This is doc/gcc.info, produced by makeinfo version 4.5 from doc/gcc.texi. 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 59 Temple Place - Suite 330 Boston, MA 02111-1307 USA Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002 Free Software Foundation, Inc. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.1 or any later version published by the Free Software Foundation; with the Invariant Sections being "GNU General Public License" and "Funding Free Software", the Front-Cover texts being (a) (see below), and with the Back-Cover Texts being (b) (see below). A copy of the license is included in the section entitled "GNU Free Documentation License". (a) The FSF's Front-Cover Text is: A GNU Manual (b) The FSF's Back-Cover Text is: You have freedom to copy and modify this GNU Manual, like GNU software. Copies published by the Free Software Foundation raise funds for GNU development.  File: 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. `-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 macros. The common 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. It is dangerous to specify a standard system include directory in an `-I' option. This defeats the special treatment of system headers . It can also defeat the repairs to buggy system headers which GCC makes when it is installed. `-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' and `-Wtrigraphs'. 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' Warn if any trigraphs are encountered. This option used to take effect only if `-trigraphs' was also specified, but now works independently. Warnings are not given for trigraphs within comments, as they do not affect the meaning of the program. `-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. `-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 DEPENDENCIES_OUTPUT::). Debug output will still be sent to the regular output stream as normal. Passing `-M' to the driver implies `-E'. `-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' When used with `-M' or `-MM', `-MG' says to treat missing header files as generated files and assume they live in the same directory as the source file. It suppresses preprocessed output, as a missing header file is ordinarily an error. 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. `-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 only knows about the standards for C; other language standards will 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. `-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 '. 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. `-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. `-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. `-A-' Cancel all predefined assertions and all assertions preceding it on the command line. Also, undefine all predefined macros and all macros preceding it on the command line. (This is a historical wart and may change in the future.) `-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 `#'. `-gcc' Define the macros __GNUC__, __GNUC_MINOR__ and __GNUC_PATCHLEVEL__. These are defined automatically when you use `gcc -E'; you can turn them off in that case with `-no-gcc'. `-traditional' Try to imitate the behavior of old-fashioned C, as opposed to ISO C. `-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. `-$' Forbid the use of `$' in identifiers. The C standard allows implementations to define extra characters that can appear in identifiers. By default GNU CPP permits `$', a common extension. `-h' `--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. `-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.  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..) `-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 inadvertantly 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 '. 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-lib/'. 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.