blob: 68ff3d1f95d53a9fd289f4fc3268591247448dcd [file] [log] [blame]
// Copyright (c) 2011 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "base/native_library.h"
#include <windows.h>
#include "base/files/file_util.h"
#include "base/metrics/histogram_macros.h"
#include "base/strings/string_util.h"
#include "base/strings/stringprintf.h"
#include "base/strings/utf_string_conversions.h"
#include "base/threading/thread_restrictions.h"
namespace base {
using AddDllDirectory = HMODULE (*)(PCWSTR new_directory);
namespace {
// This enum is used to back an UMA histogram, and should therefore be treated
// as append-only.
enum LoadLibraryResult {
// LoadLibraryExW API/flags are available and the call succeeds.
// LoadLibraryExW API/flags are availabe to use but the call fails, then
// LoadLibraryW is used and succeeds.
// LoadLibraryExW API/flags are availabe to use but the call fails, then
// LoadLibraryW is used but fails as well.
// LoadLibraryExW API/flags are unavailabe to use, then LoadLibraryW is used
// and succeeds.
// LoadLibraryExW API/flags are unavailabe to use, then LoadLibraryW is used
// but fails.
// Add new items before this one, always keep this one at the end.
// A helper method to log library loading result to UMA.
void LogLibrarayLoadResultToUMA(LoadLibraryResult result) {
UMA_HISTOGRAM_ENUMERATION("LibraryLoader.LoadNativeLibraryWindows", result,
// A helper method to check if AddDllDirectory method is available, thus
// LOAD_LIBRARY_SEARCH_* flags are available on systems.
bool AreSearchFlagsAvailable() {
// The LOAD_LIBRARY_SEARCH_* flags are available on systems that have
// KB2533623 installed. To determine whether the flags are available, use
// GetProcAddress to get the address of the AddDllDirectory,
// RemoveDllDirectory, or SetDefaultDllDirectories function. If GetProcAddress
// succeeds, the LOAD_LIBRARY_SEARCH_* flags can be used with LoadLibraryEx.
// The LOAD_LIBRARY_SEARCH_* flags are used in the LoadNativeLibraryHelper
// method.
auto add_dll_dir_func = reinterpret_cast<AddDllDirectory>(
GetProcAddress(GetModuleHandle(L"kernel32.dll"), "AddDllDirectory"));
return !!add_dll_dir_func;
// A helper method to encode the library loading result to enum
// LoadLibraryResult.
LoadLibraryResult GetLoadLibraryResult(bool are_search_flags_available,
bool has_load_library_succeeded) {
LoadLibraryResult result;
if (are_search_flags_available) {
if (has_load_library_succeeded)
result = LoadLibraryResult::FAIL_AND_SUCCEED;
result = LoadLibraryResult::FAIL_AND_FAIL;
} else if (has_load_library_succeeded) {
result = LoadLibraryResult::UNAVAILABLE_AND_SUCCEED;
} else {
result = LoadLibraryResult::UNAVAILABLE_AND_FAIL;
return result;
NativeLibrary LoadNativeLibraryHelper(const FilePath& library_path,
NativeLibraryLoadError* error) {
// LoadLibrary() opens the file off disk.
HMODULE module = nullptr;
// This variable records the library loading result.
LoadLibraryResult load_library_result = LoadLibraryResult::SUCCEED;
bool are_search_flags_available = AreSearchFlagsAvailable();
if (are_search_flags_available) {
// LOAD_LIBRARY_SEARCH_DLL_LOAD_DIR flag is needed to search the library
// directory as the library may have dependencies on DLLs in this
// directory.
module = ::LoadLibraryExW(
library_path.value().c_str(), nullptr,
// If LoadLibraryExW succeeds, log this metric and return.
if (module) {
return module;
// GetLastError() needs to be called immediately after
// LoadLibraryExW call.
if (error)
error->code = GetLastError();
// If LoadLibraryExW API/flags are unavailable or API call fails, try
// LoadLibraryW API.
// TODO(chengx): Currently, if LoadLibraryExW API call fails, LoadLibraryW is
// still tried. We should strictly prefer the LoadLibraryExW over the
// LoadLibraryW if LoadLibraryW is statistically showing no extra benefits. If
// UMA metric shows that FAIL_AND_FAIL is the primary failure mode and/or
// FAIL_AND_SUCCESS is close to zero, we should remove this fallback.
// (
// Switch the current directory to the library directory as the library
// may have dependencies on DLLs in this directory.
bool restore_directory = false;
FilePath current_directory;
if (GetCurrentDirectory(&current_directory)) {
FilePath plugin_path = library_path.DirName();
if (!plugin_path.empty()) {
restore_directory = true;
module = ::LoadLibraryW(library_path.value().c_str());
// GetLastError() needs to be called immediately after LoadLibraryW call.
if (!module && error)
error->code = GetLastError();
if (restore_directory)
// Get the library loading result and log it to UMA.
GetLoadLibraryResult(are_search_flags_available, !!module));
return module;
} // namespace
std::string NativeLibraryLoadError::ToString() const {
return StringPrintf("%u", code);
// static
NativeLibrary LoadNativeLibraryWithOptions(const FilePath& library_path,
const NativeLibraryOptions& options,
NativeLibraryLoadError* error) {
return LoadNativeLibraryHelper(library_path, error);
// static
void UnloadNativeLibrary(NativeLibrary library) {
// static
void* GetFunctionPointerFromNativeLibrary(NativeLibrary library,
StringPiece name) {
return GetProcAddress(library,;
// static
std::string GetNativeLibraryName(StringPiece name) {
return name.as_string() + ".dll";
} // namespace base