How do I link a library file in GCC that does not start with lib?

You can have the linker search for a library named without the lib prefix:

gcc main.o -L/path/to/foo -l:foo.a

This is especially useful in environments where a list of libraries is specified and the -l flag is prepended later (eg some makefiles or eclipse CDT)

You can link against any library, e.g. foo.a, by specifying full path to it on the link line:

gcc main.o /path/to/foo.a

What you lose with non-standard library name is the ability for the linker to search for it, e.g. this will not work:

gcc main.o -L/path/to foo.a

You can avoid that lack of search by using -l:foo.a syntax:

gcc main.o -L/path/one -L/path/two -l:foo.a

When I link a library such as libm in with ld

Note that in general you should not link anything with ld. Use the compiler driver instead -- it adds objects and libraries to the link line that are required for correct result.