glib/gbacktrace.c - third_party/glib - Git at Google

 /* GLIB - Library of useful routines for C programming
  * Copyright (C) 1995-1997  Peter Mattis, Spencer Kimball and Josh MacDonald
  *
  * SPDX-License-Identifier: LGPL-2.1-or-later
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
  * License as published by the Free Software Foundation; either
  * version 2.1 of the License, or (at your option) any later version.
  *
  * This library 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
  * Lesser General Public License for more details.
  *
  * You should have received a copy of the GNU Lesser General Public
  * License along with this library; if not, see <http://www.gnu.org/licenses/>.
  */

 /*
  * Modified by the GLib Team and others 1997-2000.  See the AUTHORS
  * file for a list of people on the GLib Team.  See the ChangeLog
  * files for a list of changes.  These files are distributed with
  * GLib at ftp://ftp.gtk.org/pub/gtk/.
  */

 /*
  * MT safe ; except for g_on_error_stack_trace, but who wants thread safety
  * then
  */

 #include "config.h"
 #include "glibconfig.h"

 #include <signal.h>
 #include <stdarg.h>
 #include <stdio.h>
 #include <stdlib.h>

 #ifdef HAVE_SYS_TIME_H
 #include <sys/time.h>
 #endif
 #include <sys/types.h>

 #include <time.h>

 #ifdef G_OS_UNIX
 #include "glib-unixprivate.h"
 #include <errno.h>
 #include <unistd.h>
 #include <sys/wait.h>
 #ifdef HAVE_SYS_SELECT_H
 #include <sys/select.h>
 #endif /* HAVE_SYS_SELECT_H */
 #endif

 #include <string.h>

 #ifdef G_OS_WIN32
 #  define STRICT                /* Strict typing, please */
 #  define _WIN32_WINDOWS 0x0401 /* to get IsDebuggerPresent */
 #  include <windows.h>
 #  undef STRICT
 #else
 #  include <fcntl.h>
 #endif

 #include "gbacktrace.h"

 #include "gtypes.h"
 #include "gmain.h"
 #include "gprintfint.h"
 #include "gunicode.h"
 #include "gutils.h"

 #ifndef G_OS_WIN32
 static void stack_trace (const char * const *args);
 #endif

 /* Default to using LLDB for backtraces on macOS. */
 #ifdef __APPLE__
 #define USE_LLDB
 #endif

 #ifdef USE_LLDB
 #define DEBUGGER "lldb"
 #else
 #define DEBUGGER "gdb"
 #endif

 /* People want to hit this from their debugger... */
 GLIB_AVAILABLE_IN_ALL volatile gboolean glib_on_error_halt;
 volatile gboolean glib_on_error_halt = TRUE;

 /**
  * g_on_error_query:
  * @prg_name: the program name, needed by gdb for the "[S]tack trace"
  *     option. If @prg_name is %NULL, g_get_prgname() is called to get
  *     the program name (which will work correctly if gdk_init() or
  *     gtk_init() has been called)
  *
  * Prompts the user with
  * `[E]xit, [H]alt, show [S]tack trace or [P]roceed`.
  * This function is intended to be used for debugging use only.
  * The following example shows how it can be used together with
  * the g_log() functions.
  *
  * |[<!-- language="C" -->
  * #include <glib.h>
  *
  * static void
  * log_handler (const gchar   *log_domain,
  *              GLogLevelFlags log_level,
  *              const gchar   *message,
  *              gpointer       user_data)
  * {
  *   g_log_default_handler (log_domain, log_level, message, user_data);
  *
  *   g_on_error_query (MY_PROGRAM_NAME);
  * }
  *
  * int
  * main (int argc, char *argv[])
  * {
  *   g_log_set_handler (MY_LOG_DOMAIN,
  *                      G_LOG_LEVEL_WARNING |
  *                      G_LOG_LEVEL_ERROR |
  *                      G_LOG_LEVEL_CRITICAL,
  *                      log_handler,
  *                      NULL);
  *   ...
  * ]|
  *
  * If "[E]xit" is selected, the application terminates with a call
  * to _exit(0).
  *
  * If "[S]tack" trace is selected, g_on_error_stack_trace() is called.
  * This invokes gdb, which attaches to the current process and shows
  * a stack trace. The prompt is then shown again.
  *
  * If "[P]roceed" is selected, the function returns.
  *
  * This function may cause different actions on non-UNIX platforms.
  *
  * On Windows consider using the `G_DEBUGGER` environment
  * variable (see [Running GLib Applications](glib-running.html)) and
  * calling g_on_error_stack_trace() instead.
  */
 void
 g_on_error_query (const gchar *prg_name)
 {
 #ifndef G_OS_WIN32
   static const gchar * const query1 = "[E]xit, [H]alt";
   static const gchar * const query2 = ", show [S]tack trace";
   static const gchar * const query3 = " or [P]roceed";
   gchar buf[16];

   if (!prg_name)
     prg_name = g_get_prgname ();

  retry:

   if (prg_name)
     _g_fprintf (stdout,
                 "%s (pid:%u): %s%s%s: ",
                 prg_name,
                 (guint) getpid (),
                 query1,
                 query2,
                 query3);
   else
     _g_fprintf (stdout,
                 "(process:%u): %s%s: ",
                 (guint) getpid (),
                 query1,
                 query3);
   fflush (stdout);

   if (isatty(0) && isatty(1))
     {
       if (fgets (buf, 8, stdin) == NULL)
         _exit (0);
     }
   else
     {
       strcpy (buf, "E\n");
     }

   if ((buf[0] == 'E' || buf[0] == 'e')
       && buf[1] == '\n')
     _exit (0);
   else if ((buf[0] == 'P' || buf[0] == 'p')
            && buf[1] == '\n')
     return;
   else if (prg_name
            && (buf[0] == 'S' || buf[0] == 's')
            && buf[1] == '\n')
     {
       g_on_error_stack_trace (prg_name);
       goto retry;
     }
   else if ((buf[0] == 'H' || buf[0] == 'h')
            && buf[1] == '\n')
     {
       while (glib_on_error_halt)
         ;
       glib_on_error_halt = TRUE;
       return;
     }
   else
     goto retry;
 #else
   if (!prg_name)
     prg_name = g_get_prgname ();

   /* MessageBox is allowed on UWP apps only when building against
    * the debug CRT, which will set -D_DEBUG */
 #if defined(_DEBUG) || !defined(G_WINAPI_ONLY_APP)
   {
     WCHAR *caption = NULL;

     if (prg_name && *prg_name)
       {
         caption = g_utf8_to_utf16 (prg_name, -1, NULL, NULL, NULL);
       }

     MessageBoxW (NULL, L"g_on_error_query called, program terminating",
                  caption,
                  MB_OK|MB_ICONERROR);

     g_free (caption);
   }
 #else
   printf ("g_on_error_query called, program '%s' terminating\n",
       (prg_name && *prg_name) ? prg_name : "(null)");
 #endif
   _exit(0);
 #endif
 }

 /**
  * g_on_error_stack_trace:
  * @prg_name: the program name, needed by gdb for the "[S]tack trace"
  *     option
  *
  * Invokes gdb, which attaches to the current process and shows a
  * stack trace. Called by g_on_error_query() when the "[S]tack trace"
  * option is selected. You can get the current process's program name
  * with g_get_prgname(), assuming that you have called gtk_init() or
  * gdk_init().
  *
  * This function may cause different actions on non-UNIX platforms.
  *
  * When running on Windows, this function is *not* called by
  * g_on_error_query(). If called directly, it will raise an
  * exception, which will crash the program. If the `G_DEBUGGER` environment
  * variable is set, a debugger will be invoked to attach and
  * handle that exception (see [Running GLib Applications](glib-running.html)).
  */
 void
 g_on_error_stack_trace (const gchar *prg_name)
 {
 #if defined(G_OS_UNIX)
   pid_t pid;
   gchar buf[16];
   const gchar *args[5] = { DEBUGGER, NULL, NULL, NULL, NULL };
   int status;

   if (!prg_name)
     return;

   _g_sprintf (buf, "%u", (guint) getpid ());

 #ifdef USE_LLDB
   args[1] = prg_name;
   args[2] = "-p";
   args[3] = buf;
 #else
   args[1] = prg_name;
   args[2] = buf;
 #endif

   pid = fork ();
   if (pid == 0)
     {
       stack_trace (args);
       _exit (0);
     }
   else if (pid == (pid_t) -1)
     {
       perror ("unable to fork " DEBUGGER);
       return;
     }

   /* Wait until the child really terminates. On Mac OS X waitpid ()
    * will also return when the child is being stopped due to tracing.
    */
   while (1)
     {
       pid_t retval = waitpid (pid, &status, 0);
       if (WIFEXITED (retval) || WIFSIGNALED (retval))
         break;
     }
 #else
   if (IsDebuggerPresent ())
     G_BREAKPOINT ();
   else
     g_abort ();
 #endif
 }

 #ifndef G_OS_WIN32

 static gboolean stack_trace_done = FALSE;

 static void
 stack_trace_sigchld (int signum)
 {
   stack_trace_done = TRUE;
 }

 #define BUFSIZE 1024

 static inline const char *
 get_strerror (char *buffer, gsize n)
 {
 #if defined(STRERROR_R_CHAR_P)
   return strerror_r (errno, buffer, n);
 #elif defined(HAVE_STRERROR_R)
   int ret = strerror_r (errno, buffer, n);
   if (ret == 0 || ret == EINVAL)
     return buffer;
   return NULL;
 #else
   const char *error_str = strerror (errno);
   if (!error_str)
     return NULL;

   strncpy (buffer, error_str, n);
   return buffer;
 #endif
 }

 static gssize
 checked_write (int fd, gconstpointer buf, gsize n)
 {
   gssize written = write (fd, buf, n);

   if (written == -1)
     {
       char msg[BUFSIZE] = {0};
       char error_str[BUFSIZE / 2] = {0};

       get_strerror (error_str, sizeof (error_str) - 1);
       snprintf (msg, sizeof (msg) - 1, "Unable to write to fd %d: %s", fd, error_str);
       perror (msg);
       _exit (0);
     }

   return written;
 }

 static int
 checked_dup (int fd)
 {
   int new_fd = dup (fd);

   if (new_fd == -1)
     {
       char msg[BUFSIZE] = {0};
       char error_str[BUFSIZE / 2] = {0};

       get_strerror (error_str, sizeof (error_str) - 1);
       snprintf (msg, sizeof (msg) - 1, "Unable to duplicate fd %d: %s", fd, error_str);
       perror (msg);
       _exit (0);
     }

   return new_fd;
 }

 static void
 stack_trace (const char * const *args)
 {
   pid_t pid;
   int in_fd[2];
   int out_fd[2];
   fd_set fdset;
   fd_set readset;
   struct timeval tv;
   int sel, idx, state;
 #ifdef USE_LLDB
   int line_idx;
 #endif
   char buffer[BUFSIZE];
   char c;

   stack_trace_done = FALSE;
   signal (SIGCHLD, stack_trace_sigchld);

   if (!g_unix_open_pipe_internal (in_fd, TRUE, FALSE) ||
       !g_unix_open_pipe_internal (out_fd, TRUE, FALSE))
     {
       perror ("unable to open pipe");
       _exit (0);
     }

   pid = fork ();
   if (pid == 0)
     {
       /* Save stderr for printing failure below */
       int old_err = dup (2);
       if (old_err != -1)
 	{
 	  int getfd = fcntl (old_err, F_GETFD);
 	  if (getfd != -1)
 	    (void) fcntl (old_err, F_SETFD, getfd | FD_CLOEXEC);
 	}

       close (0);
       checked_dup (in_fd[0]);   /* set the stdin to the in pipe */
       close (1);
       checked_dup (out_fd[1]);  /* set the stdout to the out pipe */
       close (2);
       checked_dup (out_fd[1]);  /* set the stderr to the out pipe */

       execvp (args[0], (char **) args);      /* exec gdb */

       /* Print failure to original stderr */
       if (old_err != -1)
         {
           close (2);
           /* We can ignore the return value here as we're failing anyways */
           (void) !dup (old_err);
         }
       perror ("exec " DEBUGGER " failed");
       _exit (0);
     }
   else if (pid == (pid_t) -1)
     {
       perror ("unable to fork");
       _exit (0);
     }

   FD_ZERO (&fdset);
   FD_SET (out_fd[0], &fdset);

 #ifdef USE_LLDB
   checked_write (in_fd[1], "bt\n", 3);
   checked_write (in_fd[1], "p x = 0\n", 8);
   checked_write (in_fd[1], "process detach\n", 15);
   checked_write (in_fd[1], "quit\n", 5);
 #else
   /* Don't wrap so that lines are not truncated */
   checked_write (in_fd[1], "set width unlimited\n", 20);
   checked_write (in_fd[1], "backtrace\n", 10);
   checked_write (in_fd[1], "p x = 0\n", 8);
   checked_write (in_fd[1], "quit\n", 5);
 #endif

   idx = 0;
 #ifdef USE_LLDB
   line_idx = 0;
 #endif
   state = 0;

   while (1)
     {
       readset = fdset;
       tv.tv_sec = 1;
       tv.tv_usec = 0;

       sel = select (FD_SETSIZE, &readset, NULL, NULL, &tv);
       if (sel == -1)
         break;

       if ((sel > 0) && (FD_ISSET (out_fd[0], &readset)))
         {
           if (read (out_fd[0], &c, 1))
             {
 #ifdef USE_LLDB
               line_idx += 1;
 #endif

               switch (state)
                 {
                 case 0:
 #ifdef USE_LLDB
                   if (c == '*' || (c == ' ' && line_idx == 1))
 #else
                   if (c == '#')
 #endif
                     {
                       state = 1;
                       idx = 0;
                       buffer[idx++] = c;
                     }
                   break;
                 case 1:
                   if (idx < BUFSIZE)
                     buffer[idx++] = c;
                   if ((c == '\n') || (c == '\r'))
                     {
                       buffer[idx] = 0;
                       _g_fprintf (stdout, "%s", buffer);
                       state = 0;
                       idx = 0;
 #ifdef USE_LLDB
                       line_idx = 0;
 #endif
                     }
                   break;
                 default:
                   break;
                 }
             }
         }
       else if (stack_trace_done)
         break;
     }

   close (in_fd[0]);
   close (in_fd[1]);
   close (out_fd[0]);
   close (out_fd[1]);
   _exit (0);
 }

 #endif /* !G_OS_WIN32 */
	/* GLIB - Library of useful routines for C programming
	* Copyright (C) 1995-1997 Peter Mattis, Spencer Kimball and Josh MacDonald
	*
	* SPDX-License-Identifier: LGPL-2.1-or-later
	*
	* This library is free software; you can redistribute it and/or
	* modify it under the terms of the GNU Lesser General Public
	* License as published by the Free Software Foundation; either
	* version 2.1 of the License, or (at your option) any later version.
	*
	* This library 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
	* Lesser General Public License for more details.
	*
	* You should have received a copy of the GNU Lesser General Public
	* License along with this library; if not, see <http://www.gnu.org/licenses/>.
	*/

	/*
	* Modified by the GLib Team and others 1997-2000. See the AUTHORS
	* file for a list of people on the GLib Team. See the ChangeLog
	* files for a list of changes. These files are distributed with
	* GLib at ftp://ftp.gtk.org/pub/gtk/.
	*/

	/*
	* MT safe ; except for g_on_error_stack_trace, but who wants thread safety
	* then
	*/

	#include "config.h"
	#include "glibconfig.h"

	#include <signal.h>
	#include <stdarg.h>
	#include <stdio.h>
	#include <stdlib.h>

	#ifdef HAVE_SYS_TIME_H
	#include <sys/time.h>
	#endif
	#include <sys/types.h>

	#include <time.h>

	#ifdef G_OS_UNIX
	#include "glib-unixprivate.h"
	#include <errno.h>
	#include <unistd.h>
	#include <sys/wait.h>
	#ifdef HAVE_SYS_SELECT_H
	#include <sys/select.h>
	#endif /* HAVE_SYS_SELECT_H */
	#endif

	#include <string.h>

	#ifdef G_OS_WIN32
	# define STRICT /* Strict typing, please */
	# define _WIN32_WINDOWS 0x0401 /* to get IsDebuggerPresent */
	# include <windows.h>
	# undef STRICT
	#else
	# include <fcntl.h>
	#endif

	#include "gbacktrace.h"

	#include "gtypes.h"
	#include "gmain.h"
	#include "gprintfint.h"
	#include "gunicode.h"
	#include "gutils.h"

	#ifndef G_OS_WIN32
	static void stack_trace (const char * const *args);
	#endif

	/* Default to using LLDB for backtraces on macOS. */
	#ifdef __APPLE__
	#define USE_LLDB
	#endif

	#ifdef USE_LLDB
	#define DEBUGGER "lldb"
	#else
	#define DEBUGGER "gdb"
	#endif

	/* People want to hit this from their debugger... */
	GLIB_AVAILABLE_IN_ALL volatile gboolean glib_on_error_halt;
	volatile gboolean glib_on_error_halt = TRUE;

	/**
	* g_on_error_query:
	* @prg_name: the program name, needed by gdb for the "[S]tack trace"
	* option. If @prg_name is %NULL, g_get_prgname() is called to get
	* the program name (which will work correctly if gdk_init() or
	* gtk_init() has been called)
	*
	* Prompts the user with
	* `[E]xit, [H]alt, show [S]tack trace or [P]roceed`.
	* This function is intended to be used for debugging use only.
	* The following example shows how it can be used together with
	* the g_log() functions.
	*
	* \|[<!-- language="C" -->
	* #include <glib.h>
	*
	* static void
	* log_handler (const gchar *log_domain,
	* GLogLevelFlags log_level,
	* const gchar *message,
	* gpointer user_data)
	* {
	* g_log_default_handler (log_domain, log_level, message, user_data);
	*
	* g_on_error_query (MY_PROGRAM_NAME);
	* }
	*
	* int
	* main (int argc, char *argv[])
	* {
	* g_log_set_handler (MY_LOG_DOMAIN,
	* G_LOG_LEVEL_WARNING \|
	* G_LOG_LEVEL_ERROR \|
	* G_LOG_LEVEL_CRITICAL,
	* log_handler,
	* NULL);
	* ...
	* ]\|
	*
	* If "[E]xit" is selected, the application terminates with a call
	* to _exit(0).
	*
	* If "[S]tack" trace is selected, g_on_error_stack_trace() is called.
	* This invokes gdb, which attaches to the current process and shows
	* a stack trace. The prompt is then shown again.
	*
	* If "[P]roceed" is selected, the function returns.
	*
	* This function may cause different actions on non-UNIX platforms.
	*
	* On Windows consider using the `G_DEBUGGER` environment
	* variable (see [Running GLib Applications](glib-running.html)) and
	* calling g_on_error_stack_trace() instead.
	*/
	void
	g_on_error_query (const gchar *prg_name)
	{
	#ifndef G_OS_WIN32
	static const gchar * const query1 = "[E]xit, [H]alt";
	static const gchar * const query2 = ", show [S]tack trace";
	static const gchar * const query3 = " or [P]roceed";
	gchar buf[16];

	if (!prg_name)
	prg_name = g_get_prgname ();

	retry:

	if (prg_name)
	_g_fprintf (stdout,
	"%s (pid:%u): %s%s%s: ",
	prg_name,
	(guint) getpid (),
	query1,
	query2,
	query3);
	else
	_g_fprintf (stdout,
	"(process:%u): %s%s: ",
	(guint) getpid (),
	query1,
	query3);
	fflush (stdout);

	if (isatty(0) && isatty(1))
	{
	if (fgets (buf, 8, stdin) == NULL)
	_exit (0);
	}
	else
	{
	strcpy (buf, "E\n");
	}

	if ((buf[0] == 'E' \|\| buf[0] == 'e')
	&& buf[1] == '\n')
	_exit (0);
	else if ((buf[0] == 'P' \|\| buf[0] == 'p')
	&& buf[1] == '\n')
	return;
	else if (prg_name
	&& (buf[0] == 'S' \|\| buf[0] == 's')
	&& buf[1] == '\n')
	{
	g_on_error_stack_trace (prg_name);
	goto retry;
	}
	else if ((buf[0] == 'H' \|\| buf[0] == 'h')
	&& buf[1] == '\n')
	{
	while (glib_on_error_halt)
	;
	glib_on_error_halt = TRUE;
	return;
	}
	else
	goto retry;
	#else
	if (!prg_name)
	prg_name = g_get_prgname ();

	/* MessageBox is allowed on UWP apps only when building against
	* the debug CRT, which will set -D_DEBUG */
	#if defined(_DEBUG) \|\| !defined(G_WINAPI_ONLY_APP)
	{
	WCHAR *caption = NULL;

	if (prg_name && *prg_name)
	{
	caption = g_utf8_to_utf16 (prg_name, -1, NULL, NULL, NULL);
	}

	MessageBoxW (NULL, L"g_on_error_query called, program terminating",
	caption,
	MB_OK\|MB_ICONERROR);

	g_free (caption);
	}
	#else
	printf ("g_on_error_query called, program '%s' terminating\n",
	(prg_name && *prg_name) ? prg_name : "(null)");
	#endif
	_exit(0);
	#endif
	}

	/**
	* g_on_error_stack_trace:
	* @prg_name: the program name, needed by gdb for the "[S]tack trace"
	* option
	*
	* Invokes gdb, which attaches to the current process and shows a
	* stack trace. Called by g_on_error_query() when the "[S]tack trace"
	* option is selected. You can get the current process's program name
	* with g_get_prgname(), assuming that you have called gtk_init() or
	* gdk_init().
	*
	* This function may cause different actions on non-UNIX platforms.
	*
	* When running on Windows, this function is not called by
	* g_on_error_query(). If called directly, it will raise an
	* exception, which will crash the program. If the `G_DEBUGGER` environment
	* variable is set, a debugger will be invoked to attach and
	* handle that exception (see [Running GLib Applications](glib-running.html)).
	*/
	void
	g_on_error_stack_trace (const gchar *prg_name)
	{
	#if defined(G_OS_UNIX)
	pid_t pid;
	gchar buf[16];
	const gchar *args[5] = { DEBUGGER, NULL, NULL, NULL, NULL };
	int status;

	if (!prg_name)
	return;

	_g_sprintf (buf, "%u", (guint) getpid ());

	#ifdef USE_LLDB
	args[1] = prg_name;
	args[2] = "-p";
	args[3] = buf;
	#else
	args[1] = prg_name;
	args[2] = buf;
	#endif

	pid = fork ();
	if (pid == 0)
	{
	stack_trace (args);
	_exit (0);
	}
	else if (pid == (pid_t) -1)
	{
	perror ("unable to fork " DEBUGGER);
	return;
	}

	/* Wait until the child really terminates. On Mac OS X waitpid ()
	* will also return when the child is being stopped due to tracing.
	*/
	while (1)
	{
	pid_t retval = waitpid (pid, &status, 0);
	if (WIFEXITED (retval) \|\| WIFSIGNALED (retval))
	break;
	}
	#else
	if (IsDebuggerPresent ())
	G_BREAKPOINT ();
	else
	g_abort ();
	#endif
	}

	#ifndef G_OS_WIN32

	static gboolean stack_trace_done = FALSE;

	static void
	stack_trace_sigchld (int signum)
	{
	stack_trace_done = TRUE;
	}

	#define BUFSIZE 1024

	static inline const char *
	get_strerror (char *buffer, gsize n)
	{
	#if defined(STRERROR_R_CHAR_P)
	return strerror_r (errno, buffer, n);
	#elif defined(HAVE_STRERROR_R)
	int ret = strerror_r (errno, buffer, n);
	if (ret == 0 \|\| ret == EINVAL)
	return buffer;
	return NULL;
	#else
	const char *error_str = strerror (errno);
	if (!error_str)
	return NULL;

	strncpy (buffer, error_str, n);
	return buffer;
	#endif
	}

	static gssize
	checked_write (int fd, gconstpointer buf, gsize n)
	{
	gssize written = write (fd, buf, n);

	if (written == -1)
	{
	char msg[BUFSIZE] = {0};
	char error_str[BUFSIZE / 2] = {0};

	get_strerror (error_str, sizeof (error_str) - 1);
	snprintf (msg, sizeof (msg) - 1, "Unable to write to fd %d: %s", fd, error_str);
	perror (msg);
	_exit (0);
	}

	return written;
	}

	static int
	checked_dup (int fd)
	{
	int new_fd = dup (fd);

	if (new_fd == -1)
	{
	char msg[BUFSIZE] = {0};
	char error_str[BUFSIZE / 2] = {0};

	get_strerror (error_str, sizeof (error_str) - 1);
	snprintf (msg, sizeof (msg) - 1, "Unable to duplicate fd %d: %s", fd, error_str);
	perror (msg);
	_exit (0);
	}

	return new_fd;
	}

	static void
	stack_trace (const char * const *args)
	{
	pid_t pid;
	int in_fd[2];
	int out_fd[2];
	fd_set fdset;
	fd_set readset;
	struct timeval tv;
	int sel, idx, state;
	#ifdef USE_LLDB
	int line_idx;
	#endif
	char buffer[BUFSIZE];
	char c;

	stack_trace_done = FALSE;
	signal (SIGCHLD, stack_trace_sigchld);

	if (!g_unix_open_pipe_internal (in_fd, TRUE, FALSE) \|\|
	!g_unix_open_pipe_internal (out_fd, TRUE, FALSE))
	{
	perror ("unable to open pipe");
	_exit (0);
	}

	pid = fork ();
	if (pid == 0)
	{
	/* Save stderr for printing failure below */
	int old_err = dup (2);
	if (old_err != -1)
	{
	int getfd = fcntl (old_err, F_GETFD);
	if (getfd != -1)
	(void) fcntl (old_err, F_SETFD, getfd \| FD_CLOEXEC);
	}

	close (0);
	checked_dup (in_fd[0]); /* set the stdin to the in pipe */
	close (1);
	checked_dup (out_fd[1]); /* set the stdout to the out pipe */
	close (2);
	checked_dup (out_fd[1]); /* set the stderr to the out pipe */

	execvp (args[0], (char *) args); / exec gdb */

	/* Print failure to original stderr */
	if (old_err != -1)
	{
	close (2);
	/* We can ignore the return value here as we're failing anyways */
	(void) !dup (old_err);
	}
	perror ("exec " DEBUGGER " failed");
	_exit (0);
	}
	else if (pid == (pid_t) -1)
	{
	perror ("unable to fork");
	_exit (0);
	}

	FD_ZERO (&fdset);
	FD_SET (out_fd[0], &fdset);

	#ifdef USE_LLDB
	checked_write (in_fd[1], "bt\n", 3);
	checked_write (in_fd[1], "p x = 0\n", 8);
	checked_write (in_fd[1], "process detach\n", 15);
	checked_write (in_fd[1], "quit\n", 5);
	#else
	/* Don't wrap so that lines are not truncated */
	checked_write (in_fd[1], "set width unlimited\n", 20);
	checked_write (in_fd[1], "backtrace\n", 10);
	checked_write (in_fd[1], "p x = 0\n", 8);
	checked_write (in_fd[1], "quit\n", 5);
	#endif

	idx = 0;
	#ifdef USE_LLDB
	line_idx = 0;
	#endif
	state = 0;

	while (1)
	{
	readset = fdset;
	tv.tv_sec = 1;
	tv.tv_usec = 0;

	sel = select (FD_SETSIZE, &readset, NULL, NULL, &tv);
	if (sel == -1)
	break;

	if ((sel > 0) && (FD_ISSET (out_fd[0], &readset)))
	{
	if (read (out_fd[0], &c, 1))
	{
	#ifdef USE_LLDB
	line_idx += 1;
	#endif

	switch (state)
	{
	case 0:
	#ifdef USE_LLDB
	if (c == '*' \|\| (c == ' ' && line_idx == 1))
	#else
	if (c == '#')
	#endif
	{
	state = 1;
	idx = 0;
	buffer[idx++] = c;
	}
	break;
	case 1:
	if (idx < BUFSIZE)
	buffer[idx++] = c;
	if ((c == '\n') \|\| (c == '\r'))
	{
	buffer[idx] = 0;
	_g_fprintf (stdout, "%s", buffer);
	state = 0;
	idx = 0;
	#ifdef USE_LLDB
	line_idx = 0;
	#endif
	}
	break;
	default:
	break;
	}
	}
	}
	else if (stack_trace_done)
	break;
	}

	close (in_fd[0]);
	close (in_fd[1]);
	close (out_fd[0]);
	close (out_fd[1]);
	_exit (0);
	}

	#endif /* !G_OS_WIN32 */