gdbserver/linux-low.cc

/* Low level interface to ptrace, for the remote server for GDB.
   Copyright (C) 1995-2024 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 "linux-low.h"
#include "nat/linux-osdata.h"
#include "gdbsupport/agent.h"
#include "tdesc.h"
#include "gdbsupport/event-loop.h"
#include "gdbsupport/event-pipe.h"
#include "gdbsupport/rsp-low.h"
#include "gdbsupport/signals-state-save-restore.h"
#include "nat/linux-nat.h"
#include "nat/linux-waitpid.h"
#include "gdbsupport/gdb_wait.h"
#include "nat/gdb_ptrace.h"
#include "nat/linux-ptrace.h"
#include "nat/linux-procfs.h"
#include "nat/linux-personality.h"
#include <signal.h>
#include <sys/ioctl.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/syscall.h>
#include <sched.h>
#include <pwd.h>
#include <sys/types.h>
#include <dirent.h>
#include <sys/stat.h>
#include <sys/vfs.h>
#include <sys/uio.h>
#include <langinfo.h>
#include <iconv.h>
#include "gdbsupport/filestuff.h"
#include "gdbsupport/gdb-safe-ctype.h"
#include "tracepoint.h"
#include <inttypes.h>
#include "gdbsupport/common-inferior.h"
#include "nat/fork-inferior.h"
#include "gdbsupport/environ.h"
#include "gdbsupport/gdb-sigmask.h"
#include "gdbsupport/scoped_restore.h"
#ifndef ELFMAG0
/* Don't include <linux/elf.h> here.  If it got included by gdb_proc_service.h
   then ELFMAG0 will have been defined.  If it didn't get included by
   gdb_proc_service.h then including it will likely introduce a duplicate
   definition of elf_fpregset_t.  */
#include <elf.h>
#endif
#include "nat/linux-namespaces.h"

#ifndef O_LARGEFILE
#define O_LARGEFILE 0
#endif

#ifndef AT_HWCAP2
#define AT_HWCAP2 26
#endif

/* Some targets did not define these ptrace constants from the start,
   so gdbserver defines them locally here.  In the future, these may
   be removed after they are added to asm/ptrace.h.  */
#if !(defined(PT_TEXT_ADDR) \
      || defined(PT_DATA_ADDR) \
      || defined(PT_TEXT_END_ADDR))
#if defined(__mcoldfire__)
/* These are still undefined in 3.10 kernels.  */
#define PT_TEXT_ADDR 49*4
#define PT_DATA_ADDR 50*4
#define PT_TEXT_END_ADDR  51*4
/* These are still undefined in 3.10 kernels.  */
#elif defined(__TMS320C6X__)
#define PT_TEXT_ADDR     (0x10000*4)
#define PT_DATA_ADDR     (0x10004*4)
#define PT_TEXT_END_ADDR (0x10008*4)
#endif
#endif

#if (defined(__UCLIBC__)		\
     && defined(HAS_NOMMU)		\
     && defined(PT_TEXT_ADDR)		\
     && defined(PT_DATA_ADDR)		\
     && defined(PT_TEXT_END_ADDR))
#define SUPPORTS_READ_OFFSETS
#endif

#ifdef HAVE_LINUX_BTRACE
# include "nat/linux-btrace.h"
# include "gdbsupport/btrace-common.h"
#endif

#ifndef HAVE_ELF32_AUXV_T
/* Copied from glibc's elf.h.  */
typedef struct
{
  uint32_t a_type;		/* Entry type */
  union
    {
      uint32_t a_val;		/* Integer value */
      /* We use to have pointer elements added here.  We cannot do that,
	 though, since it does not work when using 32-bit definitions
	 on 64-bit platforms and vice versa.  */
    } a_un;
} Elf32_auxv_t;
#endif

#ifndef HAVE_ELF64_AUXV_T
/* Copied from glibc's elf.h.  */
typedef struct
{
  uint64_t a_type;		/* Entry type */
  union
    {
      uint64_t a_val;		/* Integer value */
      /* We use to have pointer elements added here.  We cannot do that,
	 though, since it does not work when using 32-bit definitions
	 on 64-bit platforms and vice versa.  */
    } a_un;
} Elf64_auxv_t;
#endif

/* See nat/linux-nat.h.  */
enum tribool have_ptrace_getregset = TRIBOOL_UNKNOWN;

/* Return TRUE if THREAD is the leader thread of the process.  */

static bool
is_leader (thread_info *thread)
{
  ptid_t ptid = ptid_of (thread);
  return ptid.pid () == ptid.lwp ();
}

/* Return true if we should report thread exit events to GDB, for
   THR.  */

static bool
report_exit_events_for (thread_info *thr)
{
  client_state &cs = get_client_state ();

  return (cs.report_thread_events
	  || (thr->thread_options & GDB_THREAD_OPTION_EXIT) != 0);
}

/* LWP accessors.  */

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

ptid_t
ptid_of_lwp (struct lwp_info *lwp)
{
  return ptid_of (get_lwp_thread (lwp));
}

/* 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->stepping;
}

/* A list of all unknown processes which receive stop signals.  Some
   other process will presumably claim each of these as forked
   children momentarily.  */

struct simple_pid_list
{
  /* The process ID.  */
  int pid;

  /* The status as reported by waitpid.  */
  int status;

  /* Next in chain.  */
  struct simple_pid_list *next;
};
static struct simple_pid_list *stopped_pids;

/* 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;
}

enum stopping_threads_kind
  {
    /* Not stopping threads presently.  */
    NOT_STOPPING_THREADS,

    /* Stopping threads.  */
    STOPPING_THREADS,

    /* Stopping and suspending threads.  */
    STOPPING_AND_SUSPENDING_THREADS
  };

/* This is set while stop_all_lwps is in effect.  */
static stopping_threads_kind stopping_threads = NOT_STOPPING_THREADS;

/* FIXME make into a target method?  */
int using_threads = 1;

/* True if we're presently stabilizing threads (moving them out of
   jump pads).  */
static int stabilizing_threads;

static void unsuspend_all_lwps (struct lwp_info *except);
static void mark_lwp_dead (struct lwp_info *lwp, int wstat,
			   bool thread_event);
static int lwp_is_marked_dead (struct lwp_info *lwp);
static int kill_lwp (unsigned long lwpid, int signo);
static void enqueue_pending_signal (struct lwp_info *lwp, int signal, siginfo_t *info);
static int linux_low_ptrace_options (int attached);
static int check_ptrace_stopped_lwp_gone (struct lwp_info *lp);

/* When the event-loop is doing a step-over, this points at the thread
   being stepped.  */
static ptid_t step_over_bkpt;

bool
linux_process_target::low_supports_breakpoints ()
{
  return false;
}

CORE_ADDR
linux_process_target::low_get_pc (regcache *regcache)
{
  return 0;
}

void
linux_process_target::low_set_pc (regcache *regcache, CORE_ADDR newpc)
{
  gdb_assert_not_reached ("linux target op low_set_pc is not implemented");
}

std::vector<CORE_ADDR>
linux_process_target::low_get_next_pcs (regcache *regcache)
{
  gdb_assert_not_reached ("linux target op low_get_next_pcs is not "
			  "implemented");
}

int
linux_process_target::low_decr_pc_after_break ()
{
  return 0;
}

/* True if LWP is stopped in its stepping range.  */

static int
lwp_in_step_range (struct lwp_info *lwp)
{
  CORE_ADDR pc = lwp->stop_pc;

  return (pc >= lwp->step_range_start && pc < lwp->step_range_end);
}

/* The event pipe registered as a waitable file in the event loop.  */
static event_pipe linux_event_pipe;

/* True if we're currently in async mode.  */
#define target_is_async_p() (linux_event_pipe.is_open ())

static void send_sigstop (struct lwp_info *lwp);

/* Return non-zero if HEADER is a 64-bit ELF file.  */

static int
elf_64_header_p (const Elf64_Ehdr *header, unsigned int *machine)
{
  if (header->e_ident[EI_MAG0] == ELFMAG0
      && header->e_ident[EI_MAG1] == ELFMAG1
      && header->e_ident[EI_MAG2] == ELFMAG2
      && header->e_ident[EI_MAG3] == ELFMAG3)
    {
      *machine = header->e_machine;
      return header->e_ident[EI_CLASS] == ELFCLASS64;

    }
  *machine = EM_NONE;
  return -1;
}

/* Return non-zero if FILE is a 64-bit ELF file,
   zero if the file is not a 64-bit ELF file,
   and -1 if the file is not accessible or doesn't exist.  */

static int
elf_64_file_p (const char *file, unsigned int *machine)
{
  Elf64_Ehdr header;
  int fd;

  fd = open (file, O_RDONLY);
  if (fd < 0)
    return -1;

  if (read (fd, &header, sizeof (header)) != sizeof (header))
    {
      close (fd);
      return 0;
    }
  close (fd);

  return elf_64_header_p (&header, machine);
}

/* Accepts an integer PID; Returns true if the executable PID is
   running is a 64-bit ELF file..  */

int
linux_pid_exe_is_elf_64_file (int pid, unsigned int *machine)
{
  char file[PATH_MAX];

  sprintf (file, "/proc/%d/exe", pid);
  return elf_64_file_p (file, machine);
}

void
linux_process_target::delete_lwp (lwp_info *lwp)
{
  struct thread_info *thr = get_lwp_thread (lwp);

  threads_debug_printf ("deleting %ld", lwpid_of (thr));

  remove_thread (thr);

  low_delete_thread (lwp->arch_private);

  delete lwp;
}

void
linux_process_target::low_delete_thread (arch_lwp_info *info)
{
  /* Default implementation should be overridden if architecture-specific
     info is being used.  */
  gdb_assert (info == nullptr);
}

/* Open the /proc/PID/mem file for PROC.  */

static void
open_proc_mem_file (process_info *proc)
{
  gdb_assert (proc->priv->mem_fd == -1);

  char filename[64];
  xsnprintf (filename, sizeof filename, "/proc/%d/mem", proc->pid);

  proc->priv->mem_fd
    = gdb_open_cloexec (filename, O_RDWR | O_LARGEFILE, 0).release ();
}

process_info *
linux_process_target::add_linux_process_no_mem_file (int pid, int attached)
{
  struct process_info *proc;

  proc = add_process (pid, attached);
  proc->priv = XCNEW (struct process_info_private);

  proc->priv->arch_private = low_new_process ();
  proc->priv->mem_fd = -1;

  return proc;
}


process_info *
linux_process_target::add_linux_process (int pid, int attached)
{
  process_info *proc = add_linux_process_no_mem_file (pid, attached);
  open_proc_mem_file (proc);
  return proc;
}

void
linux_process_target::remove_linux_process (process_info *proc)
{
  if (proc->priv->mem_fd >= 0)
    close (proc->priv->mem_fd);

  this->low_delete_process (proc->priv->arch_private);

  xfree (proc->priv);
  proc->priv = nullptr;

  remove_process (proc);
}

arch_process_info *
linux_process_target::low_new_process ()
{
  return nullptr;
}

void
linux_process_target::low_delete_process (arch_process_info *info)
{
  /* Default implementation must be overridden if architecture-specific
     info exists.  */
  gdb_assert (info == nullptr);
}

void
linux_process_target::low_new_fork (process_info *parent, process_info *child)
{
  /* Nop.  */
}

void
linux_process_target::arch_setup_thread (thread_info *thread)
{
  scoped_restore_current_thread restore_thread;
  switch_to_thread (thread);

  low_arch_setup ();
}

int
linux_process_target::handle_extended_wait (lwp_info **orig_event_lwp,
					    int wstat)
{
  client_state &cs = get_client_state ();
  struct lwp_info *event_lwp = *orig_event_lwp;
  int event = linux_ptrace_get_extended_event (wstat);
  struct thread_info *event_thr = get_lwp_thread (event_lwp);

  gdb_assert (event_lwp->waitstatus.kind () == TARGET_WAITKIND_IGNORE);

  /* All extended events we currently use are mid-syscall.  Only
     PTRACE_EVENT_STOP is delivered more like a signal-stop, but
     you have to be using PTRACE_SEIZE to get that.  */
  event_lwp->syscall_state = TARGET_WAITKIND_SYSCALL_ENTRY;

  if ((event == PTRACE_EVENT_FORK) || (event == PTRACE_EVENT_VFORK)
      || (event == PTRACE_EVENT_CLONE))
    {
      unsigned long new_pid;
      int ret, status;

      /* Get the pid of the new lwp.  */
      ptrace (PTRACE_GETEVENTMSG, lwpid_of (event_thr), (PTRACE_TYPE_ARG3) 0,
	      &new_pid);

      /* If we haven't already seen the new PID stop, wait for it now.  */
      if (!pull_pid_from_list (&stopped_pids, new_pid, &status))
	{
	  /* The new child has a pending SIGSTOP.  We can't affect it until it
	     hits the SIGSTOP, but we're already attached.  */

	  ret = my_waitpid (new_pid, &status, __WALL);

	  if (ret == -1)
	    perror_with_name ("waiting for new child");
	  else if (ret != new_pid)
	    warning ("wait returned unexpected PID %d", ret);
	  else if (!WIFSTOPPED (status))
	    warning ("wait returned unexpected status 0x%x", status);
	}

      if (debug_threads)
	{
	  debug_printf ("HEW: Got %s event from LWP %ld, new child is %ld\n",
			(event == PTRACE_EVENT_FORK ? "fork"
			 : event == PTRACE_EVENT_VFORK ? "vfork"
			 : event == PTRACE_EVENT_CLONE ? "clone"
			 : "???"),
			ptid_of (event_thr).lwp (),
			new_pid);
	}

      ptid_t child_ptid = (event != PTRACE_EVENT_CLONE
			   ? ptid_t (new_pid, new_pid)
			   : ptid_t (ptid_of (event_thr).pid (), new_pid));

      process_info *child_proc = nullptr;

      if (event != PTRACE_EVENT_CLONE)
	{
	  /* Add the new process to the tables before we add the LWP.
	     We need to do this even if the new process will be
	     detached.  See breakpoint cloning code further below.  */
	  child_proc = add_linux_process (new_pid, 0);
	}

      lwp_info *child_lwp = add_lwp (child_ptid);
      gdb_assert (child_lwp != NULL);
      child_lwp->stopped = 1;
      if (event != PTRACE_EVENT_CLONE)
	child_lwp->must_set_ptrace_flags = 1;
      child_lwp->status_pending_p = 0;

      thread_info *child_thr = get_lwp_thread (child_lwp);

      /* If we're suspending all threads, leave this one suspended
	 too.  If the fork/clone parent is stepping over a breakpoint,
	 all other threads have been suspended already.  Leave the
	 child suspended too.  */
      if (stopping_threads == STOPPING_AND_SUSPENDING_THREADS
	  || event_lwp->bp_reinsert != 0)
	{
	  threads_debug_printf ("leaving child suspended");
	  child_lwp->suspended = 1;
	}

      if (event_lwp->bp_reinsert != 0
	  && supports_software_single_step ()
	  && event == PTRACE_EVENT_VFORK)
	{
	  /* If we leave single-step breakpoints there, child will
	     hit it, so uninsert single-step breakpoints from parent
	     (and child).  Once vfork child is done, reinsert
	     them back to parent.  */
	  uninsert_single_step_breakpoints (event_thr);
	}

      if (event != PTRACE_EVENT_CLONE)
	{
	  /* Clone the breakpoint lists of the parent.  We need to do
	     this even if the new process will be detached, since we
	     will need the process object and the breakpoints to
	     remove any breakpoints from memory when we detach, and
	     the client side will access registers.  */
	  gdb_assert (child_proc != NULL);

	  process_info *parent_proc = get_thread_process (event_thr);
	  child_proc->attached = parent_proc->attached;

	  clone_all_breakpoints (child_thr, event_thr);

	  target_desc_up tdesc = allocate_target_description ();
	  copy_target_description (tdesc.get (), parent_proc->tdesc);
	  child_proc->tdesc = tdesc.release ();

	  /* Clone arch-specific process data.  */
	  low_new_fork (parent_proc, child_proc);
	}

      /* Save fork/clone info in the parent thread.  */
      if (event == PTRACE_EVENT_FORK)
	event_lwp->waitstatus.set_forked (child_ptid);
      else if (event == PTRACE_EVENT_VFORK)
	event_lwp->waitstatus.set_vforked (child_ptid);
      else if (event == PTRACE_EVENT_CLONE
	       && (event_thr->thread_options & GDB_THREAD_OPTION_CLONE) != 0)
	event_lwp->waitstatus.set_thread_cloned (child_ptid);

      if (event != PTRACE_EVENT_CLONE
	  || (event_thr->thread_options & GDB_THREAD_OPTION_CLONE) != 0)
	{
	  /* The status_pending field contains bits denoting the
	     extended event, so when the pending event is handled, the
	     handler will look at lwp->waitstatus.  */
	  event_lwp->status_pending_p = 1;
	  event_lwp->status_pending = wstat;

	  /* Link the threads until the parent's event is passed on to
	     GDB.  */
	  event_lwp->relative = child_lwp;
	  child_lwp->relative = event_lwp;
	}

      /* If the parent thread is doing step-over with single-step
	 breakpoints, the list of single-step breakpoints are cloned
	 from the parent's.  Remove them from the child process.
	 In case of vfork, we'll reinsert them back once vforked
	 child is done.  */
      if (event_lwp->bp_reinsert != 0
	  && supports_software_single_step ())
	{
	  /* The child process is forked and stopped, so it is safe
	     to access its memory without stopping all other threads
	     from other processes.  */
	  delete_single_step_breakpoints (child_thr);

	  gdb_assert (has_single_step_breakpoints (event_thr));
	  gdb_assert (!has_single_step_breakpoints (child_thr));
	}

      /* Normally we will get the pending SIGSTOP.  But in some cases
	 we might get another signal delivered to the group first.
	 If we do get another signal, be sure not to lose it.  */
      if (WSTOPSIG (status) != SIGSTOP)
	{
	  child_lwp->stop_expected = 1;
	  child_lwp->status_pending_p = 1;
	  child_lwp->status_pending = status;
	}
      else if (event == PTRACE_EVENT_CLONE && cs.report_thread_events)
	{
	  child_lwp->waitstatus.set_thread_created ();
	  child_lwp->status_pending_p = 1;
	  child_lwp->status_pending = status;
	}

      if (event == PTRACE_EVENT_CLONE)
	{
#ifdef USE_THREAD_DB
	  thread_db_notice_clone (event_thr, child_ptid);
#endif
	}

      if (event == PTRACE_EVENT_CLONE
	  && (event_thr->thread_options & GDB_THREAD_OPTION_CLONE) == 0)
	{
	  threads_debug_printf
	    ("not reporting clone event from LWP %ld, new child is %ld\n",
	     ptid_of (event_thr).lwp (),
	     new_pid);
	  return 1;
	}

      /* Leave the child stopped until GDB processes the parent
	 event.  */
      child_thr->last_resume_kind = resume_stop;
      child_thr->last_status.set_stopped (GDB_SIGNAL_0);

      /* Report the event.  */
      threads_debug_printf
	("reporting %s event from LWP %ld, new child is %ld\n",
	 (event == PTRACE_EVENT_FORK ? "fork"
	  : event == PTRACE_EVENT_VFORK ? "vfork"
	  : event == PTRACE_EVENT_CLONE ? "clone"
	  : "???"),
	 ptid_of (event_thr).lwp (),
	 new_pid);
      return 0;
    }
  else if (event == PTRACE_EVENT_VFORK_DONE)
    {
      event_lwp->waitstatus.set_vfork_done ();

      if (event_lwp->bp_reinsert != 0 && supports_software_single_step ())
	{
	  reinsert_single_step_breakpoints (event_thr);

	  gdb_assert (has_single_step_breakpoints (event_thr));
	}

      /* Report the event.  */
      return 0;
    }
  else if (event == PTRACE_EVENT_EXEC && cs.report_exec_events)
    {
      struct process_info *proc;
      std::vector<int> syscalls_to_catch;
      ptid_t event_ptid;
      pid_t event_pid;

      threads_debug_printf ("Got exec event from LWP %ld",
			    lwpid_of (event_thr));

      /* Get the event ptid.  */
      event_ptid = ptid_of (event_thr);
      event_pid = event_ptid.pid ();

      /* Save the syscall list from the execing process.  */
      proc = get_thread_process (event_thr);
      syscalls_to_catch = std::move (proc->syscalls_to_catch);

      /* Delete the execing process and all its threads.  */
      mourn (proc);
      switch_to_thread (nullptr);

      /* Create a new process/lwp/thread.  */
      proc = add_linux_process (event_pid, 0);
      event_lwp = add_lwp (event_ptid);
      event_thr = get_lwp_thread (event_lwp);
      gdb_assert (current_thread == event_thr);
      arch_setup_thread (event_thr);

      /* Set the event status.  */
      event_lwp->waitstatus.set_execd
	(make_unique_xstrdup
	   (linux_proc_pid_to_exec_file (lwpid_of (event_thr))));

      /* Mark the exec status as pending.  */
      event_lwp->stopped = 1;
      event_lwp->status_pending_p = 1;
      event_lwp->status_pending = wstat;
      event_thr->last_resume_kind = resume_continue;
      event_thr->last_status.set_ignore ();

      /* Update syscall state in the new lwp, effectively mid-syscall too.  */
      event_lwp->syscall_state = TARGET_WAITKIND_SYSCALL_ENTRY;

      /* Restore the list to catch.  Don't rely on the client, which is free
	 to avoid sending a new list when the architecture doesn't change.
	 Also, for ANY_SYSCALL, the architecture doesn't really matter.  */
      proc->syscalls_to_catch = std::move (syscalls_to_catch);

      /* Report the event.  */
      *orig_event_lwp = event_lwp;
      return 0;
    }

  internal_error (_("unknown ptrace event %d"), event);
}

CORE_ADDR
linux_process_target::get_pc (lwp_info *lwp)
{
  process_info *proc = get_thread_process (get_lwp_thread (lwp));
  gdb_assert (!proc->starting_up);

  if (!low_supports_breakpoints ())
    return 0;

  scoped_restore_current_thread restore_thread;
  switch_to_thread (get_lwp_thread (lwp));

  struct regcache *regcache = get_thread_regcache (current_thread, 1);
  CORE_ADDR pc = low_get_pc (regcache);

  threads_debug_printf ("pc is 0x%lx", (long) pc);

  return pc;
}

void
linux_process_target::get_syscall_trapinfo (lwp_info *lwp, int *sysno)
{
  struct regcache *regcache;

  scoped_restore_current_thread restore_thread;
  switch_to_thread (get_lwp_thread (lwp));

  regcache = get_thread_regcache (current_thread, 1);
  low_get_syscall_trapinfo (regcache, sysno);

  threads_debug_printf ("get_syscall_trapinfo sysno %d", *sysno);
}

void
linux_process_target::low_get_syscall_trapinfo (regcache *regcache, int *sysno)
{
  /* By default, report an unknown system call number.  */
  *sysno = UNKNOWN_SYSCALL;
}

bool
linux_process_target::save_stop_reason (lwp_info *lwp)
{
  CORE_ADDR pc;
  CORE_ADDR sw_breakpoint_pc;
  siginfo_t siginfo;

  if (!low_supports_breakpoints ())
    return false;

  process_info *proc = get_thread_process (get_lwp_thread (lwp));
  if (proc->starting_up)
    {
      /* Claim we have the stop PC so that the caller doesn't try to
	 fetch it itself.  */
      return true;
    }

  pc = get_pc (lwp);
  sw_breakpoint_pc = pc - low_decr_pc_after_break ();

  /* breakpoint_at reads from the current thread.  */
  scoped_restore_current_thread restore_thread;
  switch_to_thread (get_lwp_thread (lwp));

  if (ptrace (PTRACE_GETSIGINFO, lwpid_of (current_thread),
	      (PTRACE_TYPE_ARG3) 0, &siginfo) == 0)
    {
      if (siginfo.si_signo == SIGTRAP)
	{
	  if (GDB_ARCH_IS_TRAP_BRKPT (siginfo.si_code)
	      && GDB_ARCH_IS_TRAP_HWBKPT (siginfo.si_code))
	    {
	      /* The si_code is ambiguous on this arch -- check debug
		 registers.  */
	      if (!check_stopped_by_watchpoint (lwp))
		lwp->stop_reason = TARGET_STOPPED_BY_SW_BREAKPOINT;
	    }
	  else if (GDB_ARCH_IS_TRAP_BRKPT (siginfo.si_code))
	    {
	      /* If we determine the LWP stopped for a SW breakpoint,
		 trust it.  Particularly don't check watchpoint
		 registers, because at least on s390, we'd find
		 stopped-by-watchpoint as long as there's a watchpoint
		 set.  */
	      lwp->stop_reason = TARGET_STOPPED_BY_SW_BREAKPOINT;
	    }
	  else if (GDB_ARCH_IS_TRAP_HWBKPT (siginfo.si_code))
	    {
	      /* This can indicate either a hardware breakpoint or
		 hardware watchpoint.  Check debug registers.  */
	      if (!check_stopped_by_watchpoint (lwp))
		lwp->stop_reason = TARGET_STOPPED_BY_HW_BREAKPOINT;
	    }
	  else if (siginfo.si_code == TRAP_TRACE)
	    {
	      /* We may have single stepped an instruction that
		 triggered a watchpoint.  In that case, on some
		 architectures (such as x86), instead of TRAP_HWBKPT,
		 si_code indicates TRAP_TRACE, and we need to check
		 the debug registers separately.  */
	      if (!check_stopped_by_watchpoint (lwp))
		lwp->stop_reason = TARGET_STOPPED_BY_SINGLE_STEP;
	    }
	}
    }

  if (lwp->stop_reason == TARGET_STOPPED_BY_SW_BREAKPOINT)
    {
      threads_debug_printf
	("%s stopped by software breakpoint",
	 target_pid_to_str (ptid_of (get_lwp_thread (lwp))).c_str ());

      /* Back up the PC if necessary.  */
      if (pc != sw_breakpoint_pc)
	{
	  struct regcache *regcache
	    = get_thread_regcache (current_thread, 1);
	  low_set_pc (regcache, sw_breakpoint_pc);
	}

      /* Update this so we record the correct stop PC below.  */
      pc = sw_breakpoint_pc;
    }
  else if (lwp->stop_reason == TARGET_STOPPED_BY_HW_BREAKPOINT)
    threads_debug_printf
      ("%s stopped by hardware breakpoint",
       target_pid_to_str (ptid_of (get_lwp_thread (lwp))).c_str ());
  else if (lwp->stop_reason == TARGET_STOPPED_BY_WATCHPOINT)
    threads_debug_printf
      ("%s stopped by hardware watchpoint",
       target_pid_to_str (ptid_of (get_lwp_thread (lwp))).c_str ());
  else if (lwp->stop_reason == TARGET_STOPPED_BY_SINGLE_STEP)
    threads_debug_printf
      ("%s stopped by trace",
       target_pid_to_str (ptid_of (get_lwp_thread (lwp))).c_str ());

  lwp->stop_pc = pc;
  return true;
}

lwp_info *
linux_process_target::add_lwp (ptid_t ptid)
{
  lwp_info *lwp = new lwp_info;

  lwp->thread = add_thread (ptid, lwp);

  low_new_thread (lwp);

  return lwp;
}

void
linux_process_target::low_new_thread (lwp_info *info)
{
  /* Nop.  */
}

/* Callback to be used when calling fork_inferior, responsible for
   actually initiating the tracing of the inferior.  */

static void
linux_ptrace_fun ()
{
  if (ptrace (PTRACE_TRACEME, 0, (PTRACE_TYPE_ARG3) 0,
	      (PTRACE_TYPE_ARG4) 0) < 0)
    trace_start_error_with_name ("ptrace");

  if (setpgid (0, 0) < 0)
    trace_start_error_with_name ("setpgid");

  /* If GDBserver is connected to gdb via stdio, redirect the inferior's
     stdout to stderr so that inferior i/o doesn't corrupt the connection.
     Also, redirect stdin to /dev/null.  */
  if (remote_connection_is_stdio ())
    {
      if (close (0) < 0)
	trace_start_error_with_name ("close");
      if (open ("/dev/null", O_RDONLY) < 0)
	trace_start_error_with_name ("open");
      if (dup2 (2, 1) < 0)
	trace_start_error_with_name ("dup2");
      if (write (2, "stdin/stdout redirected\n",
		 sizeof ("stdin/stdout redirected\n") - 1) < 0)
	{
	  /* Errors ignored.  */;
	}
    }
}

/* Start an inferior process and returns its pid.
   PROGRAM is the name of the program to be started, and PROGRAM_ARGS
   are its arguments.  */

int
linux_process_target::create_inferior (const char *program,
				       const std::vector<char *> &program_args)
{
  client_state &cs = get_client_state ();
  struct lwp_info *new_lwp;
  int pid;
  ptid_t ptid;

  {
    maybe_disable_address_space_randomization restore_personality
      (cs.disable_randomization);
    std::string str_program_args = construct_inferior_arguments (program_args);

    pid = fork_inferior (program,
			 str_program_args.c_str (),
			 get_environ ()->envp (), linux_ptrace_fun,
			 NULL, NULL, NULL, NULL);
  }

  /* When spawning a new process, we can't open the mem file yet.  We
     still have to nurse the process through the shell, and that execs
     a couple times.  The address space a /proc/PID/mem file is
     accessing is destroyed on exec.  */
  process_info *proc = add_linux_process_no_mem_file (pid, 0);

  ptid = ptid_t (pid, pid);
  new_lwp = add_lwp (ptid);
  new_lwp->must_set_ptrace_flags = 1;

  post_fork_inferior (pid, program);

  /* PROC is now past the shell running the program we want, so we can
     open the /proc/PID/mem file.  */
  open_proc_mem_file (proc);

  return pid;
}

/* Implement the post_create_inferior target_ops method.  */

void
linux_process_target::post_create_inferior ()
{
  struct lwp_info *lwp = get_thread_lwp (current_thread);

  low_arch_setup ();

  if (lwp->must_set_ptrace_flags)
    {
      struct process_info *proc = current_process ();
      int options = linux_low_ptrace_options (proc->attached);

      linux_enable_event_reporting (lwpid_of (current_thread), options);
      lwp->must_set_ptrace_flags = 0;
    }
}

int
linux_process_target::attach_lwp (ptid_t ptid)
{
  struct lwp_info *new_lwp;
  int lwpid = ptid.lwp ();

  if (ptrace (PTRACE_ATTACH, lwpid, (PTRACE_TYPE_ARG3) 0, (PTRACE_TYPE_ARG4) 0)
      != 0)
    return errno;

  new_lwp = add_lwp (ptid);

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

  if (linux_proc_pid_is_stopped (lwpid))
    {
      threads_debug_printf ("Attached 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 (lwpid, SIGSTOP);

      /* Finally, resume the stopped process.  This will deliver the
	 SIGSTOP (or a higher priority signal, just like normal
	 PTRACE_ATTACH), which we'll catch later on.  */
      ptrace (PTRACE_CONT, lwpid, (PTRACE_TYPE_ARG3) 0, (PTRACE_TYPE_ARG4) 0);
    }

  /* The next time we wait for this LWP we'll see a SIGSTOP as PTRACE_ATTACH
     brings it to a halt.

     There are several cases to consider here:

     1) gdbserver has already attached to the process and is being notified
	of a new thread that is being created.
	In this case we should ignore that SIGSTOP and resume the
	process.  This is handled below by setting stop_expected = 1,
	and the fact that add_thread sets last_resume_kind ==
	resume_continue.

     2) This is the first thread (the process thread), and we're attaching
	to it via attach_inferior.
	In this case we want the process thread to stop.
	This is handled by having linux_attach set last_resume_kind ==
	resume_stop after we return.

	If the pid we are attaching to is also the tgid, we attach to and
	stop all the existing threads.  Otherwise, we attach to pid and
	ignore any other threads in the same group as this pid.

     3) GDB is connecting to gdbserver and is requesting an enumeration of all
	existing threads.
	In this case we want the thread to stop.
	FIXME: This case is currently not properly handled.
	We should wait for the SIGSTOP but don't.  Things work apparently
	because enough time passes between when we ptrace (ATTACH) and when
	gdb makes the next ptrace call on the thread.

     On the other hand, if we are currently trying to stop all threads, we
     should treat the new thread as if we had sent it a SIGSTOP.  This works
     because we are guaranteed that the add_lwp call above added us to the
     end of the list, and so the new thread has not yet reached
     wait_for_sigstop (but will).  */
  new_lwp->stop_expected = 1;

  return 0;
}

/* 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)
{
  /* Is this a new thread?  */
  if (find_thread_ptid (ptid) == NULL)
    {
      int lwpid = ptid.lwp ();
      int err;

      threads_debug_printf ("Found new lwp %d", lwpid);

      err = the_linux_target->attach_lwp (ptid);

      /* 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)))
	threads_debug_printf
	  ("Cannot attach to lwp %d: thread is gone (%d: %s)",
	   lwpid, err, safe_strerror (err));
      else if (err != 0)
	{
	  std::string reason
	    = linux_ptrace_attach_fail_reason_string (ptid, err);

	  error (_("Cannot attach to lwp %d: %s"), lwpid, reason.c_str ());
	}

      return 1;
    }
  return 0;
}

static void async_file_mark (void);

/* Attach to PID.  If PID is the tgid, attach to it and all
   of its threads.  */

int
linux_process_target::attach (unsigned long pid)
{
  struct process_info *proc;
  struct thread_info *initial_thread;
  ptid_t ptid = ptid_t (pid, pid);
  int err;

  /* Delay opening the /proc/PID/mem file until we've successfully
     attached.  */
  proc = add_linux_process_no_mem_file (pid, 1);

  /* Attach to PID.  We will check for other threads
     soon.  */
  err = attach_lwp (ptid);
  if (err != 0)
    {
      this->remove_linux_process (proc);

      std::string reason = linux_ptrace_attach_fail_reason_string (ptid, err);
      error ("Cannot attach to process %ld: %s", pid, reason.c_str ());
    }

  open_proc_mem_file (proc);

  /* Don't ignore the initial SIGSTOP if we just attached to this
     process.  It will be collected by wait shortly.  */
  initial_thread = find_thread_ptid (ptid_t (pid, pid));
  gdb_assert (initial_thread != nullptr);
  initial_thread->last_resume_kind = resume_stop;

  /* We must attach to every LWP.  If /proc is mounted, use that to
     find them now.  On the one hand, the inferior may be using raw
     clone instead of using pthreads.  On the other hand, even if it
     is using pthreads, GDB may not be connected yet (thread_db needs
     to do symbol lookups, through qSymbol).  Also, 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.  */
  try
    {
      linux_proc_attach_tgid_threads (pid, attach_proc_task_lwp_callback);
    }
  catch (const gdb_exception_error &)
    {
      /* Make sure we do not deliver the SIGSTOP to the process.  */
      initial_thread->last_resume_kind = resume_continue;

      this->detach (proc);
      throw;
    }

  /* GDB will shortly read the xml target description for this
     process, to figure out the process' architecture.  But the target
     description is only filled in when the first process/thread in
     the thread group reports its initial PTRACE_ATTACH SIGSTOP.  Do
     that now, otherwise, if GDB is fast enough, it could read the
     target description _before_ that initial stop.  */
  if (non_stop)
    {
      struct lwp_info *lwp;
      int wstat, lwpid;
      ptid_t pid_ptid = ptid_t (pid);

      lwpid = wait_for_event_filtered (pid_ptid, pid_ptid, &wstat, __WALL);
      gdb_assert (lwpid > 0);

      lwp = find_lwp_pid (ptid_t (lwpid));
      gdb_assert (lwp != nullptr);

      if (!WIFSTOPPED (wstat) || WSTOPSIG (wstat) != SIGSTOP)
	{
	  lwp->status_pending_p = 1;
	  lwp->status_pending = wstat;
	}

      initial_thread->last_resume_kind = resume_continue;

      async_file_mark ();

      gdb_assert (proc->tdesc != NULL);
    }

  return 0;
}

static int
last_thread_of_process_p (int pid)
{
  bool seen_one = false;

  thread_info *thread = find_thread (pid, [&] (thread_info *thr_arg)
    {
      if (!seen_one)
	{
	  /* This is the first thread of this process we see.  */
	  seen_one = true;
	  return false;
	}
      else
	{
	  /* This is the second thread of this process we see.  */
	  return true;
	}
    });

  return thread == NULL;
}

/* Kill LWP.  */

static void
linux_kill_one_lwp (struct lwp_info *lwp)
{
  struct thread_info *thr = get_lwp_thread (lwp);
  int pid = lwpid_of (thr);

  /* PTRACE_KILL is unreliable.  After stepping into a signal handler,
     there is no signal context, and ptrace(PTRACE_KILL) (or
     ptrace(PTRACE_CONT, SIGKILL), pretty much the same) acts like
     ptrace(CONT, pid, 0,0) and just resumes the tracee.  A better
     alternative is to kill with SIGKILL.  We only need one SIGKILL
     per process, not one for each thread.  But since we still support
     support debugging programs using raw clone without CLONE_THREAD,
     we send one for each thread.  For years, we used PTRACE_KILL
     only, so we're being a bit paranoid about some old kernels where
     PTRACE_KILL might work better (dubious if there are any such, but
     that's why it's paranoia), so we try SIGKILL first, PTRACE_KILL
     second, and so we're fine everywhere.  */

  errno = 0;
  kill_lwp (pid, SIGKILL);
  if (debug_threads)
    {
      int save_errno = errno;

      threads_debug_printf ("kill_lwp (SIGKILL) %s, 0, 0 (%s)",
			    target_pid_to_str (ptid_of (thr)).c_str (),
			    save_errno ? safe_strerror (save_errno) : "OK");
    }

  errno = 0;
  ptrace (PTRACE_KILL, pid, (PTRACE_TYPE_ARG3) 0, (PTRACE_TYPE_ARG4) 0);
  if (debug_threads)
    {
      int save_errno = errno;

      threads_debug_printf ("PTRACE_KILL %s, 0, 0 (%s)",
			    target_pid_to_str (ptid_of (thr)).c_str (),
			    save_errno ? safe_strerror (save_errno) : "OK");
    }
}

/* Kill LWP and wait for it to die.  */

static void
kill_wait_lwp (struct lwp_info *lwp)
{
  struct thread_info *thr = get_lwp_thread (lwp);
  int pid = ptid_of (thr).pid ();
  int lwpid = ptid_of (thr).lwp ();
  int wstat;
  int res;

  threads_debug_printf ("killing lwp %d, for pid: %d", lwpid, pid);

  do
    {
      linux_kill_one_lwp (lwp);

      /* Make sure it died.  Notes:

	 - The loop is most likely unnecessary.

	 - We don't use wait_for_event as that could delete lwps
	   while we're iterating over them.  We're not interested in
	   any pending status at this point, only in making sure all
	   wait status on the kernel side are collected until the
	   process is reaped.

	 - We don't use __WALL here as the __WALL emulation relies on
	   SIGCHLD, and killing a stopped process doesn't generate
	   one, nor an exit status.
      */
      res = my_waitpid (lwpid, &wstat, 0);
      if (res == -1 && errno == ECHILD)
	res = my_waitpid (lwpid, &wstat, __WCLONE);
    } while (res > 0 && WIFSTOPPED (wstat));

  /* Even if it was stopped, the child may have already disappeared.
     E.g., if it was killed by SIGKILL.  */
  if (res < 0 && errno != ECHILD)
    perror_with_name ("kill_wait_lwp");
}

/* Callback for `for_each_thread'.  Kills an lwp of a given process,
   except the leader.  */

static void
kill_one_lwp_callback (thread_info *thread, int pid)
{
  struct lwp_info *lwp = get_thread_lwp (thread);

  /* We avoid killing the first thread here, because of a Linux kernel (at
     least 2.6.0-test7 through 2.6.8-rc4) bug; if we kill the parent before
     the children get a chance to be reaped, it will remain a zombie
     forever.  */

  if (lwpid_of (thread) == pid)
    {
      threads_debug_printf ("is last of process %s",
			    target_pid_to_str (thread->id).c_str ());
      return;
    }

  kill_wait_lwp (lwp);
}

int
linux_process_target::kill (process_info *process)
{
  int pid = process->pid;

  /* If we're killing a running inferior, make sure it is stopped
     first, as PTRACE_KILL will not work otherwise.  */
  stop_all_lwps (0, NULL);

  for_each_thread (pid, [&] (thread_info *thread)
    {
      kill_one_lwp_callback (thread, pid);
    });

  /* See the comment in linux_kill_one_lwp.  We did not kill the first
     thread in the list, so do so now.  */
  lwp_info *lwp = find_lwp_pid (ptid_t (pid));

  if (lwp == NULL)
    threads_debug_printf ("cannot find lwp for pid: %d", pid);
  else
    kill_wait_lwp (lwp);

  mourn (process);

  /* Since we presently can only stop all lwps of all processes, we
     need to unstop lwps of other processes.  */
  unstop_all_lwps (0, NULL);
  return 0;
}

/* Get pending signal of THREAD, 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 thread_info *thread)
{
  client_state &cs = get_client_state ();
  enum gdb_signal signo = GDB_SIGNAL_0;
  int status;
  struct lwp_info *lp = get_thread_lwp (thread);

  if (lp->status_pending_p)
    status = lp->status_pending;
  else
    {
      /* If the thread had been suspended by gdbserver, and it stopped
	 cleanly, then it'll have stopped with SIGSTOP.  But we don't
	 want to deliver that SIGSTOP.  */
      if (thread->last_status.kind () != TARGET_WAITKIND_STOPPED
	  || thread->last_status.sig () == GDB_SIGNAL_0)
	return 0;

      /* Otherwise, we may need to deliver the signal we
	 intercepted.  */
      status = lp->last_status;
    }

  if (!WIFSTOPPED (status))
    {
      threads_debug_printf ("lwp %s hasn't stopped: no pending signal",
			    target_pid_to_str (ptid_of (thread)).c_str ());
      return 0;
    }

  /* Extended wait statuses aren't real SIGTRAPs.  */
  if (WSTOPSIG (status) == SIGTRAP && linux_is_extended_waitstatus (status))
    {
      threads_debug_printf ("lwp %s had stopped with extended "
			    "status: no pending signal",
			    target_pid_to_str (ptid_of (thread)).c_str ());
      return 0;
    }

  signo = gdb_signal_from_host (WSTOPSIG (status));

  if (cs.program_signals_p && !cs.program_signals[signo])
    {
      threads_debug_printf ("lwp %s had signal %s, but it is in nopass state",
			    target_pid_to_str (ptid_of (thread)).c_str (),
			    gdb_signal_to_string (signo));
      return 0;
    }
  else if (!cs.program_signals_p
	   /* If we have no way to know which signals GDB does not
	      want to have passed to the program, assume
	      SIGTRAP/SIGINT, which is GDB's default.  */
	   && (signo == GDB_SIGNAL_TRAP || signo == GDB_SIGNAL_INT))
    {
      threads_debug_printf ("lwp %s had signal %s, "
			    "but we don't know if we should pass it. "
			    "Default to not.",
			    target_pid_to_str (ptid_of (thread)).c_str (),
			    gdb_signal_to_string (signo));
      return 0;
    }
  else
    {
      threads_debug_printf ("lwp %s has pending signal %s: delivering it",
			    target_pid_to_str (ptid_of (thread)).c_str (),
			    gdb_signal_to_string (signo));

      return WSTOPSIG (status);
    }
}

void
linux_process_target::detach_one_lwp (lwp_info *lwp)
{
  struct thread_info *thread = get_lwp_thread (lwp);
  int sig;
  int lwpid;

  /* If there is a pending SIGSTOP, get rid of it.  */
  if (lwp->stop_expected)
    {
      threads_debug_printf ("Sending SIGCONT to %s",
			    target_pid_to_str (ptid_of (thread)).c_str ());

      kill_lwp (lwpid_of (thread), SIGCONT);
      lwp->stop_expected = 0;
    }

  /* Pass on any pending signal for this thread.  */
  sig = get_detach_signal (thread);

  /* 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
    {
      /* Flush any pending changes to the process's registers.  */
      regcache_invalidate_thread (thread);

      /* Finally, let it resume.  */
      low_prepare_to_resume (lwp);
    }
  catch (const gdb_exception_error &ex)
    {
      if (!check_ptrace_stopped_lwp_gone (lwp))
	throw;
    }

  lwpid = lwpid_of (thread);
  if (ptrace (PTRACE_DETACH, lwpid, (PTRACE_TYPE_ARG3) 0,
	      (PTRACE_TYPE_ARG4) (long) sig) < 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 (ptid_of (thread)).c_str (),
		 safe_strerror (save_errno));
	}
    }
  else
    threads_debug_printf ("PTRACE_DETACH (%s, %s, 0) (OK)",
			  target_pid_to_str (ptid_of (thread)).c_str (),
			  strsignal (sig));

  delete_lwp (lwp);
}

int
linux_process_target::detach (process_info *process)
{
  struct lwp_info *main_lwp;

  /* As there's a step over already in progress, let it finish first,
     otherwise nesting a stabilize_threads operation on top gets real
     messy.  */
  complete_ongoing_step_over ();

  /* Stop all threads before detaching.  First, ptrace requires that
     the thread is stopped to successfully detach.  Second, thread_db
     may need to uninstall thread event breakpoints from memory, which
     only works with a stopped process anyway.  */
  stop_all_lwps (0, NULL);

#ifdef USE_THREAD_DB
  thread_db_detach (process);
#endif

  /* Stabilize threads (move out of jump pads).  */
  target_stabilize_threads ();

  /* Detach from the clone lwps first.  If the thread group exits just
     while we're detaching, we must reap the clone lwps before we're
     able to reap the leader.  */
  for_each_thread (process->pid, [this] (thread_info *thread)
    {
      /* 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 (thread->id.pid () == thread->id.lwp ())
	return;

      lwp_info *lwp = get_thread_lwp (thread);
      detach_one_lwp (lwp);
    });

  main_lwp = find_lwp_pid (ptid_t (process->pid));
  gdb_assert (main_lwp != nullptr);
  detach_one_lwp (main_lwp);

  mourn (process);

  /* Since we presently can only stop all lwps of all processes, we
     need to unstop lwps of other processes.  */
  unstop_all_lwps (0, NULL);
  return 0;
}

/* Remove all LWPs that belong to process PROC from the lwp list.  */

void
linux_process_target::mourn (process_info *process)
{
#ifdef USE_THREAD_DB
  thread_db_mourn (process);
#endif

  for_each_thread (process->pid, [this] (thread_info *thread)
    {
      delete_lwp (get_thread_lwp (thread));
    });

  this->remove_linux_process (process);
}

void
linux_process_target::join (int pid)
{
  int status, ret;

  do {
    ret = my_waitpid (pid, &status, 0);
    if (WIFEXITED (status) || WIFSIGNALED (status))
      break;
  } while (ret != -1 || errno != ECHILD);
}

/* Return true if the given thread is still alive.  */

bool
linux_process_target::thread_alive (ptid_t ptid)
{
  struct lwp_info *lwp = find_lwp_pid (ptid);

  /* We assume we always know if a thread exits.  If a whole process
     exited but we still haven't been able to report it to GDB, we'll
     hold on to the last lwp of the dead process.  */
  if (lwp != NULL)
    return !lwp_is_marked_dead (lwp);
  else
    return 0;
}

bool
linux_process_target::thread_still_has_status_pending (thread_info *thread)
{
  struct lwp_info *lp = get_thread_lwp (thread);

  if (!lp->status_pending_p)
    return 0;

  if (thread->last_resume_kind != resume_stop
      && (lp->stop_reason == TARGET_STOPPED_BY_SW_BREAKPOINT
	  || lp->stop_reason == TARGET_STOPPED_BY_HW_BREAKPOINT))
    {
      CORE_ADDR pc;
      int discard = 0;

      gdb_assert (lp->last_status != 0);

      pc = get_pc (lp);

      scoped_restore_current_thread restore_thread;
      switch_to_thread (thread);

      if (pc != lp->stop_pc)
	{
	  threads_debug_printf ("PC of %ld changed",
				lwpid_of (thread));
	  discard = 1;
	}

      if (discard)
	{
	  threads_debug_printf ("discarding pending breakpoint status");
	  lp->status_pending_p = 0;
	  return 0;
	}
    }

  return 1;
}

/* Returns true if LWP is resumed from the client's perspective.  */

static int
lwp_resumed (struct lwp_info *lwp)
{
  struct thread_info *thread = get_lwp_thread (lwp);

  if (thread->last_resume_kind != resume_stop)
    return 1;

  /* Did gdb send us a `vCont;t', but we haven't reported the
     corresponding stop to gdb yet?  If so, the thread is still
     resumed/running from gdb's perspective.  */
  if (thread->last_resume_kind == resume_stop
      && thread->last_status.kind () == TARGET_WAITKIND_IGNORE)
    return 1;

  return 0;
}

bool
linux_process_target::status_pending_p_callback (thread_info *thread,
						 ptid_t ptid)
{
  struct lwp_info *lp = get_thread_lwp (thread);

  /* Check if we're only interested in events from a specific process
     or a specific LWP.  */
  if (!thread->id.matches (ptid))
    return 0;

  if (!lwp_resumed (lp))
    return 0;

  if (lp->status_pending_p
      && !thread_still_has_status_pending (thread))
    {
      resume_one_lwp (lp, lp->stepping, GDB_SIGNAL_0, NULL);
      return 0;
    }

  return lp->status_pending_p;
}

struct lwp_info *
find_lwp_pid (ptid_t ptid)
{
  long lwp = ptid.lwp () != 0 ? ptid.lwp () : ptid.pid ();
  thread_info *thread = find_thread ([lwp] (thread_info *thr_arg)
    {
      return thr_arg->id.lwp () == lwp;
    });

  if (thread == NULL)
    return NULL;

  return get_thread_lwp (thread);
}

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

static int
num_lwps (int pid)
{
  int count = 0;

  for_each_thread (pid, [&] (thread_info *thread)
    {
      count++;
    });

  return count;
}

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

struct lwp_info *
iterate_over_lwps (ptid_t filter,
		   gdb::function_view<iterate_over_lwps_ftype> callback)
{
  thread_info *thread = find_thread (filter, [&] (thread_info *thr_arg)
    {
      lwp_info *lwp = get_thread_lwp (thr_arg);

      return callback (lwp);
    });

  if (thread == NULL)
    return NULL;

  return get_thread_lwp (thread);
}

bool
linux_process_target::check_zombie_leaders ()
{
  bool new_pending_event = false;

  for_each_process ([&] (process_info *proc)
    {
      pid_t leader_pid = pid_of (proc);
      lwp_info *leader_lp = find_lwp_pid (ptid_t (leader_pid));

      threads_debug_printf ("leader_pid=%d, leader_lp!=NULL=%d, "
			    "num_lwps=%d, zombie=%d",
			    leader_pid, leader_lp!= NULL, num_lwps (leader_pid),
			    linux_proc_pid_is_zombie (leader_pid));

      if (leader_lp != NULL && !leader_lp->stopped
	  /* Check if there are other threads in the group, as we may
	     have raced with the inferior simply exiting.  Note this
	     isn't a watertight check.  If the inferior is
	     multi-threaded and is exiting, it may be we see the
	     leader as zombie before we reap all the non-leader
	     threads.  See comments below.  */
	  && !last_thread_of_process_p (leader_pid)
	  && linux_proc_pid_is_zombie (leader_pid))
	{
	  /* A zombie leader in a multi-threaded program can mean one
	     of three things:

	     #1 - Only the leader exited, not the whole program, e.g.,
	     with pthread_exit.  Since we can't reap the leader's exit
	     status until all other threads are gone and reaped too,
	     we want to delete the zombie leader right away, as it
	     can't be debugged, we can't read its registers, etc.
	     This is the main reason we check for zombie leaders
	     disappearing.

	     #2 - The whole thread-group/process exited (a group exit,
	     via e.g. exit(3), and there is (or will be shortly) an
	     exit reported for each thread in the process, and then
	     finally an exit for the leader once the non-leaders are
	     reaped.

	     #3 - There are 3 or more threads in the group, and a
	     thread other than the leader exec'd.  See comments on
	     exec events at the top of the file.

	     Ideally we would never delete the leader for case #2.
	     Instead, we want to collect the exit status of each
	     non-leader thread, and then finally collect the exit
	     status of the leader as normal and use its exit code as
	     whole-process exit code.  Unfortunately, there's no
	     race-free way to distinguish cases #1 and #2.  We can't
	     assume the exit events for the non-leaders threads are
	     already pending in the kernel, nor can we assume the
	     non-leader threads are in zombie state already.  Between
	     the leader becoming zombie and the non-leaders exiting
	     and becoming zombie themselves, there's a small time
	     window, so such a check would be racy.  Temporarily
	     pausing all threads and checking to see if all threads
	     exit or not before re-resuming them would work in the
	     case that all threads are running right now, but it
	     wouldn't work if some thread is currently already
	     ptrace-stopped, e.g., due to scheduler-locking.

	     So what we do is we delete the leader anyhow, and then
	     later on when we see its exit status, we re-add it back.
	     We also make sure that we only report a whole-process
	     exit when we see the leader exiting, as opposed to when
	     the last LWP in the LWP list exits, which can be a
	     non-leader if we deleted the leader here.  */
	  threads_debug_printf ("Thread group leader %d zombie "
				"(it exited, or another thread execd), "
				"deleting it.",
				leader_pid);

	  thread_info *leader_thread = get_lwp_thread (leader_lp);
	  if (report_exit_events_for (leader_thread))
	    {
	      mark_lwp_dead (leader_lp, W_EXITCODE (0, 0), true);
	      new_pending_event = true;
	    }
	  else
	    delete_lwp (leader_lp);
	}
    });

  return new_pending_event;
}

/* Callback for `find_thread'.  Returns the first LWP that is not
   stopped.  */

static bool
not_stopped_callback (thread_info *thread, ptid_t filter)
{
  if (!thread->id.matches (filter))
    return false;

  lwp_info *lwp = get_thread_lwp (thread);

  return !lwp->stopped;
}

/* Increment LWP's suspend count.  */

static void
lwp_suspended_inc (struct lwp_info *lwp)
{
  lwp->suspended++;

  if (lwp->suspended > 4)
    threads_debug_printf
      ("LWP %ld has a suspiciously high suspend count, suspended=%d",
       lwpid_of (get_lwp_thread (lwp)), lwp->suspended);
}

/* Decrement LWP's suspend count.  */

static void
lwp_suspended_decr (struct lwp_info *lwp)
{
  lwp->suspended--;

  if (lwp->suspended < 0)
    {
      struct thread_info *thread = get_lwp_thread (lwp);

      internal_error ("unsuspend LWP %ld, suspended=%d\n", lwpid_of (thread),
		      lwp->suspended);
    }
}

/* This function should only be called if the LWP got a SIGTRAP.

   Handle any tracepoint steps or hits.  Return true if a tracepoint
   event was handled, 0 otherwise.  */

static int
handle_tracepoints (struct lwp_info *lwp)
{
  struct thread_info *tinfo = get_lwp_thread (lwp);
  int tpoint_related_event = 0;

  gdb_assert (lwp->suspended == 0);

  /* If this tracepoint hit causes a tracing stop, we'll immediately
     uninsert tracepoints.  To do this, we temporarily pause all
     threads, unpatch away, and then unpause threads.  We need to make
     sure the unpausing doesn't resume LWP too.  */
  lwp_suspended_inc (lwp);

  /* And we need to be sure that any all-threads-stopping doesn't try
     to move threads out of the jump pads, as it could deadlock the
     inferior (LWP could be in the jump pad, maybe even holding the
     lock.)  */

  /* Do any necessary step collect actions.  */
  tpoint_related_event |= tracepoint_finished_step (tinfo, lwp->stop_pc);

  tpoint_related_event |= handle_tracepoint_bkpts (tinfo, lwp->stop_pc);

  /* See if we just hit a tracepoint and do its main collect
     actions.  */
  tpoint_related_event |= tracepoint_was_hit (tinfo, lwp->stop_pc);

  lwp_suspended_decr (lwp);

  gdb_assert (lwp->suspended == 0);
  gdb_assert (!stabilizing_threads
	      || (lwp->collecting_fast_tracepoint
		  != fast_tpoint_collect_result::not_collecting));

  if (tpoint_related_event)
    {
      threads_debug_printf ("got a tracepoint event");
      return 1;
    }

  return 0;
}

fast_tpoint_collect_result
linux_process_target::linux_fast_tracepoint_collecting
  (lwp_info *lwp, fast_tpoint_collect_status *status)
{
  CORE_ADDR thread_area;
  struct thread_info *thread = get_lwp_thread (lwp);

  /* Get the thread area address.  This is used to recognize which
     thread is which when tracing with the in-process agent library.
     We don't read anything from the address, and treat it as opaque;
     it's the address itself that we assume is unique per-thread.  */
  if (low_get_thread_area (lwpid_of (thread), &thread_area) == -1)
    return fast_tpoint_collect_result::not_collecting;

  return fast_tracepoint_collecting (thread_area, lwp->stop_pc, status);
}

int
linux_process_target::low_get_thread_area (int lwpid, CORE_ADDR *addrp)
{
  return -1;
}

bool
linux_process_target::maybe_move_out_of_jump_pad (lwp_info *lwp, int *wstat)
{
  scoped_restore_current_thread restore_thread;
  switch_to_thread (get_lwp_thread (lwp));

  if ((wstat == NULL
       || (WIFSTOPPED (*wstat) && WSTOPSIG (*wstat) != SIGTRAP))
      && supports_fast_tracepoints ()
      && agent_loaded_p ())
    {
      struct fast_tpoint_collect_status status;

      threads_debug_printf
	("Checking whether LWP %ld needs to move out of the jump pad.",
	 lwpid_of (current_thread));

      fast_tpoint_collect_result r
	= linux_fast_tracepoint_collecting (lwp, &status);

      if (wstat == NULL
	  || (WSTOPSIG (*wstat) != SIGILL
	      && WSTOPSIG (*wstat) != SIGFPE
	      && WSTOPSIG (*wstat) != SIGSEGV
	      && WSTOPSIG (*wstat) != SIGBUS))
	{
	  lwp->collecting_fast_tracepoint = r;

	  if (r != fast_tpoint_collect_result::not_collecting)
	    {
	      if (r == fast_tpoint_collect_result::before_insn
		  && lwp->exit_jump_pad_bkpt == NULL)
		{
		  /* Haven't executed the original instruction yet.
		     Set breakpoint there, and wait till it's hit,
		     then single-step until exiting the jump pad.  */
		  lwp->exit_jump_pad_bkpt
		    = set_breakpoint_at (status.adjusted_insn_addr, NULL);
		}

	      threads_debug_printf
		("Checking whether LWP %ld needs to move out of the jump pad..."
		 " it does", lwpid_of (current_thread));

	      return true;
	    }
	}
      else
	{
	  /* If we get a synchronous signal while collecting, *and*
	     while executing the (relocated) original instruction,
	     reset the PC to point at the tpoint address, before
	     reporting to GDB.  Otherwise, it's an IPA lib bug: just
	     report the signal to GDB, and pray for the best.  */

	  lwp->collecting_fast_tracepoint
	    = fast_tpoint_collect_result::not_collecting;

	  if (r != fast_tpoint_collect_result::not_collecting
	      && (status.adjusted_insn_addr <= lwp->stop_pc
		  && lwp->stop_pc < status.adjusted_insn_addr_end))
	    {
	      siginfo_t info;
	      struct regcache *regcache;

	      /* The si_addr on a few signals references the address
		 of the faulting instruction.  Adjust that as
		 well.  */
	      if ((WSTOPSIG (*wstat) == SIGILL
		   || WSTOPSIG (*wstat) == SIGFPE
		   || WSTOPSIG (*wstat) == SIGBUS
		   || WSTOPSIG (*wstat) == SIGSEGV)
		  && ptrace (PTRACE_GETSIGINFO, lwpid_of (current_thread),
			     (PTRACE_TYPE_ARG3) 0, &info) == 0
		  /* Final check just to make sure we don't clobber
		     the siginfo of non-kernel-sent signals.  */
		  && (uintptr_t) info.si_addr == lwp->stop_pc)
		{
		  info.si_addr = (void *) (uintptr_t) status.tpoint_addr;
		  ptrace (PTRACE_SETSIGINFO, lwpid_of (current_thread),
			  (PTRACE_TYPE_ARG3) 0, &info);
		}

	      regcache = get_thread_regcache (current_thread, 1);
	      low_set_pc (regcache, status.tpoint_addr);
	      lwp->stop_pc = status.tpoint_addr;

	      /* Cancel any fast tracepoint lock this thread was
		 holding.  */
	      force_unlock_trace_buffer ();
	    }

	  if (lwp->exit_jump_pad_bkpt != NULL)
	    {
	      threads_debug_printf
		("Cancelling fast exit-jump-pad: removing bkpt."
		 "stopping all threads momentarily.");

	      stop_all_lwps (1, lwp);

	      delete_breakpoint (lwp->exit_jump_pad_bkpt);
	      lwp->exit_jump_pad_bkpt = NULL;

	      unstop_all_lwps (1, lwp);

	      gdb_assert (lwp->suspended >= 0);
	    }
	}
    }

  threads_debug_printf
    ("Checking whether LWP %ld needs to move out of the jump pad... no",
     lwpid_of (current_thread));

  return false;
}

/* Enqueue one signal in the "signals to report later when out of the
   jump pad" list.  */

static void
enqueue_one_deferred_signal (struct lwp_info *lwp, int *wstat)
{
  struct thread_info *thread = get_lwp_thread (lwp);

  threads_debug_printf ("Deferring signal %d for LWP %ld.",
			WSTOPSIG (*wstat), lwpid_of (thread));

  if (debug_threads)
    {
      for (const auto &sig : lwp->pending_signals_to_report)
	threads_debug_printf ("   Already queued %d", sig.signal);

      threads_debug_printf ("   (no more currently queued signals)");
    }

  /* Don't enqueue non-RT signals if they are already in the deferred
     queue.  (SIGSTOP being the easiest signal to see ending up here
     twice)  */
  if (WSTOPSIG (*wstat) < __SIGRTMIN)
    {
      for (const auto &sig : lwp->pending_signals_to_report)
	{
	  if (sig.signal == WSTOPSIG (*wstat))
	    {
	      threads_debug_printf
		("Not requeuing already queued non-RT signal %d for LWP %ld",
		 sig.signal, lwpid_of (thread));
	      return;
	    }
	}
    }

  lwp->pending_signals_to_report.emplace_back (WSTOPSIG (*wstat));

  ptrace (PTRACE_GETSIGINFO, lwpid_of (thread), (PTRACE_TYPE_ARG3) 0,
	  &lwp->pending_signals_to_report.back ().info);
}

/* Dequeue one signal from the "signals to report later when out of
   the jump pad" list.  */

static int
dequeue_one_deferred_signal (struct lwp_info *lwp, int *wstat)
{
  struct thread_info *thread = get_lwp_thread (lwp);

  if (!lwp->pending_signals_to_report.empty ())
    {
      const pending_signal &p_sig = lwp->pending_signals_to_report.front ();

      *wstat = W_STOPCODE (p_sig.signal);
      if (p_sig.info.si_signo != 0)
	ptrace (PTRACE_SETSIGINFO, lwpid_of (thread), (PTRACE_TYPE_ARG3) 0,
		&p_sig.info);

      lwp->pending_signals_to_report.pop_front ();

      threads_debug_printf ("Reporting deferred signal %d for LWP %ld.",
			    WSTOPSIG (*wstat), lwpid_of (thread));

      if (debug_threads)
	{
	  for (const auto &sig : lwp->pending_signals_to_report)
	    threads_debug_printf ("   Still queued %d", sig.signal);

	  threads_debug_printf ("   (no more queued signals)");
	}

      return 1;
    }

  return 0;
}

bool
linux_process_target::check_stopped_by_watchpoint (lwp_info *child)
{
  scoped_restore_current_thread restore_thread;
  switch_to_thread (get_lwp_thread (child));

  if (low_stopped_by_watchpoint ())
    {
      child->stop_reason = TARGET_STOPPED_BY_WATCHPOINT;
      child->stopped_data_address = low_stopped_data_address ();
    }

  return child->stop_reason == TARGET_STOPPED_BY_WATCHPOINT;
}

bool
linux_process_target::low_stopped_by_watchpoint ()
{
  return false;
}

CORE_ADDR
linux_process_target::low_stopped_data_address ()
{
  return 0;
}

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

static int
linux_low_ptrace_options (int attached)
{
  client_state &cs = get_client_state ();
  int options = 0;

  if (!attached)
    options |= PTRACE_O_EXITKILL;

  if (cs.report_fork_events)
    options |= PTRACE_O_TRACEFORK;

  if (cs.report_vfork_events)
    options |= (PTRACE_O_TRACEVFORK | PTRACE_O_TRACEVFORKDONE);

  if (cs.report_exec_events)
    options |= PTRACE_O_TRACEEXEC;

  options |= PTRACE_O_TRACESYSGOOD;

  return options;
}

void
linux_process_target::filter_event (int lwpid, int wstat)
{
  struct lwp_info *child;
  struct thread_info *thread;
  int have_stop_pc = 0;

  child = find_lwp_pid (ptid_t (lwpid));

  /* Check for events reported by anything not in our LWP list.  */
  if (child == nullptr)
    {
      if (WIFSTOPPED (wstat))
	{
	  if (WSTOPSIG (wstat) == SIGTRAP
	      && linux_ptrace_get_extended_event (wstat) == PTRACE_EVENT_EXEC)
	    {
	      /* A non-leader thread exec'ed after we've seen the
		 leader zombie, and removed it from our lists (in
		 check_zombie_leaders).  The non-leader thread changes
		 its tid to the tgid.  */
	      threads_debug_printf
		("Re-adding thread group leader LWP %d after exec.",
		 lwpid);

	      child = add_lwp (ptid_t (lwpid, lwpid));
	      child->stopped = 1;
	      switch_to_thread (child->thread);
	    }
	  else
	    {
	      /* A process we are controlling has forked and the new
		 child's stop was reported to us by the kernel.  Save
		 its PID and go back to waiting for the fork event to
		 be reported - the stopped process might be returned
		 from waitpid before or after the fork event is.  */
	      threads_debug_printf
		("Saving LWP %d status %s in stopped_pids list",
		 lwpid, status_to_str (wstat).c_str ());
	      add_to_pid_list (&stopped_pids, lwpid, wstat);
	    }
	}
      else
	{
	  /* Don't report an event for the exit of an LWP not in our
	     list, i.e. not part of any inferior we're debugging.
	     This can happen if we detach from a program we originally
	     forked and then it exits.  However, note that we may have
	     earlier deleted a leader of an inferior we're debugging,
	     in check_zombie_leaders.  Re-add it back here if so.  */
	  find_process ([&] (process_info *proc)
	    {
	      if (proc->pid == lwpid)
		{
		  threads_debug_printf
		    ("Re-adding thread group leader LWP %d after exit.",
		     lwpid);

		  child = add_lwp (ptid_t (lwpid, lwpid));
		  return true;
		}
	      return false;
	    });
	}

      if (child == nullptr)
	return;
    }

  thread = get_lwp_thread (child);

  child->stopped = 1;

  child->last_status = wstat;

  /* Check if the thread has exited.  */
  if ((WIFEXITED (wstat) || WIFSIGNALED (wstat)))
    {
      threads_debug_printf ("%d exited", lwpid);

      if (finish_step_over (child))
	{
	  /* Unsuspend all other LWPs, and set them back running again.  */
	  unsuspend_all_lwps (child);
	}

      /* If this is not the leader LWP, then the exit signal was not
	 the end of the debugged application and should be ignored,
	 unless GDB wants to hear about thread exits.  */
      if (report_exit_events_for (thread) || is_leader (thread))
	{
	  /* Since events are serialized to GDB core, and we can't
	     report this one right now.  Leave the status pending for
	     the next time we're able to report it.  */
	  mark_lwp_dead (child, wstat, false);
	  return;
	}
      else
	{
	  delete_lwp (child);
	  return;
	}
    }

  gdb_assert (WIFSTOPPED (wstat));

  if (WIFSTOPPED (wstat))
    {
      struct process_info *proc;

      /* Architecture-specific setup after inferior is running.  */
      proc = find_process_pid (pid_of (thread));
      if (proc->tdesc == NULL)
	{
	  if (proc->attached)
	    {
	      /* This needs to happen after we have attached to the
		 inferior and it is stopped for the first time, but
		 before we access any inferior registers.  */
	      arch_setup_thread (thread);
	    }
	  else
	    {
	      /* The process is started, but GDBserver will do
		 architecture-specific setup after the program stops at
		 the first instruction.  */
	      child->status_pending_p = 1;
	      child->status_pending = wstat;
	      return;
	    }
	}
    }

  if (WIFSTOPPED (wstat) && child->must_set_ptrace_flags)
    {
      struct process_info *proc = find_process_pid (pid_of (thread));
      int options = linux_low_ptrace_options (proc->attached);

      linux_enable_event_reporting (lwpid, options);
      child->must_set_ptrace_flags = 0;
    }

  /* Always update syscall_state, even if it will be filtered later.  */
  if (WIFSTOPPED (wstat) && WSTOPSIG (wstat) == SYSCALL_SIGTRAP)
    {
      child->syscall_state
	= (child->syscall_state == TARGET_WAITKIND_SYSCALL_ENTRY
	   ? TARGET_WAITKIND_SYSCALL_RETURN
	   : TARGET_WAITKIND_SYSCALL_ENTRY);
    }
  else
    {
      /* Almost all other ptrace-stops are known to be outside of system
	 calls, with further exceptions in handle_extended_wait.  */
      child->syscall_state = TARGET_WAITKIND_IGNORE;
    }

  /* Be careful to not overwrite stop_pc until save_stop_reason is
     called.  */
  if (WIFSTOPPED (wstat) && WSTOPSIG (wstat) == SIGTRAP
      && linux_is_extended_waitstatus (wstat))
    {
      child->stop_pc = get_pc (child);
      if (handle_extended_wait (&child, wstat))
	{
	  /* The event has been handled, so just return without
	     reporting it.  */
	  return;
	}
    }

  if (linux_wstatus_maybe_breakpoint (wstat))
    {
      if (save_stop_reason (child))
	have_stop_pc = 1;
    }

  if (!have_stop_pc)
    child->stop_pc = get_pc (child);

  if (WIFSTOPPED (wstat) && WSTOPSIG (wstat) == SIGSTOP
      && child->stop_expected)
    {
      threads_debug_printf ("Expected stop.");

      child->stop_expected = 0;

      if (thread->last_resume_kind == resume_stop)
	{
	  /* We want to report the stop to the core.  Treat the
	     SIGSTOP as a normal event.  */
	  threads_debug_printf ("resume_stop SIGSTOP caught for %s.",
				target_pid_to_str (ptid_of (thread)).c_str ());
	}
      else if (stopping_threads != NOT_STOPPING_THREADS)
	{
	  /* Stopping threads.  We don't want this SIGSTOP to end up
	     pending.  */
	  threads_debug_printf ("SIGSTOP caught for %s while stopping threads.",
				target_pid_to_str (ptid_of (thread)).c_str ());
	  return;
	}
      else
	{
	  /* This is a delayed SIGSTOP.  Filter out the event.  */
	  threads_debug_printf ("%s %s, 0, 0 (discard delayed SIGSTOP)",
			  child->stepping ? "step" : "continue",
			  target_pid_to_str (ptid_of (thread)).c_str ());

	  resume_one_lwp (child, child->stepping, 0, NULL);
	  return;
	}
    }

  child->status_pending_p = 1;
  child->status_pending = wstat;
  return;
}

bool
linux_process_target::maybe_hw_step (thread_info *thread)
{
  if (supports_hardware_single_step ())
    return true;
  else
    {
      /* GDBserver must insert single-step breakpoint for software
	 single step.  */
      gdb_assert (has_single_step_breakpoints (thread));
      return false;
    }
}

void
linux_process_target::resume_stopped_resumed_lwps (thread_info *thread)
{
  struct lwp_info *lp = get_thread_lwp (thread);

  if (lp->stopped
      && !lp->suspended
      && !lp->status_pending_p
      && thread->last_status.kind () == TARGET_WAITKIND_IGNORE)
    {
      int step = 0;

      if (thread->last_resume_kind == resume_step)
	{
	  if (supports_software_single_step ())
	    install_software_single_step_breakpoints (lp);

	  step = maybe_hw_step (thread);
	}

      threads_debug_printf ("resuming stopped-resumed LWP %s at %s: step=%d",
			    target_pid_to_str (ptid_of (thread)).c_str (),
			    paddress (lp->stop_pc), step);

      resume_one_lwp (lp, step, GDB_SIGNAL_0, NULL);
    }
}

int
linux_process_target::wait_for_event_filtered (ptid_t wait_ptid,
					       ptid_t filter_ptid,
					       int *wstatp, int options)
{
  struct thread_info *event_thread;
  struct lwp_info *event_child, *requested_child;
  sigset_t block_mask, prev_mask;

 retry:
  /* N.B. event_thread points to the thread_info struct that contains
     event_child.  Keep them in sync.  */
  event_thread = NULL;
  event_child = NULL;
  requested_child = NULL;

  /* Check for a lwp with a pending status.  */

  if (filter_ptid == minus_one_ptid || filter_ptid.is_pid ())
    {
      event_thread = find_thread_in_random ([&] (thread_info *thread)
	{
	  return status_pending_p_callback (thread, filter_ptid);
	});

      if (event_thread != NULL)
	{
	  event_child = get_thread_lwp (event_thread);
	  threads_debug_printf ("Got a pending child %ld", lwpid_of (event_thread));
	}
    }
  else if (filter_ptid != null_ptid)
    {
      requested_child = find_lwp_pid (filter_ptid);
      gdb_assert (requested_child != nullptr);

      if (stopping_threads == NOT_STOPPING_THREADS
	  && requested_child->status_pending_p
	  && (requested_child->collecting_fast_tracepoint
	      != fast_tpoint_collect_result::not_collecting))
	{
	  enqueue_one_deferred_signal (requested_child,
				       &requested_child->status_pending);
	  requested_child->status_pending_p = 0;
	  requested_child->status_pending = 0;
	  resume_one_lwp (requested_child, 0, 0, NULL);
	}

      if (requested_child->suspended
	  && requested_child->status_pending_p)
	{
	  internal_error ("requesting an event out of a"
			  " suspended child?");
	}

      if (requested_child->status_pending_p)
	{
	  event_child = requested_child;
	  event_thread = get_lwp_thread (event_child);
	}
    }

  if (event_child != NULL)
    {
      threads_debug_printf ("Got an event from pending child %ld (%04x)",
			    lwpid_of (event_thread),
			    event_child->status_pending);

      *wstatp = event_child->status_pending;
      event_child->status_pending_p = 0;
      event_child->status_pending = 0;
      switch_to_thread (event_thread);
      return lwpid_of (event_thread);
    }

  /* But if we don't find a pending event, we'll have to wait.

     We only enter this loop if no process has a pending wait status.
     Thus any action taken in response to a wait status inside this
     loop is responding as soon as we detect the status, not after any
     pending events.  */

  /* Make sure SIGCHLD is blocked until the sigsuspend below.  Block
     all signals while here.  */
  sigfillset (&block_mask);
  gdb_sigmask (SIG_BLOCK, &block_mask, &prev_mask);

  /* Always pull all events out of the kernel.  We'll randomly select
     an event LWP out of all that have events, to prevent
     starvation.  */
  while (event_child == NULL)
    {
      pid_t ret = 0;

      /* Always use -1 and WNOHANG, due to couple of a kernel/ptrace
	 quirks:

	 - 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 reported to
	   the TGID pid.  */
      errno = 0;
      ret = my_waitpid (-1, wstatp, options | WNOHANG);

      threads_debug_printf ("waitpid(-1, ...) returned %d, %s",
			    ret, errno ? safe_strerror (errno) : "ERRNO-OK");

      if (ret > 0)
	{
	  threads_debug_printf ("waitpid %ld received %s",
				(long) ret, status_to_str (*wstatp).c_str ());

	  /* Filter all events.  IOW, leave all events pending.  We'll
	     randomly select an event LWP out of all that have events
	     below.  */
	  filter_event (ret, *wstatp);
	  /* Retry until nothing comes out of waitpid.  A single
	     SIGCHLD can indicate more than one child stopped.  */
	  continue;
	}

      /* Now that we've pulled all events out of the kernel, resume
	 LWPs that don't have an interesting event to report.  */
      if (stopping_threads == NOT_STOPPING_THREADS)
	for_each_thread ([this] (thread_info *thread)
	  {
	    resume_stopped_resumed_lwps (thread);
	  });

      /* ... and find an LWP with a status to report to the core, if
	 any.  */
      event_thread = find_thread_in_random ([&] (thread_info *thread)
	{
	  return status_pending_p_callback (thread, filter_ptid);
	});

      if (event_thread != NULL)
	{
	  event_child = get_thread_lwp (event_thread);
	  *wstatp = event_child->status_pending;
	  event_child->status_pending_p = 0;
	  event_child->status_pending = 0;
	  break;
	}

      /* Check for zombie thread group leaders.  Those can't be reaped
	 until all other threads in the thread group are.  */
      if (check_zombie_leaders ())
	goto retry;

      auto not_stopped = [&] (thread_info *thread)
	{
	  return not_stopped_callback (thread, wait_ptid);
	};

      /* If there are no resumed children left in the set of LWPs we
	 want to wait for, bail.  We can't just block in
	 waitpid/sigsuspend, because lwps might have been left stopped
	 in trace-stop state, and we'd be stuck forever waiting for
	 their status to change (which would only happen if we resumed
	 them).  Even if WNOHANG is set, this return code is preferred
	 over 0 (below), as it is more detailed.  */
      if (find_thread (not_stopped) == NULL)
	{
	  threads_debug_printf ("exit (no unwaited-for LWP)");

	  gdb_sigmask (SIG_SETMASK, &prev_mask, NULL);
	  return -1;
	}

      /* No interesting event to report to the caller.  */
      if ((options & WNOHANG))
	{
	  threads_debug_printf ("WNOHANG set, no event found");

	  gdb_sigmask (SIG_SETMASK, &prev_mask, NULL);
	  return 0;
	}

      /* Block until we get an event reported with SIGCHLD.  */
      threads_debug_printf ("sigsuspend'ing");

      sigsuspend (&prev_mask);
      gdb_sigmask (SIG_SETMASK, &prev_mask, NULL);
      goto retry;
    }

  gdb_sigmask (SIG_SETMASK, &prev_mask, NULL);

  switch_to_thread (event_thread);

  return lwpid_of (event_thread);
}

int
linux_process_target::wait_for_event (ptid_t ptid, int *wstatp, int options)
{
  return wait_for_event_filtered (ptid, ptid, wstatp, options);
}

/* Select one LWP out of those that have events pending.  */

static void
select_event_lwp (struct lwp_info **orig_lp)
{
  struct thread_info *event_thread = NULL;

  /* In all-stop, give preference to the LWP that is being
     single-stepped.  There will be at most one, and it's the LWP that
     the core is most interested in.  If we didn't do this, then we'd
     have to handle pending step SIGTRAPs somehow in case the core
     later continues the previously-stepped thread, otherwise we'd
     report the pending SIGTRAP, and the core, not having stepped the
     thread, wouldn't understand what the trap was for, and therefore
     would report it to the user as a random signal.  */
  if (!non_stop)
    {
      event_thread = find_thread ([] (thread_info *thread)
	{
	  lwp_info *lp = get_thread_lwp (thread);

	  return (thread->last_status.kind () == TARGET_WAITKIND_IGNORE
		  && thread->last_resume_kind == resume_step
		  && lp->status_pending_p);
	});

      if (event_thread != NULL)
	threads_debug_printf
	  ("Select single-step %s",
	   target_pid_to_str (ptid_of (event_thread)).c_str ());
    }
  if (event_thread == NULL)
    {
      /* No single-stepping LWP.  Select one at random, out of those
	 which have had events.  */

      event_thread = find_thread_in_random ([&] (thread_info *thread)
	{
	  lwp_info *lp = get_thread_lwp (thread);

	  /* Only resumed LWPs that have an event pending. */
	  return (thread->last_status.kind () == TARGET_WAITKIND_IGNORE
		  && lp->status_pending_p);
	});
    }

  if (event_thread != NULL)
    {
      struct lwp_info *event_lp = get_thread_lwp (event_thread);

      /* Switch the event LWP.  */
      *orig_lp = event_lp;
    }
}

/* Decrement the suspend count of all LWPs, except EXCEPT, if non
   NULL.  */

static void
unsuspend_all_lwps (struct lwp_info *except)
{
  for_each_thread ([&] (thread_info *thread)
    {
      lwp_info *lwp = get_thread_lwp (thread);

      if (lwp != except)
	lwp_suspended_decr (lwp);
    });
}

static bool lwp_running (thread_info *thread);

/* Stabilize threads (move out of jump pads).

   If a thread is midway collecting a fast tracepoint, we need to
   finish the collection and move it out of the jump pad before
   reporting the signal.

   This avoids recursion while collecting (when a signal arrives
   midway, and the signal handler itself collects), which would trash
   the trace buffer.  In case the user set a breakpoint in a signal
   handler, this avoids the backtrace showing the jump pad, etc..
   Most importantly, there are certain things we can't do safely if
   threads are stopped in a jump pad (or in its callee's).  For
   example:

     - starting a new trace run.  A thread still collecting the
   previous run, could trash the trace buffer when resumed.  The trace
   buffer control structures would have been reset but the thread had
   no way to tell.  The thread could even midway memcpy'ing to the
   buffer, which would mean that when resumed, it would clobber the
   trace buffer that had been set for a new run.

     - we can't rewrite/reuse the jump pads for new tracepoints
   safely.  Say you do tstart while a thread is stopped midway while
   collecting.  When the thread is later resumed, it finishes the
   collection, and returns to the jump pad, to execute the original
   instruction that was under the tracepoint jump at the time the
   older run had been started.  If the jump pad had been rewritten
   since for something else in the new run, the thread would now
   execute the wrong / random instructions.  */

void
linux_process_target::stabilize_threads ()
{
  thread_info *thread_stuck = find_thread ([this] (thread_info *thread)
				{
				  return stuck_in_jump_pad (thread);
				});

  if (thread_stuck != NULL)
    {
      threads_debug_printf ("can't stabilize, LWP %ld is stuck in jump pad",
			    lwpid_of (thread_stuck));
      return;
    }

  scoped_restore_current_thread restore_thread;

  stabilizing_threads = 1;

  /* Kick 'em all.  */
  for_each_thread ([this] (thread_info *thread)
    {
      move_out_of_jump_pad (thread);
    });

  /* Loop until all are stopped out of the jump pads.  */
  while (find_thread (lwp_running) != NULL)
    {
      struct target_waitstatus ourstatus;
      struct lwp_info *lwp;
      int wstat;

      /* Note that we go through the full wait even loop.  While
	 moving threads out of jump pad, we need to be able to step
	 over internal breakpoints and such.  */
      wait_1 (minus_one_ptid, &ourstatus, 0);

      if (ourstatus.kind () == TARGET_WAITKIND_STOPPED)
	{
	  lwp = get_thread_lwp (current_thread);

	  /* Lock it.  */
	  lwp_suspended_inc (lwp);

	  if (ourstatus.sig () != GDB_SIGNAL_0
	      || current_thread->last_resume_kind == resume_stop)
	    {
	      wstat = W_STOPCODE (gdb_signal_to_host (ourstatus.sig ()));
	      enqueue_one_deferred_signal (lwp, &wstat);
	    }
	}
    }

  unsuspend_all_lwps (NULL);

  stabilizing_threads = 0;

  if (debug_threads)
    {
      thread_stuck = find_thread ([this] (thread_info *thread)
		       {
			 return stuck_in_jump_pad (thread);
		       });

      if (thread_stuck != NULL)
	threads_debug_printf
	  ("couldn't stabilize, LWP %ld got stuck in jump pad",
	   lwpid_of (thread_stuck));
    }
}

/* Convenience function that is called when the kernel reports an
   event that is not passed out to GDB.  */

static ptid_t
ignore_event (struct target_waitstatus *ourstatus)
{
  /* If we got an event, there may still be others, as a single
     SIGCHLD can indicate more than one child stopped.  This forces
     another target_wait call.  */
  async_file_mark ();

  ourstatus->set_ignore ();
  return null_ptid;
}

ptid_t
linux_process_target::filter_exit_event (lwp_info *event_child,
					 target_waitstatus *ourstatus)
{
  struct thread_info *thread = get_lwp_thread (event_child);
  ptid_t ptid = ptid_of (thread);

  if (ourstatus->kind () == TARGET_WAITKIND_THREAD_EXITED)
    {
      /* We're reporting a thread exit for the leader.  The exit was
	 detected by check_zombie_leaders.  */
      gdb_assert (is_leader (thread));
      gdb_assert (report_exit_events_for (thread));

      delete_lwp (event_child);
      return ptid;
    }

  /* Note we must filter TARGET_WAITKIND_SIGNALLED as well, otherwise
     if a non-leader thread exits with a signal, we'd report it to the
     core which would interpret it as the whole-process exiting.
     There is no TARGET_WAITKIND_THREAD_SIGNALLED event kind.  */
  if (ourstatus->kind () != TARGET_WAITKIND_EXITED
      && ourstatus->kind () != TARGET_WAITKIND_SIGNALLED)
    return ptid;

  if (!is_leader (thread))
    {
      if (report_exit_events_for (thread))
	ourstatus->set_thread_exited (0);
      else
	ourstatus->set_ignore ();

      delete_lwp (event_child);
    }
  return ptid;
}

/* Returns 1 if GDB is interested in any event_child syscalls.  */

static int
gdb_catching_syscalls_p (struct lwp_info *event_child)
{
  struct thread_info *thread = get_lwp_thread (event_child);
  struct process_info *proc = get_thread_process (thread);

  return !proc->syscalls_to_catch.empty ();
}

bool
linux_process_target::gdb_catch_this_syscall (lwp_info *event_child)
{
  int sysno;
  struct thread_info *thread = get_lwp_thread (event_child);
  struct process_info *proc = get_thread_process (thread);

  if (proc->syscalls_to_catch.empty ())
    return false;

  if (proc->syscalls_to_catch[0] == ANY_SYSCALL)
    return true;

  get_syscall_trapinfo (event_child, &sysno);

  for (int iter : proc->syscalls_to_catch)
    if (iter == sysno)
      return true;

  return false;
}

ptid_t
linux_process_target::wait_1 (ptid_t ptid, target_waitstatus *ourstatus,
			      target_wait_flags target_options)
{
  THREADS_SCOPED_DEBUG_ENTER_EXIT;

  client_state &cs = get_client_state ();
  int w;
  struct lwp_info *event_child;
  int options;
  int pid;
  int step_over_finished;
  int bp_explains_trap;
  int maybe_internal_trap;
  int report_to_gdb;
  int trace_event;
  int in_step_range;

  threads_debug_printf ("[%s]", target_pid_to_str (ptid).c_str ());

  /* Translate generic target options into linux options.  */
  options = __WALL;
  if (target_options & TARGET_WNOHANG)
    options |= WNOHANG;

  bp_explains_trap = 0;
  trace_event = 0;
  in_step_range = 0;
  ourstatus->set_ignore ();

  bool was_any_resumed = any_resumed ();

  if (step_over_bkpt == null_ptid)
    pid = wait_for_event (ptid, &w, options);
  else
    {
      threads_debug_printf ("step_over_bkpt set [%s], doing a blocking wait",
			    target_pid_to_str (step_over_bkpt).c_str ());
      pid = wait_for_event (step_over_bkpt, &w, options & ~WNOHANG);
    }

  if (pid == 0 || (pid == -1 && !was_any_resumed))
    {
      gdb_assert (target_options & TARGET_WNOHANG);

      threads_debug_printf ("ret = null_ptid, TARGET_WAITKIND_IGNORE");

      ourstatus->set_ignore ();
      return null_ptid;
    }
  else if (pid == -1)
    {
      threads_debug_printf ("ret = null_ptid, TARGET_WAITKIND_NO_RESUMED");

      ourstatus->set_no_resumed ();
      return null_ptid;
    }

  event_child = get_thread_lwp (current_thread);

  /* wait_for_event only returns an exit status for the last
     child of a process.  Report it.  */
  if (WIFEXITED (w) || WIFSIGNALED (w))
    {
      if (WIFEXITED (w))
	{
	  /* If we already have the exit recorded in waitstatus, use
	     it.  This will happen when we detect a zombie leader,
	     when we had GDB_THREAD_OPTION_EXIT enabled for it.  We
	     want to report its exit as TARGET_WAITKIND_THREAD_EXITED,
	     as the whole process hasn't exited yet.  */
	  const target_waitstatus &ws = event_child->waitstatus;
	  if (ws.kind () != TARGET_WAITKIND_IGNORE)
	    {
	      gdb_assert (ws.kind () == TARGET_WAITKIND_EXITED
			  || ws.kind () == TARGET_WAITKIND_THREAD_EXITED);
	      *ourstatus = ws;
	    }
	  else
	    ourstatus->set_exited (WEXITSTATUS (w));

	  threads_debug_printf
	    ("ret = %s, exited with retcode %d",
	     target_pid_to_str (ptid_of (current_thread)).c_str (),
	     WEXITSTATUS (w));
	}
      else
	{
	  ourstatus->set_signalled (gdb_signal_from_host (WTERMSIG (w)));

	  threads_debug_printf
	    ("ret = %s, terminated with signal %d",
	     target_pid_to_str (ptid_of (current_thread)).c_str (),
	     WTERMSIG (w));
	}

      return filter_exit_event (event_child, ourstatus);
    }

  /* If step-over executes a breakpoint instruction, in the case of a
     hardware single step it means a gdb/gdbserver breakpoint had been
     planted on top of a permanent breakpoint, in the case of a software
     single step it may just mean that gdbserver hit the reinsert breakpoint.
     The PC has been adjusted by save_stop_reason to point at
     the breakpoint address.
     So in the case of the hardware single step advance the PC manually
     past the breakpoint and in the case of software single step advance only
     if it's not the single_step_breakpoint we are hitting.
     This avoids that a program would keep trapping a permanent breakpoint
     forever.  */
  if (step_over_bkpt != null_ptid
      && event_child->stop_reason == TARGET_STOPPED_BY_SW_BREAKPOINT
      && (event_child->stepping
	  || !single_step_breakpoint_inserted_here (event_child->stop_pc)))
    {
      int increment_pc = 0;
      int breakpoint_kind = 0;
      CORE_ADDR stop_pc = event_child->stop_pc;

      breakpoint_kind = breakpoint_kind_from_current_state (&stop_pc);
      sw_breakpoint_from_kind (breakpoint_kind, &increment_pc);

      threads_debug_printf
	("step-over for %s executed software breakpoint",
	 target_pid_to_str (ptid_of (current_thread)).c_str ());

      if (increment_pc != 0)
	{
	  struct regcache *regcache
	    = get_thread_regcache (current_thread, 1);

	  event_child->stop_pc += increment_pc;
	  low_set_pc (regcache, event_child->stop_pc);

	  if (!low_breakpoint_at (event_child->stop_pc))
	    event_child->stop_reason = TARGET_STOPPED_BY_NO_REASON;
	}
    }

  /* If this event was not handled before, and is not a SIGTRAP, we
     report it.  SIGILL and SIGSEGV are also treated as traps in case
     a breakpoint is inserted at the current PC.  If this target does
     not support internal breakpoints at all, we also report the
     SIGTRAP without further processing; it's of no concern to us.  */
  maybe_internal_trap
    = (low_supports_breakpoints ()
       && (WSTOPSIG (w) == SIGTRAP
	   || ((WSTOPSIG (w) == SIGILL
		|| WSTOPSIG (w) == SIGSEGV)
	       && low_breakpoint_at (event_child->stop_pc))));

  if (maybe_internal_trap)
    {
      /* Handle anything that requires bookkeeping before deciding to
	 report the event or continue waiting.  */

      /* First check if we can explain the SIGTRAP with an internal
	 breakpoint, or if we should possibly report the event to GDB.
	 Do this before anything that may remove or insert a
	 breakpoint.  */
      bp_explains_trap = breakpoint_inserted_here (event_child->stop_pc);

      /* We have a SIGTRAP, possibly a step-over dance has just
	 finished.  If so, tweak the state machine accordingly,
	 reinsert breakpoints and delete any single-step
	 breakpoints.  */
      step_over_finished = finish_step_over (event_child);

      /* Now invoke the callbacks of any internal breakpoints there.  */
      check_breakpoints (event_child->stop_pc);

      /* Handle tracepoint data collecting.  This may overflow the
	 trace buffer, and cause a tracing stop, removing
	 breakpoints.  */
      trace_event = handle_tracepoints (event_child);

      if (bp_explains_trap)
	threads_debug_printf ("Hit a gdbserver breakpoint.");
    }
  else
    {
      /* We have some other signal, possibly a step-over dance was in
	 progress, and it should be cancelled too.  */
      step_over_finished = finish_step_over (event_child);
    }

  /* We have all the data we need.  Either report the event to GDB, or
     resume threads and keep waiting for more.  */

  /* If we're collecting a fast tracepoint, finish the collection and
     move out of the jump pad before delivering a signal.  See
     linux_stabilize_threads.  */

  if (WIFSTOPPED (w)
      && WSTOPSIG (w) != SIGTRAP
      && supports_fast_tracepoints ()
      && agent_loaded_p ())
    {
      threads_debug_printf ("Got signal %d for LWP %ld.  Check if we need "
			    "to defer or adjust it.",
			    WSTOPSIG (w), lwpid_of (current_thread));

      /* Allow debugging the jump pad itself.  */
      if (current_thread->last_resume_kind != resume_step
	  && maybe_move_out_of_jump_pad (event_child, &w))
	{
	  enqueue_one_deferred_signal (event_child, &w);

	  threads_debug_printf ("Signal %d for LWP %ld deferred (in jump pad)",
				WSTOPSIG (w), lwpid_of (current_thread));

	  resume_one_lwp (event_child, 0, 0, NULL);

	  return ignore_event (ourstatus);
	}
    }

  if (event_child->collecting_fast_tracepoint
      != fast_tpoint_collect_result::not_collecting)
    {
      threads_debug_printf
	("LWP %ld was trying to move out of the jump pad (%d). "
	 "Check if we're already there.",
	 lwpid_of (current_thread),
	 (int) event_child->collecting_fast_tracepoint);

      trace_event = 1;

      event_child->collecting_fast_tracepoint
	= linux_fast_tracepoint_collecting (event_child, NULL);

      if (event_child->collecting_fast_tracepoint
	  != fast_tpoint_collect_result::before_insn)
	{
	  /* No longer need this breakpoint.  */
	  if (event_child->exit_jump_pad_bkpt != NULL)
	    {
	      threads_debug_printf
		("No longer need exit-jump-pad bkpt; removing it."
		 "stopping all threads momentarily.");

	      /* Other running threads could hit this breakpoint.
		 We don't handle moribund locations like GDB does,
		 instead we always pause all threads when removing
		 breakpoints, so that any step-over or
		 decr_pc_after_break adjustment is always taken
		 care of while the breakpoint is still
		 inserted.  */
	      stop_all_lwps (1, event_child);

	      delete_breakpoint (event_child->exit_jump_pad_bkpt);
	      event_child->exit_jump_pad_bkpt = NULL;

	      unstop_all_lwps (1, event_child);

	      gdb_assert (event_child->suspended >= 0);
	    }
	}

      if (event_child->collecting_fast_tracepoint
	  == fast_tpoint_collect_result::not_collecting)
	{
	  threads_debug_printf
	    ("fast tracepoint finished collecting successfully.");

	  /* We may have a deferred signal to report.  */
	  if (dequeue_one_deferred_signal (event_child, &w))
	    threads_debug_printf ("dequeued one signal.");
	  else
	    {
	      threads_debug_printf ("no deferred signals.");

	      if (stabilizing_threads)
		{
		  ourstatus->set_stopped (GDB_SIGNAL_0);

		  threads_debug_printf
		    ("ret = %s, stopped while stabilizing threads",
		     target_pid_to_str (ptid_of (current_thread)).c_str ());

		  return ptid_of (current_thread);
		}
	    }
	}
    }

  /* Check whether GDB would be interested in this event.  */

  /* Check if GDB is interested in this syscall.  */
  if (WIFSTOPPED (w)
      && WSTOPSIG (w) == SYSCALL_SIGTRAP
      && !gdb_catch_this_syscall (event_child))
    {
      threads_debug_printf ("Ignored syscall for LWP %ld.",
			    lwpid_of (current_thread));

      resume_one_lwp (event_child, event_child->stepping, 0, NULL);

      return ignore_event (ourstatus);
    }

  /* If GDB is not interested in this signal, don't stop other
     threads, and don't report it to GDB.  Just resume the inferior
     right away.  We do this for threading-related signals as well as
     any that GDB specifically requested we ignore.  But never ignore
     SIGSTOP if we sent it ourselves, and do not ignore signals when
     stepping - they may require special handling to skip the signal
     handler. Also never ignore signals that could be caused by a
     breakpoint.  */
  if (WIFSTOPPED (w)
      && current_thread->last_resume_kind != resume_step
      && (
#if defined (USE_THREAD_DB) && !defined (__ANDROID__)
	  (current_process ()->priv->thread_db != NULL
	   && (WSTOPSIG (w) == __SIGRTMIN
	       || WSTOPSIG (w) == __SIGRTMIN + 1))
	  ||
#endif
	  (cs.pass_signals[gdb_signal_from_host (WSTOPSIG (w))]
	   && !(WSTOPSIG (w) == SIGSTOP
		&& current_thread->last_resume_kind == resume_stop)
	   && !linux_wstatus_maybe_breakpoint (w))))
    {
      siginfo_t info, *info_p;

      threads_debug_printf ("Ignored signal %d for LWP %ld.",
			    WSTOPSIG (w), lwpid_of (current_thread));

      if (ptrace (PTRACE_GETSIGINFO, lwpid_of (current_thread),
		  (PTRACE_TYPE_ARG3) 0, &info) == 0)
	info_p = &info;
      else
	info_p = NULL;

      if (step_over_finished)
	{
	  /* We cancelled this thread's step-over above.  We still
	     need to unsuspend all other LWPs, and set them back
	     running again while the signal handler runs.  */
	  unsuspend_all_lwps (event_child);

	  /* Enqueue the pending signal info so that proceed_all_lwps
	     doesn't lose it.  */
	  enqueue_pending_signal (event_child, WSTOPSIG (w), info_p);

	  proceed_all_lwps ();
	}
      else
	{
	  resume_one_lwp (event_child, event_child->stepping,
			  WSTOPSIG (w), info_p);
	}

      return ignore_event (ourstatus);
    }

  /* Note that all addresses are always "out of the step range" when
     there's no range to begin with.  */
  in_step_range = lwp_in_step_range (event_child);

  /* If GDB wanted this thread to single step, and the thread is out
     of the step range, we always want to report the SIGTRAP, and let
     GDB handle it.  Watchpoints should always be reported.  So should
     signals we can't explain.  A SIGTRAP we can't explain could be a
     GDB breakpoint --- we may or not support Z0 breakpoints.  If we
     do, we're be able to handle GDB breakpoints on top of internal
     breakpoints, by handling the internal breakpoint and still
     reporting the event to GDB.  If we don't, we're out of luck, GDB
     won't see the breakpoint hit.  If we see a single-step event but
     the thread should be continuing, don't pass the trap to gdb.
     That indicates that we had previously finished a single-step but
     left the single-step pending -- see
     complete_ongoing_step_over.  */
  report_to_gdb = (!maybe_internal_trap
		   || (current_thread->last_resume_kind == resume_step
		       && !in_step_range)
		   || event_child->stop_reason == TARGET_STOPPED_BY_WATCHPOINT
		   || (!in_step_range
		       && !bp_explains_trap
		       && !trace_event
		       && !step_over_finished
		       && !(current_thread->last_resume_kind == resume_continue
			    && event_child->stop_reason == TARGET_STOPPED_BY_SINGLE_STEP))
		   || (gdb_breakpoint_here (event_child->stop_pc)
		       && gdb_condition_true_at_breakpoint (event_child->stop_pc)
		       && gdb_no_commands_at_breakpoint (event_child->stop_pc))
		   || event_child->waitstatus.kind () != TARGET_WAITKIND_IGNORE);

  run_breakpoint_commands (event_child->stop_pc);

  /* We found no reason GDB would want us to stop.  We either hit one
     of our own breakpoints, or finished an internal step GDB
     shouldn't know about.  */
  if (!report_to_gdb)
    {
      if (bp_explains_trap)
	threads_debug_printf ("Hit a gdbserver breakpoint.");

      if (step_over_finished)
	threads_debug_printf ("Step-over finished.");

      if (trace_event)
	threads_debug_printf ("Tracepoint event.");

      if (lwp_in_step_range (event_child))
	threads_debug_printf ("Range stepping pc 0x%s [0x%s, 0x%s).",
			      paddress (event_child->stop_pc),
			      paddress (event_child->step_range_start),
			      paddress (event_child->step_range_end));

      /* We're not reporting this breakpoint to GDB, so apply the
	 decr_pc_after_break adjustment to the inferior's regcache
	 ourselves.  */

      if (low_supports_breakpoints ())
	{
	  struct regcache *regcache
	    = get_thread_regcache (current_thread, 1);
	  low_set_pc (regcache, event_child->stop_pc);
	}

      if (step_over_finished)
	{
	  /* If we have finished stepping over a breakpoint, we've
	     stopped and suspended all LWPs momentarily except the
	     stepping one.  This is where we resume them all again.
	     We're going to keep waiting, so use proceed, which
	     handles stepping over the next breakpoint.  */
	  unsuspend_all_lwps (event_child);
	}
      else
	{
	  /* Remove the single-step breakpoints if any.  Note that
	     there isn't single-step breakpoint if we finished stepping
	     over.  */
	  if (supports_software_single_step ()