int
fork_exec(char *argv0, char **argv,
mach_port_name_t *task,
mach_port_t *port_set,
mach_port_t *exception_port,
mach_port_t *notification_port)
{
int fd[2];
if (pipe(fd) < 0) return -1;
kern_return_t kret;
pid_t pid = fork();
if (pid > 0) {
// In parent.
close(fd[0]);
kret = acquire_mach_task(pid, task, port_set, exception_port, notification_port);
if (kret != KERN_SUCCESS) return -1;
char msg = 'c';
write(fd[1], &msg, 1);
close(fd[1]);
return pid;
}
// Fork succeeded, we are in the child.
int pret;
char sig;
close(fd[1]);
read(fd[0], &sig, 1);
close(fd[0]);
// Set errno to zero before a call to ptrace.
// It is documented that ptrace can return -1 even
// for successful calls.
errno = 0;
pret = ptrace(PT_TRACE_ME, 0, 0, 0);
if (pret != 0 && errno != 0) return -errno;
errno = 0;
pret = ptrace(PT_SIGEXC, 0, 0, 0);
if (pret != 0 && errno != 0) return -errno;
// Create the child process.
execve(argv0, argv, NULL);
exit(1);
}
int
fork_exec(char *argv0, char **argv, int size,
mach_port_name_t *task,
mach_port_t *port_set,
mach_port_t *exception_port,
mach_port_t *notification_port)
{
// In order to call PT_SIGEXC below, we must ensure that we have acquired the mach task first.
// We facilitate this by creating a pipe and using it to let the forked process know that we've
// finishing acquiring the mach task, and it can go ahead with the calls to PT_TRACE_ME and PT_SIGEXC.
int fd[2];
if (pipe(fd) < 0) return -1;
// Create another pipe so that we know when we're about to exec. This ensures that control only returns
// back to Go-land when we call exec, effectively eliminating a race condition between launching the new
// process and trying to read its memory.
int wfd[2];
if (pipe(wfd) < 0) return -1;
kern_return_t kret;
pid_t pid = fork();
if (pid > 0) {
// In parent.
close(fd[0]);
kret = acquire_mach_task(pid, task, port_set, exception_port, notification_port);
if (kret != KERN_SUCCESS) return -1;
char msg = 'c';
write(fd[1], &msg, 1);
close(fd[1]);
char w;
read(wfd[0], &w, 1);
close(wfd[0]);
return pid;
}
// Fork succeeded, we are in the child.
int pret;
char sig;
close(fd[1]);
read(fd[0], &sig, 1);
close(fd[0]);
// Create a new process group.
if (setpgid(0, 0) < 0) {
return -1;
}
// Set errno to zero before a call to ptrace.
// It is documented that ptrace can return -1 even
// for successful calls.
errno = 0;
pret = ptrace(PT_TRACE_ME, 0, 0, 0);
if (pret != 0 && errno != 0) return -errno;
errno = 0;
pret = ptrace(PT_SIGEXC, 0, 0, 0);
if (pret != 0 && errno != 0) return -errno;
char msg = 'd';
write(wfd[1], &msg, 1);
close(wfd[1]);
// Create the child process.
execve(argv0, argv, environ);
// We should never reach here, but if we did something went wrong.
exit(1);
}
