Clang is the main supported compiler when building Chromium on all platforms.
This happens by default, with clang binaries being fetched by gclient during the
gclient runhooks phase. To fetch them manually, or build a local custom clang, use
gn args and make sure there is no
is_clang = false in your args.gn file.
ninja -C out/gn chrome
There are no bots that test this but
is_clang = false will revert to gcc on Linux and to Visual Studio on Windows. There is no guarantee it will work.
The chromium style plugin is used by default when clang is used.
If you're working on the plugin, you can build it locally like so:
./tools/clang/scripts/update.py --force-local-build --without-androidto build the plugin.
ninja -C third_party/llvm-build/Release+Asserts/to build incrementally.
To test the FindBadConstructs plugin, run:
(cd tools/clang/plugins/tests && \ ./test.py ../../../../third_party/llvm-build/Release+Asserts/bin/clang \ ../../../../third_party/llvm-build/Release+Asserts/lib/libFindBadConstructs.so)
Since the plugin is rolled with clang changes, behavior changes to the plugin should be guarded by flags to make it easy to roll clang. A general outline:
GNand verify the new behavior.
Since October 2017, clang is the default compiler on Windows. It uses MSVC's linker and SDK, so you still need to have Visual Studio with C++ support installed.
To use MSVC's compiler (if it still works), use
is_clang = false.
clang_base_path in your args.gn to the llvm build directory containing
bin/clang (i.e. the directory you ran cmake). This [must] be an absolute path. You also need to disable chromium's clang plugin.
Here's an example that also disables debug info and enables the component build (both not strictly necessary, but they will speed up your build):
clang_base_path = getenv("HOME") + "/src/llvm-build" clang_use_chrome_plugins = false is_debug = false symbol_level = 1 is_component_build = true
You can then run
head out/gn/toolchain.ninja and check that the first to lines set
cxx to your clang binary. If things look good, run
ninja -C out/gn to build.
If your clang revision is very different from the one currently used in chromium
tools/clang/scripts/update.pyto find chromium's clang revision
LLD is a relatively new linker from LLVM. The current focus is on Windows and Linux support, where it can link Chrome approximately twice as fast as gold and MSVC's link.exe as of this writing.
use_lld = true in args.gn.