int check_fa_work (const char *, const char *) __attribute__((noinline)); int check_fa_mid (const char *) __attribute__((noinline)); int check_fa (char *) __attribute__((noinline)); int how_much (void) __attribute__((noinline)); int check_fa_work (const char *c, const char *f) { const char d = 0; if (c >= &d) return c >= f && f >= &d; else return c <= f && f <= &d; } int check_fa_mid (const char *c) { const char *f = __builtin_frame_address (0); /* Prevent a tail call to check_fa_work, eliding the current stack frame. */ return check_fa_work (c, f) != 0; } int check_fa (char *unused) { const char c = 0; /* Prevent a tail call to check_fa_mid, eliding the current stack frame. */ return check_fa_mid (&c) != 0; } int how_much (void) { return 8; } int main (void) { char *unused = __builtin_alloca (how_much ()); if (!check_fa(unused)) abort(); return 0; }