/**
 * cc -pthread -o /tmp/singlestep /public/singlestep.c
 */

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

#include <machine/reg.h>


#include <assert.h>
#include <stddef.h>

void
handler(int n)
{
	asm("nop");
}

int
child(void)
{
	assert(ptrace(PT_TRACE_ME, 0,0,0) == 0);
	signal(SIGALRM, handler);
	kill(getpid(), SIGALRM);
	return 0x23;
}

void *
getip(int pid)
{
	struct reg regs;
	ptrace(PT_GETREGS, pid, (void*)&regs, 0);

#if defined(__powerpc__)
	return (void*)regs.pc;
#elif defined(__amd64__)
	return (void*)regs.r_rip;
#else
#error "I don't know how to get the program counter"
#endif

}

int
main(void)
{
	int pid, status;

	pid = fork();
	if (!pid)
		return child();

	assert(wait(&status) == pid);
	assert(WIFSTOPPED(status) && WSTOPSIG(status) == SIGALRM);

	printf("Child pid: %d\n", pid);
	printf("Handler address: %p\n", &handler);

	printf("At initial SIGALRM point. IP = %p\n", getip(pid));

	assert(ptrace(PT_STEP, pid, 0, SIGALRM) == 0);
	assert(wait(&status) == pid);
	assert(WIFSTOPPED(status) && WSTOPSIG(status) == SIGTRAP);
	printf("At SIGTRAP. IP = %p\n", getip(pid));

	assert(ptrace(PT_STEP, pid, 0, SIGALRM) == 0);
	assert(wait(&status) == pid);
	assert(WIFSTOPPED(status) && WSTOPSIG(status) == SIGTRAP);
	printf("At second SIGTRAP. IP = %p\n", getip(pid));

	assert(ptrace(PT_CONTINUE, pid, 0,0) == 0);
	assert(wait(&status) == pid);
	printf("Child exit status was %d (expected %d)\n", WEXITSTATUS(status), 0x23);
	//assert(WIFEXITED(status));

	return 0;
}