/* GMODULE - GLIB wrapper code for dynamic module loading

 * Copyright (C) 1998, 2000 Tim Janik

 *

 * 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

 */

#include "config.h"

#include <dlfcn.h>

#include <glib.h>

/* Perl includes <nlist.h> and <link.h> instead of <dlfcn.h> on some systems? */

/* dlerror() is not implemented on all systems

 */

#ifndef G_MODULE_HAVE_DLERROR

#  ifdef __NetBSD__

#    define dlerror() g_strerror (errno)

#  else /* !__NetBSD__ */

/* could we rely on errno's state here? */

#    define dlerror() "unknown dl-error"

#  endif /* !__NetBSD__ */

#endif  /* G_MODULE_HAVE_DLERROR */

/* some flags are missing on some systems, so we provide

 * harmless defaults.

 * The Perl sources say, RTLD_LAZY needs to be defined as (1),

 * at least for Solaris 1.

 *

 * Mandatory:

 * RTLD_LAZY   - resolve undefined symbols as code from the dynamic library

 *     is executed.

 * RTLD_NOW    - resolve all undefined symbols before dlopen returns, and fail

 *     if this cannot be done.

 * Optionally:

 * RTLD_GLOBAL - the external symbols defined in the library will be made

 *     available to subsequently loaded libraries.

 */

#ifndef HAVE_RTLD_LAZY

#define RTLD_LAZY 1

#endif  /* RTLD_LAZY */

#ifndef HAVE_RTLD_NOW

#define RTLD_NOW  0

#endif  /* RTLD_NOW */

/* some systems (OSF1 V5.0) have broken RTLD_GLOBAL linkage */

#ifdef G_MODULE_BROKEN_RTLD_GLOBAL

#undef  RTLD_GLOBAL

#undef  HAVE_RTLD_GLOBAL

#endif /* G_MODULE_BROKEN_RTLD_GLOBAL */

#ifndef HAVE_RTLD_GLOBAL

#define RTLD_GLOBAL 0

#endif  /* RTLD_GLOBAL */

/* According to POSIX.1-2001, dlerror() is not necessarily thread-safe

 * (see https://pubs.opengroup.org/onlinepubs/009695399/), and so must be

 * called within the same locked section as the dlopen()/dlsym() call which

 * may have caused an error.

 *

 * However, some libc implementations, such as glibc, implement dlerror() using

 * thread-local storage, so are thread-safe. As of early 2021:

 *  - glibc is thread-safe: https://github.com/bminor/glibc/blob/HEAD/dlfcn/libc_dlerror_result.c

 *  - uclibc-ng is not thread-safe: https://cgit.uclibc-ng.org/cgi/cgit/uclibc-ng.git/tree/ldso/libdl/libdl.c?id=132decd2a043d0ccf799f42bf89f3ae0c11e95d5#n1075

 *  - Other libc implementations have not been checked, and no problems have

 *    been reported with them in 10 years, so default to assuming that they

 *    don’t need additional thread-safety from GLib

 */

#if defined(__UCLIBC__)

G_LOCK_DEFINE_STATIC (errors);

#else

#define DLERROR_IS_THREADSAFE 1

#endif

static void

lock_dlerror (void)

{

#ifndef DLERROR_IS_THREADSAFE

  G_LOCK (errors);

#endif

}

static void

unlock_dlerror (void)

{

#ifndef DLERROR_IS_THREADSAFE

  G_UNLOCK (errors);

#endif

}

/* This should be called with lock_dlerror() held */

static const gchar *

fetch_dlerror (gboolean replace_null)

{

  const gchar *msg = dlerror ();

  /* make sure we always return an error message != NULL, if

   * expected to do so. */

  if (!msg && replace_null)

    return "unknown dl-error";

  return msg;

}

static gpointer

_g_module_open (const gchar *file_name,

    gboolean     bind_lazy,

    gboolean     bind_local,

                GError     **error)

{

  gpointer handle;

  lock_dlerror ();

  handle = dlopen (file_name,

       (bind_local ? 0 : RTLD_GLOBAL) | (bind_lazy ? RTLD_LAZY : RTLD_NOW));

  if (!handle)

    {

      const gchar *message = fetch_dlerror (TRUE);

      g_module_set_error (message);

      g_set_error_literal (error, G_MODULE_ERROR, G_MODULE_ERROR_FAILED, message);

    }

  unlock_dlerror ();

  return handle;

}

static gpointer

_g_module_self (void)

{

  gpointer handle;

  /* to query symbols from the program itself, special link options

   * are required on some systems.

   */

  /* On Android 32 bit (i.e. not __LP64__), dlopen(NULL)

   * does not work reliable and generally no symbols are found

   * at all. RTLD_DEFAULT works though.

   * On Android 64 bit, dlopen(NULL) seems to work but dlsym(handle)

   * always returns 'undefined symbol'. Only if RTLD_DEFAULT or 

   * NULL is given, dlsym returns an appropriate pointer.

   */

  lock_dlerror ();

#if defined(__BIONIC__) || defined(__NetBSD__)

  handle = RTLD_DEFAULT;

#else

  handle = dlopen (NULL, RTLD_GLOBAL | RTLD_LAZY);

#endif

  if (!handle)

    g_module_set_error (fetch_dlerror (TRUE));

  unlock_dlerror ();

  return handle;

}

static void

_g_module_close (gpointer handle)

{

#if defined(__BIONIC__) || defined(__NetBSD__)

  if (handle != RTLD_DEFAULT)

#endif

    {

      lock_dlerror ();

      if (dlclose (handle) != 0)

        g_module_set_error (fetch_dlerror (TRUE));

      unlock_dlerror ();

    }

}

static gpointer

_g_module_symbol (gpointer     handle,

      const gchar *symbol_name)

{

  gpointer p;

  const gchar *msg;

  lock_dlerror ();

  fetch_dlerror (FALSE);

  p = dlsym (handle, symbol_name);

  msg = fetch_dlerror (FALSE);

  if (msg)

    g_module_set_error (msg);

  unlock_dlerror ();

  return p;

}