/* C standard headers */
#include <errno.h>
#include <inttypes.h>
#include <setjmp.h>
#include <stdbool.h>
#include <stddef.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

/* Linux headers */
#include <dirent.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <sys/ptrace.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>
#include <sys/user.h>
/* Architecture-specific headers */
#include <asm/ptrace.h>
#include <asm/unistd.h>

#include <signal.h>
#include <assert.h>

typedef void fun_moved_from_context();
// using namespace std;
void attachTo(pid_t pid, char* id) {
  long ret = ptrace(PTRACE_ATTACH, pid, NULL, NULL);
  printf("\t%s\tattachTo: %ld\n", id, ret);
  if (ret == -1) perror("err: ");
}
void seizeTo(pid_t pid, char* id) {
  long ret = ptrace(PTRACE_SEIZE, pid, NULL, NULL);
  assert(ret > 0);
  printf("\t%s\tseizeTo: %ld\n", id, ret);
}
void detachFrom(pid_t pid, char* id) {
  long ret = ptrace(PTRACE_DETACH, pid, NULL, NULL);
  printf("\t%s\tdetachFrom: %ld\n", id, ret);
}
void setOptions(pid_t pid, char* id) {
  long ret = ptrace(
      PTRACE_SETOPTIONS, pid, NULL,
      (void*)(PTRACE_O_TRACECLONE | PTRACE_O_TRACEEXEC | PTRACE_O_TRACEEXIT |
              PTRACE_O_TRACEFORK | PTRACE_O_TRACEVFORK));
  printf("\t%s\tsetOptions: %ld\n", id, ret);
}
void setVarData(pid_t pid, volatile bool* can_run, void* data, char* id) {
  long ret = ptrace(PTRACE_POKEDATA, pid, (void*)can_run, (void*)data);
  printf("\t%s\tsetVarData: %ld\n", id, ret);
}
void cont(pid_t pid, char* id) {
  long ret = ptrace(PTRACE_CONT, pid, NULL, NULL);
  printf("\t%s\tcont: %ld\n", id, ret);
}
void interrupt(pid_t pid, char* id) {
  long ret = ptrace(PTRACE_INTERRUPT, pid, NULL, NULL);
  printf("\t%s\tinterrupt: %ld\n", id, ret);
}

int main() {
  volatile bool can_runA = false, can_runB = false;
  pid_t procA = getpid();
  volatile pid_t procB = 0;

  if (fork() > 0) {  // process A
    while (!can_runA) {
      printf("\tA\twaiting to continue...\n");
      sleep(1);
    }
    attachTo(procB, "A");
    waitpid(procB, NULL, __WALL);
    setOptions(procB, "A");
    setVarData(procB, &can_runB, 1, "A");
    cont(procB, "A");
    printf("\tA\tfinished\n");
  } else {  // process B
    procB = getpid();
    attachTo(procA, "B");
    waitpid(procA, NULL, __WALL);
    setOptions(procA, "B");
    setVarData(procA, &can_runA, 1, "B");
    setVarData(procA, &procB, procB, "B");
    cont(procA, "B");
    while (!can_runB) {
      printf("\tB\twaiting to continue...\n");
      sleep(1);
    }
    printf("\tB\tfinished\n");
  }
  return 0;
}