#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/ptrace.h>
#include <signal.h>

void
traced_process(void) {
	if (ptrace(PTRACE_TRACEME, 0, 0, 0) < 0)
		exit(1);
	kill(getpid(), SIGCONT);
	if (fork()) {
		sleep(2);
/*		printf("parent: *sync=%d\n", *(unsigned char*)sync); */
	} else {
		printf("child is alive (*sync=%d)\n", *(unsigned char*)sync);
		sleep(1);
		printf("child: *sync=%d\n", *(unsigned char*)sync);
	}
	exit(0);
}

int
main(void) {
	pid_t pid;
	int status;
	int i=0;

	pid = fork();
	if (!pid) traced_process();

	while(1) {
		if (wait(&status)==-1) {
			break;
		}
		printf("ptrace(PTRACE_POKETEXT, %d, sync, %d)...\n", pid, ++i);
		ptrace(PTRACE_POKETEXT, pid, sync, i);
		ptrace(PTRACE_SYSCALL, pid, 0, 0);
	}
	exit(0);
}