#include <stdio.h>
#include <signal.h>
#include <sched.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/mman.h>
#include <sys/ptrace.h>
#include <asm/ptrace.h>
#include <unistd.h>
#include <asm/unistd.h>
#include <errno.h>

char childstack[ 8*1024];


int my_getpid()
{
	long res;
	__asm__ volatile ("	int $0x80\n\t"
				: "=a" (res)
				: "0" (__NR_getpid));
	return res;
}


int
child_fn( void * unused)
{
	pid_t me = my_getpid();

	printf("Child: my PID via 'int $0x80' is %d\n", me);

	ptrace(PTRACE_TRACEME, 0, 0, 0);
	kill( me, SIGSTOP);

	printf("Child: my PID via 'getpid()' is %d\n", getpid());

	return 0;
}


int
main( int argc, char ** argv)
{
	int ret, status, suppress=0;
	pid_t child;

	printf("Parent: my PID is %d\n", getpid());
	printf("Parent: my PID is %d\n", getpid());

	if ( argc < 2 || strcmp( argv[1], "clone") )
		return 0;

	child = clone( child_fn, childstack+8*1024-4, SIGCHLD, NULL);

	if ( child < 0 ) {
		perror("clone");
		exit(1);
	}
	printf("Parent: childs PID is %d\n", child);

	do {
		ret = waitpid(child, &status, WUNTRACED);
		if(ret < 0) {
			perror("waitpid()");
			exit(1);
		}
	} while(WIFSTOPPED(status) && (WSTOPSIG(status) == SIGVTALRM));

	if(!WIFSTOPPED(status) || (WSTOPSIG(status) != SIGSTOP)) {
		printf("Parent: waitpid(): expected SIGSTOP, got status = %d\n", status);
		return 1;
	}

	while (1) {
		if ( ptrace( PTRACE_SYSCALL, child, (void *)0, 0) < 0 ) {
			perror("ptrace( PTRACE_SYSCALL, child, 0, 0)");
			exit(1);
		}
		ret = waitpid( child, &status, 0);
		if ( ret != child ) {
			perror("waitpid");
			return 1;
		}
		if ( WIFSTOPPED(status) && WSTOPSIG(status) == SIGTRAP ) {
			errno = 0;
			ret = ptrace( PTRACE_PEEKUSER, child, (void *)(ORIG_EAX*4), NULL);
			if ( errno ) {
				perror("ptrace( PTRACE_PEEKUSER, child, ORIG_EAX, NULL)");
				return 1;
			}
			if ( ret == __NR_getpid ) {
				if ( (suppress ^= 1) )
					printf("Parent: Child does a getpid() syscall!\n");
			}
		}
		else {
			printf("Parent: Child's status is %x: exiting\n", status);
			return (status != 0);
		}
	}
}