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

#define ERRCHECK(E)\
	if ((E) == -1) {perror(argv[0]); kill(pid, SIGHUP); return -1;}

int main(int argc, char *argv[]) {
	if (argc < 2) {
		fprintf(stderr, "usage: %s COMMAND [ARGS]...\n" , argv[0]);
		return -1;
	}
	pid_t pid = fork();
	if (pid == -1) {
		perror(argv[0]);
		return -1;
	}
	if (pid == 0) {
		ptrace(PTRACE_TRACEME, 0, NULL, NULL);
		raise(SIGSTOP);
		if (execvp(argv[1], argv + 1) == -1) {
			perror(argv[0]);
			return -1;
		}
	} else {
		ERRCHECK(ptrace(PTRACE_ATTACH, pid, NULL, NULL));
		int status;
		pid_t w = waitpid(pid, &status, __WALL);
		ERRCHECK(w);
		ERRCHECK(ptrace(PTRACE_CONT, pid, NULL, NULL));
		while (1) {
			pid_t w = waitpid(pid, &status, __WALL);
			ERRCHECK(w);
			if (WIFEXITED(status))
				return WEXITSTATUS(status);
			if (WIFSTOPPED(status)) {
				if (WIFSIGNALED(status)) {
					errno = 0;
					switch (WSTOPSIG(status)) {
						case SIGABRT:
						case SIGBUS:
						case SIGFPE:
						case SIGILL:
						case SIGSEGV:
							ptrace(PTRACE_CONT, pid, NULL, NULL);
							break;
						default:
							ptrace(PTRACE_CONT, pid, NULL, WSTOPSIG(status));
							break;
					}
					if (errno && errno != ESRCH) {
						perror("ptrace");
						kill(pid, SIGHUP);
						return -1;
					}
				} else ptrace(PTRACE_CONT, pid, NULL, NULL);
			}
		}
	}
}