#define _GNU_SOURCE
#include <errno.h>
#include <signal.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/ptrace.h>
#include <sys/wait.h>

#define fail(msg, args...) \
do { \
	fprintf(stderr, "FAIL:%i: " msg "\n", __LINE__, ## args); \
	exit(1); \
} while (0)

static void child_exit(int sig)
{
	int status;
	printf("failure, child exited with %i: %s\n", sig, strsignal(sig));
	printf("wait() = %i\n", wait(&status));
	printf("status = %i\n", status);
	printf("\tWIFEXITED = %i\n", WIFEXITED(status));
	printf("\tWEXITSTATUS = %i\n", WEXITSTATUS(status));
	printf("\tWIFSIGNALED = %i\n", WIFSIGNALED(status));
	printf("\tWTERMSIG = %i (%s)\n", WTERMSIG(status), strsignal(WTERMSIG(status)));
	exit(1);
}

int main(int argc, char *argv[])
{
	long pret;
	pid_t pid;

	/* child process ... shouldnt be executed, but just in case ... */
	if (argc > 1 && !strcmp(argv[1], "child"))
		fail("kernel should have halted me...");

	pid = vfork();
	if (pid == -1)
		fail("vfork() didnt work: %m");
	else if (!pid) {
		/* do the child stuff here */
		errno = 0;
		pret = ptrace(PTRACE_TRACEME, 0, NULL, NULL);
		if (pret && errno)
			fail("ptrace(PTRACE_TRACEME) = %li: %m", pret);

		int eret = execlp(argv[0], argv[0], "child", NULL);
		fail("execlp() = %i", eret);
	}

	/* do the parent stuff here */
	signal(SIGCHLD, child_exit);

	errno = 0;
	pret = ptrace(PTRACE_PEEKUSER, pid, NULL, NULL);
	if (pret && errno)
		fail("ptrace(PTRACE_PEEKUSER, %i) = %li: %m", pid, pret);

	puts("SUCCESS! :D");

	return 0;
}