/* Copyright 2007, Red Hat Inc.  */

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

#include "debugger.h"


#if 0
#define USLEEP (1000000 / 2)
#endif
#define TIMEOUT_SECS 10


#define ARRAY_SIZE(a) (sizeof (a) / sizeof ((a)[0]))

void delay (void)
{
#ifdef USLEEP
  int i;

  i = usleep (USLEEP);
  assert (i == 0);
#endif
}

static __attribute__((__noreturn__)) void crash (void)
{
#if 0
  void *array[0x100];
  int count;
#endif
  char command[256];

  fputs (">>> CRASH START\n", stderr);
#if 0
  count = backtrace (array, ARRAY_SIZE (array));
  backtrace_symbols_fd (array, count, STDERR_FILENO);
#endif
  snprintf (command, sizeof (command), "echo -e \"bt\\nquit\""
	    " >/tmp/debugger.%d; gdb --batch -nx --command=/tmp/debugger.%d"
	    " /proc/%d/exe %d </dev/null;rm -f /tmp/debugger.%d",
	    (int) getpid(), (int) getpid(), (int) getpid(), (int) getpid(),
	    (int) getpid());
  system (command);
  fputs (">>> CRASH FINISH\n", stderr);
  abort ();
}

enum state
  {
    /* Separate the valid `1 << enum state' and `enum state' ranges.  */
    STATE_FIRST = 4,
    STATE_INSTABLE,
    STATE_ENOENT,
    STATE_SLEEPING,
    STATE_RUNNING,
    STATE_STOPPED,
    STATE_PTRACED,
    STATE_ZOMBIE,
    STATE_LAST
  };

static const char *state_to_name (enum state state)
{
  switch (state)
    {
      case STATE_INSTABLE: return "STATE_INSTABLE";
      case STATE_ENOENT:   return "STATE_ENOENT";
      case STATE_SLEEPING: return "STATE_SLEEPING";
      case STATE_RUNNING:  return "STATE_RUNNING";
      case STATE_STOPPED:  return "STATE_STOPPED";
      case STATE_PTRACED:  return "STATE_PTRACED";
      case STATE_ZOMBIE:   return "STATE_ZOMBIE";
      default: crash ();
    }
  /* NOTREACHED */
  crash ();
}

static enum state state_get (pid_t pid)
{
  char status_name[32];
  char line[LINE_MAX];
  FILE *f;
  enum state found;

  delay ();

  snprintf (status_name, sizeof (status_name), "/proc/%d/status", (int) pid);
  f = fopen (status_name, "r");
  if (f == NULL && errno == ENOENT)
    found = STATE_ENOENT;
  else if (f == NULL)
    {
      fprintf (stderr, "errno = %d\n", errno);
      crash ();
    }
  else
    {
      int i;

      found = STATE_INSTABLE;
      while (errno = 0, fgets (line, sizeof (line), f) != NULL)
	{
	  const char *const string = "State:\t";
	  const size_t length = sizeof "State:\t" - 1;

	  if (strncmp (line, string, length) != 0)
	    continue;
	  if (strcmp (line + length, "S (sleeping)\n") == 0)
	    found = STATE_SLEEPING;
	  else if (strcmp (line + length, "R (running)\n") == 0)
	    found = STATE_RUNNING;
	  else if (strcmp (line + length, "T (stopped)\n") == 0)
	    found = STATE_STOPPED;
	  else if (strcmp (line + length, "T (tracing stop)\n") == 0)
	    found = STATE_PTRACED;
	  else if (strcmp (line + length, "Z (zombie)\n") == 0)
	    found = STATE_ZOMBIE;
	  else
	    {
	      fprintf (stderr, "Found an unknown state: %s", line + length);
	      crash ();
	    }
	}
      assert (found != STATE_INSTABLE || errno == ESRCH);
      i = fclose (f);
      assert (i == 0);
    }
  return found;
}

#define STATE(pid, expect_mask) state ((pid), (expect_mask), #expect_mask )

static enum state state (pid_t pid, unsigned expect_mask, const char *expect_mask_string)
{
  enum state found;
  time_t timeout = time (NULL) + TIMEOUT_SECS;

  /* Sanity check `1 << enum state' was not misplaced with `enum state'.  */
  assert (1 << (STATE_FIRST + 1) >= STATE_LAST);
  assert (expect_mask != 0);
#define MASK_UNDER_EXCLUSIVE(bit) ((1 << (bit)) - 1)
#define MASK_ABOVE_INCLUSIVE(bit) (~MASK_UNDER_EXCLUSIVE (bit))
  assert ((expect_mask & MASK_UNDER_EXCLUSIVE (STATE_FIRST + 1)) == 0);
  assert ((expect_mask & MASK_ABOVE_INCLUSIVE (STATE_LAST)) == 0);
#undef MASK_ABOVE_INCLUSIVE
#undef MASK_UNDER_EXCLUSIVE

  do
    {
      found = state_get (pid);

      if (((1 << found) & expect_mask) != 0)
        return found;
    }
  while (time (NULL) < timeout);

  fprintf (stderr, "Found for PID %d state %s but expecting (%s)\n",
	   (int) pid, state_to_name (found), expect_mask_string);
  crash ();
}

/* Debugging only: Number of signal needing redelivery on PTRACE_ATTACH.  */
int attach_redelivered;

int attach (pid_t pid)
{
  int i;
  int status;
  int stopped;

  attach_redelivered = 0;

  delay ();

#if 1
  stopped = (STATE (pid, (1 << STATE_SLEEPING) | (1 << STATE_RUNNING)
			 | (1 << STATE_STOPPED)) == STATE_STOPPED);
#endif

  i = ptrace (PTRACE_ATTACH, pid, NULL, NULL);
  assert (i == 0);

  /* FIXME: Why it does not work?
     Disable also the STATE () call above.  */
#if 0
  delay();

  i = ptrace (PTRACE_CONT, pid, (void *) 1, (void *) SIGSTOP);
  /* `STOPPED == 1' may be false, even if the process was not stopped.  */
  if (i == 0)
    stopped = 1;
  else if (errno == ESRCH)
    stopped = 0;
  else
    crash ();
#endif

  for (;;)
    {
      delay ();

      i = waitpid (pid, &status, 0);
      assert (i == pid);
      if (!WIFSTOPPED (status))
        {
	  /* Process may have exited.  */
	  fprintf (stderr, "PID %d waitpid(2) status %d\n", (int) pid,
		   status);
	  exit (EXIT_FAILURE);
	}
      if (WSTOPSIG (status) == SIGSTOP)
	break;

      if (attach_redelivered == 0)
	attach_redelivered = WSTOPSIG (status);
      else
	attach_redelivered = -1;

      delay ();

      /* Re-deliver the signal received before SIGSTOP.
         It happens with about only 1:200000 probability.  */
      i = ptrace (PTRACE_CONT, pid, (void *) 1,
		  (void *) (unsigned long) WSTOPSIG (status));
      assert (i == 0);
    }

  return stopped;
}

void detach (pid_t pid, int stopped)
{
  int i;

  delay ();

  i = ptrace (PTRACE_DETACH, pid, NULL,
	      (void *) (unsigned long) (stopped ? SIGSTOP : 0));
  assert (i == 0);

  delay ();
}

#ifndef LIBRARY

int main (int argc, char **argv)
{
  pid_t pid;
  int stopped;

  if (argc != 2)
    {
      fprintf (stderr, "Usage: %s <PID>\n", argv[0]);
      exit (EXIT_FAILURE);
    }

  pid = atoi (argv[1]);

  stopped = attach (pid);

  detach (pid, stopped);

  return EXIT_SUCCESS;
}

#endif /* !LIBRARY */