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gstplugin: Better warnings on plugin load failure on Windows

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It is an extremely common mistake on Windows to have incorrect PATH
values when loading a plugin, and the error from g_module_error()
(which just calls FormatMessageW()) is very confusing in this case:

 The specified module could not be found.

 https://docs.microsoft.com/en-us/windows/win32/debug/system-error-codes--0-499-#ERROR_MOD_NOT_FOUND

It implies the plugin itself could not be found. The actual issue is
that a DLL dependency could not be found. We need to detect this case
and print a more useful error message.

We should still print the error fetched from FormatMessage() so that
people are able to google for it.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/1589>
This commit is contained in:
Nirbheek Chauhan 2022-01-19 20:58:36 +05:30 committed by Tim-Philipp Müller
parent 9e58632c71
commit 912a39ba6e
1 changed files with 75 additions and 4 deletions
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79
gst/gstplugin.c
View file

@ -727,6 +727,69 @@ extract_symname (const char *filename)
return symname;
}
#ifdef G_OS_WIN32
/*
* It is an extremely common mistake on Windows to have incorrect PATH values
* when loading a plugin, and the error message is very confusing in this case:
* 'The specified module could not be found.' which implies the plugin itself
* could not be found. The actual issue is that a DLL dependency could not be
* found. We need to detect this case and print a more useful error message.
*
* Unfortunately, g_module_open() doesn't actually give us the GetLastError()
* code from LoadLibraryW() and only gives us a literal message from
* FormatMessageW(). We can't do a string comparison on that because it is
* locale-dependent.
*
* The only way out is for us to try loading the module ourselves on failure and
* get the error DWORD again from GetLastError().
*/
static char *
get_better_module_load_error (const char *filename, const char *orig_err_msg)
{
BOOL ret;
DWORD mode;
wchar_t *wfilename;
HMODULE handle;
char *err_msg = NULL;
wfilename = g_utf8_to_utf16 (filename, -1, NULL, NULL, NULL);
ret = SetThreadErrorMode (SEM_NOOPENFILEERRORBOX | SEM_FAILCRITICALERRORS,
&mode);
#ifdef GST_WINAPI_ONLY_APP
handle = LoadPackagedLibrary (wfilename, 0);
#else
handle = LoadLibraryW (wfilename);
#endif
g_free (wfilename);
if (handle == NULL) {
DWORD err = GetLastError ();
char *win32_err_msg = g_win32_error_message (err);
if (err == ERROR_MOD_NOT_FOUND) {
err_msg = g_strdup_printf ("%s\nThis usually means Windows was unable "
"to find a DLL dependency of the plugin. Please check that PATH is "
"correct.\nYou can run 'dumpbin -dependents' (provided by the "
"Visual Studio developer prompt) to list the DLL deps of any DLL.\n"
"There are also some third-party GUIs to list and debug DLL "
"dependencies recursively.", win32_err_msg);
g_free (win32_err_msg);
} else {
err_msg = win32_err_msg;
}
} else {
err_msg = g_strdup_printf ("g_module_open() failed on %s with \"%s\" but "
"manual loading succeeded; this should be impossible! Please "
"report this as a GStreamer bug.", filename, orig_err_msg);
FreeLibrary (handle);
}
if (ret > 0)
SetThreadErrorMode (mode, NULL);
return err_msg;
}
#endif /* G_OS_WIN32 */
/* Note: The return value is (transfer full) although we work with floating
* references here. If a new plugin instance is created, it is always sinked
* in the registry first and a new reference is returned
@ -802,15 +865,23 @@ _priv_gst_plugin_load_file_for_registry (const gchar * filename,
module = g_module_open (filename, flags);
if (module == NULL) {
GST_CAT_WARNING (GST_CAT_PLUGIN_LOADING, "module_open failed: %s",
g_module_error ());
#ifdef G_OS_WIN32
/* flags are meaningless / ignored on Windows */
char *err_msg = get_better_module_load_error (filename, g_module_error ());
#else
const char *err_msg = g_module_error ();
#endif
GST_CAT_WARNING (GST_CAT_PLUGIN_LOADING, "module_open failed: %s", err_msg);
g_set_error (error,
GST_PLUGIN_ERROR, GST_PLUGIN_ERROR_MODULE, "Opening module failed: %s",
g_module_error ());
err_msg);
/* If we failed to open the shared object, then it's probably because a
* plugin is linked against the wrong libraries. Print out an easy-to-see
* message in this case. */
g_warning ("Failed to load plugin '%s': %s", filename, g_module_error ());
g_warning ("Failed to load plugin '%s': %s", filename, err_msg);
#ifdef G_OS_WIN32
g_free (err_msg);
#endif
goto return_error;
}