#include <stdint.h>

# ifdef __GNUC__

typedef __attribute__((__aligned__(8))) uint64_t ATOMIC_U64;

# else

typedef uint64_t ATOMIC_U64;

# endif

int main() {return 0;}

#ifdef BUGGY

uint64_t foo(uint64_t *val, uint64_t op)

#else

uint64_t foo(ATOMIC_U64 *val, uint64_t op)

#endif

{

    return __atomic_or_fetch(val, op, __ATOMIC_ACQ_REL);

}

/tmp/a.c:17:12: warning: misaligned atomic operation may incur significant performance penalty; the expected alignment (8 bytes) exceeds the actual alignment (4 bytes) [-Watomic-alignment]

    return __atomic_or_fetch(val, op, __ATOMIC_ACQ_REL);

           ^

1 warning generated.

/usr/bin/ld: /tmp/a-4a5d79.o: in function `foo':

a.c:(.text+0x6b): undefined reference to `__atomic_fetch_or_8'

clang-13: error: linker command failed with exit code 1 (use -v to see invocation)