Test of gcc extensions __builtin_return_address && __label__

gcc_extensions_example.c

#include <stdio.h>

void *
test2(void)
{
   return __builtin_return_address(1);
}

void *
test1(void *( *func )( void ))
{
   return (func) ? func() :
                   __builtin_return_address(0);
}

int main(int argc, char **argv)
{
   __label__ l1, l2;
   void *test1_ra, *test2_ra;

   printf("Main addr: %p;\n", &main);
   printf("label1: %p; label2: %p;\n", &&l1, &&l2);

l1:   test1_ra = test1(NULL);
l2:   test2_ra = test1(&test2);

   printf("test1: %p; test2: %p;\n", test1_ra, test2_ra);

   return 0;
}