Using and Porting GNU CC
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.
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 `
after file `
foo.o' but before `
bar.o'. If `
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 `
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 `
and searches several directories.
-l' option in order to link an Objective C program.
One of the standard libraries bypassed by `
libgcc.a', a library of internal subroutines that GNU CC uses to
overcome shortcomings of particular machines, or special needs for some
(See Interface, for more discussion of
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.)
-Xlinker -z -Xlinker defs'). Only a few systems support this option.
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.
-u' multiple times with different symbols to force loading of additional library modules.