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INFO-DIR-SECTION Programming
START-INFO-DIR-ENTRY
* gcc: (gcc).                  The GNU Compiler Collection.
END-INFO-DIR-ENTRY
   This file documents the use of the GNU compilers.

   Published by the Free Software Foundation
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File: gcc.info,  Node: Preprocessor Options,  Next: Assembler Options,  Prev: Optimize Options,  Up: Invoking GCC

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'
     Predefine NAME as a macro, with definition DEFINITION.  There are
     no restrictions on the contents of DEFINITION, but 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 .

`-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 basename of the source file with any suffix
     replaced with object file suffix.  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, including any
     path, deletes 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 take the basename of the input file
     and applies a `.d' suffix.

     If `-MD' is used in conjunction with `-E', any `-o' switch is
     understood to specify the dependency output file (but *note
     -MF::), 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.

`-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"'.

`-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.

`-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.

     Use of these options is discouraged.

`-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.

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

`-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
     `-ftarget-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'.

`-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.

    `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

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

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 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, and memcpy for
     System V (and ISO C) environments or to bcopy and bzero for BSD
     environments.  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, and memcpy for System V (and ISO C) environments
     or to bcopy and bzero for BSD environments.  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.

`-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 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

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.

`-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.

`-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.

