| // Copyright 2018 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. |
| |
| #ifndef UI_BASE_RESOURCE_WHITELIST_H_ |
| #define UI_BASE_RESOURCE_WHITELIST_H_ |
| |
| namespace ui { |
| |
| // The purpose of this function template is to support resource whitelisting, |
| // which is a mechanism for filtering out unused resources from the .pak files |
| // that we ship (currently only supported on Android). The grit program |
| // generates macros that look like this: |
| // |
| // #define IDS_FOO (::ui::WhitelistedResource<123>(), 123) |
| // |
| // A reference via the macro to the resource causes the function template to be |
| // instantiated with the given resource identifier and (because of the used |
| // attribute) emitted into the object file. After the program is linked, the |
| // used resource identifiers can be found by searching the debug info in the |
| // linker's output file for instantiations of the template. The implementation |
| // of this lives in build/toolchain/gcc_solink_wrapper.py. |
| // |
| // In ELF linkers, the function definitions themselves are dropped from the |
| // final output file because of --gc-sections (debug info is immune to |
| // --gc-sections). In COFF and Mach-O, the used attribute also causes the linker |
| // to preserve the function definitions in the output file, but that shouldn't |
| // affect binary size significantly because all of the function definitions are |
| // the same, which means that they can be ICF'd together (or, more likely, ICF'd |
| // with an existing empty function). |
| // |
| // Because the WhitelistedResource function is constexpr, the definitions of the |
| // resource macros are integral constant expressions, which means that they can |
| // appear in places like case statements in switches. |
| template <int ResourceId> |
| __attribute__((used)) constexpr void WhitelistedResource() {} |
| |
| } // namespace ui |
| |
| #endif |
