How do you debug libc in OSX?

Question

I would expect to be able to statically link against a build of libc with debug symbols, then run my program through lldb.

otool -L <my binary>

makes it look like the only dynamically linked library (dll) is:

/usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1226.10.1)

Which I would guess is the libc dll is (though nm doesn't list everything I'd expect in libc). Maybe just some kind of stub loader.

In /usr/lib/ it seems that Apple does not supply a debug build of libSystem.

How do you debug libc on OSX (10.11.3)?

Possible duplicate of: On Mac OS X, how can you get a debug build of System/LibC for source level debugging?

Answer 1

I'm having a hard time following your question, but there are certain points to be made which I think will cover what you're asking:

otool -L will show all dylibs that you are linking against.

/usr/lib/libSystem.B.dylib is an umbrella library that re-exports multiple dylibs, including libc (/usr/lib/system/libsystem_c.dylib). If you want to see what symbols are part of the system's C runtime, you will want to use nm on that dylib, not libSystem.

If you are statically linking in your own libc, then it won't show up in 'otool -L' because it's a static library and is thus part of your executable.

If you staticy linked your own libc into your executable, then using nm on your binary will possibly not show all the symbols you are expecting because the linker will optimize away dead code that is not needed by your executable. You can ensure that everything is added by using the -force_load option to ld. Check out the ld man page for more details on that.