“thread-local storage not supported for this target”, suitable #ifdef?

Question

Since every compiler has its own version of thread local storage, I ended up creating a macro for it. The only problem now is GCC (with pthreads turned off), which gives me:

"thread-local storage not supported for this target"

Fair enough, given that pthreads are actually turned off in this case. The question is, is there a generic way of detecting this using some macro e.g. #ifdef __GCC_XXX_NO_THREADS_XXX ?

EDIT: See the accepted answer below. Also, here's my lazy solution:

$ touch test.c
$ gcc -E -dM test.c > out.1
$ gcc -pthread -E -dM test.c > out.2
$ diff out.*
28a29
> #define _REENTRANT 1

This is on Mac OS X. I am not sure if it's portable or anything...

Answer 1

Your compile command line either has -lpthread or not: You could include a -DHAVE_PTHREADS there as well.

If you really want GCC/ELF specific runtime dectection, you could resort to weak refs:

#include <pthread.h>

extern void *pthread_getspecific(pthread_key_t key) __attribute__ ((weak));

int
main()
{
    if (pthread_getspecific)
        printf("have pthreads\n");
    else
        printf("no pthreads\n");
}

Here's what it looks like:

$ gcc -o x x.c
$ ./x
no pthreads
$ gcc -o x x.c -lpthread
$ ./x
have pthreads

Answer 2

If you use autoconf for your project you might find ax_tls.m4 useful.