gdb: fix shellcheck warnings SC2166 (&& and !! instead of -a and -o) in gdbarch.sh

[thirdparty/binutils-gdb.git] / gdb / nbsd-nat.c

/* Native-dependent code for NetBSD.

   Copyright (C) 2006-2020 Free Software Foundation, Inc.

   This file is part of GDB.

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

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

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

#include "defs.h"

#include "nbsd-nat.h"
#include "gdbthread.h"
#include "nbsd-tdep.h"
#include "inferior.h"
#include "gdbarch.h"

#include <sys/types.h>
#include <sys/ptrace.h>
#include <sys/sysctl.h>
#include <sys/wait.h>

/* Return the name of a file that can be opened to get the symbols for
   the child process identified by PID.  */

char *
nbsd_nat_target::pid_to_exec_file (int pid)
{
  static char buf[PATH_MAX];
  size_t buflen;
  int mib[4] = {CTL_KERN, KERN_PROC_ARGS, pid, KERN_PROC_PATHNAME};
  buflen = sizeof (buf);
  if (sysctl (mib, ARRAY_SIZE (mib), buf, &buflen, NULL, 0))
    return NULL;
  return buf;
}

/* Return the current directory for the process identified by PID.  */

static std::string
nbsd_pid_to_cwd (int pid)
{
  char buf[PATH_MAX];
  size_t buflen;
  int mib[4] = {CTL_KERN, KERN_PROC_ARGS, pid, KERN_PROC_CWD};
  buflen = sizeof (buf);
  if (sysctl (mib, ARRAY_SIZE (mib), buf, &buflen, NULL, 0))
    return "";
  return buf;
}

/* Return the kinfo_proc2 structure for the process identified by PID.  */

static bool
nbsd_pid_to_kinfo_proc2 (pid_t pid, struct kinfo_proc2 *kp)
{
  gdb_assert (kp != nullptr);

  size_t size = sizeof (*kp);
  int mib[6] = {CTL_KERN, KERN_PROC2, KERN_PROC_PID, pid,
		static_cast<int> (size), 1};
  return !sysctl (mib, ARRAY_SIZE (mib), kp, &size, NULL, 0);
}

/* Return the command line for the process identified by PID.  */

static gdb::unique_xmalloc_ptr<char[]>
nbsd_pid_to_cmdline (int pid)
{
  int mib[4] = {CTL_KERN, KERN_PROC_ARGS, pid, KERN_PROC_ARGV};

  size_t size = 0;
  if (sysctl (mib, ARRAY_SIZE (mib), NULL, &size, NULL, 0) == -1 || size == 0)
    return nullptr;

  gdb::unique_xmalloc_ptr<char[]> args (XNEWVAR (char, size));

  if (sysctl (mib, ARRAY_SIZE (mib), args.get (), &size, NULL, 0) == -1
      || size == 0)
    return nullptr;

  /* Arguments are returned as a flattened string with NUL separators.
     Join the arguments with spaces to form a single string.  */
  for (size_t i = 0; i < size - 1; i++)
    if (args[i] == '\0')
      args[i] = ' ';
  args[size - 1] = '\0';

  return args;
}

/* Generic thread (LWP) lister within a specified process.  The callback
   parameters is a C++ function that is called for each detected thread.  */

static bool
nbsd_thread_lister (const pid_t pid,
		    gdb::function_view<bool (const struct kinfo_lwp *)>
		    callback)
{
  int mib[5] = {CTL_KERN, KERN_LWP, pid, sizeof (struct kinfo_lwp), 0};
  size_t size;

  if (sysctl (mib, ARRAY_SIZE (mib), NULL, &size, NULL, 0) == -1 || size == 0)
    perror_with_name (("sysctl"));

  mib[4] = size / sizeof (size_t);

  gdb::unique_xmalloc_ptr<struct kinfo_lwp[]> kl
    ((struct kinfo_lwp *) xcalloc (size, 1));

  if (sysctl (mib, ARRAY_SIZE (mib), kl.get (), &size, NULL, 0) == -1
      || size == 0)
    perror_with_name (("sysctl"));

  for (size_t i = 0; i < size / sizeof (struct kinfo_lwp); i++)
    {
      struct kinfo_lwp *l = &kl[i];

      /* Return true if the specified thread is alive.  */
      auto lwp_alive
	= [] (struct kinfo_lwp *lwp)
	  {
	    switch (lwp->l_stat)
	      {
	      case LSSLEEP:
	      case LSRUN:
	      case LSONPROC:
	      case LSSTOP:
	      case LSSUSPENDED:
		return true;
	      default:
		return false;
	      }
	  };

      /* Ignore embryonic or demised threads.  */
      if (!lwp_alive (l))
	continue;

      if (callback (l))
	return true;
    }

  return false;
}

/* Return true if PTID is still active in the inferior.  */

bool
nbsd_nat_target::thread_alive (ptid_t ptid)
{
  pid_t pid = ptid.pid ();
  int lwp = ptid.lwp ();

  auto fn
    = [&lwp] (const struct kinfo_lwp *kl)
      {
        return kl->l_lid == lwp;
      };

  return nbsd_thread_lister (pid, fn);
}

/* Return the name assigned to a thread by an application.  Returns
   the string in a static buffer.  */

const char *
nbsd_nat_target::thread_name (struct thread_info *thr)
{
  ptid_t ptid = thr->ptid;
  pid_t pid = ptid.pid ();
  int lwp = ptid.lwp ();

  static char buf[KI_LNAMELEN] = {};

  auto fn
    = [&lwp] (const struct kinfo_lwp *kl)
      {
	if (kl->l_lid == lwp)
	  {
	    xsnprintf (buf, sizeof buf, "%s", kl->l_name);
	    return true;
	  }
	return false;
      };

  if (nbsd_thread_lister (pid, fn))
    return buf;
  else
    return NULL;
}

/* Implement the "post_attach" target_ops method.  */

static void
nbsd_add_threads (nbsd_nat_target *target, pid_t pid)
{
  auto fn
    = [&target, &pid] (const struct kinfo_lwp *kl)
      {
	ptid_t ptid = ptid_t (pid, kl->l_lid, 0);
	if (!in_thread_list (target, ptid))
	  {
	    if (inferior_ptid.lwp () == 0)
	      thread_change_ptid (target, inferior_ptid, ptid);
	    else
	      add_thread (target, ptid);
	  }
	return false;
      };

  nbsd_thread_lister (pid, fn);
}

/* Implement the "post_attach" target_ops method.  */

void
nbsd_nat_target::post_attach (int pid)
{
  nbsd_add_threads (this, pid);
}

/* Implement the "update_thread_list" target_ops method.  */

void
nbsd_nat_target::update_thread_list ()
{
  prune_threads ();

  nbsd_add_threads (this, inferior_ptid.pid ());
}

/* Convert PTID to a string.  */

std::string
nbsd_nat_target::pid_to_str (ptid_t ptid)
{
  int lwp = ptid.lwp ();

  if (lwp != 0)
    {
      pid_t pid = ptid.pid ();

      return string_printf ("LWP %d of process %d", lwp, pid);
    }

  return normal_pid_to_str (ptid);
}

/* Retrieve all the memory regions in the specified process.  */

static gdb::unique_xmalloc_ptr<struct kinfo_vmentry[]>
nbsd_kinfo_get_vmmap (pid_t pid, size_t *size)
{
  int mib[5] = {CTL_VM, VM_PROC, VM_PROC_MAP, pid,
		sizeof (struct kinfo_vmentry)};

  size_t length = 0;
  if (sysctl (mib, ARRAY_SIZE (mib), NULL, &length, NULL, 0))
    {
      *size = 0;
      return NULL;
    }

  /* Prereserve more space.  The length argument is volatile and can change
     between the sysctl(3) calls as this function can be called against a
     running process.  */
  length = length * 5 / 3;

  gdb::unique_xmalloc_ptr<struct kinfo_vmentry[]> kiv
    (XNEWVAR (kinfo_vmentry, length));

  if (sysctl (mib, ARRAY_SIZE (mib), kiv.get (), &length, NULL, 0))
    {
      *size = 0;
      return NULL;
    }

  *size = length / sizeof (struct kinfo_vmentry);
  return kiv;
}

/* Iterate over all the memory regions in the current inferior,
   calling FUNC for each memory region.  OBFD is passed as the last
   argument to FUNC.  */

int
nbsd_nat_target::find_memory_regions (find_memory_region_ftype func,
				      void *data)
{
  pid_t pid = inferior_ptid.pid ();

  size_t nitems;
  gdb::unique_xmalloc_ptr<struct kinfo_vmentry[]> vmentl
    = nbsd_kinfo_get_vmmap (pid, &nitems);
  if (vmentl == NULL)
    perror_with_name (_("Couldn't fetch VM map entries."));

  for (size_t i = 0; i < nitems; i++)
    {
      struct kinfo_vmentry *kve = &vmentl[i];

      /* Skip unreadable segments and those where MAP_NOCORE has been set.  */
      if (!(kve->kve_protection & KVME_PROT_READ)
	  || kve->kve_flags & KVME_FLAG_NOCOREDUMP)
	continue;

      /* Skip segments with an invalid type.  */
      switch (kve->kve_type)
	{
	case KVME_TYPE_VNODE:
	case KVME_TYPE_ANON:
	case KVME_TYPE_SUBMAP:
	case KVME_TYPE_OBJECT:
	  break;
	default:
	  continue;
	}

      size_t size = kve->kve_end - kve->kve_start;
      if (info_verbose)
	{
	  fprintf_filtered (gdb_stdout,
			    "Save segment, %ld bytes at %s (%c%c%c)\n",
			    (long) size,
			    paddress (target_gdbarch (), kve->kve_start),
			    kve->kve_protection & KVME_PROT_READ ? 'r' : '-',
			    kve->kve_protection & KVME_PROT_WRITE ? 'w' : '-',
			    kve->kve_protection & KVME_PROT_EXEC ? 'x' : '-');
	}

      /* Invoke the callback function to create the corefile segment.
	 Pass MODIFIED as true, we do not know the real modification state.  */
      func (kve->kve_start, size, kve->kve_protection & KVME_PROT_READ,
	    kve->kve_protection & KVME_PROT_WRITE,
	    kve->kve_protection & KVME_PROT_EXEC, 1, data);
    }
  return 0;
}

/* Implement the "info_proc" target_ops method.  */

bool
nbsd_nat_target::info_proc (const char *args, enum info_proc_what what)
{
  pid_t pid;
  bool do_cmdline = false;
  bool do_cwd = false;
  bool do_exe = false;
  bool do_mappings = false;
  bool do_status = false;

  switch (what)
    {
    case IP_MINIMAL:
      do_cmdline = true;
      do_cwd = true;
      do_exe = true;
      break;
    case IP_STAT:
    case IP_STATUS:
      do_status = true;
      break;
    case IP_MAPPINGS:
      do_mappings = true;
      break;
    case IP_CMDLINE:
      do_cmdline = true;
      break;
    case IP_EXE:
      do_exe = true;
      break;
    case IP_CWD:
      do_cwd = true;
      break;
    case IP_ALL:
      do_cmdline = true;
      do_cwd = true;
      do_exe = true;
      do_mappings = true;
      do_status = true;
      break;
    default:
      error (_("Not supported on this target."));
    }

  gdb_argv built_argv (args);
  if (built_argv.count () == 0)
    {
      pid = inferior_ptid.pid ();
      if (pid == 0)
        error (_("No current process: you must name one."));
    }
  else if (built_argv.count () == 1 && isdigit (built_argv[0][0]))
    pid = strtol (built_argv[0], NULL, 10);
  else
    error (_("Invalid arguments."));

  printf_filtered (_("process %d\n"), pid);

  if (do_cmdline)
    {
      gdb::unique_xmalloc_ptr<char[]> cmdline = nbsd_pid_to_cmdline (pid);
      if (cmdline != nullptr)
	printf_filtered ("cmdline = '%s'\n", cmdline.get ());
      else
	warning (_("unable to fetch command line"));
    }
  if (do_cwd)
    {
      std::string cwd = nbsd_pid_to_cwd (pid);
      if (cwd != "")
	printf_filtered ("cwd = '%s'\n", cwd.c_str ());
      else
	warning (_("unable to fetch current working directory"));
    }
  if (do_exe)
    {
      const char *exe = pid_to_exec_file (pid);
      if (exe != nullptr)
	printf_filtered ("exe = '%s'\n", exe);
      else
	warning (_("unable to fetch executable path name"));
    }
  if (do_mappings)
    {
      size_t nvment;
      gdb::unique_xmalloc_ptr<struct kinfo_vmentry[]> vmentl
	= nbsd_kinfo_get_vmmap (pid, &nvment);

      if (vmentl != nullptr)
	{
	  int addr_bit = TARGET_CHAR_BIT * sizeof (void *);
	  nbsd_info_proc_mappings_header (addr_bit);

	  struct kinfo_vmentry *kve = vmentl.get ();
	  for (int i = 0; i < nvment; i++, kve++)
	    nbsd_info_proc_mappings_entry (addr_bit, kve->kve_start,
					   kve->kve_end, kve->kve_offset,
					   kve->kve_flags, kve->kve_protection,
					   kve->kve_path);
	}
      else
	warning (_("unable to fetch virtual memory map"));
    }
  if (do_status)
    {
      struct kinfo_proc2 kp;
      if (!nbsd_pid_to_kinfo_proc2 (pid, &kp))
	warning (_("Failed to fetch process information"));
      else
	{
	  auto process_status
	    = [] (int8_t stat)
	      {
		switch (stat)
		  {
		  case SIDL:
		    return "IDL";
		  case SACTIVE:
		    return "ACTIVE";
		  case SDYING:
		    return "DYING";
		  case SSTOP:
		    return "STOP";
		  case SZOMB:
		    return "ZOMB";
		  case SDEAD:
		    return "DEAD";
		  default:
		    return "? (unknown)";
		  }
	      };

	  printf_filtered ("Name: %s\n", kp.p_comm);
	  printf_filtered ("State: %s\n", process_status(kp.p_realstat));
	  printf_filtered ("Parent process: %" PRId32 "\n", kp.p_ppid);
	  printf_filtered ("Process group: %" PRId32 "\n", kp.p__pgid);
	  printf_filtered ("Session id: %" PRId32 "\n", kp.p_sid);
	  printf_filtered ("TTY: %" PRId32 "\n", kp.p_tdev);
	  printf_filtered ("TTY owner process group: %" PRId32 "\n", kp.p_tpgid);
	  printf_filtered ("User IDs (real, effective, saved): "
			   "%" PRIu32 " %" PRIu32 " %" PRIu32 "\n",
			   kp.p_ruid, kp.p_uid, kp.p_svuid);
	  printf_filtered ("Group IDs (real, effective, saved): "
			   "%" PRIu32 " %" PRIu32 " %" PRIu32 "\n",
			   kp.p_rgid, kp.p_gid, kp.p_svgid);

	  printf_filtered ("Groups:");
	  for (int i = 0; i < kp.p_ngroups; i++)
	    printf_filtered (" %" PRIu32, kp.p_groups[i]);
	  printf_filtered ("\n");
	  printf_filtered ("Minor faults (no memory page): %" PRIu64 "\n",
			   kp.p_uru_minflt);
	  printf_filtered ("Major faults (memory page faults): %" PRIu64 "\n",
			   kp.p_uru_majflt);
	  printf_filtered ("utime: %" PRIu32 ".%06" PRIu32 "\n",
			   kp.p_uutime_sec, kp.p_uutime_usec);
	  printf_filtered ("stime: %" PRIu32 ".%06" PRIu32 "\n",
			   kp.p_ustime_sec, kp.p_ustime_usec);
	  printf_filtered ("utime+stime, children: %" PRIu32 ".%06" PRIu32 "\n",
			   kp.p_uctime_sec, kp.p_uctime_usec);
	  printf_filtered ("'nice' value: %" PRIu8 "\n", kp.p_nice);
	  printf_filtered ("Start time: %" PRIu32 ".%06" PRIu32 "\n",
			   kp.p_ustart_sec, kp.p_ustart_usec);
	  int pgtok = getpagesize () / 1024;
	  printf_filtered ("Data size: %" PRIuMAX " kB\n",
			   (uintmax_t) kp.p_vm_dsize * pgtok);
	  printf_filtered ("Stack size: %" PRIuMAX " kB\n",
			   (uintmax_t) kp.p_vm_ssize * pgtok);
	  printf_filtered ("Text size: %" PRIuMAX " kB\n",
			   (uintmax_t) kp.p_vm_tsize * pgtok);
	  printf_filtered ("Resident set size: %" PRIuMAX " kB\n",
			   (uintmax_t) kp.p_vm_rssize * pgtok);
	  printf_filtered ("Maximum RSS: %" PRIu64 " kB\n", kp.p_uru_maxrss);
	  printf_filtered ("Pending Signals:");
	  for (size_t i = 0; i < ARRAY_SIZE (kp.p_siglist.__bits); i++)
	    printf_filtered (" %08" PRIx32, kp.p_siglist.__bits[i]);
	  printf_filtered ("\n");
	  printf_filtered ("Ignored Signals:");
	  for (size_t i = 0; i < ARRAY_SIZE (kp.p_sigignore.__bits); i++)
	    printf_filtered (" %08" PRIx32, kp.p_sigignore.__bits[i]);
	  printf_filtered ("\n");
	  printf_filtered ("Caught Signals:");
	  for (size_t i = 0; i < ARRAY_SIZE (kp.p_sigcatch.__bits); i++)
	    printf_filtered (" %08" PRIx32, kp.p_sigcatch.__bits[i]);
	  printf_filtered ("\n");
	}
    }

  return true;
}

/* Resume execution of a specified PTID, that points to a process or a thread
   within a process.  If one thread is specified, all other threads are
   suspended.  If STEP is nonzero, single-step it.  If SIGNAL is nonzero,
   give it that signal.  */

static void
nbsd_resume(nbsd_nat_target *target, ptid_t ptid, int step,
	    enum gdb_signal signal)
{
  int request;

  gdb_assert (minus_one_ptid != ptid);

  if (ptid.lwp_p ())
    {
      /* If ptid is a specific LWP, suspend all other LWPs in the process.  */
      inferior *inf = find_inferior_ptid (target, ptid);

      for (thread_info *tp : inf->non_exited_threads ())
        {
          if (tp->ptid.lwp () == ptid.lwp ())
            request = PT_RESUME;
          else
            request = PT_SUSPEND;

          if (ptrace (request, tp->ptid.pid (), NULL, tp->ptid.lwp ()) == -1)
            perror_with_name (("ptrace"));
        }
    }
  else
    {
      /* If ptid is a wildcard, resume all matching threads (they won't run
         until the process is continued however).  */
      for (thread_info *tp : all_non_exited_threads (target, ptid))
        if (ptrace (PT_RESUME, tp->ptid.pid (), NULL, tp->ptid.lwp ()) == -1)
          perror_with_name (("ptrace"));
    }

  if (step)
    {
      for (thread_info *tp : all_non_exited_threads (target, ptid))
	if (ptrace (PT_SETSTEP, tp->ptid.pid (), NULL, tp->ptid.lwp ()) == -1)
	  perror_with_name (("ptrace"));
    }
  else
    {
      for (thread_info *tp : all_non_exited_threads (target, ptid))
	if (ptrace (PT_CLEARSTEP, tp->ptid.pid (), NULL, tp->ptid.lwp ()) == -1)
	  perror_with_name (("ptrace"));
    }

  if (catch_syscall_enabled () > 0)
    request = PT_SYSCALL;
  else
    request = PT_CONTINUE;

  /* An address of (void *)1 tells ptrace to continue from
     where it was.  If GDB wanted it to start some other way, we have
     already written a new program counter value to the child.  */
  if (ptrace (request, ptid.pid (), (void *)1, gdb_signal_to_host (signal)) == -1)
    perror_with_name (("ptrace"));
}

/* Resume execution of thread PTID, or all threads of all inferiors
   if PTID is -1.  If STEP is nonzero, single-step it.  If SIGNAL is nonzero,
   give it that signal.  */

void
nbsd_nat_target::resume (ptid_t ptid, int step, enum gdb_signal signal)
{
  if (minus_one_ptid != ptid)
    nbsd_resume (this, ptid, step, signal);
  else
    {
      for (inferior *inf : all_non_exited_inferiors (this))
	nbsd_resume (this, ptid_t (inf->pid, 0, 0), step, signal);
    }
}

/* Implement a safe wrapper around waitpid().  */

static pid_t
nbsd_wait (ptid_t ptid, struct target_waitstatus *ourstatus, int options)
{
  pid_t pid;
  int status;

  set_sigint_trap ();

  do
    {
      /* The common code passes WNOHANG that leads to crashes, overwrite it.  */
      pid = waitpid (ptid.pid (), &status, 0);
    }
  while (pid == -1 && errno == EINTR);

  clear_sigint_trap ();

  if (pid == -1)
    perror_with_name (_("Child process unexpectedly missing"));

  store_waitstatus (ourstatus, status);
  return pid;
}

/* Wait for the child specified by PTID to do something.  Return the
   process ID of the child, or MINUS_ONE_PTID in case of error; store
   the status in *OURSTATUS.  */

ptid_t
nbsd_nat_target::wait (ptid_t ptid, struct target_waitstatus *ourstatus,
		       int target_options)
{
  pid_t pid = nbsd_wait (ptid, ourstatus, target_options);
  ptid_t wptid = ptid_t (pid);

  /* If the child stopped, keep investigating its status.  */
  if (ourstatus->kind != TARGET_WAITKIND_STOPPED)
    return wptid;

  /* Extract the event and thread that received a signal.  */
  ptrace_siginfo_t psi;
  if (ptrace (PT_GET_SIGINFO, pid, &psi, sizeof (psi)) == -1)
    perror_with_name (("ptrace"));

  /* Pick child's siginfo_t.  */
  siginfo_t *si = &psi.psi_siginfo;

  int lwp = psi.psi_lwpid;

  int signo = si->si_signo;
  const int code = si->si_code;

  /* Construct PTID with a specified thread that received the event.
     If a signal was targeted to the whole process, lwp is 0.  */
  wptid = ptid_t (pid, lwp, 0);

  /* Bail out on non-debugger oriented signals..  */
  if (signo != SIGTRAP)
    return wptid;

  /* Stop examining non-debugger oriented SIGTRAP codes.  */
  if (code <= SI_USER || code == SI_NOINFO)
    return wptid;

  if (in_thread_list (this, ptid_t (pid)))
      thread_change_ptid (this, ptid_t (pid), wptid);

  if (code == TRAP_EXEC)
    {
      ourstatus->kind = TARGET_WAITKIND_EXECD;
      ourstatus->value.execd_pathname = xstrdup (pid_to_exec_file (pid));
      return wptid;
    }

  if (code == TRAP_TRACE)
    {
      /* Unhandled at this level.  */
      return wptid;
    }

  if (code == TRAP_SCE || code == TRAP_SCX)
    {
      int sysnum = si->si_sysnum;

      if (!catch_syscall_enabled () || !catching_syscall_number (sysnum))
	{
	  /* If the core isn't interested in this event, ignore it.  */
	  ourstatus->kind = TARGET_WAITKIND_SPURIOUS;
	  return wptid;
	}

      ourstatus->kind =
	(code == TRAP_SCE) ? TARGET_WAITKIND_SYSCALL_ENTRY :
	TARGET_WAITKIND_SYSCALL_RETURN;
      ourstatus->value.syscall_number = sysnum;
      return wptid;
    }

  if (code == TRAP_BRKPT)
    {
      /* Unhandled at this level.  */
      return wptid;
    }

  /* Unclassified SIGTRAP event.  */
  ourstatus->kind = TARGET_WAITKIND_SPURIOUS;
  return wptid;
}

/* Implement the "insert_exec_catchpoint" target_ops method.  */

int
nbsd_nat_target::insert_exec_catchpoint (int pid)
{
  /* Nothing to do.  */
  return 0;
}

/* Implement the "remove_exec_catchpoint" target_ops method.  */

int
nbsd_nat_target::remove_exec_catchpoint (int pid)
{
  /* Nothing to do.  */
  return 0;
}

/* Implement the "set_syscall_catchpoint" target_ops method.  */

int
nbsd_nat_target::set_syscall_catchpoint (int pid, bool needed,
                                         int any_count,
                                         gdb::array_view<const int> syscall_counts)
{
  /* Ignore the arguments.  inf-ptrace.c will use PT_SYSCALL which
     will catch all system call entries and exits.  The system calls
     are filtered by GDB rather than the kernel.  */
  return 0;
}