Stripping unused functions

benno raised an interesting question on getting rid of unused functions from a binary. If you link a group of object files together, the linker will be smart enough to leave out any files that it know doesn't get used. But what about functions that don't get used?

The best solution I could think of was to use -ffunction-sections and then --gc-sections to remove those sections that aren't used.

$ cat foo.c
int foo(void) {};
int bar(void) {};

$ cat main.c
  return 0;

$ gcc -c main.c
$ gcc -c -ffunction-sections foo.c
$ gcc -Wl,--gc-sections foo.o main.o -o program
$ objdump -d ./program | grep bar

This seems well out of scope for the linker to resolve, as it's job isn't to splice and dice text sections. The compiler doesn't really have enough information to see what is going on either. I think it would be possible to analyse the relocations in a group of pre-linked object files, and then compare that against a list of global functions in those same object files and if there isn't a relocation against it, prune the function out of the object.

I think the nicest way to do that would be with libelf wrappers for Python. But surely someone has looked at doing that before?