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3.11: 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.

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.
If any of these options is used, then the linker is not run, and object file names should not be used as arguments. See Overall Options.
Search the library named library when linking.

It makes a difference where in the command you write this option; the linker searches 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.

You need this special case of the `-l' option in order to link an Objective C program.
Do not use the standard system startup files when linking. The standard libraries are used normally.
Do not use the standard system libraries and startup files when linking. Only the files you specify will be passed to the linker.

One of the standard libraries bypassed by `-nostdlib' is `libgcc.a', a library of internal subroutines that GNU CC uses to overcome shortcomings of particular machines, or special needs for some languages. (See 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' you should usually specify `-lgcc' as well. This ensures that you have no unresolved references to internal GNU CC library subroutines. (For example, `__main', used to ensure C++ constructors will be called; see Collect2.)

On systems that support dynamic linking, this prevents linking with the shared libraries. On other systems, this option has no effect.
Produce a shared object which can then be linked with other objects to form an executable. Only a few systems support this option.
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 GNU CC 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.

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.