LD_PRELOAD and varargs

fcntl.c

#define _GNU_SOURCE
#include <dlfcn.h>
#include <fcntl.h>

int fcntl(int fd, int cmd, ...)
{
	if (cmd == F_OFD_SETLKW || cmd == F_OFD_SETLK) {
		return 0;
	}
	int (*orig)(int, int, ...) = dlsym(RTLD_NEXT, "fcntl");
	int *arg = __builtin_apply_args();
	void *ret = __builtin_apply((void *)orig, arg, 100);
	__builtin_return(ret);
}