gprof/.gdbinit


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/* GNU/Linux native-dependent code common to multiple platforms.

   Copyright (C) 2001-2021 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"
#include "inferior.h"
#include "infrun.h"
#include "target.h"
#include "nat/linux-nat.h"
#include "nat/linux-waitpid.h"
#include "gdbsupport/gdb_wait.h"
#include <unistd.h>
#include <sys/syscall.h>
#include "nat/gdb_ptrace.h"
#include "linux-nat.h"
#include "nat/linux-ptrace.h"
#include "nat/linux-procfs.h"
#include "nat/linux-personality.h"
#include "linux-fork.h"
#include "gdbthread.h"
#include "gdbcmd.h"
#include "regcache.h"
#include "regset.h"
#include "inf-child.h"
#include "inf-ptrace.h"
#include "auxv.h"
#include <sys/procfs.h>		/* for elf_gregset etc.  */
#include "elf-bfd.h"		/* for elfcore_write_* */
#include "gregset.h"		/* for gregset */
#include "gdbcore.h"		/* for get_exec_file */
#include <ctype.h>		/* for isdigit */
#include <sys/stat.h>		/* for struct stat */
#include <fcntl.h>		/* for O_RDONLY */
#include "inf-loop.h"
#include "gdbsupport/event-loop.h"
#include "event-top.h"
#include <pwd.h>
#include <sys/types.h>
#include <dirent.h>
#include "xml-support.h"
#include <sys/vfs.h>
#include "solib.h"
#include "nat/linux-osdata.h"
#include "linux-tdep.h"
#include "symfile.h"
#include "gdbsupport/agent.h"
#include "tracepoint.h"
#include "gdbsupport/buffer.h"
#include "target-descriptions.h"
#include "gdbsupport/filestuff.h"
#include "objfiles.h"
#include "nat/linux-namespaces.h"
#include "gdbsupport/fileio.h"
#include "gdbsupport/scope-exit.h"
#include "gdbsupport/gdb-sigmask.h"
#include "gdbsupport/common-debug.h"

/* This comment documents high-level logic of this file.

Waiting for events in sync mode
===============================

When waiting for an event in a specific thread, we just use waitpid,
passing the specific pid, and not passing WNOHANG.

When waiting for an event in all threads, waitpid is not quite good:

- If the thread group leader exits while other threads in the thread
  group still exist, waitpid(TGID, ...) hangs.  That waitpid won't
  return an exit status until the other threads in the group are
  reaped.

- When a non-leader thread execs, that thread just vanishes without
  reporting an exit (so we'd hang if we waited for it explicitly in
  that case).  The exec event is instead reported to the TGID pid.

The solution is to always use -1 and WNOHANG, together with
sigsuspend.

First, we use non-blocking waitpid to check for events.  If nothing is
found, we use sigsuspend to wait for SIGCHLD.  When SIGCHLD arrives,
it means something happened to a child process.  As soon as we know
there's an event, we get back to calling nonblocking waitpid.

Note that SIGCHLD should be blocked between waitpid and sigsuspend
calls, so that we don't miss a signal.  If SIGCHLD arrives in between,
when it's blocked, the signal becomes pending and sigsuspend
immediately notices it and returns.

Waiting for events in async mode (TARGET_WNOHANG)
=================================================

In async mode, GDB should always be ready to handle both user input
and target events, so neither blocking waitpid nor sigsuspend are
viable options.  Instead, we should asynchronously notify the GDB main
event loop whenever there's an unprocessed event from the target.  We
detect asynchronous target events by handling SIGCHLD signals.  To
notify the event loop about target events, the self-pipe trick is used
--- a pipe is registered as waitable event source in the event loop,
the event loop select/poll's on the read end of this pipe (as well on
other event sources, e.g., stdin), and the SIGCHLD handler writes a
byte to this pipe.  This is more portable than relying on
pselect/ppoll, since on kernels that lack those syscalls, libc
emulates them with select/poll+sigprocmask, and that is racy
(a.k.a. plain broken).

Obviously, if we fail to notify the event loop if there's a target
event, it's bad.  OTOH, if we notify the event loop when there's no
event from the target, linux_nat_wait will detect that there's no real
event to report, and return event of type TARGET_WAITKIND_IGNORE.
This is mostly harmless, but it will waste time and is better avoided.

The main design point is that every time GDB is outside linux-nat.c,
we have a SIGCHLD handler installed that is called when something
happens to the target and notifies the GDB event loop.  Whenever GDB
core decides to handle the event, and calls into linux-nat.c, we
process things as in sync mode, except that the we never block in
sigsuspend.

While processing an event, we may end up momentarily blocked in
waitpid calls.  Those waitpid calls, while blocking, are guarantied to
return quickly.  E.g., in all-stop mode, before reporting to the core
that an LWP hit a breakpoint, all LWPs are stopped by sending them
SIGSTOP, and synchronously waiting for the SIGSTOP to be reported.
Note that this is different from blocking indefinitely waiting for the
next event --- here, we're already handling an event.

Use of signals
==============

We stop threads by sending a SIGSTOP.  The use of SIGSTOP instead of another
signal is not entirely significant; we just need for a signal to be delivered,
so that we can intercept it.  SIGSTOP's advantage is that it can not be
blocked.  A disadvantage is that it is not a real-time signal, so it can only
be queued once; we do not keep track of other sources of SIGSTOP.

Two other signals that can't be blocked are SIGCONT and SIGKILL.  But we can't
use them, because they have special behavior when the signal is generated -
not when it is delivered.  SIGCONT resumes the entire thread group and SIGKILL
kills the entire thread group.

A delivered SIGSTOP would stop the entire thread group, not just the thread we
tkill'd.  But we never let the SIGSTOP be delivered; we always intercept and 
cancel it (by PTRACE_CONT without passing SIGSTOP).

We could use a real-time signal instead.  This would solve those problems; we
could use PTRACE_GETSIGINFO to locate the specific stop signals sent by GDB.
But we would still have to have some support for SIGSTOP, since PTRACE_ATTACH
generates it, and there are races with trying to find a signal that is not
blocked.

Exec events
===========

The case of a thread group (process) with 3 or more threads, and a
thread other than the leader execs is worth detailing:

On an exec, the Linux kernel destroys all threads except the execing
one in the thread group, and resets the execing thread's tid to the
tgid.  No exit notification is sent for the execing thread -- from the
ptracer's perspective, it appears as though the execing thread just
vanishes.  Until we reap all other threads except the leader and the
execing thread, the leader will be zombie, and the execing thread will
be in `D (disc sleep)' state.  As soon as all other threads are
reaped, the execing thread changes its tid to the tgid, and the
previous (zombie) leader vanishes, giving place to the "new"
leader.  */

#ifndef O_LARGEFILE
#define O_LARGEFILE 0
#endif

struct linux_nat_target *linux_target;

/* Does the current host support PTRACE_GETREGSET?  */
enum tribool have_ptrace_getregset = TRIBOOL_UNKNOWN;

static unsigned int debug_linux_nat;
static void
show_debug_linux_nat (struct ui_file *file, int from_tty,
		      struct cmd_list_element *c, const char *value)
{
  fprintf_filtered (file, _("Debugging of GNU/Linux lwp module is %s.\n"),
		    value);
}

/* Print a linux-nat debug statement.  */

#define linux_nat_debug_printf(fmt, ...) \
  debug_prefixed_printf_cond (debug_linux_nat, "linux-nat", fmt, ##__VA_ARGS__)

struct simple_pid_list
{
  int pid;
  int status;
  struct simple_pid_list *next;
};
static struct simple_pid_list *stopped_pids;

/* Whether target_thread_events is in effect.  */
static int report_thread_events;

/* Async mode support.  */

/* The read/write ends of the pipe registered as waitable file in the
   event loop.  */
static int linux_nat_event_pipe[2] = { -1, -1 };

/* True if we're currently in async mode.  */
#define linux_is_async_p() (linux_nat_event_pipe[0] != -1)

/* Flush the event pipe.  */

static void
async_file_flush (void)
{
  int ret;
  char buf;

  do
    {
      ret = read (linux_nat_event_pipe[0], &buf, 1);
    }
  while (ret >= 0 || (ret == -1 && errno == EINTR));
}

/* Put something (anything, doesn't matter what, or how much) in event
   pipe, so that the select/poll in the event-loop realizes we have
   something to process.  */

static void
async_file_mark (void)
{
  int ret;

  /* It doesn't really matter what the pipe contains, as long we end
     up with something in it.  Might as well flush the previous
     left-overs.  */
  async_file_flush ();

  do
    {
      ret = write (linux_nat_event_pipe[1], "+", 1);
    }
  while (ret == -1 && errno == EINTR);

  /* Ignore EAGAIN.  If the pipe is full, the event loop will already
     be awakened anyway.  */
}

static int kill_lwp (int lwpid, int signo);

static int stop_callback (struct lwp_info *lp);

static void block_child_signals (sigset_t *prev_mask);
static void restore_child_signals_mask (sigset_t *prev_mask);

struct lwp_info;
static struct lwp_info *add_lwp (ptid_t ptid);
static void purge_lwp_list (int pid);
static void delete_lwp (ptid_t ptid);
static struct lwp_info *find_lwp_pid (ptid_t ptid);

static int lwp_status_pending_p (struct lwp_info *lp);

static void save_stop_reason (struct lwp_info *lp);


/* LWP accessors.  */

/* See nat/linux-nat.h.  */

ptid_t
ptid_of_lwp (struct lwp_info *lwp)
{
  return lwp->ptid;
}

/* See nat/linux-nat.h.  */

void
lwp_set_arch_private_info (struct lwp_info *lwp,
			   struct arch_lwp_info *info)
{
  lwp->arch_private = info;
}

/* See nat/linux-nat.h.  */

struct arch_lwp_info *
lwp_arch_private_info (struct lwp_info *lwp)
{
  return lwp->arch_private;
}

/* See nat/linux-nat.h.  */

int
lwp_is_stopped (struct lwp_info *lwp)
{
  return lwp->stopped;
}

/* See nat/linux-nat.h.  */

enum target_stop_reason
lwp_stop_reason (struct lwp_info *lwp)
{
  return lwp->stop_reason;
}

/* See nat/linux-nat.h.  */

int
lwp_is_stepping (struct lwp_info *lwp)
{
  return lwp->step;
}


/* Trivial list manipulation functions to keep track of a list of
   new stopped processes.  */
static void
add_to_pid_list (struct simple_pid_list **listp, int pid, int status)
{
  struct simple_pid_list *new_pid = XNEW (struct simple_pid_list);

  new_pid->pid = pid;
  new_pid->status = status;
  new_pid->next = *listp;
  *listp = new_pid;
}

static int
pull_pid_from_list (struct simple_pid_list **listp, int pid, int *statusp)
{
  struct simple_pid_list **p;

  for (p = listp; *p != NULL; p = &(*p)->next)
    if ((*p)->pid == pid)
      {
	struct simple_pid_list *next = (*p)->next;

	*statusp = (*p)->status;
	xfree (*p);
	*p = next;
	return 1;
      }
  return 0;
}

/* Return the ptrace options that we want to try to enable.  */

static int
linux_nat_ptrace_options (int attached)
{
  int options = 0;

  if (!attached)
    options |= PTRACE_O_EXITKILL;

  options |= (PTRACE_O_TRACESYSGOOD
	      | PTRACE_O_TRACEVFORKDONE
	      | PTRACE_O_TRACEVFORK
	      | PTRACE_O_TRACEFORK
	      | PTRACE_O_TRACEEXEC);

  return options;
}

/* Initialize ptrace and procfs warnings and check for supported
   ptrace features given PID.

   ATTACHED should be nonzero iff we attached to the inferior.  */

static void
linux_init_ptrace_procfs (pid_t pid, int attached)
{
  int options = linux_nat_ptrace_options (attached);

  linux_enable_event_reporting (pid, options);
  linux_ptrace_init_warnings ();
  linux_proc_init_warnings ();
}

linux_nat_target::~linux_nat_target ()
{}

void
linux_nat_target::post_attach (int pid)
{
  linux_init_ptrace_procfs (pid, 1);
}

void
linux_nat_target::post_startup_inferior (ptid_t ptid)
{
  linux_init_ptrace_procfs (ptid.pid (), 0);
}

/* Return the number of known LWPs in the tgid given by PID.  */

static int
num_lwps (int pid)
{
  int count = 0;
  struct lwp_info *lp;

  for (lp = lwp_list; lp; lp = lp->next)
    if (lp->ptid.pid () == pid)
      count++;

  return count;
}

/* Deleter for lwp_info unique_ptr specialisation.  */

struct lwp_deleter
{
  void operator() (struct lwp_info *lwp) const
  {
    delete_lwp (lwp->ptid);
  }
};

/* A unique_ptr specialisation for lwp_info.  */

typedef std::unique_ptr<struct lwp_info, lwp_deleter> lwp_info_up;

/* Target hook for follow_fork.  On entry inferior_ptid must be the
   ptid of the followed inferior.  At return, inferior_ptid will be
   unchanged.  */

void
linux_nat_target::follow_fork (bool follow_child, bool detach_fork)
{
  if (!follow_child)
    {
      struct lwp_info *child_lp = NULL;
      int has_vforked;
      ptid_t parent_ptid, child_ptid;
      int parent_pid, child_pid;

      has_vforked = (inferior_thread ()->pending_follow.kind
		     == TARGET_WAITKIND_VFORKED);
      parent_ptid = inferior_ptid;
      child_ptid = inferior_thread ()->pending_follow.value.related_pid;
      parent_pid = parent_ptid.lwp ();
      child_pid = child_ptid.lwp ();

      /* We're already attached to the parent, by default.  */
      child_lp = add_lwp (child_ptid);
      child_lp->stopped = 1;
      child_lp->last_resume_kind = resume_stop;

      /* Detach new forked process?  */
      if (detach_fork)
	{
	  int child_stop_signal = 0;
	  bool detach_child = true;

	  /* Move CHILD_LP into a unique_ptr and clear the source pointer
	     to prevent us doing anything stupid with it.  */
	  lwp_info_up child_lp_ptr (child_lp);
	  child_lp = nullptr;

	  linux_target->low_prepare_to_resume (child_lp_ptr.get ());

	  /* When debugging an inferior in an architecture that supports
	     hardware single stepping on a kernel without commit
	     6580807da14c423f0d0a708108e6df6ebc8bc83d, the vfork child
	     process starts with the TIF_SINGLESTEP/X86_EFLAGS_TF bits
	     set if the parent process had them set.
	     To work around this, single step the child process
	     once before detaching to clear the flags.  */

	  /* Note that we consult the parent's architecture instead of
	     the child's because there's no inferior for the child at
	     this point.  */
	  if (!gdbarch_software_single_step_p (target_thread_architecture
					       (parent_ptid)))
	    {
	      int status;

	      linux_disable_event_reporting (child_pid);
	      if (ptrace (PTRACE_SINGLESTEP, child_pid, 0, 0) < 0)
		perror_with_name (_("Couldn't do single step"));
	      if (my_waitpid (child_pid, &status, 0) < 0)
		perror_with_name (_("Couldn't wait vfork process"));
	      else
		{
		  detach_child = WIFSTOPPED (status);
		  child_stop_signal = WSTOPSIG (status);
		}
	    }

	  if (detach_child)
	    {
	      int signo = child_stop_signal;

	      if (signo != 0
		  && !signal_pass_state (gdb_signal_from_host (signo)))
		signo = 0;
	      ptrace (PTRACE_DETACH, child_pid, 0, signo);
	    }
	}
      else
	{
	  /* Switching inferior_ptid is not enough, because then
	     inferior_thread () would crash by not finding the thread
	     in the current inferior.  */
	  scoped_restore_current_thread restore_current_thread;
	  thread_info *child = find_thread_ptid (this, child_ptid);
	  switch_to_thread (child);

	  /* Let the thread_db layer learn about this new process.  */
	  check_for_thread_db ();
	}

      if (has_vforked)
	{
	  struct lwp_info *parent_lp;

	  parent_lp = find_lwp_pid (parent_ptid);
	  gdb_assert (linux_supports_tracefork () >= 0);

	  if (linux_supports_tracevforkdone ())
	    {
	      linux_nat_debug_printf ("waiting for VFORK_DONE on %d",
				      parent_pid);
	      parent_lp->stopped = 1;

	      /* We'll handle the VFORK_DONE event like any other
		 event, in target_wait.  */
	    }
	  else
	    {
	      /* We can't insert breakpoints until the child has
		 finished with the shared memory region.  We need to
		 wait until that happens.  Ideal would be to just
		 call:
		 - ptrace (PTRACE_SYSCALL, parent_pid, 0, 0);
		 - waitpid (parent_pid, &status, __WALL);
		 However, most architectures can't handle a syscall
		 being traced on the way out if it wasn't traced on
		 the way in.

		 We might also think to loop, continuing the child
		 until it exits or gets a SIGTRAP.  One problem is
		 that the child might call ptrace with PTRACE_TRACEME.

		 There's no simple and reliable way to figure out when
		 the vforked child will be done with its copy of the
		 shared memory.  We could step it out of the syscall,
		 two instructions, let it go, and then single-step the
		 parent once.  When we have hardware single-step, this
		 would work; with software single-step it could still
		 be made to work but we'd have to be able to insert
		 single-step breakpoints in the child, and we'd have
		 to insert -just- the single-step breakpoint in the
		 parent.  Very awkward.

		 In the end, the best we can do is to make sure it
		 runs for a little while.  Hopefully it will be out of
		 range of any breakpoints we reinsert.  Usually this
		 is only the single-step breakpoint at vfork's return
		 point.  */

	      linux_nat_debug_printf ("no VFORK_DONE support, sleeping a bit");

	      usleep (10000);

	      /* Pretend we've seen a PTRACE_EVENT_VFORK_DONE event,
		 and leave it pending.  The next linux_nat_resume call
		 will notice a pending event, and bypasses actually
		 resuming the inferior.  */
	      parent_lp->status = 0;
	      parent_lp->waitstatus.kind = TARGET_WAITKIND_VFORK_DONE;
	      parent_lp->stopped = 1;

	      /* If we're in async mode, need to tell the event loop
		 there's something here to process.  */
	      if (target_is_async_p ())
		async_file_mark ();
	    }
	}
    }
  else
    {
      struct lwp_info *child_lp;

      child_lp = add_lwp (inferior_ptid);
      child_lp->stopped = 1;
      child_lp->last_resume_kind = resume_stop;

      /* Let the thread_db layer learn about this new process.  */
      check_for_thread_db ();
    }
}


int
linux_nat_target::insert_fork_catchpoint (int pid)
{
  return !linux_supports_tracefork ();
}

int
linux_nat_target::remove_fork_catchpoint (int pid)
{
  return 0;
}

int
linux_nat_target::insert_vfork_catchpoint (int pid)
{
  return !linux_supports_tracefork ();
}

int
linux_nat_target::remove_vfork_catchpoint (int pid)
{
  return 0;
}

int
linux_nat_target::insert_exec_catchpoint (int pid)
{
  return !linux_supports_tracefork ();
}

int
linux_nat_target::remove_exec_catchpoint (int pid)
{
  return 0;
}

int
linux_nat_target::set_syscall_catchpoint (int pid, bool needed, int any_count,
					  gdb::array_view<const int> syscall_counts)
{
  if (!linux_supports_tracesysgood ())
    return 1;

  /* On GNU/Linux, we ignore the arguments.  It means that we only
     enable the syscall catchpoints, but do not disable them.

     Also, we do not use the `syscall_counts' information because we do not
     filter system calls here.  We let GDB do the logic for us.  */
  return 0;
}

/* List of known LWPs, keyed by LWP PID.  This speeds up the common
   case of mapping a PID returned from the kernel to our corresponding
   lwp_info data structure.  */
static htab_t lwp_lwpid_htab;

/* Calculate a hash from a lwp_info's LWP PID.  */

static hashval_t
lwp_info_hash (const void *ap)
{
  const struct lwp_info *lp = (struct lwp_info *) ap;
  pid_t pid = lp->ptid.lwp ();

  return iterative_hash_object (pid, 0);
}

/* Equality function for the lwp_info hash table.  Compares the LWP's
   PID.  */

static int
lwp_lwpid_htab_eq (const void *a, const void *b)
{
  const struct lwp_info *entry = (const struct lwp_info *) a;
  const struct lwp_info *element = (const struct lwp_info *) b;

  return entry->ptid.lwp () == element->ptid.lwp ();
}

/* Create the lwp_lwpid_htab hash table.  */

static void
lwp_lwpid_htab_create (void)
{
  lwp_lwpid_htab = htab_create (100, lwp_info_hash, lwp_lwpid_htab_eq, NULL);
}

/* Add LP to the hash table.  */

static void
lwp_lwpid_htab_add_lwp (struct lwp_info *lp)
{
  void **slot;

  slot = htab_find_slot (lwp_lwpid_htab, lp, INSERT);
  gdb_assert (slot != NULL && *slot == NULL);
  *slot = lp;
}

/* Head of doubly-linked list of known LWPs.  Sorted by reverse
   creation order.  This order is assumed in some cases.  E.g.,
   reaping status after killing alls lwps of a process: the leader LWP
   must be reaped last.  */
struct lwp_info *lwp_list;

/* Add LP to sorted-by-reverse-creation-order doubly-linked list.  */

static void
lwp_list_add (struct lwp_info *lp)
{
  lp->next = lwp_list;
  if (lwp_list != NULL)
    lwp_list->prev = lp;
  lwp_list = lp;
}

/* Remove LP from sorted-by-reverse-creation-order doubly-linked
   list.  */

static void
lwp_list_remove (struct lwp_info *lp)
{
  /* Remove from sorted-by-creation-order list.  */
  if (lp->next != NULL)
    lp->next->prev = lp->prev;
  if (lp->prev != NULL)
    lp->prev->next = lp->next;
  if (lp == lwp_list)
    lwp_list = lp->next;
}


/* Signal mask for use with sigsuspend in linux_nat_wait, initialized in
   _initialize_linux_nat.  */
static sigset_t suspend_mask;

/* Signals to block to make that sigsuspend work.  */
static sigset_t blocked_mask;

/* SIGCHLD action.  */
static struct sigaction sigchld_action;

/* Block child signals (SIGCHLD and linux threads signals), and store
   the previous mask in PREV_MASK.  */

static void
block_child_signals (sigset_t *prev_mask)
{
  /* Make sure SIGCHLD is blocked.  */
  if (!sigismember (&blocked_mask, SIGCHLD))
    sigaddset (&blocked_mask, SIGCHLD);

  gdb_sigmask (SIG_BLOCK, &blocked_mask, prev_mask);
}

/* Restore child signals mask, previously returned by
   block_child_signals.  */

static void
restore_child_signals_mask (sigset_t *prev_mask)
{
  gdb_sigmask (SIG_SETMASK, prev_mask, NULL);
}

/* Mask of signals to pass directly to the inferior.  */
static sigset_t pass_mask;

/* Update signals to pass to the inferior.  */
void
linux_nat_target::pass_signals
  (gdb::array_view<const unsigned char> pass_signals)
{
  int signo;

  sigemptyset (&pass_mask);

  for (signo = 1; signo < NSIG; signo++)
    {
      int target_signo = gdb_signal_from_host (signo);
      if (target_signo < pass_signals.size () && pass_signals[target_signo])
	sigaddset (&pass_mask, signo);
    }
}


/* Prototypes for local functions.  */
static int stop_wait_callback (struct lwp_info *lp);
static int resume_stopped_resumed_lwps (struct lwp_info *lp, const ptid_t wait_ptid);
static int check_ptrace_stopped_lwp_gone (struct lwp_info *lp);


/* Destroy and free LP.  */

static void
lwp_free (struct lwp_info *lp)
{
  /* Let the arch specific bits release arch_lwp_info.  */
  linux_target->low_delete_thread (lp->arch_private);

  xfree (lp);
}

/* Traversal function for purge_lwp_list.  */

static int
lwp_lwpid_htab_remove_pid (void **slot, void *info)
{
  struct lwp_info *lp = (struct lwp_info *) *slot;
  int pid = *(int *) info;

  if (lp->ptid.pid () == pid)
    {
      htab_clear_slot (lwp_lwpid_htab, slot);
      lwp_list_remove (lp);
      lwp_free (lp);
    }

  return 1;
}

/* Remove all LWPs belong to PID from the lwp list.  */

static void
purge_lwp_list (int pid)
{
  htab_traverse_noresize (lwp_lwpid_htab, lwp_lwpid_htab_remove_pid, &pid);
}

/* Add the LWP specified by PTID to the list.  PTID is the first LWP
   in the process.  Return a pointer to the structure describing the
   new LWP.

   This differs from add_lwp in that we don't let the arch specific
   bits know about this new thread.  Current clients of this callback
   take the opportunity to install watchpoints in the new thread, and
   we shouldn't do that for the first thread.  If we're spawning a
   child ("run"), the thread executes the shell wrapper first, and we
   shouldn't touch it until it execs the program we want to debug.
   For "attach", it'd be okay to call the callback, but it's not
   necessary, because watchpoints can't yet have been inserted into
   the inferior.  */

static struct lwp_info *
add_initial_lwp (ptid_t ptid)
{
  struct lwp_info *lp;

  gdb_assert (ptid.lwp_p ());

  lp = XNEW (struct lwp_info);

  memset (lp, 0, sizeof (struct lwp_info));

  lp->last_resume_kind = resume_continue;
  lp->waitstatus.kind = TARGET_WAITKIND_IGNORE;

  lp->ptid = ptid;
  lp->core = -1;

  /* Add to sorted-by-reverse-creation-order list.  */
  lwp_list_add (lp);

  /* Add to keyed-by-pid htab.  */
  lwp_lwpid_htab_add_lwp (lp);

  return lp;
}

/* Add the LWP specified by PID to the list.  Return a pointer to the
   structure describing the new LWP.  The LWP should already be
   stopped.  */

static struct lwp_info *
add_lwp (ptid_t ptid)
{
  struct lwp_info *lp;

  lp = add_initial_lwp (ptid);

  /* Let the arch specific bits know about this new thread.  Current
     clients of this callback take the opportunity to install
     watchpoints in the new thread.  We don't do this for the first
     thread though.  See add_initial_lwp.  */
  linux_target->low_new_thread (lp);

  return lp;
}

/* Remove the LWP specified by PID from the list.  */

static void
delete_lwp (ptid_t ptid)
{
  struct lwp_info *lp;
  void **slot;
  struct lwp_info dummy;

  dummy.ptid = ptid;
  slot = htab_find_slot (lwp_lwpid_htab, &dummy, NO_INSERT);
  if (slot == NULL)
    return;

  lp = *(struct lwp_info **) slot;
  gdb_assert (lp != NULL);

  htab_clear_slot (lwp_lwpid_htab, slot);

  /* Remove from sorted-by-creation-order list.  */
  lwp_list_remove (lp);

  /* Release.  */
  lwp_free (lp);
}

/* Return a pointer to the structure describing the LWP corresponding
   to PID.  If no corresponding LWP could be found, return NULL.  */

static struct lwp_info *
find_lwp_pid (ptid_t ptid)
{
  struct lwp_info *lp;
  int lwp;
  struct lwp_info dummy;

  if (ptid.lwp_p ())
    lwp = ptid.lwp ();
  else
    lwp = ptid.pid ();

  dummy.ptid = ptid_t (0, lwp, 0);
  lp = (struct lwp_info *) htab_find (lwp_lwpid_htab, &dummy);
  return lp;
}

/* See nat/linux-nat.h.  */

struct lwp_info *
iterate_over_lwps (ptid_t filter,
		   gdb::function_view<iterate_over_lwps_ftype> callback)
{
  struct lwp_info *lp, *lpnext;

  for (lp = lwp_list; lp; lp = lpnext)
    {
      lpnext = lp->next;

      if (lp->ptid.matches (filter))
	{
	  if (callback (lp) != 0)
	    return lp;
	}
    }

  return NULL;
}

/* Update our internal state when changing from one checkpoint to
   another indicated by NEW_PTID.  We can only switch single-threaded
   applications, so we only create one new LWP, and the previous list
   is discarded.  */

void
linux_nat_switch_fork (ptid_t new_ptid)
{
  struct lwp_info *lp;

  purge_lwp_list (inferior_ptid.pid ());

  lp = add_lwp (new_ptid);
  lp->stopped = 1;

  /* This changes the thread's ptid while preserving the gdb thread
     num.  Also changes the inferior pid, while preserving the
     inferior num.  */
  thread_change_ptid (linux_target, inferior_ptid, new_ptid);

  /* We've just told GDB core that the thread changed target id, but,
     in fact, it really is a different thread, with different register
     contents.  */
  registers_changed ();
}

/* Handle the exit of a single thread LP.  */

static void
exit_lwp (struct lwp_info *lp)
{
  struct thread_info *th = find_thread_ptid (linux_target, lp->ptid);

  if (th)
    {
      if (print_thread_events)
	printf_unfiltered (_("[%s exited]\n"),
			   target_pid_to_str (lp->ptid).c_str ());

      delete_thread (th);
    }

  delete_lwp (lp->ptid);
}

/* Wait for the LWP specified by LP, which we have just attached to.
   Returns a wait status for that LWP, to cache.  */

static int
linux_nat_post_attach_wait (ptid_t ptid, int *signalled)
{
  pid_t new_pid, pid = ptid.lwp ();
  int status;

  if (linux_proc_pid_is_stopped (pid))
    {
      linux_nat_debug_printf ("Attaching to a stopped process");

      /* The process is definitely stopped.  It is in a job control
	 stop, unless the kernel predates the TASK_STOPPED /
	 TASK_TRACED distinction, in which case it might be in a
	 ptrace stop.  Make sure it is in a ptrace stop; from there we
	 can kill it, signal it, et cetera.

	 First make sure there is a pending SIGSTOP.  Since we are
	 already attached, the process can not transition from stopped
	 to running without a PTRACE_CONT; so we know this signal will
	 go into the queue.  The SIGSTOP generated by PTRACE_ATTACH is
	 probably already in the queue (unless this kernel is old
	 enough to use TASK_STOPPED for ptrace stops); but since SIGSTOP
	 is not an RT signal, it can only be queued once.  */
      kill_lwp (pid, SIGSTOP);

      /* Finally, resume the stopped process.  This will deliver the SIGSTOP
	 (or a higher priority signal, just like normal PTRACE_ATTACH).  */
      ptrace (PTRACE_CONT, pid, 0, 0);
    }

  /* Make sure the initial process is stopped.  The user-level threads
     layer might want to poke around in the inferior, and that won't
     work if things haven't stabilized yet.  */
  new_pid = my_waitpid (pid, &status, __WALL);
  gdb_assert (pid == new_pid);

  if (!WIFSTOPPED (status))
    {
      /* The pid we tried to attach has apparently just exited.  */
      linux_nat_debug_printf ("Failed to stop %d: %s", pid,
			      status_to_str (status).c_str ());
      return status;
    }

  if (WSTOPSIG (status) != SIGSTOP)
    {
      *signalled = 1;
      linux_nat_debug_printf ("Received %s after attaching",
			      status_to_str (status).c_str ());
    }

  return status;
}

void
linux_nat_target::create_inferior (const char *exec_file,
				   const std::string &allargs,
				   char **env, int from_tty)
{
  maybe_disable_address_space_randomization restore_personality
    (disable_randomization);

  /* The fork_child mechanism is synchronous and calls target_wait, so
     we have to mask the async mode.  */

  /* Make sure we report all signals during startup.  */
  pass_signals ({});

  inf_ptrace_target::create_inferior (exec_file, allargs, env, from_tty);
}

/* Callback for linux_proc_attach_tgid_threads.  Attach to PTID if not
   already attached.  Returns true if a new LWP is found, false
   otherwise.  */

static int
attach_proc_task_lwp_callback (ptid_t ptid)
{
  struct lwp_info *lp;

  /* Ignore LWPs we're already attached to.  */
  lp = find_lwp_pid (ptid);
  if (lp == NULL)
    {
      int lwpid = ptid.lwp ();

      if (ptrace (PTRACE_ATTACH, lwpid, 0, 0) < 0)
	{
	  int err = errno;

	  /* Be quiet if we simply raced with the thread exiting.
	     EPERM is returned if the thread's task still exists, and
	     is marked as exited or zombie, as well as other
	     conditions, so in that case, confirm the status in
	     /proc/PID/status.  */
	  if (err == ESRCH
	      || (err == EPERM && linux_proc_pid_is_gone (lwpid)))
	    {
	      linux_nat_debug_printf
		("Cannot attach to lwp %d: thread is gone (%d: %s)",
		 lwpid, err, safe_strerror (err));

	    }
	  else
	    {
	      std::string reason
		= linux_ptrace_attach_fail_reason_string (ptid, err);

	      warning (_("Cannot attach to lwp %d: %s"),
		       lwpid, reason.c_str ());
	    }
	}
      else
	{
	  linux_nat_debug_printf ("PTRACE_ATTACH %s, 0, 0 (OK)",
				  target_pid_to_str (ptid).c_str ());

	  lp = add_lwp (ptid);

	  /* The next time we wait for this LWP we'll see a SIGSTOP as
	     PTRACE_ATTACH brings it to a halt.  */
	  lp->signalled = 1;

	  /* We need to wait for a stop before being able to make the
	     next ptrace call on this LWP.  */
	  lp->must_set_ptrace_flags = 1;

	  /* So that wait collects the SIGSTOP.  */
	  lp->resumed = 1;

	  /* Also add the LWP to gdb's thread list, in case a
	     matching libthread_db is not found (or the process uses
	     raw clone).  */
	  add_thread (linux_target, lp->ptid);
	  set_running (linux_target, lp->ptid, true);
	  set_executing (linux_target, lp->ptid, true);
	}

      return 1;
    }
  return 0;
}

void
linux_nat_target::attach (const char *args, int from_tty)
{
  struct lwp_info *lp;
  int status;
  ptid_t ptid;

  /* Make sure we report all signals during attach.  */
  pass_signals ({});

  try
    {
      inf_ptrace_target::attach (args, from_tty);
    }
  catch (const gdb_exception_error &ex)
    {
      pid_t pid = parse_pid_to_attach (args);
      std::string reason = linux_ptrace_attach_fail_reason (pid);

      if (!reason.empty ())
	throw_error (ex.error, "warning: %s\n%s", reason.c_str (),
		     ex.what ());
      else
	throw_error (ex.error, "%s", ex.what ());
    }

  /* The ptrace base target adds the main thread with (pid,0,0)
     format.  Decorate it with lwp info.  */
  ptid = ptid_t (inferior_ptid.pid (),
		 inferior_ptid.pid (),
		 0);
  thread_change_ptid (linux_target, inferior_ptid, ptid);

  /* Add the initial process as the first LWP to the list.  */
  lp = add_initial_lwp (ptid);

  status = linux_nat_post_attach_wait (lp->ptid, &lp->signalled);
  if (!WIFSTOPPED (status))
    {
      if (WIFEXITED (status))
	{
	  int exit_code = WEXITSTATUS (status);

	  target_terminal::ours ();
	  target_mourn_inferior (inferior_ptid);
	  if (exit_code == 0)
	    error (_("Unable to attach: program exited normally."));
	  else
	    error (_("Unable to attach: program exited with code %d."),
		   exit_code);
	}
      else if (WIFSIGNALED (status))
	{
	  enum gdb_signal signo;

	  target_terminal::ours ();
	  target_mourn_inferior (inferior_ptid);

	  signo = gdb_signal_from_host (WTERMSIG (status));
	  error (_("Unable to attach: program terminated with signal "
		   "%s, %s."),
		 gdb_signal_to_name (signo),
		 gdb_signal_to_string (signo));
	}

      internal_error (__FILE__, __LINE__,
		      _("unexpected status %d for PID %ld"),
		      status, (long) ptid.lwp ());
    }

  lp->stopped = 1;

  /* Save the wait status to report later.  */
  lp->resumed = 1;
  linux_nat_debug_printf ("waitpid %ld, saving status %s",
			  (long) lp->ptid.pid (),
			  status_to_str (status).c_str ());

  lp->status = status;

  /* We must attach to every LWP.  If /proc is mounted, use that to
     find them now.  The inferior may be using raw clone instead of
     using pthreads.  But even if it is using pthreads, thread_db
     walks structures in the inferior's address space to find the list
     of threads/LWPs, and those structures may well be corrupted.
     Note that once thread_db is loaded, we'll still use it to list
     threads and associate pthread info with each LWP.  */
  linux_proc_attach_tgid_threads (lp->ptid.pid (),
				  attach_proc_task_lwp_callback);

  if (target_can_async_p ())
    target_async (1);
}

/* Get pending signal of THREAD as a host signal number, for detaching
   purposes.  This is the signal the thread last stopped for, which we
   need to deliver to the thread when detaching, otherwise, it'd be
   suppressed/lost.  */

static int
get_detach_signal (struct lwp_info *lp)
{
  enum gdb_signal signo = GDB_SIGNAL_0;

  /* If we paused threads momentarily, we may have stored pending
     events in lp->status or lp->waitstatus (see stop_wait_callback),
     and GDB core hasn't seen any signal for those threads.
     Otherwise, the last signal reported to the core is found in the
     thread object's stop_signal.

     There's a corner case that isn't handled here at present.  Only
     if the thread stopped with a TARGET_WAITKIND_STOPPED does
     stop_signal make sense as a real signal to pass to the inferior.
     Some catchpoint related events, like
     TARGET_WAITKIND_(V)FORK|EXEC|SYSCALL, have their stop_signal set
     to GDB_SIGNAL_SIGTRAP when the catchpoint triggers.  But,
     those traps are debug API (ptrace in our case) related and
     induced; the inferior wouldn't see them if it wasn't being
     traced.  Hence, we should never pass them to the inferior, even
     when set to pass state.  Since this corner case isn't handled by
     infrun.c when proceeding with a signal, for consistency, neither
     do we handle it here (or elsewhere in the file we check for
     signal pass state).  Normally SIGTRAP isn't set to pass state, so
     this is really a corner case.  */

  if (lp->waitstatus.kind != TARGET_WAITKIND_IGNORE)
    signo = GDB_SIGNAL_0; /* a pending ptrace event, not a real signal.  */
  else if (lp->status)
    signo = gdb_signal_from_host (WSTOPSIG (lp->status));
  else
    {
      struct thread_info *tp = find_thread_ptid (linux_target, lp->ptid);

      if (target_is_non_stop_p () && !tp->executing)
	{
	  if (tp->suspend.waitstatus_pending_p)
	    signo = tp->suspend.waitstatus.value.sig;
	  else
	    signo = tp->suspend.stop_signal;
	}
      else if (!target_is_non_stop_p ())
	{
	  ptid_t last_ptid;
	  process_stratum_target *last_target;

	  get_last_target_status (&last_target, &last_ptid, nullptr);

	  if (last_target == linux_target
	      && lp->ptid.lwp () == last_ptid.lwp ())
	    signo = tp->suspend.stop_signal;
	}
    }

  if (signo == GDB_SIGNAL_0)
    {
      linux_nat_debug_printf ("lwp %s has no pending signal",
			      target_pid_to_str (lp->ptid).c_str ());
    }
  else if (!signal_pass_state (signo))
    {
      linux_nat_debug_printf
	("lwp %s had signal %s but it is in no pass state",
	 target_pid_to_str (lp->ptid).c_str (), gdb_signal_to_string (signo));
    }
  else
    {
      linux_nat_debug_printf ("lwp %s has pending signal %s",
			      target_pid_to_str (lp->ptid).c_str (),
			      gdb_signal_to_string (signo));

      return gdb_signal_to_host (signo);
    }

  return 0;
}

/* Detach from LP.  If SIGNO_P is non-NULL, then it points to the
   signal number that should be passed to the LWP when detaching.
   Otherwise pass any pending signal the LWP may have, if any.  */

static void
detach_one_lwp (struct lwp_info *lp, int *signo_p)
{
  int lwpid = lp->ptid.lwp ();
  int signo;

  gdb_assert (lp->status == 0 || WIFSTOPPED (lp->status));

  if (lp->status != 0)
    linux_nat_debug_printf ("Pending %s for %s on detach.",
			    strsignal (WSTOPSIG (lp->status)),
			    target_pid_to_str (lp->ptid).c_str ());

  /* If there is a pending SIGSTOP, get rid of it.  */
  if (lp->signalled)
    {
      linux_nat_debug_printf ("Sending SIGCONT to %s",
			      target_pid_to_str (lp->ptid).c_str ());

      kill_lwp (lwpid, SIGCONT);
      lp->signalled = 0;
    }

  if (signo_p == NULL)
    {
      /* Pass on any pending signal for this LWP.  */
      signo = get_detach_signal (lp);
    }
  else
    signo = *signo_p;

  /* Preparing to resume may try to write registers, and fail if the
     lwp is zombie.  If that happens, ignore the error.  We'll handle
     it below, when detach fails with ESRCH.  */
  try
    {
      linux_target->low_prepare_to_resume (lp);
    }
  catch (const gdb_exception_error &ex)
    {
      if (!check_ptrace_stopped_lwp_gone (lp))
	throw;
    }

  if (ptrace (PTRACE_DETACH, lwpid, 0, signo) < 0)
    {
      int save_errno = errno;

      /* We know the thread exists, so ESRCH must mean the lwp is
	 zombie.  This can happen if one of the already-detached
	 threads exits the whole thread group.  In that case we're
	 still attached, and must reap the lwp.  */
      if (save_errno == ESRCH)
	{
	  int ret, status;

	  ret = my_waitpid (lwpid, &status, __WALL);
	  if (ret == -1)
	    {
	      warning (_("Couldn't reap LWP %d while detaching: %s"),
		       lwpid, safe_strerror (errno));
	    }
	  else if (!WIFEXITED (status) && !WIFSIGNALED (status))
	    {
	      warning (_("Reaping LWP %d while detaching "
			 "returned unexpected status 0x%x"),
		       lwpid, status);
	    }
	}
      else
	{
	  error (_("Can't detach %s: %s"),
		 target_pid_to_str (lp->ptid).c_str (),
		 safe_strerror (save_errno));
	}
    }
  else
    linux_nat_debug_printf ("PTRACE_DETACH (%s, %s, 0) (OK)",
			    target_pid_to_str (lp->ptid).c_str (),
			    strsignal (signo));

  delete_lwp (lp->ptid);
}

static int
detach_callback (struct lwp_info *lp)
{
  /* We don't actually detach from the thread group leader just yet.
     If the thread group exits, we must reap the zombie clone lwps
     before we're able to reap the leader.  */
  if (lp->ptid.lwp () != lp->ptid.pid ())
    detach_one_lwp (lp, NULL);
  return 0;
}

void
linux_nat_target::detach (inferior *inf, int from_tty)
{
  struct lwp_info *main_lwp;
  int pid = inf->pid;

  /* Don't unregister from the event loop, as there may be other
     inferiors running. */

  /* Stop all threads before detaching.  ptrace requires that the
     thread is stopped to successfully detach.  */
  iterate_over_lwps (ptid_t (pid), stop_callback);
  /* ... and wait until all of them have reported back that
     they're no longer running.  */
  iterate_over_lwps (ptid_t (pid), stop_wait_callback);

  /* We can now safely remove breakpoints.  We don't this in earlier
     in common code because this target doesn't currently support
     writing memory while the inferior is running.  */
  remove_breakpoints_inf (current_inferior ());

  iterate_over_lwps (ptid_t (pid), detach_callback);

  /* Only the initial process should be left right now.  */
  gdb_assert (num_lwps (pid) == 1);

  main_lwp = find_lwp_pid (ptid_t (pid));

  if (forks_exist_p ())
    {
      /* Multi-fork case.  The current inferior_ptid is being detached
	 from, but there are other viable forks to debug.  Detach from
	 the current fork, and context-switch to the first
	 available.  */
      linux_fork_detach (from_tty);
    }
  else
    {
      target_announce_detach (from_tty);

      /* Pass on any pending signal for the last LWP.  */
      int signo = get_detach_signal (main_lwp);

      detach_one_lwp (main_lwp, &signo);

      detach_success (inf);
    }
}

/* Resume execution of the inferior process.  If STEP is nonzero,
   single-step it.  If SIGNAL is nonzero, give it that signal.  */

static void
linux_resume_one_lwp_throw (struct lwp_info *lp, int step,
			    enum gdb_signal signo)
{
  lp->step = step;

  /* stop_pc doubles as the PC the LWP had when it was last resumed.
     We only presently need that if the LWP is stepped though (to
     handle the case of stepping a breakpoint instruction).  */
  if (step)
    {
      struct regcache *regcache = get_thread_regcache (linux_target, lp->ptid);

      lp->stop_pc = regcache_read_pc (regcache);
    }
  else
    lp->stop_pc = 0;

  linux_target->low_prepare_to_resume (lp);
  linux_target->low_resume (lp->ptid, step, signo);

  /* Successfully resumed.  Clear state that no longer makes sense,
     and mark the LWP as running.  Must not do this before resuming
     otherwise if that fails other code will be confused.  E.g., we'd
     later try to stop the LWP and hang forever waiting for a stop
     status.  Note that we must not throw after this is cleared,
     otherwise handle_zombie_lwp_error would get confused.  */
  lp->stopped = 0;
  lp->core = -1;
  lp->stop_reason = TARGET_STOPPED_BY_NO_REASON;
  registers_changed_ptid (linux_target, lp->ptid);
}

/* Called when we try to resume a stopped LWP and that errors out.  If
   the LWP is no longer in ptrace-stopped state (meaning it's zombie,
   or about to become), discard the error, clear any pending status
   the LWP may have, and return true (we'll collect the exit status
   soon enough).  Otherwise, return false.  */

static int
check_ptrace_stopped_lwp_gone (struct lwp_info *lp)
{
  /* If we get an error after resuming the LWP successfully, we'd
     confuse !T state for the LWP being gone.  */
  gdb_assert (lp->stopped);

  /* We can't just check whether the LWP is in 'Z (Zombie)' state,
     because even if ptrace failed with ESRCH, the tracee may be "not
     yet fully dead", but already refusing ptrace requests.  In that
     case the tracee has 'R (Running)' state for a little bit
     (observed in Linux 3.18).  See also the note on ESRCH in the
     ptrace(2) man page.  Instead, check whether the LWP has any state
     other than ptrace-stopped.  */

  /* Don't assume anything if /proc/PID/status can't be read.  */
  if (linux_proc_pid_is_trace_stopped_nowarn (lp->ptid.lwp ()) == 0)
    {
      lp->stop_reason = TARGET_STOPPED_BY_NO_REASON;
      lp->status = 0;
      lp->waitstatus.kind = TARGET_WAITKIND_IGNORE;
      return 1;
    }
  return 0;
}

/* Like linux_resume_one_lwp_throw, but no error is thrown if the LWP
   disappears while we try to resume it.  */

static void
linux_resume_one_lwp (struct lwp_info *lp, int step, enum gdb_signal signo)
{
  try
    {
      linux_resume_one_lwp_throw (lp, step, signo);
    }
  catch (const gdb_exception_error &ex)
    {
      if (!check_ptrace_stopped_lwp_gone (lp))
	throw;
    }
}

/* Resume LP.  */

static void
resume_lwp (struct lwp_info *lp, int step, enum gdb_signal signo)
{
  if (lp->stopped)
    {
      struct inferior *inf = find_inferior_ptid (linux_target, lp->ptid);

      if (inf->vfork_child != NULL)
	{
	  linux_nat_debug_printf ("Not resuming %s (vfork parent)",
				  target_pid_to_str (lp->ptid).c_str ());
	}
      else if (!lwp_status_pending_p (lp))
	{
	  linux_nat_debug_printf ("Resuming sibling %s, %s, %s",
				  target_pid_to_str (lp->ptid).c_str (),
				  (signo != GDB_SIGNAL_0
				   ? strsignal (gdb_signal_to_host (signo))
				   : "0"),
				  step ? "step" : "resume");

	  linux_resume_one_lwp (lp, step, signo);
	}
      else
	{
	  linux_nat_debug_printf ("Not resuming sibling %s (has pending)",
				  target_pid_to_str (lp->ptid).c_str ());
	}
    }
  else
    linux_nat_debug_printf ("Not resuming sibling %s (not stopped)",
			    target_pid_to_str (lp->ptid).c_str ());
}

/* Callback for iterate_over_lwps.  If LWP is EXCEPT, do nothing.
   Resume LWP with the last stop signal, if it is in pass state.  */

static int
linux_nat_resume_callback (struct lwp_info *lp, struct lwp_info *except)
{
  enum gdb_signal signo = GDB_SIGNAL_0;

  if (lp == except)
    return 0;

  if (lp->stopped)
    {
      struct thread_info *thread;

      thread = find_thread_ptid (linux_target, lp->ptid);
      if (thread != NULL)
	{
	  signo = thread->suspend.stop_signal;
	  thread->suspend.stop_signal = GDB_SIGNAL_0;
	}
    }

  resume_lwp (lp, 0, signo);
  return 0;
}

static int
resume_clear_callback (struct lwp_info *lp)
{
  lp->resumed = 0;
  lp->last_resume_kind = resume_stop;
  return 0;
}

static int
resume_set_callback (struct lwp_info *lp)
{
  lp->resumed = 1;
  lp->last_resume_kind = resume_continue;
  return 0;
}

void
linux_nat_target::resume (ptid_t ptid, int step, enum gdb_signal signo)
{
  struct lwp_info *lp;
  int resume_many;

  linux_nat_debug_printf ("Preparing to %s %s, %s, inferior_ptid %s",
			  step ? "step" : "resume",
			  target_pid_to_str (ptid).c_str (),
			  (signo != GDB_SIGNAL_0
			   ? strsignal (gdb_signal_to_host (signo)) : "0"),
			  target_pid_to_str (inferior_ptid).c_str ());

  /* A specific PTID means `step only this process id'.  */
  resume_many = (minus_one_ptid == ptid
		 || ptid.is_pid ());

  /* Mark the lwps we're resuming as resumed and update their
     last_resume_kind to resume_continue.  */
  iterate_over_lwps (ptid, resume_set_callback);

  /* See if it's the current inferior that should be handled
     specially.  */
  if (resume_many)
    lp = find_lwp_pid (inferior_ptid);
  else
    lp = find_lwp_pid (ptid);
  gdb_assert (lp != NULL);

  /* Remember if we're stepping.  */
  lp->last_resume_kind = step ? resume_step : resume_continue;

  /* If we have a pending wait status for this thread, there is no
     point in resuming the process.  But first make sure that
     linux_nat_wait won't preemptively handle the event - we
     should never take this short-circuit if we are going to
     leave LP running, since we have skipped resuming all the
     other threads.  This bit of code needs to be synchronized
     with linux_nat_wait.  */

  if (lp->status && WIFSTOPPED (lp->status))
    {
      if (!lp->step
	  && WSTOPSIG (lp->status)
	  && sigismember (&pass_mask, WSTOPSIG (lp->status)))
	{
	  linux_nat_debug_printf
	    ("Not short circuiting for ignored status 0x%x", lp->status);

	  /* FIXME: What should we do if we are supposed to continue
	     this thread with a signal?  */
	  gdb_assert (signo == GDB_SIGNAL_0);
	  signo = gdb_signal_from_host (WSTOPSIG (lp->status));
	  lp->status = 0;
	}
    }

  if (lwp_status_pending_p (lp))
    {
      /* FIXME: What should we do if we are supposed to continue
	 this thread with a signal?  */
      gdb_assert (signo == GDB_SIGNAL_0);

      linux_nat_debug_printf ("Short circuiting for status 0x%x",
			      lp->status);

      if (target_can_async_p ())
	{
	  target_async (1);
	  /* Tell the event loop we have something to process.  */
	  async_file_mark ();
	}
      return;
    }

  if (resume_many)
    iterate_over_lwps (ptid, [=] (struct lwp_info *info)
			     {
			       return linux_nat_resume_callback (info, lp);
			     });

  linux_nat_debug_printf ("%s %s, %s (resume event thread)",
			  step ? "PTRACE_SINGLESTEP" : "PTRACE_CONT",
			  target_pid_to_str (lp->ptid).c_str (),
			  (signo != GDB_SIGNAL_0
			   ? strsignal (gdb_signal_to_host (signo)) : "0"));

  linux_resume_one_lwp (lp, step, signo);

  if (target_can_async_p ())
    target_async (1);
}

/* Send a signal to an LWP.  */

static int
kill_lwp (int lwpid, int signo)
{
  int ret;

  errno = 0;
  ret = syscall (__NR_tkill, lwpid, signo);
  if (errno == ENOSYS)
    {
      /* If tkill fails, then we are not using nptl threads, a
	 configuration we no longer support.  */
      perror_with_name (("tkill"));
    }
  return ret;
}

/* Handle a GNU/Linux syscall trap wait response.  If we see a syscall
   event, check if the core is interested in it: if not, ignore the
   event, and keep waiting; otherwise, we need to toggle the LWP's
   syscall entry/exit status, since the ptrace event itself doesn't
   indicate it, and report the trap to higher layers.  */

static int
linux_handle_syscall_trap (struct lwp_info *lp, int stopping)
{
  struct target_waitstatus *ourstatus = &lp->waitstatus;
  struct gdbarch *gdbarch = target_thread_architecture (lp->ptid);
  thread_info *thread = find_thread_ptid (linux_target, lp->ptid);
  int syscall_number = (int) gdbarch_get_syscall_number (gdbarch, thread);

  if (stopping)
    {
      /* If we're stopping threads, there's a SIGSTOP pending, which
	 makes it so that the LWP reports an immediate syscall return,
	 followed by the SIGSTOP.  Skip seeing that "return" using
	 PTRACE_CONT directly, and let stop_wait_callback collect the
	 SIGSTOP.  Later when the thread is resumed, a new syscall
	 entry event.  If we didn't do this (and returned 0), we'd
	 leave a syscall entry pending, and our caller, by using
	 PTRACE_CONT to collect the SIGSTOP, skips the syscall return
	 itself.  Later, when the user re-resumes this LWP, we'd see
	 another syscall entry event and we'd mistake it for a return.

	 If stop_wait_callback didn't force the SIGSTOP out of the LWP
	 (leaving immediately with LWP->signalled set, without issuing
	 a PTRACE_CONT), it would still be problematic to leave this
	 syscall enter pending, as later when the thread is resumed,
	 it would then see the same syscall exit mentioned above,
	 followed by the delayed SIGSTOP, while the syscall didn't
	 actually get to execute.  It seems it would be even more
	 confusing to the user.  */

      linux_nat_debug_printf
	("ignoring syscall %d for LWP %ld (stopping threads), resuming with "
	 "PTRACE_CONT for SIGSTOP", syscall_number, lp->ptid.lwp ());

      lp->syscall_state = TARGET_WAITKIND_IGNORE;
      ptrace (PTRACE_CONT, lp->ptid.lwp (), 0, 0);
      lp->stopped = 0;
      return 1;
    }

  /* Always update the entry/return state, even if this particular
     syscall isn't interesting to the core now.  In async mode,
     the user could install a new catchpoint for this syscall
     between syscall enter/return, and we'll need to know to
     report a syscall return if that happens.  */
  lp->syscall_state = (lp->syscall_state == TARGET_WAITKIND_SYSCALL_ENTRY
		       ? TARGET_WAITKIND_SYSCALL_RETURN
		       : TARGET_WAITKIND_SYSCALL_ENTRY);

  if (catch_syscall_enabled ())
    {
      if (catching_syscall_number (syscall_number))
	{
	  /* Alright, an event to report.  */
	  ourstatus->kind = lp->syscall_state;
	  ourstatus->value.syscall_number = syscall_number;

	  linux_nat_debug_printf
	    ("stopping for %s of syscall %d for LWP %ld",
	     (lp->syscall_state == TARGET_WAITKIND_SYSCALL_ENTRY
	      ? "entry" : "return"), syscall_number, lp->ptid.lwp ());

	  return 0;
	}

      linux_nat_debug_printf
	("ignoring %s of syscall %d for LWP %ld",
	 (lp->syscall_state == TARGET_WAITKIND_SYSCALL_ENTRY
	  ? "entry" : "return"), syscall_number, lp->ptid.lwp ());
    }
  else
    {
      /* If we had been syscall tracing, and hence used PT_SYSCALL
	 before on this LWP, it could happen that the user removes all
	 syscall catchpoints before we get to process this event.
	 There are two noteworthy issues here:

	 - When stopped at a syscall entry event, resuming with
	   PT_STEP still resumes executing the syscall and reports a
	   syscall return.

	 - Only PT_SYSCALL catches syscall enters.  If we last
	   single-stepped this thread, then this event can't be a
	   syscall enter.  If we last single-stepped this thread, this
	   has to be a syscall exit.

	 The points above mean that the next resume, be it PT_STEP or
	 PT_CONTINUE, can not trigger a syscall trace event.  */
      linux_nat_debug_printf
	("caught syscall event with no syscall catchpoints. %d for LWP %ld, "
	 "ignoring", syscall_number, lp->ptid.lwp ());
      lp->syscall_state = TARGET_WAITKIND_IGNORE;
    }

  /* The core isn't interested in this event.  For efficiency, avoid
     stopping all threads only to have the core resume them all again.
     Since we're not stopping threads, if we're still syscall tracing
     and not stepping, we can't use PTRACE_CONT here, as we'd miss any
     subsequent syscall.  Simply resume using the inf-ptrace layer,
     which knows when to use PT_SYSCALL or PT_CONTINUE.  */

  linux_resume_one_lwp (lp, lp->step, GDB_SIGNAL_0);
  return 1;
}

/* Handle a GNU/Linux extended wait response.  If we see a clone
   event, we need to add the new LWP to our list (and not report the
   trap to higher layers).  This function returns non-zero if the
   event should be ignored and we should wait again.  If STOPPING is
   true, the new LWP remains stopped, otherwise it is continued.  */

static int
linux_handle_extended_wait (struct lwp_info *lp, int status)
{
  int pid = lp->ptid.lwp ();