test/pthread/test_pthread_tls_main.c

#include <assert.h>
#include <threads.h>

thread_local int tls = 1330;
thread_local int tls2;

__attribute__((constructor))
void init_tls2(void) {
  tls2 = 7;
}

int main(void) {
  assert(tls + tls2 == 1330 + 7);
  return 0;
}