GCC, PIE, PIC, archives and shared objects - what works with what?

Question

I have a question about GCC, ThreadSanitizer and the use of archives, shared libraries and PIE and PIC.

I've been reading about as best I can all morning, but I just can't find useful, clear information on-line.

I understand what PIC does. I think I understand that PIE is if you like an optimized version of PIC, which is only for executables.

Now come the questions...

1. Can I compile an executable with PIC, rather than PIE?

2. If I compile a shared library (.so) with PIC, must I then use PIC with any executable which uses that library, rather than PIE?

3. If I compile an archive (.a), can I use PIE? (I have read -static and -pie should not be used together, which implies not).

I'm using ThreadSanitizer. This requires PIC (and perhaps PIE is okay too - but as you can see, I'm not clear about this). I have a library, which can be compiled as an archive (.a) or a shared library (.so). The library needs to use ThreadSanitizer. However, the binary which uses it also needs to use ThreadSanitizer (as it has some code of its own which needs checking).

The library when built as a shared library in fact fails to link when used wih ThreadSanitizer - I think the link is failing to link to libtsan (but this is I suspect not a real library, but a bunch of compiler instrincs built into GCC). This is almost certainly me getting something wrong somewhere.

What I really want to do is use an archive (.a) since the binary is a test programme and should be able to compile without the library being installed (so users can conveniently check/test the library - the makefile for the test binary has a hard coded path to the archive binary).

If I can use PIE with archives (.a), then I'd PIE the library and the test binary. If PIE cannot be used with archives, then I think I need to use PIC with both the library and test binary. I don't want to use a shared library at all, since ThreadSanitizer uses TLS (thread local store) heavily and shared libraries with PIC have absolutely terrible TLS performance.

Answer 1

Ultimate functionality of pic and pie are same but in gcc -fpic is used to create shared libraries whereas -fpie is used to for exes.

1. No you cannot use pic for an executable

2. Shared libraries don't care where pie (PIE just make the exec position independent) or normal execs are using it. It is dynamic linker's (ld.so) job to link the shared library.

3. No you can't make a exec position independent while using a static library. When you link a exec with static library it creates a dependency on exec and the symbols have to be resolved at compile-time.So in short you can't.

I've to go answer rest after office