path: root/gdb/inf-ttrace.c

/* Low-level child interface to ttrace.

   Copyright (C) 2004-2014 Free Software Foundation, Inc.

   This file is part of GDB.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */

#include "defs.h"

/* The ttrace(2) system call didn't exist before HP-UX 10.30.  Don't
   try to compile this code unless we have it.  */
#ifdef HAVE_TTRACE

#include "command.h"
#include "gdbcore.h"
#include "gdbthread.h"
#include "inferior.h"
#include "terminal.h"
#include "target.h"

#include "gdb_assert.h"
#include <string.h>
#include <sys/mman.h>
#include <sys/ttrace.h>
#include <signal.h>

#include "inf-child.h"
#include "inf-ttrace.h"
#include "common/filestuff.h"



/* HP-UX uses a threading model where each user-space thread
   corresponds to a kernel thread.  These kernel threads are called
   lwps.  The ttrace(2) interface gives us almost full control over
   the threads, which makes it very easy to support them in GDB.  We
   identify the threads by process ID and lwp ID.  The ttrace(2) also
   provides us with a thread's user ID (in the `tts_user_tid' member
   of `ttstate_t') but we don't use that (yet) as it isn't necessary
   to uniquely label the thread.  */

/* Number of active lwps.  */
static int inf_ttrace_num_lwps;


/* On HP-UX versions that have the ttrace(2) system call, we can
   implement "hardware" watchpoints by fiddling with the protection of
   pages in the address space that contain the variable being watched.
   In order to implement this, we keep a dictionary of pages for which
   we have changed the protection.  */

struct inf_ttrace_page
{
  CORE_ADDR addr;		/* Page address.  */
  int prot;			/* Protection.  */
  int refcount;			/* Reference count.  */
  struct inf_ttrace_page *next;
  struct inf_ttrace_page *prev;
};

struct inf_ttrace_page_dict
{
  struct inf_ttrace_page buckets[128];
  int pagesize;			/* Page size.  */
  int count;			/* Number of pages in this dictionary.  */
} inf_ttrace_page_dict;

struct inf_ttrace_private_thread_info
{
  int dying;
};

/* Number of lwps that are currently in a system call.  */
static int inf_ttrace_num_lwps_in_syscall;

/* Flag to indicate whether we should re-enable page protections after
   the next wait.  */
static int inf_ttrace_reenable_page_protections;

/* Enable system call events for process PID.  */

static void
inf_ttrace_enable_syscall_events (pid_t pid)
{
  ttevent_t tte;
  ttstate_t tts;

  gdb_assert (inf_ttrace_num_lwps_in_syscall == 0);

  if (ttrace (TT_PROC_GET_EVENT_MASK, pid, 0,
	      (uintptr_t)&tte, sizeof tte, 0) == -1)
    perror_with_name (("ttrace"));

  tte.tte_events |= (TTEVT_SYSCALL_ENTRY | TTEVT_SYSCALL_RETURN);

  if (ttrace (TT_PROC_SET_EVENT_MASK, pid, 0,
	      (uintptr_t)&tte, sizeof tte, 0) == -1)
    perror_with_name (("ttrace"));

  if (ttrace (TT_PROC_GET_FIRST_LWP_STATE, pid, 0,
	      (uintptr_t)&tts, sizeof tts, 0) == -1)
    perror_with_name (("ttrace"));

  if (tts.tts_flags & TTS_INSYSCALL)
    inf_ttrace_num_lwps_in_syscall++;

  /* FIXME: Handle multiple threads.  */
}

/* Disable system call events for process PID.  */

static void
inf_ttrace_disable_syscall_events (pid_t pid)
{
  ttevent_t tte;

  gdb_assert (inf_ttrace_page_dict.count == 0);

  if (ttrace (TT_PROC_GET_EVENT_MASK, pid, 0,
	      (uintptr_t)&tte, sizeof tte, 0) == -1)
    perror_with_name (("ttrace"));

  tte.tte_events &= ~(TTEVT_SYSCALL_ENTRY | TTEVT_SYSCALL_RETURN);

  if (ttrace (TT_PROC_SET_EVENT_MASK, pid, 0,
	      (uintptr_t)&tte, sizeof tte, 0) == -1)
    perror_with_name (("ttrace"));

  inf_ttrace_num_lwps_in_syscall = 0;
}

/* Get information about the page at address ADDR for process PID from
   the dictionary.  */

static struct inf_ttrace_page *
inf_ttrace_get_page (pid_t pid, CORE_ADDR addr)
{
  const int num_buckets = ARRAY_SIZE (inf_ttrace_page_dict.buckets);
  const int pagesize = inf_ttrace_page_dict.pagesize;
  int bucket;
  struct inf_ttrace_page *page;

  bucket = (addr / pagesize) % num_buckets;
  page = &inf_ttrace_page_dict.buckets[bucket];
  while (page)
    {
      if (page->addr == addr)
	break;

      page = page->next;
    }

  return page;
}

/* Add the page at address ADDR for process PID to the dictionary.  */

static struct inf_ttrace_page *
inf_ttrace_add_page (pid_t pid, CORE_ADDR addr)
{
  const int num_buckets = ARRAY_SIZE (inf_ttrace_page_dict.buckets);
  const int pagesize = inf_ttrace_page_dict.pagesize;
  int bucket;
  struct inf_ttrace_page *page;
  struct inf_ttrace_page *prev = NULL;

  bucket = (addr / pagesize) % num_buckets;
  page = &inf_ttrace_page_dict.buckets[bucket];
  while (page)
    {
      if (page->addr == addr)
	break;

      prev = page;
      page = page->next;
    }
  
  if (!page)
    {
      int prot;

      if (ttrace (TT_PROC_GET_MPROTECT, pid, 0,
		  addr, 0, (uintptr_t)&prot) == -1)
	perror_with_name (("ttrace"));
      
      page = XNEW (struct inf_ttrace_page);
      page->addr = addr;
      page->prot = prot;
      page->refcount = 0;
      page->next = NULL;

      page->prev = prev;
      prev->next = page;

      inf_ttrace_page_dict.count++;
      if (inf_ttrace_page_dict.count == 1)
	inf_ttrace_enable_syscall_events (pid);

      if (inf_ttrace_num_lwps_in_syscall == 0)
	{
	  if (ttrace (TT_PROC_SET_MPROTECT, pid, 0,
		      addr, pagesize, prot & ~PROT_WRITE) == -1)
	    perror_with_name (("ttrace"));
	}
    }

  return page;
}

/* Insert the page at address ADDR of process PID to the dictionary.  */

static void
inf_ttrace_insert_page (pid_t pid, CORE_ADDR addr)
{
  struct inf_ttrace_page *page;

  page = inf_ttrace_get_page (pid, addr);
  if (!page)
    page = inf_ttrace_add_page (pid, addr);

  page->refcount++;
}

/* Remove the page at address ADDR of process PID from the dictionary.  */

static void
inf_ttrace_remove_page (pid_t pid, CORE_ADDR addr)
{
  const int pagesize = inf_ttrace_page_dict.pagesize;
  struct inf_ttrace_page *page;

  page = inf_ttrace_get_page (pid, addr);
  page->refcount--;

  gdb_assert (page->refcount >= 0);

  if (page->refcount == 0)
    {
      if (inf_ttrace_num_lwps_in_syscall == 0)
	{
	  if (ttrace (TT_PROC_SET_MPROTECT, pid, 0,
		      addr, pagesize, page->prot) == -1)
	    perror_with_name (("ttrace"));
	}

      inf_ttrace_page_dict.count--;
      if (inf_ttrace_page_dict.count == 0)
	inf_ttrace_disable_syscall_events (pid);

      page->prev->next = page->next;
      if (page->next)
	page->next->prev = page->prev;

      xfree (page);
    }
}

/* Mask the bits in PROT from the page protections that are currently
   in the dictionary for process PID.  */

static void
inf_ttrace_mask_page_protections (pid_t pid, int prot)
{
  const int num_buckets = ARRAY_SIZE (inf_ttrace_page_dict.buckets);
  const int pagesize = inf_ttrace_page_dict.pagesize;
  int bucket;

  for (bucket = 0; bucket < num_buckets; bucket++)
    {
      struct inf_ttrace_page *page;

      page = inf_ttrace_page_dict.buckets[bucket].next;
      while (page)
	{
	  if (ttrace (TT_PROC_SET_MPROTECT, pid, 0,
		      page->addr, pagesize, page->prot & ~prot) == -1)
	    perror_with_name (("ttrace"));

	  page = page->next;
	}
    }
}

/* Write-protect the pages in the dictionary for process PID.  */

static void
inf_ttrace_enable_page_protections (pid_t pid)
{
  inf_ttrace_mask_page_protections (pid, PROT_WRITE);
}

/* Restore the protection of the pages in the dictionary for process
   PID.  */

static void
inf_ttrace_disable_page_protections (pid_t pid)
{
  inf_ttrace_mask_page_protections (pid, 0);
}

/* Insert a "hardware" watchpoint for LEN bytes at address ADDR of
   type TYPE.  */

static int
inf_ttrace_insert_watchpoint (struct target_ops *self,
			      CORE_ADDR addr, int len, int type,
			      struct expression *cond)
{
  const int pagesize = inf_ttrace_page_dict.pagesize;
  pid_t pid = ptid_get_pid (inferior_ptid);
  CORE_ADDR page_addr;
  int num_pages;
  int page;

  gdb_assert (type == hw_write);

  page_addr = (addr / pagesize) * pagesize;
  num_pages = (len + pagesize - 1) / pagesize;

  for (page = 0; page < num_pages; page++, page_addr += pagesize)
    inf_ttrace_insert_page (pid, page_addr);

  return 1;
}

/* Remove a "hardware" watchpoint for LEN bytes at address ADDR of
   type TYPE.  */

static int
inf_ttrace_remove_watchpoint (struct target_ops *self,
			      CORE_ADDR addr, int len, int type,
			      struct expression *cond)
{
  const int pagesize = inf_ttrace_page_dict.pagesize;
  pid_t pid = ptid_get_pid (inferior_ptid);
  CORE_ADDR page_addr;
  int num_pages;
  int page;

  gdb_assert (type == hw_write);

  page_addr = (addr / pagesize) * pagesize;
  num_pages = (len + pagesize - 1) / pagesize;

  for (page = 0; page < num_pages; page++, page_addr += pagesize)
    inf_ttrace_remove_page (pid, page_addr);

  return 1;
}

static int
inf_ttrace_can_use_hw_breakpoint (struct target_ops *self,
				  int type, int len, int ot)
{
  return (type == bp_hardware_watchpoint);
}

static int
inf_ttrace_region_ok_for_hw_watchpoint (struct target_ops *self,
					CORE_ADDR addr, int len)
{
  return 1;
}

/* Return non-zero if the current inferior was (potentially) stopped
   by hitting a "hardware" watchpoint.  */

static int
inf_ttrace_stopped_by_watchpoint (struct target_ops *ops)
{
  pid_t pid = ptid_get_pid (inferior_ptid);
  lwpid_t lwpid = ptid_get_lwp (inferior_ptid);
  ttstate_t tts;

  if (inf_ttrace_page_dict.count > 0)
    {
      if (ttrace (TT_LWP_GET_STATE, pid, lwpid,
		  (uintptr_t)&tts, sizeof tts, 0) == -1)
	perror_with_name (("ttrace"));

      if (tts.tts_event == TTEVT_SIGNAL
	  && tts.tts_u.tts_signal.tts_signo == SIGBUS)
	{
	  const int pagesize = inf_ttrace_page_dict.pagesize;
	  void *addr = tts.tts_u.tts_signal.tts_siginfo.si_addr;
	  CORE_ADDR page_addr = ((uintptr_t)addr / pagesize) * pagesize;

	  if (inf_ttrace_get_page (pid, page_addr))
	    return 1;
	}
    }

  return 0;
}


/* When tracking a vfork(2), we cannot detach from the parent until
   after the child has called exec(3) or has exited.  If we are still
   attached to the parent, this variable will be set to the process ID
   of the parent.  Otherwise it will be set to zero.  */
static pid_t inf_ttrace_vfork_ppid = -1;

static int
inf_ttrace_follow_fork (struct target_ops *ops, int follow_child,
			int detach_fork)
{
  pid_t pid, fpid;
  lwpid_t lwpid, flwpid;
  ttstate_t tts;
  struct thread_info *tp = inferior_thread ();

  gdb_assert (tp->pending_follow.kind == TARGET_WAITKIND_FORKED
	      || tp->pending_follow.kind == TARGET_WAITKIND_VFORKED);

  pid = ptid_get_pid (inferior_ptid);
  lwpid = ptid_get_lwp (inferior_ptid);

  /* Get all important details that core GDB doesn't (and shouldn't)
     know about.  */
  if (ttrace (TT_LWP_GET_STATE, pid, lwpid,
	      (uintptr_t)&tts, sizeof tts, 0) == -1)
    perror_with_name (("ttrace"));

  gdb_assert (tts.tts_event == TTEVT_FORK || tts.tts_event == TTEVT_VFORK);

  if (tts.tts_u.tts_fork.tts_isparent)
    {
      pid = tts.tts_pid;
      lwpid = tts.tts_lwpid;
      fpid = tts.tts_u.tts_fork.tts_fpid;
      flwpid = tts.tts_u.tts_fork.tts_flwpid;
    }
  else
    {
      pid = tts.tts_u.tts_fork.tts_fpid;
      lwpid = tts.tts_u.tts_fork.tts_flwpid;
      fpid = tts.tts_pid;
      flwpid = tts.tts_lwpid;
    }

  if (follow_child)
    {
      struct inferior *inf;
      struct inferior *parent_inf;

      parent_inf = find_inferior_pid (pid);

      inferior_ptid = ptid_build (fpid, flwpid, 0);
      inf = add_inferior (fpid);
      inf->attach_flag = parent_inf->attach_flag;
      inf->pspace = parent_inf->pspace;
      inf->aspace = parent_inf->aspace;
      copy_terminal_info (inf, parent_inf);
      detach_breakpoints (ptid_build (pid, lwpid, 0));

      target_terminal_ours ();
      fprintf_unfiltered (gdb_stdlog,
			  _("Attaching after fork to child process %ld.\n"),
			  (long)fpid);
    }
  else
    {
      inferior_ptid = ptid_build (pid, lwpid, 0);
      /* Detach any remaining breakpoints in the child.  In the case
	 of fork events, we do not need to do this, because breakpoints
	 should have already been removed earlier.  */
      if (tts.tts_event == TTEVT_VFORK)
	detach_breakpoints (ptid_build (fpid, flwpid, 0));

      target_terminal_ours ();
      fprintf_unfiltered (gdb_stdlog,
			  _("Detaching after fork from child process %ld.\n"),
			  (long)fpid);
    }

  if (tts.tts_event == TTEVT_VFORK)
    {
      gdb_assert (!tts.tts_u.tts_fork.tts_isparent);

      if (follow_child)
	{
	  /* We can't detach from the parent yet.  */
	  inf_ttrace_vfork_ppid = pid;

	  reattach_breakpoints (fpid);
	}
      else
	{
	  if (ttrace (TT_PROC_DETACH, fpid, 0, 0, 0, 0) == -1)
	    perror_with_name (("ttrace"));

	  /* Wait till we get the TTEVT_VFORK event in the parent.
	     This indicates that the child has called exec(3) or has
	     exited and that the parent is ready to be traced again.  */
	  if (ttrace_wait (pid, lwpid, TTRACE_WAITOK, &tts, sizeof tts) == -1)
	    perror_with_name (("ttrace_wait"));
	  gdb_assert (tts.tts_event == TTEVT_VFORK);
	  gdb_assert (tts.tts_u.tts_fork.tts_isparent);

	  reattach_breakpoints (pid);
	}
    }
  else
    {
      gdb_assert (tts.tts_u.tts_fork.tts_isparent);

      if (follow_child)
	{
	  if (ttrace (TT_PROC_DETACH, pid, 0, 0, 0, 0) == -1)
	    perror_with_name (("ttrace"));
	}
      else
	{
	  if (ttrace (TT_PROC_DETACH, fpid, 0, 0, 0, 0) == -1)
	    perror_with_name (("ttrace"));
	}
    }

  if (follow_child)
    {
      struct thread_info *ti;

      /* The child will start out single-threaded.  */
      inf_ttrace_num_lwps = 1;
      inf_ttrace_num_lwps_in_syscall = 0;

      /* Delete parent.  */
      delete_thread_silent (ptid_build (pid, lwpid, 0));
      detach_inferior (pid);

      /* Add child thread.  inferior_ptid was already set above.  */
      ti = add_thread_silent (inferior_ptid);
      ti->private =
	xmalloc (sizeof (struct inf_ttrace_private_thread_info));
      memset (ti->private, 0,
	      sizeof (struct inf_ttrace_private_thread_info));
    }

  return 0;
}


/* File descriptors for pipes used as semaphores during initial
   startup of an inferior.  */
static int inf_ttrace_pfd1[2];
static int inf_ttrace_pfd2[2];

static void
do_cleanup_pfds (void *dummy)
{
  close (inf_ttrace_pfd1[0]);
  close (inf_ttrace_pfd1[1]);
  close (inf_ttrace_pfd2[0]);
  close (inf_ttrace_pfd2[1]);

  unmark_fd_no_cloexec (inf_ttrace_pfd1[0]);
  unmark_fd_no_cloexec (inf_ttrace_pfd1[1]);
  unmark_fd_no_cloexec (inf_ttrace_pfd2[0]);
  unmark_fd_no_cloexec (inf_ttrace_pfd2[1]);
}

static void
inf_ttrace_prepare (void)
{
  if (pipe (inf_ttrace_pfd1) == -1)
    perror_with_name (("pipe"));

  if (pipe (inf_ttrace_pfd2) == -1)
    {
      close (inf_ttrace_pfd1[0]);
      close (inf_ttrace_pfd2[0]);
      perror_with_name (("pipe"));
    }

  mark_fd_no_cloexec (inf_ttrace_pfd1[0]);
  mark_fd_no_cloexec (inf_ttrace_pfd1[1]);
  mark_fd_no_cloexec (inf_ttrace_pfd2[0]);
  mark_fd_no_cloexec (inf_ttrace_pfd2[1]);
}

/* Prepare to be traced.  */

static void
inf_ttrace_me (void)
{
  struct cleanup *old_chain = make_cleanup (do_cleanup_pfds, 0);
  char c;

  /* "Trace me, Dr. Memory!"  */
  if (ttrace (TT_PROC_SETTRC, 0, 0, 0, TT_VERSION, 0) == -1)
    perror_with_name (("ttrace"));

  /* Tell our parent that we are ready to be traced.  */
  if (write (inf_ttrace_pfd1[1], &c, sizeof c) != sizeof c)
    perror_with_name (("write"));

  /* Wait until our parent has set the initial event mask.  */
  if (read (inf_ttrace_pfd2[0], &c, sizeof c) != sizeof c)
    perror_with_name (("read"));

  do_cleanups (old_chain);
}

/* Start tracing PID.  */

static void
inf_ttrace_him (struct target_ops *ops, int pid)
{
  struct cleanup *old_chain = make_cleanup (do_cleanup_pfds, 0);
  ttevent_t tte;
  char c;

  /* Wait until our child is ready to be traced.  */
  if (read (inf_ttrace_pfd1[0], &c, sizeof c) != sizeof c)
    perror_with_name (("read"));

  /* Set the initial event mask.  */
  memset (&tte, 0, sizeof (tte));
  tte.tte_events |= TTEVT_EXEC | TTEVT_EXIT | TTEVT_FORK | TTEVT_VFORK;
  tte.tte_events |= TTEVT_LWP_CREATE | TTEVT_LWP_EXIT | TTEVT_LWP_TERMINATE;
#ifdef TTEVT_BPT_SSTEP
  tte.tte_events |= TTEVT_BPT_SSTEP;
#endif
  tte.tte_opts |= TTEO_PROC_INHERIT;
  if (ttrace (TT_PROC_SET_EVENT_MASK, pid, 0,
	      (uintptr_t)&tte, sizeof tte, 0) == -1)
    perror_with_name (("ttrace"));

  /* Tell our child that we have set the initial event mask.  */
  if (write (inf_ttrace_pfd2[1], &c, sizeof c) != sizeof c)
    perror_with_name (("write"));

  do_cleanups (old_chain);

  push_target (ops);

  startup_inferior (START_INFERIOR_TRAPS_EXPECTED);

  /* On some targets, there must be some explicit actions taken after
     the inferior has been started up.  */
  target_post_startup_inferior (pid_to_ptid (pid));
}

static void
inf_ttrace_create_inferior (struct target_ops *ops, char *exec_file, 
			    char *allargs, char **env, int from_tty)
{
  int pid;

  gdb_assert (inf_ttrace_num_lwps == 0);
  gdb_assert (inf_ttrace_num_lwps_in_syscall == 0);
  gdb_assert (inf_ttrace_page_dict.count == 0);
  gdb_assert (inf_ttrace_reenable_page_protections == 0);
  gdb_assert (inf_ttrace_vfork_ppid == -1);

  pid = fork_inferior (exec_file, allargs, env, inf_ttrace_me, NULL,
		       inf_ttrace_prepare, NULL, NULL);

  inf_ttrace_him (ops, pid);
}

static void
inf_ttrace_mourn_inferior (struct target_ops *ops)
{
  const int num_buckets = ARRAY_SIZE (inf_ttrace_page_dict.buckets);
  int bucket;

  inf_ttrace_num_lwps = 0;
  inf_ttrace_num_lwps_in_syscall = 0;

  for (bucket = 0; bucket < num_buckets; bucket++)
    {
      struct inf_ttrace_page *page;
      struct inf_ttrace_page *next;

      page = inf_ttrace_page_dict.buckets[bucket].next;
      while (page)
	{
	  next = page->next;
	  xfree (page);
	  page = next;
	}
    }
  inf_ttrace_page_dict.count = 0;

  unpush_target (ops);
  generic_mourn_inferior ();
}

/* Assuming we just attached the debugger to a new inferior, create
   a new thread_info structure for each thread, and add it to our
   list of threads.  */

static void
inf_ttrace_create_threads_after_attach (int pid)
{
  int status;
  ptid_t ptid;
  ttstate_t tts;
  struct thread_info *ti;

  status = ttrace (TT_PROC_GET_FIRST_LWP_STATE, pid, 0,
		   (uintptr_t) &tts, sizeof (ttstate_t), 0);
  if (status < 0)
    perror_with_name (_("TT_PROC_GET_FIRST_LWP_STATE ttrace call failed"));
  gdb_assert (tts.tts_pid == pid);

  /* Add the stopped thread.  */
  ptid = ptid_build (pid, tts.tts_lwpid, 0);
  ti = add_thread (ptid);
  ti->private = xzalloc (sizeof (struct inf_ttrace_private_thread_info));
  inf_ttrace_num_lwps++;

  /* We use the "first stopped thread" as the currently active thread.  */
  inferior_ptid = ptid;

  /* Iterative over all the remaining threads.  */

  for (;;)
    {
      ptid_t ptid;

      status = ttrace (TT_PROC_GET_NEXT_LWP_STATE, pid, 0,
		       (uintptr_t) &tts, sizeof (ttstate_t), 0);
      if (status < 0)
	perror_with_name (_("TT_PROC_GET_NEXT_LWP_STATE ttrace call failed"));
      if (status == 0)
        break;  /* End of list.  */

      ptid = ptid_build (tts.tts_pid, tts.tts_lwpid, 0);
      ti = add_thread (ptid);
      ti->private = xzalloc (sizeof (struct inf_ttrace_private_thread_info));
      inf_ttrace_num_lwps++;
    }
}

static void
inf_ttrace_attach (struct target_ops *ops, char *args, int from_tty)
{
  char *exec_file;
  pid_t pid;
  ttevent_t tte;
  struct inferior *inf;

  pid = parse_pid_to_attach (args);

  if (pid == getpid ())		/* Trying to masturbate?  */
    error (_("I refuse to debug myself!"));

  if (from_tty)
    {
      exec_file = get_exec_file (0);

      if (exec_file)
	printf_unfiltered (_("Attaching to program: %s, %s\n"), exec_file,
			   target_pid_to_str (pid_to_ptid (pid)));
      else
	printf_unfiltered (_("Attaching to %s\n"),
			   target_pid_to_str (pid_to_ptid (pid)));

      gdb_flush (gdb_stdout);
    }

  gdb_assert (inf_ttrace_num_lwps == 0);
  gdb_assert (inf_ttrace_num_lwps_in_syscall == 0);
  gdb_assert (inf_ttrace_vfork_ppid == -1);

  if (ttrace (TT_PROC_ATTACH, pid, 0, TT_KILL_ON_EXIT, TT_VERSION, 0) == -1)
    perror_with_name (("ttrace"));

  inf = current_inferior ();
  inferior_appeared (inf, pid);
  inf->attach_flag = 1;

  /* Set the initial event mask.  */
  memset (&tte, 0, sizeof (tte));
  tte.tte_events |= TTEVT_EXEC | TTEVT_EXIT | TTEVT_FORK | TTEVT_VFORK;
  tte.tte_events |= TTEVT_LWP_CREATE | TTEVT_LWP_EXIT | TTEVT_LWP_TERMINATE;
#ifdef TTEVT_BPT_SSTEP
  tte.tte_events |= TTEVT_BPT_SSTEP;
#endif
  tte.tte_opts |= TTEO_PROC_INHERIT;
  if (ttrace (TT_PROC_SET_EVENT_MASK, pid, 0,
	      (uintptr_t)&tte, sizeof tte, 0) == -1)
    perror_with_name (("ttrace"));

  push_target (ops);

  inf_ttrace_create_threads_after_attach (pid);
}

static void
inf_ttrace_detach (struct target_ops *ops, const char *args, int from_tty)
{
  pid_t pid = ptid_get_pid (inferior_ptid);
  int sig = 0;

  if (from_tty)
    {
      char *exec_file = get_exec_file (0);
      if (exec_file == 0)
	exec_file = "";
      printf_unfiltered (_("Detaching from program: %s, %s\n"), exec_file,
			 target_pid_to_str (pid_to_ptid (pid)));
      gdb_flush (gdb_stdout);
    }
  if (args)
    sig = atoi (args);

  /* ??? The HP-UX 11.0 ttrace(2) manual page doesn't mention that we
     can pass a signal number here.  Does this really work?  */
  if (ttrace (TT_PROC_DETACH, pid, 0, 0, sig, 0) == -1)
    perror_with_name (("ttrace"));

  if (inf_ttrace_vfork_ppid != -1)
    {
      if (ttrace (TT_PROC_DETACH, inf_ttrace_vfork_ppid, 0, 0, 0, 0) == -1)
	perror_with_name (("ttrace"));
      inf_ttrace_vfork_ppid = -1;
    }

  inf_ttrace_num_lwps = 0;
  inf_ttrace_num_lwps_in_syscall = 0;

  inferior_ptid = null_ptid;
  detach_inferior (pid);

  unpush_target (ops);
}

static void
inf_ttrace_kill (struct target_ops *ops)
{
  pid_t pid = ptid_get_pid (inferior_ptid);

  if (pid == 0)
    return;

  if (ttrace (TT_PROC_EXIT, pid, 0, 0, 0, 0) == -1)
    perror_with_name (("ttrace"));
  /* ??? Is it necessary to call ttrace_wait() here?  */

  if (inf_ttrace_vfork_ppid != -1)
    {
      if (ttrace (TT_PROC_DETACH, inf_ttrace_vfork_ppid, 0, 0, 0, 0) == -1)
	perror_with_name (("ttrace"));
      inf_ttrace_vfork_ppid = -1;
    }

  target_mourn_inferior ();
}

/* Check is a dying thread is dead by now, and delete it from GDBs
   thread list if so.  */
static int
inf_ttrace_delete_dead_threads_callback (struct thread_info *info, void *arg)
{
  lwpid_t lwpid;
  struct inf_ttrace_private_thread_info *p;

  if (is_exited (info->ptid))
    return 0;

  lwpid = ptid_get_lwp (info->ptid);
  p = (struct inf_ttrace_private_thread_info *) info->private;

  /* Check if an lwp that was dying is still there or not.  */
  if (p->dying && (kill (lwpid, 0) == -1))
    /* It's gone now.  */
    delete_thread (info->ptid);

  return 0;
}

/* Resume the lwp pointed to by INFO, with REQUEST, and pass it signal
   SIG.  */

static void
inf_ttrace_resume_lwp (struct thread_info *info, ttreq_t request, int sig)
{
  pid_t pid = ptid_get_pid (info->ptid);
  lwpid_t lwpid = ptid_get_lwp (info->ptid);

  if (ttrace (request, pid, lwpid, TT_NOPC, sig, 0) == -1)
    {
      struct inf_ttrace_private_thread_info *p
	= (struct inf_ttrace_private_thread_info *) info->private;
      if (p->dying && errno == EPROTO)
	/* This is expected, it means the dying lwp is really gone
	   by now.  If ttrace had an event to inform the debugger
	   the lwp is really gone, this wouldn't be needed.  */
	delete_thread (info->ptid);
      else
	/* This was really unexpected.  */
	perror_with_name (("ttrace"));
    }
}

/* Callback for iterate_over_threads.  */

static int
inf_ttrace_resume_callback (struct thread_info *info, void *arg)
{
  if (!ptid_equal (info->ptid, inferior_ptid) && !is_exited (info->ptid))
    inf_ttrace_resume_lwp (info, TT_LWP_CONTINUE, 0);

  return 0;
}

static void
inf_ttrace_resume (struct target_ops *ops,
		   ptid_t ptid, int step, enum gdb_signal signal)
{
  int resume_all;
  ttreq_t request = step ? TT_LWP_SINGLE : TT_LWP_CONTINUE;
  int sig = gdb_signal_to_host (signal);
  struct thread_info *info;

  /* A specific PTID means `step only this process id'.  */
  resume_all = (ptid_equal (ptid, minus_one_ptid));

  /* If resuming all threads, it's the current thread that should be
     handled specially.  */
  if (resume_all)
    ptid = inferior_ptid;

  info = find_thread_ptid (ptid);
  inf_ttrace_resume_lwp (info, request, sig);

  if (resume_all)
    /* Let all the other threads run too.  */
    iterate_over_threads (inf_ttrace_resume_callback, NULL);
}

static ptid_t
inf_ttrace_wait (struct target_ops *ops,
		 ptid_t ptid, struct target_waitstatus *ourstatus, int options)
{
  pid_t pid = ptid_get_pid (ptid);
  lwpid_t lwpid = ptid_get_lwp (ptid);
  ttstate_t tts;
  struct thread_info *ti;
  ptid_t related_ptid;

  /* Until proven otherwise.  */
  ourstatus->kind = TARGET_WAITKIND_SPURIOUS;

  if (pid == -1)
    pid = lwpid = 0;

  gdb_assert (pid != 0 || lwpid == 0);

  do
    {
      set_sigint_trap ();

      if (ttrace_wait (pid, lwpid, TTRACE_WAITOK, &tts, sizeof tts) == -1)
	perror_with_name (("ttrace_wait"));

      if (tts.tts_event == TTEVT_VFORK && tts.tts_u.tts_fork.tts_isparent)
	{
	  if (inf_ttrace_vfork_ppid != -1)
	    {
	      gdb_assert (inf_ttrace_vfork_ppid == tts.tts_pid);

	      if (ttrace (TT_PROC_DETACH, tts.tts_pid, 0, 0, 0, 0) == -1)
		perror_with_name (("ttrace"));
	      inf_ttrace_vfork_ppid = -1;
	    }

	  tts.tts_event = TTEVT_NONE;
	}

      clear_sigint_trap ();
    }
  while (tts.tts_event == TTEVT_NONE);

  /* Now that we've waited, we can re-enable the page protections.  */
  if (inf_ttrace_reenable_page_protections)
    {
      gdb_assert (inf_ttrace_num_lwps_in_syscall == 0);
      inf_ttrace_enable_page_protections (tts.tts_pid);
      inf_ttrace_reenable_page_protections = 0;
    }

  ptid = ptid_build (tts.tts_pid, tts.tts_lwpid, 0);

  if (inf_ttrace_num_lwps == 0)
    {
      struct thread_info *ti;

      inf_ttrace_num_lwps = 1;

      /* This is the earliest we hear about the lwp member of
	 INFERIOR_PTID, after an attach or fork_inferior.  */
      gdb_assert (ptid_get_lwp (inferior_ptid) == 0);

      /* We haven't set the private member on the main thread yet.  Do
	 it now.  */
      ti = find_thread_ptid (inferior_ptid);
      gdb_assert (ti != NULL && ti->private == NULL);
      ti->private =
	xmalloc (sizeof (struct inf_ttrace_private_thread_info));
      memset (ti->private, 0,
	      sizeof (struct inf_ttrace_private_thread_info));

      /* Notify the core that this ptid changed.  This changes
	 inferior_ptid as well.  */
      thread_change_ptid (inferior_ptid, ptid);
    }

  switch (tts.tts_event)
    {
#ifdef TTEVT_BPT_SSTEP
    case TTEVT_BPT_SSTEP:
      /* Make it look like a breakpoint.  */
      ourstatus->kind = TARGET_WAITKIND_STOPPED;
      ourstatus->value.sig = GDB_SIGNAL_TRAP;
      break;
#endif

    case TTEVT_EXEC:
      ourstatus->kind = TARGET_WAITKIND_EXECD;
      ourstatus->value.execd_pathname =
	xmalloc (tts.tts_u.tts_exec.tts_pathlen + 1);
      if (ttrace (TT_PROC_GET_PATHNAME, tts.tts_pid, 0,
		  (uintptr_t)ourstatus->value.execd_pathname,
		  tts.tts_u.tts_exec.tts_pathlen, 0) == -1)
	perror_with_name (("ttrace"));
      ourstatus->value.execd_pathname[tts.tts_u.tts_exec.tts_pathlen] = 0;

      /* At this point, all inserted breakpoints are gone.  Doing this
	 as soon as we detect an exec prevents the badness of deleting
	 a breakpoint writing the current "shadow contents" to lift
	 the bp.  That shadow is NOT valid after an exec.  */
      mark_breakpoints_out ();
      break;

    case TTEVT_EXIT:
      store_waitstatus (ourstatus, tts.tts_u.tts_exit.tts_exitcode);
      inf_ttrace_num_lwps = 0;
      break;

    case TTEVT_FORK:
      related_ptid = ptid_build (tts.tts_u.tts_fork.tts_fpid,
				 tts.tts_u.tts_fork.tts_flwpid, 0);

      ourstatus->kind = TARGET_WAITKIND_FORKED;
      ourstatus->value.related_pid = related_ptid;

      /* Make sure the other end of the fork is stopped too.  */
      if (ttrace_wait (tts.tts_u.tts_fork.tts_fpid,
		       tts.tts_u.tts_fork.tts_flwpid,
		       TTRACE_WAITOK, &tts, sizeof tts) == -1)
	perror_with_name (("ttrace_wait"));

      gdb_assert (tts.tts_event == TTEVT_FORK);
      if (tts.tts_u.tts_fork.tts_isparent)
	{
	  related_ptid = ptid_build (tts.tts_u.tts_fork.tts_fpid,
				     tts.tts_u.tts_fork.tts_flwpid, 0);
	  ptid = ptid_build (tts.tts_pid, tts.tts_lwpid, 0);
	  ourstatus->value.related_pid = related_ptid;
	}
      break;

    case TTEVT_VFORK:
      gdb_assert (!tts.tts_u.tts_fork.tts_isparent);

      related_ptid = ptid_build (tts.tts_u.tts_fork.tts_fpid,
				 tts.tts_u.tts_fork.tts_flwpid, 0);

      ourstatus->kind = TARGET_WAITKIND_VFORKED;
      ourstatus->value.related_pid = related_ptid;

      /* HACK: To avoid touching the parent during the vfork, switch
	 away from it.  */
      inferior_ptid = ptid;
      break;

    case TTEVT_LWP_CREATE:
      lwpid = tts.tts_u.tts_thread.tts_target_lwpid;
      ptid = ptid_build (tts.tts_pid, lwpid, 0);
      ti = add_thread (ptid);
      ti->private =
	xmalloc (sizeof (struct inf_ttrace_private_thread_info));
      memset (ti->private, 0,
	      sizeof (struct inf_ttrace_private_thread_info));
      inf_ttrace_num_lwps++;
      ptid = ptid_build (tts.tts_pid, tts.tts_lwpid, 0);
      /* Let the lwp_create-caller thread continue.  */
      ttrace (TT_LWP_CONTINUE, ptid_get_pid (ptid),
              ptid_get_lwp (ptid), TT_NOPC, 0, 0);
      /* Return without stopping the whole process.  */
      ourstatus->kind = TARGET_WAITKIND_IGNORE;
      return ptid;

    case TTEVT_LWP_EXIT:
      if (print_thread_events)
	printf_unfiltered (_("[%s exited]\n"), target_pid_to_str (ptid));
      ti = find_thread_ptid (ptid);
      gdb_assert (ti != NULL);
      ((struct inf_ttrace_private_thread_info *)ti->private)->dying = 1;
      inf_ttrace_num_lwps--;
      /* Let the thread really exit.  */
      ttrace (TT_LWP_CONTINUE, ptid_get_pid (ptid),
              ptid_get_lwp (ptid), TT_NOPC, 0, 0);
      /* Return without stopping the whole process.  */
      ourstatus->kind = TARGET_WAITKIND_IGNORE;
      return ptid;

    case TTEVT_LWP_TERMINATE:
      lwpid = tts.tts_u.tts_thread.tts_target_lwpid;
      ptid = ptid_build (tts.tts_pid, lwpid, 0);
      if (print_thread_events)
	printf_unfiltered(_("[%s has been terminated]\n"),
			  target_pid_to_str (ptid));
      ti = find_thread_ptid (ptid);
      gdb_assert (ti != NULL);
      ((struct inf_ttrace_private_thread_info *)ti->private)->dying = 1;
      inf_ttrace_num_lwps--;

      /* Resume the lwp_terminate-caller thread.  */
      ptid = ptid_build (tts.tts_pid, tts.tts_lwpid, 0);
      ttrace (TT_LWP_CONTINUE, ptid_get_pid (ptid),
              ptid_get_lwp (ptid), TT_NOPC, 0, 0);
      /* Return without stopping the whole process.  */
      ourstatus->kind = TARGET_WAITKIND_IGNORE;
      return ptid;

    case TTEVT_SIGNAL:
      ourstatus->kind = TARGET_WAITKIND_STOPPED;
      ourstatus->value.sig =
	gdb_signal_from_host (tts.tts_u.tts_signal.tts_signo);
      break;

    case TTEVT_SYSCALL_ENTRY:
      gdb_assert (inf_ttrace_reenable_page_protections == 0);
      inf_ttrace_num_lwps_in_syscall++;
      if (inf_ttrace_num_lwps_in_syscall == 1)
	{
	  /* A thread has just entered a system call.  Disable any
             page protections as the kernel can't deal with them.  */
	  inf_ttrace_disable_page_protections (tts.tts_pid);
	}
      ourstatus->kind = TARGET_WAITKIND_SYSCALL_ENTRY;
      ourstatus->value.syscall_number = tts.tts_scno;
      break;

    case TTEVT_SYSCALL_RETURN:
      if (inf_ttrace_num_lwps_in_syscall > 0)
	{
	  /* If the last thread has just left the system call, this
	     would be a logical place to re-enable the page
	     protections, but that doesn't work.  We can't re-enable
	     them until we've done another wait.  */
	  inf_ttrace_reenable_page_protections = 
	    (inf_ttrace_num_lwps_in_syscall == 1);
	  inf_ttrace_num_lwps_in_syscall--;
	}
      ourstatus->kind = TARGET_WAITKIND_SYSCALL_RETURN;
      ourstatus->value.syscall_number = tts.tts_scno;
      break;

    default:
      gdb_assert (!"Unexpected ttrace event");
      break;
    }

  /* Make sure all threads within the process are stopped.  */
  if (ttrace (TT_PROC_STOP, tts.tts_pid, 0, 0, 0, 0) == -1)
    perror_with_name (("ttrace"));

  /* Now that the whole process is stopped, check if any dying thread
     is really dead by now.  If a dying thread is still alive, it will
     be stopped too, and will still show up in `info threads', tagged
     with "(Exiting)".  We could make `info threads' prune dead
     threads instead via inf_ttrace_thread_alive, but doing this here
     has the advantage that a frontend is notificed sooner of thread
     exits.  Note that a dying lwp is still alive, it still has to be
     resumed, like any other lwp.  */
  iterate_over_threads (inf_ttrace_delete_dead_threads_callback, NULL);

  return ptid;
}

/* Transfer LEN bytes from ADDR in the inferior's memory into READBUF,
   and transfer LEN bytes from WRITEBUF into the inferior's memory at
   ADDR.  Either READBUF or WRITEBUF may be null, in which case the
   corresponding transfer doesn't happen.  Return the number of bytes
   actually transferred (which may be zero if an error occurs).  */

static LONGEST
inf_ttrace_xfer_memory (CORE_ADDR addr, ULONGEST len,
			void *readbuf, const void *writebuf)
{
  pid_t pid = ptid_get_pid (inferior_ptid);

  /* HP-UX treats text space and data space differently.  GDB however,
     doesn't really know the difference.  Therefore we try both.  Try
     text space before data space though because when we're writing
     into text space the instruction cache might need to be flushed.  */

  if (readbuf
      && ttrace (TT_PROC_RDTEXT, pid, 0, addr, len, (uintptr_t)readbuf) == -1
      && ttrace (TT_PROC_RDDATA, pid, 0, addr, len, (uintptr_t)readbuf) == -1)
    return 0;

  if (writebuf
      && ttrace (TT_PROC_WRTEXT, pid, 0, addr, len, (uintptr_t)writebuf) == -1
      && ttrace (TT_PROC_WRDATA, pid, 0, addr, len, (uintptr_t)writebuf) == -1)
    return 0;

  return len;
}

static enum target_xfer_status
inf_ttrace_xfer_partial (struct target_ops *ops, enum target_object object,
			 const char *annex, gdb_byte *readbuf,
			 const gdb_byte *writebuf,
			 ULONGEST offset, ULONGEST len, ULONGEST *xfered_len)
{
  switch (object)
    {
    case TARGET_OBJECT_MEMORY:
      {
	LONGEST val = inf_ttrace_xfer_memory (offset, len, readbuf, writebuf);

	if (val == 0)
	  return TARGET_XFER_EOF;
	else
	  {
	    *xfered_len = (ULONGEST) val;
	    return TARGET_XFER_OK;
	  }
      }

    case TARGET_OBJECT_UNWIND_TABLE:
      return TARGET_XFER_E_IO;

    case TARGET_OBJECT_AUXV:
      return TARGET_XFER_E_IO;

    case TARGET_OBJECT_WCOOKIE:
      return TARGET_XFER_E_IO;

    default:
      return TARGET_XFER_E_IO;
    }
}

/* Print status information about what we're accessing.  */

static void
inf_ttrace_files_info (struct target_ops *ignore)
{
  struct inferior *inf = current_inferior ();
  printf_filtered (_("\tUsing the running image of %s %s.\n"),
		   inf->attach_flag ? "attached" : "child",
		   target_pid_to_str (inferior_ptid));
}

static int
inf_ttrace_thread_alive (struct target_ops *ops, ptid_t ptid)
{
  return 1;
}

/* Return a string describing the state of the thread specified by
   INFO.  */

static char *
inf_ttrace_extra_thread_info (struct thread_info *info)
{
  struct inf_ttrace_private_thread_info* private =
    (struct inf_ttrace_private_thread_info *) info->private;

  if (private != NULL && private->dying)
    return "Exiting";

  return NULL;
}

static char *
inf_ttrace_pid_to_str (struct target_ops *ops, ptid_t ptid)
{
  pid_t pid = ptid_get_pid (ptid);
  lwpid_t lwpid = ptid_get_lwp (ptid);
  static char buf[128];

  if (lwpid == 0)
    xsnprintf (buf, sizeof buf, "process %ld",
	       (long) pid);
  else
    xsnprintf (buf, sizeof buf, "process %ld, lwp %ld",
	       (long) pid, (long) lwpid);
  return buf;
}


/* Implement the get_ada_task_ptid target_ops method.  */

static ptid_t
inf_ttrace_get_ada_task_ptid (long lwp, long thread)
{
  return ptid_build (ptid_get_pid (inferior_ptid), lwp, 0);
}


struct target_ops *
inf_ttrace_target (void)
{
  struct target_ops *t = inf_child_target ();

  t->to_attach = inf_ttrace_attach;
  t->to_detach = inf_ttrace_detach;
  t->to_resume = inf_ttrace_resume;
  t->to_wait = inf_ttrace_wait;
  t->to_files_info = inf_ttrace_files_info;
  t->to_can_use_hw_breakpoint = inf_ttrace_can_use_hw_breakpoint;
  t->to_insert_watchpoint = inf_ttrace_insert_watchpoint;
  t->to_remove_watchpoint = inf_ttrace_remove_watchpoint;
  t->to_stopped_by_watchpoint = inf_ttrace_stopped_by_watchpoint;
  t->to_region_ok_for_hw_watchpoint =
    inf_ttrace_region_ok_for_hw_watchpoint;
  t->to_kill = inf_ttrace_kill;
  t->to_create_inferior = inf_ttrace_create_inferior;
  t->to_follow_fork = inf_ttrace_follow_fork;
  t->to_mourn_inferior = inf_ttrace_mourn_inferior;
  t->to_thread_alive = inf_ttrace_thread_alive;
  t->to_extra_thread_info = inf_ttrace_extra_thread_info;
  t->to_pid_to_str = inf_ttrace_pid_to_str;
  t->to_xfer_partial = inf_ttrace_xfer_partial;
  t->to_get_ada_task_ptid = inf_ttrace_get_ada_task_ptid;

  return t;
}
#endif


/* Prevent warning from -Wmissing-prototypes.  */
void _initialize_inf_ttrace (void);

void
_initialize_inf_ttrace (void)
{
#ifdef HAVE_TTRACE
  inf_ttrace_page_dict.pagesize = getpagesize();
#endif
}