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

void start_debugger() {
  int pid;
  if ((pid = fork()) == 0) {
    printf("child\n");
    ptrace(PTRACE_TRACEME, 0, NULL, NULL);
    kill(getpid(), SIGSTOP);
    while(1){
      printf("child: should never be reached\n");
      sleep(1);
    }
  } else if (pid > 0) {
    int status;
    printf("parent\n");
    assert(waitpid(pid, &status, 0) == pid);
    assert(WIFSTOPPED(status));
    assert(WSTOPSIG(status) == SIGSTOP);
    
#ifdef ADDITIONAL_SIGSTOP
    // send additional SIGSTOP to work around possible PTRACE_DETACH bug
    assert(kill(pid, SIGSTOP) == 0);
#endif
    assert(ptrace(PTRACE_DETACH, pid, NULL, SIGSTOP) == 0);
    
    char buf[1024];
    snprintf(buf, 1024, "gdb gdb_attach %d", pid);
    printf("parent: cmdl: %s\n", buf);
    system(buf);
  } else {
    printf("parent: fork failed\n");
  }
}


int main(int argc, char *argv[]) {
  start_debugger();
  return 0;
}