  For some
          sorts of source code the enhanced partial redundancy
          elimination optimization can run away, consuming all of the
          memory available on the host machine.  This parameter sets a
          limit on the length of the sets that are computed, which
          prevents the runaway behaviour.  Setting a value of 0 for
          this paramter will allow an unlimited set length.

    `sccvn-max-scc-size'
          Maximum size of a strongly connected component (SCC) during
          SCCVN processing.  If this limit is hit, SCCVN processing for
          the whole function will not be done and optimizations
          depending on it will be disabled.  The default maximum SCC
          size is 10000.



File: gcc.info,  Node: Preprocessor Options,  Next: Assembler Options,  Prev: Optimize Options,  Up: Invoking GCC

3.11 Options Controlling the Preprocessor
=========================================

These options control the C preprocessor, which is run on each C source
file before actual compilation.

 If you use the `-E' option, nothing is done except preprocessing.
Some of these options make sense only together with `-E' because they
cause the preprocessor output to be unsuitable for actual compilation.

     You can use `-Wp,OPTION' to bypass the compiler driver and pass
     OPTION directly through to the preprocessor.  If OPTION contains
     commas, it is split into multiple options at the commas.  However,
     many options are modified, translated or interpreted by the
     compiler driver before being passed to the preprocessor, and `-Wp'
     forcibly bypasses this phase.  The preprocessor's direct interface
     is undocumented and subject to change, so whenever possible you
     should avoid using `-Wp' and let the driver handle the options
     instead.

`-Xpreprocessor OPTION'
     Pass OPTION as an option to the preprocessor.  You can use this to
     supply system-specific preprocessor options which GCC does not
     know how to recognize.

     If you want to pass an option that takes an argument, you must use
     `-Xpreprocessor' twice, once for the option and once for the
     argument.

`-D NAME'
     Predefine NAME as a macro, with definition `1'.

`-D NAME=DEFINITION'
     The contents of DEFINITION are tokenized and processed as if they
     appeared during translation phase three in a `#define' directive.
     In particular, the definition will be truncated by embedded
     newline characters.

     If you are invoking the preprocessor from a shell or shell-like
     program you may need to use the shell's quoting syntax to protect
     characters such as spaces that have a meaning in the shell syntax.

     If you wish to define a function-like macro on the command line,
     write its argument list with surrounding parentheses before the
     equals sign (if any).  Parentheses are meaningful to most shells,
     so you will need to quote the option.  With `sh' and `csh',
     `-D'NAME(ARGS...)=DEFINITION'' works.

     `-D' and `-U' options are processed in the order they are given on
     the command line.  All `-imacros FILE' and `-include FILE' options
     are processed after all `-D' and `-U' options.

`-U NAME'
     Cancel any previous definition of NAME, either built in or
     provided with a `-D' option.

`-undef'
     Do not predefine any system-specific or GCC-specific macros.  The
     standard predefined macros remain defined.

`-I DIR'
     Add the directory DIR to the list of directories to be searched
     for header files.  Directories named by `-I' are searched before
     the standard system include directories.  If the directory DIR is
     a standard system include directory, the option is ignored to
     ensure that the default search order for system directories and
     the special treatment of system headers are not defeated .  If DIR
     begins with `=', then the `=' will be replaced by the sysroot
     prefix; see `--sysroot' and `-isysroot'.

`-o FILE'
     Write output to FILE.  This is the same as specifying FILE as the
     second non-option argument to `cpp'.  `gcc' has a different
     interpretation of a second non-option argument, so you must use
     `-o' to specify the output file.

`-Wall'
     Turns on all optional warnings which are desirable for normal code.
     At present this is `-Wcomment', `-Wtrigraphs', `-Wmultichar' and a
     warning about integer promotion causing a change of sign in `#if'
     expressions.  Note that many of the preprocessor's warnings are on
     by default and have no options to control them.

`-Wcomment'
`-Wcomments'
     Warn whenever a comment-start sequence `/*' appears in a `/*'
     comment, or whenever a backslash-newline appears in a `//' comment.
     (Both forms have the same effect.)

`-Wtrigraphs'
     Most trigraphs in comments cannot affect the meaning of the
     program.  However, a trigraph that would form an escaped newline
     (`??/' at the end of a line) can, by changing where the comment
     begins or ends.  Therefore, only trigraphs that would form escaped
     newlines produce warnings inside a comment.

     This option is implied by `-Wall'.  If `-Wall' is not given, this
     option is still enabled unless trigraphs are enabled.  To get
     trigraph conversion without warnings, but get the other `-Wall'
     warnings, use `-trigraphs -Wall -Wno-trigraphs'.

`-Wtraditional'
     Warn about certain constructs that behave differently in
     traditional and ISO C.  Also warn about ISO C constructs that have
     no traditional C equivalent, and problematic constructs which
     should be avoided.

`-Wimport'
     Warn the first time `#import' is used.

`-Wundef'
     Warn whenever an identifier which is not a macro is encountered in
     an `#if' directive, outside of `defined'.  Such identifiers are
     replaced with zero.

`-Wunused-macros'
     Warn about macros defined in the main file that are unused.  A
     macro is "used" if it is expanded or tested for existence at least
     once.  The preprocessor will also warn if the macro has not been
     used at the time it is redefined or undefined.

     Built-in macros, macros defined on the command line, and macros
     defined in include files are not warned about.

     _Note:_ If a macro is actually used, but only used in skipped
     conditional blocks, then CPP will report it as unused.  To avoid
     the warning in such a case, you might improve the scope of the
     macro's definition by, for example, moving it into the first
     skipped block.  Alternatively, you could provide a dummy use with
     something like:

          #if defined the_macro_causing_the_warning
          #endif

`-Wendif-labels'
     Warn whenever an `#else' or an `#endif' are followed by text.
     This usually happens in code of the form

          #if FOO
          ...
          #else FOO
          ...
          #endif FOO

     The second and third `FOO' should be in comments, but often are not
     in older programs.  This warning is on by default.

`-Werror'
     Make all warnings into hard errors.  Source code which triggers
     warnings will be rejected.

`-Wsystem-headers'
     Issue warnings for code in system headers.  These are normally
     unhelpful in finding bugs in your own code, therefore suppressed.
     If you are responsible for the system library, you may want to see
     them.

`-w'
     Suppress all warnings, including those which GNU CPP issues by
     default.

`-pedantic'
     Issue all the mandatory diagnostics listed in the C standard.
     Some of them are left out by default, since they trigger
     frequently on harmless code.

`-pedantic-errors'
     Issue all the mandatory diagnostics, and make all mandatory
     diagnostics into errors.  This includes mandatory diagnostics that
     GCC issues without `-pedantic' but treats as warnings.

`-M'
     Instead of outputting the result of preprocessing, output a rule
     suitable for `make' describing the dependencies of the main source
     file.  The preprocessor outputs one `make' rule containing the
     object file name for that source file, a colon, and the names of
     all the included files, including those coming from `-include' or
     `-imacros' command line options.

     Unless specified explicitly (with `-MT' or `-MQ'), the object file
     name consists of the name of the source file with any suffix
     replaced with object file suffix and with any leading directory
     parts removed.  If there are many included files then the rule is
     split into several lines using `\'-newline.  The rule has no
     commands.

     This option does not suppress the preprocessor's debug output,
     such as `-dM'.  To avoid mixing such debug output with the
     dependency rules you should explicitly specify the dependency
     output file with `-MF', or use an environment variable like
     `DEPENDENCIES_OUTPUT' (*note Environment Variables::).  Debug
     output will still be sent to the regular output stream as normal.

     Passing `-M' to the driver implies `-E', and suppresses warnings
     with an implicit `-w'.

`-MM'
     Like `-M' but do not mention header files that are found in system
     header directories, nor header files that are included, directly
     or indirectly, from such a header.

     This implies that the choice of angle brackets or double quotes in
     an `#include' directive does not in itself determine whether that
     header will appear in `-MM' dependency output.  This is a slight
     change in semantics from GCC versions 3.0 and earlier.

`-MF FILE'
     When used with `-M' or `-MM', specifies a file to write the
     dependencies to.  If no `-MF' switch is given the preprocessor
     sends the rules to the same place it would have sent preprocessed
     output.

     When used with the driver options `-MD' or `-MMD', `-MF' overrides
     the default dependency output file.

`-MG'
     In conjunction with an option such as `-M' requesting dependency
     generation, `-MG' assumes missing header files are generated files
     and adds them to the dependency list without raising an error.
     The dependency filename is taken directly from the `#include'
     directive without prepending any path.  `-MG' also suppresses
     preprocessed output, as a missing header file renders this useless.

     This feature is used in automatic updating of makefiles.

`-MP'
     This option instructs CPP to add a phony target for each dependency
     other than the main file, causing each to depend on nothing.  These
     dummy rules work around errors `make' gives if you remove header
     files without updating the `Makefile' to match.

     This is typical output:

          test.o: test.c test.h

          test.h:

`-MT TARGET'
     Change the target of the rule emitted by dependency generation.  By
     default CPP takes the name of the main input file, deletes any
     directory components and any file suffix such as `.c', and appends
     the platform's usual object suffix.  The result is the target.

     An `-MT' option will set the target to be exactly the string you
     specify.  If you want multiple targets, you can specify them as a
     single argument to `-MT', or use multiple `-MT' options.

     For example, `-MT '$(objpfx)foo.o'' might give

          $(objpfx)foo.o: foo.c

`-MQ TARGET'
     Same as `-MT', but it quotes any characters which are special to
     Make.  `-MQ '$(objpfx)foo.o'' gives

          $$(objpfx)foo.o: foo.c

     The default target is automatically quoted, as if it were given
     with `-MQ'.

`-MD'
     `-MD' is equivalent to `-M -MF FILE', except that `-E' is not
     implied.  The driver determines FILE based on whether an `-o'
     option is given.  If it is, the driver uses its argument but with
     a suffix of `.d', otherwise it takes the name of the input file,
     removes any directory components and suffix, and applies a `.d'
     suffix.

     If `-MD' is used in conjunction with `-E', any `-o' switch is
     understood to specify the dependency output file (*note -MF:
     dashMF.), but if used without `-E', each `-o' is understood to
     specify a target object file.

     Since `-E' is not implied, `-MD' can be used to generate a
     dependency output file as a side-effect of the compilation process.

`-MMD'
     Like `-MD' except mention only user header files, not system
     header files.

`-fpch-deps'
     When using precompiled headers (*note Precompiled Headers::), this
     flag will cause the dependency-output flags to also list the files
     from the precompiled header's dependencies.  If not specified only
     the precompiled header would be listed and not the files that were
     used to create it because those files are not consulted when a
     precompiled header is used.

`-fpch-preprocess'
     This option allows use of a precompiled header (*note Precompiled
     Headers::) together with `-E'.  It inserts a special `#pragma',
     `#pragma GCC pch_preprocess "<filename>"' in the output to mark
     the place where the precompiled header was found, and its
     filename.  When `-fpreprocessed' is in use, GCC recognizes this
     `#pragma' and loads the PCH.

     This option is off by default, because the resulting preprocessed
     output is only really suitable as input to GCC.  It is switched on
     by `-save-temps'.

     You should not write this `#pragma' in your own code, but it is
     safe to edit the filename if the PCH file is available in a
     different location.  The filename may be absolute or it may be
     relative to GCC's current directory.

`-x c'
`-x c++'
`-x objective-c'
`-x assembler-with-cpp'
     Specify the source language: C, C++, Objective-C, or assembly.
     This has nothing to do with standards conformance or extensions;
     it merely selects which base syntax to expect.  If you give none
     of these options, cpp will deduce the language from the extension
     of the source file: `.c', `.cc', `.m', or `.S'.  Some other common
     extensions for C++ and assembly are also recognized.  If cpp does
     not recognize the extension, it will treat the file as C; this is
     the most generic mode.

     _Note:_ Previous versions of cpp accepted a `-lang' option which
     selected both the language and the standards conformance level.
     This option has been removed, because it conflicts with the `-l'
     option.

`-std=STANDARD'
`-ansi'
     Specify the standard to which the code should conform.  Currently
     CPP knows about C and C++ standards; others may be added in the
     future.

     STANDARD may be one of:
    `iso9899:1990'
    `c89'
          The ISO C standard from 1990.  `c89' is the customary
          shorthand for this version of the standard.

          The `-ansi' option is equivalent to `-std=c89'.

    `iso9899:199409'
          The 1990 C standard, as amended in 1994.

    `iso9899:1999'
    `c99'
    `iso9899:199x'
    `c9x'
          The revised ISO C standard, published in December 1999.
          Before publication, this was known as C9X.

    `gnu89'
          The 1990 C standard plus GNU extensions.  This is the default.

    `gnu99'
    `gnu9x'
          The 1999 C standard plus GNU extensions.

    `c++98'
          The 1998 ISO C++ standard plus amendments.

    `gnu++98'
          The same as `-std=c++98' plus GNU extensions.  This is the
          default for C++ code.

`-I-'
     Split the include path.  Any directories specified with `-I'
     options before `-I-' are searched only for headers requested with
     `#include "FILE"'; they are not searched for `#include <FILE>'.
     If additional directories are specified with `-I' options after
     the `-I-', those directories are searched for all `#include'
     directives.

     In addition, `-I-' inhibits the use of the directory of the current
     file directory as the first search directory for `#include "FILE"'.
     This option has been deprecated.

`-nostdinc'
     Do not search the standard system directories for header files.
     Only the directories you have specified with `-I' options (and the
     directory of the current file, if appropriate) are searched.

`-nostdinc++'
     Do not search for header files in the C++-specific standard
     directories, but do still search the other standard directories.
     (This option is used when building the C++ library.)

`-include FILE'
     Process FILE as if `#include "file"' appeared as the first line of
     the primary source file.  However, the first directory searched
     for FILE is the preprocessor's working directory _instead of_ the
     directory containing the main source file.  If not found there, it
     is searched for in the remainder of the `#include "..."' search
     chain as normal.

     If multiple `-include' options are given, the files are included
     in the order they appear on the command line.

`-imacros FILE'
     Exactly like `-include', except that any output produced by
     scanning FILE is thrown away.  Macros it defines remain defined.
     This allows you to acquire all the macros from a header without
     also processing its declarations.

     All files specified by `-imacros' are processed before all files
     specified by `-include'.

`-idirafter DIR'
     Search DIR for header files, but do it _after_ all directories
     specified with `-I' and the standard system directories have been
     exhausted.  DIR is treated as a system include directory.  If DIR
     begins with `=', then the `=' will be replaced by the sysroot
     prefix; see `--sysroot' and `-isysroot'.

`-iprefix PREFIX'
     Specify PREFIX as the prefix for subsequent `-iwithprefix'
     options.  If the prefix represents a directory, you should include
     the final `/'.

`-iwithprefix DIR'
`-iwithprefixbefore DIR'
     Append DIR to the prefix specified previously with `-iprefix', and
     add the resulting directory to the include search path.
     `-iwithprefixbefore' puts it in the same place `-I' would;
     `-iwithprefix' puts it where `-idirafter' would.

`-isysroot DIR'
     This option is like the `--sysroot' option, but applies only to
     header files.  See the `--sysroot' option for more information.

`-imultilib DIR'
     Use DIR as a subdirectory of the directory containing
     target-specific C++ headers.

`-isystem DIR'
     Search DIR for header files, after all directories specified by
     `-I' but before the standard system directories.  Mark it as a
     system directory, so that it gets the same special treatment as is
     applied to the standard system directories.  If DIR begins with
     `=', then the `=' will be replaced by the sysroot prefix; see
     `--sysroot' and `-isysroot'.

`-iquote DIR'
     Search DIR only for header files requested with `#include "FILE"';
     they are not searched for `#include <FILE>', before all
     directories specified by `-I' and before the standard system
     directories.  If DIR begins with `=', then the `=' will be replaced
     by the sysroot prefix; see `--sysroot' and `-isysroot'.

`-fdirectives-only'
     When preprocessing, handle directives, but do not expand macros.

     The option's behavior depends on the `-E' and `-fpreprocessed'
     options.

     With `-E', preprocessing is limited to the handling of directives
     such as `#define', `#ifdef', and `#error'.  Other preprocessor
     operations, such as macro expansion and trigraph conversion are
     not performed.  In addition, the `-dD' option is implicitly
     enabled.

     With `-fpreprocessed', predefinition of command line and most
     builtin macros is disabled.  Macros such as `__LINE__', which are
     contextually dependent, are handled normally.  This enables
     compilation of files previously preprocessed with `-E
     -fdirectives-only'.

     With both `-E' and `-fpreprocessed', the rules for
     `-fpreprocessed' take precedence.  This enables full preprocessing
     of files previously preprocessed with `-E -fdirectives-only'.

`-fdollars-in-identifiers'
     Accept `$' in identifiers.

`-fextended-identifiers'
     Accept universal character names in identifiers.  This option is
     experimental; in a future version of GCC, it will be enabled by
     default for C99 and C++.

`-fpreprocessed'
     Indicate to the preprocessor that the input file has already been
     preprocessed.  This suppresses things like macro expansion,
     trigraph conversion, escaped newline splicing, and processing of
     most directives.  The preprocessor still recognizes and removes
     comments, so that you can pass a file preprocessed with `-C' to
     the compiler without problems.  In this mode the integrated
     preprocessor is little more than a tokenizer for the front ends.

     `-fpreprocessed' is implicit if the input file has one of the
     extensions `.i', `.ii' or `.mi'.  These are the extensions that
     GCC uses for preprocessed files created by `-save-temps'.

`-ftabstop=WIDTH'
     Set the distance between tab stops.  This helps the preprocessor
     report correct column numbers in warnings or errors, even if tabs
     appear on the line.  If the value is less than 1 or greater than
     100, the option is ignored.  The default is 8.

`-fexec-charset=CHARSET'
     Set the execution character set, used for string and character
     constants.  The default is UTF-8.  CHARSET can be any encoding
     supported by the system's `iconv' library routine.

`-fwide-exec-charset=CHARSET'
     Set the wide execution character set, used for wide string and
     character constants.  The default is UTF-32 or UTF-16, whichever
     corresponds to the width of `wchar_t'.  As with `-fexec-charset',
     CHARSET can be any encoding supported by the system's `iconv'
     library routine; however, you will have problems with encodings
     that do not fit exactly in `wchar_t'.

`-finput-charset=CHARSET'
     Set the input character set, used for translation from the
     character set of the input file to the source character set used
     by GCC.  If the locale does not specify, or GCC cannot get this
     information from the locale, the default is UTF-8.  This can be
     overridden by either the locale or this command line option.
     Currently the command line option takes precedence if there's a
     conflict.  CHARSET can be any encoding supported by the system's
     `iconv' library routine.

`-fworking-directory'
     Enable generation of linemarkers in the preprocessor output that
     will let the compiler know the current working directory at the
     time of preprocessing.  When this option is enabled, the
     preprocessor will emit, after the initial linemarker, a second
     linemarker with the current working directory followed by two
     slashes.  GCC will use this directory, when it's present in the
     preprocessed input, as the directory emitted as the current
     working directory in some debugging information formats.  This
     option is implicitly enabled if debugging information is enabled,
     but this can be inhibited with the negated form
     `-fno-working-directory'.  If the `-P' flag is present in the
     command line, this option has no effect, since no `#line'
     directives are emitted whatsoever.

`-fno-show-column'
     Do not print column numbers in diagnostics.  This may be necessary
     if diagnostics are being scanned by a program that does not
     understand the column numbers, such as `dejagnu'.

`-A PREDICATE=ANSWER'
     Make an assertion with the predicate PREDICATE and answer ANSWER.
     This form is preferred to the older form `-A PREDICATE(ANSWER)',
     which is still supported, because it does not use shell special
     characters.

`-A -PREDICATE=ANSWER'
     Cancel an assertion with the predicate PREDICATE and answer ANSWER.

`-dCHARS'
     CHARS is a sequence of one or more of the following characters,
     and must not be preceded by a space.  Other characters are
     interpreted by the compiler proper, or reserved for future
     versions of GCC, and so are silently ignored.  If you specify
     characters whose behavior conflicts, the result is undefined.

    `M'
          Instead of the normal output, generate a list of `#define'
          directives for all the macros defined during the execution of
          the preprocessor, including predefined macros.  This gives
          you a way of finding out what is predefined in your version
          of the preprocessor.  Assuming you have no file `foo.h', the
          command

               touch foo.h; cpp -dM foo.h

          will show all the predefined macros.

          If you use `-dM' without the `-E' option, `-dM' is
          interpreted as a synonym for `-fdump-rtl-mach'.  *Note
          Debugging Options: (gcc)Debugging Options.

    `D'
          Like `M' except in two respects: it does _not_ include the
          predefined macros, and it outputs _both_ the `#define'
          directives and the result of preprocessing.  Both kinds of
          output go to the standard output file.

    `N'
          Like `D', but emit only the macro names, not their expansions.

    `I'
          Output `#include' directives in addition to the result of
          preprocessing.

`-P'
     Inhibit generation of linemarkers in the output from the
     preprocessor.  This might be useful when running the preprocessor
     on something that is not C code, and will be sent to a program
     which might be confused by the linemarkers.

`-C'
     Do not discard comments.  All comments are passed through to the
     output file, except for comments in processed directives, which
     are deleted along with the directive.

     You should be prepared for side effects when using `-C'; it causes
     the preprocessor to treat comments as tokens in their own right.
     For example, comments appearing at the start of what would be a
     directive line have the effect of turning that line into an
     ordinary source line, since the first token on the line is no
     longer a `#'.

`-CC'
     Do not discard comments, including during macro expansion.  This is
     like `-C', except that comments contained within macros are also
     passed through to the output file where the macro is expanded.

     In addition to the side-effects of the `-C' option, the `-CC'
     option causes all C++-style comments inside a macro to be
     converted to C-style comments.  This is to prevent later use of
     that macro from inadvertently commenting out the remainder of the
     source line.

     The `-CC' option is generally used to support lint comments.

`-traditional-cpp'
     Try to imitate the behavior of old-fashioned C preprocessors, as
     opposed to ISO C preprocessors.

`-trigraphs'
     Process trigraph sequences.  These are three-character sequences,
     all starting with `??', that are defined by ISO C to stand for
     single characters.  For example, `??/' stands for `\', so `'??/n''
     is a character constant for a newline.  By default, GCC ignores
     trigraphs, but in standard-conforming modes it converts them.  See
     the `-std' and `-ansi' options.

     The nine trigraphs and their replacements are

          Trigraph:       ??(  ??)  ??<  ??>  ??=  ??/  ??'  ??!  ??-
          Replacement:      [    ]    {    }    #    \    ^    |    ~

`-remap'
     Enable special code to work around file systems which only permit
     very short file names, such as MS-DOS.

`--help'
`--target-help'
     Print text describing all the command line options instead of
     preprocessing anything.

`-v'
     Verbose mode.  Print out GNU CPP's version number at the beginning
     of execution, and report the final form of the include path.

`-H'
     Print the name of each header file used, in addition to other
     normal activities.  Each name is indented to show how deep in the
     `#include' stack it is.  Precompiled header files are also
     printed, even if they are found to be invalid; an invalid
     precompiled header file is printed with `...x' and a valid one
     with `...!' .

`-version'
`--version'
     Print out GNU CPP's version number.  With one dash, proceed to
     preprocess as normal.  With two dashes, exit immediately.


File: gcc.info,  Node: Assembler Options,  Next: Link Options,  Prev: Preprocessor Options,  Up: Invoking GCC

3.12 Passing Options to the Assembler
=====================================

You can pass options to the assembler.

`-Wa,OPTION'
     Pass OPTION as an option to the assembler.  If OPTION contains
     commas, it is split into multiple options at the commas.

`-Xassembler OPTION'
     Pass OPTION as an option to the assembler.  You can use this to
     supply system-specific assembler options which GCC does not know
     how to recognize.

     If you want to pass an option that takes an argument, you must use
     `-Xassembler' twice, once for the option and once for the argument.



File: gcc.info,  Node: Link Options,  Next: Directory Options,  Prev: Assembler Options,  Up: Invoking GCC

3.13 Options for Linking
========================

These options come into play when the compiler links object files into
an executable output file.  They are meaningless if the compiler is not
doing a link step.

`OBJECT-FILE-NAME'
     A file name that does not end in a special recognized suffix is
     considered to name an object file or library.  (Object files are
     distinguished from libraries by the linker according to the file
     contents.)  If linking is done, these object files are used as
     input to the linker.

`-c'
`-S'
`-E'
     If any of these options is used, then the linker is not run, and
     object file names should not be used as arguments.  *Note Overall
     Options::.

`-lLIBRARY'
`-l LIBRARY'
     Search the library named LIBRARY when linking.  (The second
     alternative with the library as a separate argument is only for
     POSIX compliance and is not recommended.)

     It makes a difference where in the command you write this option;
     the linker searches and processes libraries and object files in
     the order they are specified.  Thus, `foo.o -lz bar.o' searches
     library `z' after file `foo.o' but before `bar.o'.  If `bar.o'
     refers to functions in `z', those functions may not be loaded.

     The linker searches a standard list of directories for the library,
     which is actually a file named `libLIBRARY.a'.  The linker then
     uses this file as if it had been specified precisely by name.

     The directories searched include several standard system
     directories plus any that you specify with `-L'.

     Normally the files found this way are library files--archive files
     whose members are object files.  The linker handles an archive
     file by scanning through it for members which define symbols that
     have so far been referenced but not defined.  But if the file that
     is found is an ordinary object file, it is linked in the usual
     fashion.  The only difference between using an `-l' option and
     specifying a file name is that `-l' surrounds LIBRARY with `lib'
     and `.a' and searches several directories.

`-lobjc'
     You need this special case of the `-l' option in order to link an
     Objective-C or Objective-C++ program.

`-nostartfiles'
     Do not use the standard system startup files when linking.  The
     standard system libraries are used normally, unless `-nostdlib' or
     `-nodefaultlibs' is used.

`-nodefaultlibs'
     Do not use the standard system libraries when linking.  Only the
     libraries you specify will be passed to the linker.  The standard
     startup files are used normally, unless `-nostartfiles' is used.
     The compiler may generate calls to `memcmp', `memset', `memcpy'
     and `memmove'.  These entries are usually resolved by entries in
     libc.  These entry points should be supplied through some other
     mechanism when this option is specified.

`-nostdlib'
     Do not use the standard system startup files or libraries when
     linking.  No startup files and only the libraries you specify will
     be passed to the linker.  The compiler may generate calls to
     `memcmp', `memset', `memcpy' and `memmove'.  These entries are
     usually resolved by entries in libc.  These entry points should be
     supplied through some other mechanism when this option is
     specified.

     One of the standard libraries bypassed by `-nostdlib' and
     `-nodefaultlibs' is `libgcc.a', a library of internal subroutines
     that GCC uses to overcome shortcomings of particular machines, or
     special needs for some languages.  (*Note Interfacing to GCC
     Output: (gccint)Interface, for more discussion of `libgcc.a'.)  In
     most cases, you need `libgcc.a' even when you want to avoid other
     standard libraries.  In other words, when you specify `-nostdlib'
     or `-nodefaultlibs' you should usually specify `-lgcc' as well.
     This ensures that you have no unresolved references to internal GCC
     library subroutines.  (For example, `__main', used to ensure C++
     constructors will be called; *note `collect2': (gccint)Collect2.)

`-pie'
     Produce a position independent executable on targets which support
     it.  For predictable results, you must also specify the same set
     of options that were used to generate code (`-fpie', `-fPIE', or
     model suboptions) when you specify this option.

`-rdynamic'
     Pass the flag `-export-dynamic' to the ELF linker, on targets that
     support it. This instructs the linker to add all symbols, not only
     used ones, to the dynamic symbol table. This option is needed for
     some uses of `dlopen' or to allow obtaining backtraces from within
     a program.

`-s'
     Remove all symbol table and relocation information from the
     executable.

`-static'
     On systems that support dynamic linking, this prevents linking
     with the shared libraries.  On other systems, this option has no
     effect.

`-shared'
     Produce a shared object which can then be linked with other
     objects to form an executable.  Not all systems support this
     option.  For predictable results, you must also specify the same
     set of options that were used to generate code (`-fpic', `-fPIC',
     or model suboptions) when you specify this option.(1)

`-shared-libgcc'
`-static-libgcc'
     On systems that provide `libgcc' as a shared library, these options
     force the use of either the shared or static version respectively.
     If no shared version of `libgcc' was built when the compiler was
     configured, these options have no effect.

     There are several situations in which an application should use the
     shared `libgcc' instead of the static version.  The most common of
     these is when the application wishes to throw and catch exceptions
     across different shared libraries.  In that case, each of the
     libraries as well as the application itself should use the shared
     `libgcc'.

     Therefore, the G++ and GCJ drivers automatically add
     `-shared-libgcc' whenever you build a shared library or a main
     executable, because C++ and Java programs typically use
     exceptions, so this is the right thing to do.

     If, instead, you use the GCC driver to create shared libraries,
     you may find that they will not always be linked with the shared
     `libgcc'.  If GCC finds, at its configuration time, that you have
     a non-GNU linker or a GNU linker that does not support option
     `--eh-frame-hdr', it will link the shared version of `libgcc' into
     shared libraries by default.  Otherwise, it will take advantage of
     the linker and optimize away the linking with the shared version
     of `libgcc', linking with the static version of libgcc by default.
     This allows exceptions to propagate through such shared libraries,
     without incurring relocation costs at library load time.

     However, if a library or main executable is supposed to throw or
     catch exceptions, you must link it using the G++ or GCJ driver, as
     appropriate for the languages used in the program, or using the
     option `-shared-libgcc', such that it is linked with the shared
     `libgcc'.

`-symbolic'
     Bind references to global symbols when building a shared object.
     Warn about any unresolved references (unless overridden by the
     link editor option `-Xlinker -z -Xlinker defs').  Only a few
     systems support this option.

`-Xlinker OPTION'
     Pass OPTION as an option to the linker.  You can use this to
     supply system-specific linker options which GCC does not know how
     to recognize.

     If you want to pass an option that takes an argument, you must use
     `-Xlinker' twice, once for the option and once for the argument.
     For example, to pass `-assert definitions', you must write
     `-Xlinker -assert -Xlinker definitions'.  It does not work to write
     `-Xlinker "-assert definitions"', because this passes the entire
     string as a single argument, which is not what the linker expects.

`-Wl,OPTION'
     Pass OPTION as an option to the linker.  If OPTION contains
     commas, it is split into multiple options at the commas.

`-u SYMBOL'
     Pretend the symbol SYMBOL is undefined, to force linking of
     library modules to define it.  You can use `-u' multiple times with
     different symbols to force loading of additional library modules.

 ---------- Footnotes ----------

 (1) On some systems, `gcc -shared' needs to build supplementary stub
code for constructors to work.  On multi-libbed systems, `gcc -shared'
must select the correct support libraries to link against.  Failing to
supply the correct flags may lead to subtle defects.  Supplying them in
cases where they are not necessary is innocuous.


File: gcc.info,  Node: Directory Options,  Next: Spec Files,  Prev: Link Options,  Up: Invoking GCC

3.14 Options for Directory Search
=================================

These options specify directories to search for header files, for
libraries and for parts of the compiler:

`-IDIR'
     Add the directory DIR to the head of the list of directories to be
     searched for header files.  This can be used to override a system
     header file, substituting your own version, since these
     directories are searched before the system header file
     directories.  However, you should not use this option to add
     directories that contain vendor-supplied system header files (use
     `-isystem' for that).  If you use more than one `-I' option, the
     directories are scanned in left-to-right order; the standard
     system directories come after.

     If a standard system include directory, or a directory specified
     with `-isystem', is also specified with `-I', the `-I' option will
     be ignored.  The directory will still be searched but as a system
     directory at its normal position in the system include chain.
     This is to ensure that GCC's procedure to fix buggy system headers
     and the ordering for the include_next directive are not
     inadvertently changed.  If you really need to change the search
     order for system directories, use the `-nostdinc' and/or
     `-isystem' options.

`-iquoteDIR'
     Add the directory DIR to the head of the list of directories to be
     searched for header files only for the case of `#include "FILE"';
     they are not searched for `#include <FILE>', otherwise just like
     `-I'.

`-LDIR'
     Add directory DIR to the list of directories to be searched for
     `-l'.

`-BPREFIX'
     This option specifies where to find the executables, libraries,
     include files, and data files of the compiler itself.

     The compiler driver program runs one or more of the subprograms
     `cpp', `cc1', `as' and `ld'.  It tries PREFIX as a prefix for each
     program it tries to run, both with and without `MACHINE/VERSION/'
     (*note Target Options::).

     For each subprogram to be run, the compiler driver first tries the
     `-B' prefix, if any.  If that name is not found, or if `-B' was
     not specified, the driver tries two standard prefixes, which are
     `/usr/lib/gcc/' and `/usr/local/lib/gcc/'.  If neither of those
     results in a file name that is found, the unmodified program name
     is searched for using the directories specified in your `PATH'
     environment variable.

     The compiler will check to see if the path provided by the `-B'
     refers to a directory, and if necessary it will add a directory
     separator character at the end of the path.

     `-B' prefixes that effectively specify directory names also apply
     to libraries in the linker, because the compiler translates these
     options into `-L' options for the linker.  They also apply to
     includes files in the preprocessor, because the compiler
     translates these options into `-isystem' options for the
     preprocessor.  In this case, the compiler appends `include' to the
     prefix.

     The run-time support file `libgcc.a' can also be searched for using
     the `-B' prefix, if needed.  If it is not found there, the two
     standard prefixes above are tried, and that is all.  The file is
     left out of the link if it is not found by those means.

     Another way to specify a prefix much like the `-B' prefix is to use
     the environment variable `GCC_EXEC_PREFIX'.  *Note Environment
     Variables::.

     As a special kludge, if the path provided by `-B' is
     `[dir/]stageN/', where N is a number in the range 0 to 9, then it
     will be replaced by `[dir/]include'.  This is to help with
     boot-strapping the compiler.

`-specs=FILE'
     Process FILE after the compiler reads in the standard `specs'
     file, in order to override the defaults that the `gcc' driver
     program uses when determining what switches to pass to `cc1',
     `cc1plus', `as', `ld', etc.  More than one `-specs=FILE' can be
     specified on the command line, and they are processed in order,
     from left to right.

`--sysroot=DIR'
     Use DIR as the logical root directory for headers and libraries.
     For example, if the compiler would normally search for headers in
     `/usr/include' and libraries in `/usr/lib', it will instead search
     `DIR/usr/include' and `DIR/usr/lib'.

     If you use both this option and the `-isysroot' option, then the
     `--sysroot' option will apply to libraries, but the `-isysroot'
     option will apply to header files.

     The GNU linker (beginning with version 2.16) has the necessary
     support for this option.  If your linker does not support this
     option, the header file aspect of `--sysroot' will still work, but
     the library aspect will not.

`-I-'
     This option has been deprecated.  Please use `-iquote' instead for
     `-I' directories before the `-I-' and remove the `-I-'.  Any
     directories you specify with `-I' options before the `-I-' option
     are searched only for the case of `#include "FILE"'; they are not
     searched for `#include <FILE>'.

     If additional directories are specified with `-I' options after
     the `-I-', these directories are searched for all `#include'
     directives.  (Ordinarily _all_ `-I' directories are used this way.)

     In addition, the `-I-' option inhibits the use of the current
     directory (where the current input file came from) as the first
     search directory for `#include "FILE"'.  There is no way to
     override this effect of `-I-'.  With `-I.' you can specify
     searching the directory which was current when the compiler was
     invoked.  That is not exactly the same as what the preprocessor
     does by default, but it is often satisfactory.

     `-I-' does not inhibit the use of the standard system directories
     for header files.  Thus, `-I-' and `-nostdinc' are independent.


File: gcc.info,  Node: Spec Files,  Next: Target Options,  Prev: Directory Options,  Up: Invoking GCC

3.15 Specifying subprocesses and the switches to pass to them
=============================================================

`gcc' is a driver program.  It performs its job by invoking a sequence
of other programs to do the work of compiling, assembling and linking.
GCC interprets its command-line parameters and uses these to deduce
which programs it should invoke, and which command-line options it
ought to place on their command lines.  This behavior is controlled by
"spec strings".  In most cases there is one spec string for each
program that GCC can invoke, but a few programs have multiple spec
strings to control their behavior.  The spec strings built into GCC can
be overridden by using the `-specs=' command-line switch to specify a
spec file.

 "Spec files" are plaintext files that are used to construct spec
strings.  They consist of a sequence of directives separated by blank
lines.  The type of directive is determined by the first non-whitespace
character on the line and it can be one of the following:

`%COMMAND'
     Issues a COMMAND to the spec file processor.  The commands that can
     appear here are:

    `%include <FILE>'
          Search for FILE and insert its text at the current point in
          the specs file.

    `%include_noerr <FILE>'
          Just like `%include', but do not generate an error message if
          the include file cannot be found.

    `%rename OLD_NAME NEW_NAME'
          Rename the spec string OLD_NAME to NEW_NAME.


`*[SPEC_NAME]:'
     This tells the compiler to create, override or delete the named
     spec string.  All lines after this directive up to the next
     directive or blank line are considered to be the text for the spec
     string.  If this results in an empty string then the spec will be
     deleted.  (Or, if the spec did not exist, then nothing will
     happened.)  Otherwise, if the spec does not currently exist a new
     spec will be created.  If the spec does exist then its contents
     will be overridden by the text of this directive, unless the first
     character of that text is the `+' character, in which case the
     text will be appended to the spec.

`[SUFFIX]:'
     Creates a new `[SUFFIX] spec' pair.  All lines after this directive
     and up to the next directive or blank line are considered to make
     up the spec string for the indicated suffix.  When the compiler
     encounters an input file with the named suffix, it will processes
     the spec string in order to work out how to compile that file.
     For example:

          .ZZ:
          z-compile -input %i

     This says that any input file whose name ends in `.ZZ' should be
     passed to the program `z-compile', which should be invoked with the
     command-line switch `-input' and with the result of performing the
     `%i' substitution.  (See below.)

     As an alternative to providing a spec string, the text that
     follows a suffix directive can be one of the following:

    `@LANGUAGE'
          This says that the suffix is an alias for a known LANGUAGE.
          This is similar to using the `-x' command-line switch to GCC
          to specify a language explicitly.  For example:

               .ZZ:
               @c++

          Says that .ZZ files are, in fact, C++ source files.

    `#NAME'
          This causes an error messages saying:

               NAME compiler not installed on this system.

     GCC already has an extensive list of suffixes built into it.  This
     directive will add an entry to the end of the list of suffixes, but
     since the list is searched from the end backwards, it is
     effectively possible to override earlier entries using this
     technique.


 GCC has the following spec strings built into it.  Spec files can
override these strings or create their own.  Note that individual
targets can also add their own spec strings to this list.

     asm          Options to pass to the assembler
     asm_final    Options to pass to the assembler post-processor
     cpp          Options to pass to the C preprocessor
     cc1          Options to pass to the C compiler
     cc1plus      Options to pass to the C++ compiler
     endfile      Object files to include at the end of the link
     link         Options to pass to the linker
     lib          Libraries to include on the command line to the linker
     libgcc       Decides which GCC support library to pass to the linker
     linker       Sets the name of the linker
     predefines   Defines to be passed to the C preprocessor
     signed_char  Defines to pass to CPP to say whether `char' is signed
                  by default
     startfile    Object files to include at the start of the link

 Here is a small example of a spec file:

     %rename lib                 old_lib

     *lib:
     --start-group -lgcc -lc -leval1 --end-group %(old_lib)

 This example renames the spec called `lib' to `old_lib' and then
overrides the previous definition of `lib' with a new one.  The new
definition adds in some extra command-line options before including the
text of the old definition.

 "Spec strings" are a list of command-line options to be passed to their
corresponding program.  In addition, the spec strings can contain
`%'-prefixed sequences to substitute variable text or to conditionally
insert text into the command line.  Using these constructs it is
possible to generate quite complex command lines.

 Here is a table of all defined `%'-sequences for spec strings.  Note
that spaces are not generated automatically around the results of
expanding these sequences.  Therefore you can concatenate them together
or combine them with constant text in a single argument.

`%%'
     Substitute one `%' into the program name or argument.

`%i'
     Substitute the name of the input file being processed.

`%b'
     Substitute the basename of the input file being processed.  This
     is the substring up to (and not including) the last period and not
     including the directory.

`%B'
     This is the same as `%b', but include the file suffix (text after
     the last period).

`%d'
     Marks the argument containing or following the `%d' as a temporary
     file name, so that that file will be deleted if GCC exits
     successfully.  Unlike `%g', this contributes no text to the
     argument.

`%gSUFFIX'
     Substitute a file name that has suffix SUFFIX and is chosen once
     per compilation, and mark the argument in the same way as `%d'.
     To reduce exposure to denial-of-service attacks, the file name is
     now chosen in a way that is hard to predict even when previously
     chosen file names are known.  For example, `%g.s ... %g.o ... %g.s'
     might turn into `ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s'.  SUFFIX
     matches the regexp `[.A-Za-z]*' or the special string `%O', which
     is treated exactly as if `%O' had been preprocessed.  Previously,
     `%g' was simply substituted with a file name chosen once per
     compilation, without regard to any appended suffix (which was
     therefore treated just like ordinary text), making such attacks
     more likely to succeed.

`%uSUFFIX'
     Like `%g', but generates a new temporary file name even if
     `%uSUFFIX' was already seen.

`%USUFFIX'
     Substitutes the last file name generated with `%uSUFFIX',
     generating a new one if there is no such last file name.  In the
     absence of any `%uSUFFIX', this is just like `%gSUFFIX', except
     they don't share the same suffix _space_, so `%g.s ... %U.s ...
     %g.s ... %U.s' would involve the generation of two distinct file
     names, one for each `%g.s' and another for each `%U.s'.
     Previously, `%U' was simply substituted with a file name chosen
     for the previous `%u', without regard to any appended suffix.

`%jSUFFIX'
     Substitutes the name of the `HOST_BIT_BUCKET', if any, and if it is
     writable, and if save-temps is off; otherwise, substitute the name
     of a temporary file, just like `%u'.  This temporary file is not
     meant for communication between processes, but rather as a junk
     disposal mechanism.

`%|SUFFIX'
`%mSUFFIX'
     Like `%g', except if `-pipe' is in effect.  In that case `%|'
     substitutes a single dash and `%m' substitutes nothing at all.
     These are the two most common ways to instruct a program that it
     should read from standard input or write to standard output.  If
     you need something more elaborate you can use an `%{pipe:`X'}'
     construct: see for example `f/lang-specs.h'.

`%.SUFFIX'
     Substitutes .SUFFIX for the suffixes of a matched switch's args
     when it is subsequently output with `%*'.  SUFFIX is terminated by
     the next space or %.

`%w'
     Marks the argument containing or following the `%w' as the
     designated output file of this compilation.  This puts the argument
     into the sequence of arguments that `%o' will substitute later.

`%o'
     Substitutes the names of all the output files, with spaces
     automatically placed around them.  You should write spaces around
     the `%o' as well or the results are undefined.  `%o' is for use in
     the specs for running the linker.  Input files whose names have no
     recognized suffix are not compiled at all, but they are included
     among the output files, so they will be linked.

`%O'
     Substitutes the suffix for object files.  Note that this is
     handled specially when it immediately follows `%g, %u, or %U',
     because of the need for those to form complete file names.  The
     handling is such that `%O' is treated exactly as if it had already
     been substituted, except that `%g, %u, and %U' do not currently
     support additional SUFFIX characters following `%O' as they would
     following, for example, `.o'.

`%p'
     Substitutes the standard macro predefinitions for the current
     target machine.  Use this when running `cpp'.

`%P'
     Like `%p', but puts `__' before and after the name of each
     predefined macro, except for macros that start with `__' or with
     `_L', where L is an uppercase letter.  This is for ISO C.

`%I'
     Substitute any of `-iprefix' (made from `GCC_EXEC_PREFIX'),
     `-isysroot' (made from `TARGET_SYSTEM_ROOT'), `-isystem' (made
     from `COMPILER_PATH' and `-B' options) and `-imultilib' as
     necessary.

`%s'
     Current argument is the name of a library or startup file of some
     sort.  Search for that file in a standard list of directories and
     substitute the full name found.

`%eSTR'
     Print STR as an error message.  STR is terminated by a newline.
     Use this when inconsistent options are detected.

`%(NAME)'
     Substitute the contents of spec string NAME at this point.

`%[NAME]'
     Like `%(...)' but put `__' around `-D' arguments.

`%x{OPTION}'
     Accumulate an option for `%X'.

`%X'
     Output the accumulated linker options specified by `-Wl' or a `%x'
     spec string.

`%Y'
     Output the accumulated assembler options specified by `-Wa'.

`%Z'
     Output the accumulated preprocessor options specified by `-Wp'.

`%a'
     Process the `asm' spec.  This is used to compute the switches to
     be passed to the assembler.

`%A'
     Process the `asm_final' spec.  This is a spec string for passing
     switches to an assembler post-processor, if such a program is
     needed.

`%l'
     Process the `link' spec.  This is the spec for computing the
     command line passed to the linker.  Typically it will make use of
     the `%L %G %S %D and %E' sequences.

`%D'
     Dump out a `-L' option for each directory that GCC believes might
     contain startup files.  If the target supports multilibs then the
     current multilib directory will be prepended to each of these
     paths.

`%L'
     Process the `lib' spec.  This is a spec string for deciding which
     libraries should be included on the command line to the linker.

`%G'
     Process the `libgcc' spec.  This is a spec string for deciding
     which GCC support library should be included on the command line
     to the linker.

`%S'
     Process the `startfile' spec.  This is a spec for deciding which
     object files should be the first ones passed to the linker.
     Typically this might be a file named `crt0.o'.

`%E'
     Process the `endfile' spec.  This is a spec string that specifies
     the last object files that will be passed to the linker.

`%C'
     Process the `cpp' spec.  This is used to construct the arguments
     to be passed to the C preprocessor.

`%1'
     Process the `cc1' spec.  This is used to construct the options to
     be passed to the actual C compiler (`cc1').

`%2'
     Process the `cc1plus' spec.  This is used to construct the options
     to be passed to the actual C++ compiler (`cc1plus').

`%*'
     Substitute the variable part of a matched option.  See below.
     Note that each comma in the substituted string is replaced by a
     single space.

`%<`S''
     Remove all occurrences of `-S' from the command line.  Note--this
     command is position dependent.  `%' commands in the spec string
     before this one will see `-S', `%' commands in the spec string
     after this one will not.

`%:FUNCTION(ARGS)'
     Call the named function FUNCTION, passing it ARGS.  ARGS is first
     processed as a nested spec string, then split into an argument
     vector in the usual fashion.  The function returns a string which
     is processed as if it had appeared literally as part of the
     current spec.

     The following built-in spec functions are provided:

    ``getenv''
          The `getenv' spec function takes two arguments: an environment
          variable name and a string.  If the environment variable is
          not defined, a fatal error is issued.  Otherwise, the return
          value is the value of the environment variable concatenated
          with the string.  For example, if `TOPDIR' is defined as
          `/path/to/top', then:

               %:getenv(TOPDIR /include)

          expands to `/path/to/top/include'.

    ``if-exists''
          The `if-exists' spec function takes one argument, an absolute
          pathname to a file.  If the file exists, `if-exists' returns
          the pathname.  Here is a small example of its usage:

               *startfile:
               crt0%O%s %:if-exists(crti%O%s) crtbegin%O%s

    ``if-exists-else''
          The `if-exists-else' spec function is similar to the
          `if-exists' spec function, except that it takes two
          arguments.  The first argument is an absolute pathname to a
          file.  If the file exists, `if-exists-else' returns the
          pathname.  If it does not exist, it returns the second
          argument.  This way, `if-exists-else' can be used to select
          one file or another, based on the existence of the first.
          Here is a small example of its usage:

               *startfile:
               crt0%O%s %:if-exists(crti%O%s) \
               %:if-exists-else(crtbeginT%O%s crtbegin%O%s)

    ``replace-outfile''
          The `replace-outfile' spec function takes two arguments.  It
          looks for the first argument in the outfiles array and
          replaces it with the second argument.  Here is a small
          example of its usage:

               %{fgnu-runtime:%:replace-outfile(-lobjc -lobjc-gnu)}

    ``print-asm-header''
          The `print-asm-header' function takes no arguments and simply
          prints a banner like:

               Assembler options
               =================

               Use "-Wa,OPTION" to pass "OPTION" to the assembler.

          It is used to separate compiler options from assembler options
          in the `--target-help' output.

`%{`S'}'
     Substitutes the `-S' switch, if that switch was given to GCC.  If
     that switch was not specified, this substitutes nothing.  Note that
     the leading dash is omitted when specifying this option, and it is
     automatically inserted if the substitution is performed.  Thus the
     spec string `%{foo}' would match the command-line option `-foo'
     and would output the command line option `-foo'.

`%W{`S'}'
     Like %{`S'} but mark last argument supplied within as a file to be
     deleted on failure.

`%{`S'*}'
     Substitutes all the switches specified to GCC whose names start
     with `-S', but which also take an argument.  This is used for
     switches like `-o', `-D', `-I', etc.  GCC considers `-o foo' as
     being one switch whose names starts with `o'.  %{o*} would
     substitute this text, including the space.  Thus two arguments
     would be generated.

`%{`S'*&`T'*}'
     Like %{`S'*}, but preserve order of `S' and `T' options (the order
     of `S' and `T' in the spec is not significant).  There can be any
     number of ampersand-separated variables; for each the wild card is
     optional.  Useful for CPP as `%{D*&U*&A*}'.

`%{`S':`X'}'
     Substitutes `X', if the `-S' switch was given to GCC.

`%{!`S':`X'}'
     Substitutes `X', if the `-S' switch was _not_ given to GCC.

`%{`S'*:`X'}'
     Substitutes `X' if one or more switches whose names start with
     `-S' are specified to GCC.  Normally `X' is substituted only once,
     no matter how many such switches appeared.  However, if `%*'
     appears somewhere in `X', then `X' will be substituted once for
     each matching switch, with the `%*' replaced by the part of that
     switch that matched the `*'.

`%{.`S':`X'}'
     Substitutes `X', if processing a file with suffix `S'.

`%{!.`S':`X'}'
     Substitutes `X', if _not_ processing a file with suffix `S'.

`%{,`S':`X'}'
     Substitutes `X', if processing a file for language `S'.

`%{!,`S':`X'}'
     Substitutes `X', if not processing a file for language `S'.

`%{`S'|`P':`X'}'
     Substitutes `X' if either `-S' or `-P' was given to GCC.  This may
     be combined with `!', `.', `,', and `*' sequences as well,
     although they have a stronger binding than the `|'.  If `%*'
     appears in `X', all of the alternatives must be starred, and only
     the first matching alternative is substituted.

     For example, a spec string like this:

          %{.c:-foo} %{!.c:-bar} %{.c|d:-baz} %{!.c|d:-boggle}

     will output the following command-line options from the following
     input command-line options:

          fred.c        -foo -baz
          jim.d         -bar -boggle
          -d fred.c     -foo -baz -boggle
          -d jim.d      -bar -baz -boggle

`%{S:X; T:Y; :D}'
     If `S' was given to GCC, substitutes `X'; else if `T' was given to
     GCC, substitutes `Y'; else substitutes `D'.  There can be as many
     clauses as you need.  This may be combined with `.', `,', `!',
     `|', and `*' as needed.


 The conditional text `X' in a %{`S':`X'} or similar construct may
contain other nested `%' constructs or spaces, or even newlines.  They
are processed as usual, as described above.  Trailing white space in
`X' is ignored.  White space may also appear anywhere on the left side
of the colon in these constructs, except between `.' or `*' and the
corresponding word.

 The `-O', `-f', `-m', and `-W' switches are handled specifically in
these constructs.  If another value of `-O' or the negated form of a
`-f', `-m', or `-W' switch is found later in the command line, the
earlier switch value is ignored, except with {`S'*} where `S' is just
one letter, which passes all matching options.

 The character `|' at the beginning of the predicate text is used to
indicate that a command should be piped to the following command, bu