[musl] Difference in pthread behavior between glibc and musl

["Appelmans, Madeleine" <madelea@amazon.com>]

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Hello,

There seems to be a difference in pthread behavior when compiling with glibc and using the musl-gcc wrapper. The attached snippet of code creates a destructor attribute which deletes a pthread key. The code never actually creates the pthread key. This code segfaults when compiled using musl-gcc, and does not segfault when compiled with gcc.

Best guess at what is going on: When creating a pthread key, musl initializes a field called tsd<https://git.musl-libc.org/cgit/musl/tree/src/thread/pthread_key_create.c#n37>. When deleting a key, musl assumes that initialization has been done, and dereferences tsd without checking that it exists: see here<https://git.musl-libc.org/cgit/musl/tree/src/thread/pthread_key_create.c#n65>. This dereference may be the source of the segfault.

Thanks,
Madeleine

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#include <pthread.h>

static pthread_key_t per_thread_key;

static void __attribute__((destructor)) key_cleanup(void)
{
    pthread_key_delete(per_thread_key);
}

int main(int argc, char **argv)
{
    // Do nothing
}