#include <sys/mman.h>
#include <sys/wait.h>
#include <sys/time.h>
#include <assert.h>
#include <stdlib.h>
#include <stdio.h>
#include <inttypes.h>
#include <unistd.h>

#define NR_FORKS 100000

static inline uint64_t get_cycles(void)
{
	uint64_t t;
	volatile int dont_remove __attribute__((unused));
	unsigned tmp;

	__asm volatile ("cpuid" : "=a"(tmp), "=b"(tmp), "=c"(tmp), "=d"(tmp): "a" (0));

	dont_remove = tmp; 
	__asm volatile ("rdtsc" : "=A"(t));
	return t;
}

int main(int argc, char **argv)
{
	void *addr = mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_ANON|MAP_SHARED, -1, 0);
	int i = NR_FORKS, j = 1;

	assert(addr != MAP_FAILED);

	while (i-- > 0) {
		pid_t child = fork();
		uint64_t before, after;

		assert(child != -1);
		if (!child) {
			*(uint64_t *)addr = get_cycles();
			return 0;
		}
		assert(child == waitpid(child, NULL, 0));
		before = *(uint64_t *)addr;
		after = get_cycles();

		printf("%u\n", (unsigned)(after - before));
		fflush(stdout);
	}

	return 0;
}