1# Copyright (C) 2017 The Android Open Source Project 2# 3# Licensed under the Apache License, Version 2.0 (the "License"); 4# you may not use this file except in compliance with the License. 5# You may obtain a copy of the License at 6# 7# http://www.apache.org/licenses/LICENSE-2.0 8# 9# Unless required by applicable law or agreed to in writing, software 10# distributed under the License is distributed on an "AS IS" BASIS, 11# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 12# See the License for the specific language governing permissions and 13# limitations under the License. 14 15import("//gn/standalone/sanitizers/sanitizers.gni") 16import("//gn/standalone/wasm.gni") 17 18declare_args() { 19 # Background: 20 # there are mainly two C++ libraries around in the world: (i) GNU's 21 # libstdc++ and LLVM's libc++ (aka libcxx). By default Linux provides libstdc++ 22 # (even building with clang on Linux uses that by default) while Mac and 23 # Android switched to libcxx. 24 # buildtools/libcxx(abi) contains a fixed version of the libcxx, the same one 25 # that Chrome uses on most production configurations (% lagging catching up 26 # with our DEPS). 27 # The variable use_custom_libcxx tells our build system to prefer the 28 # aforementioned copy to the system one. 29 # 30 # Now, there are two reasons for using the checked in copy of libcxx: 31 # 1) LLVM sanitizers require that the c++ library is built from sources, 32 # because they need to be instrumented with -fsanitize as well (see 33 # https://github.com/google/sanitizers/wiki/MemorySanitizerLibcxxHowTo). 34 # On top of this, they also require that the c++ library is dynamically 35 # linked to prevent duplicate symbol errors when linking (see Chrome's 36 # build/config/c++/c++.gni) 37 # 2) The libstdc++ situation is too wild on Linux. Modern debian distros are 38 # fine but Ubuntu Trusty still ships a libstdc++ that doesn't fully 39 # support C++17. Hence we enable this flag on Linux by default. 40 # We still retain libstdc++ coverage on the CI bots by overriding 41 # use_custom_libcxx=false when we target a modern library (see the 42 # GCC target in infra/ci/config.py). 43 use_custom_libcxx = is_linux && is_hermetic_clang && !is_wasm 44 custom_libcxx_is_static = !using_sanitizer 45} 46 47libcxx_prefix = "//buildtools/libcxx" 48libcxxabi_prefix = "//buildtools/libcxxabi" 49