ae1e319261
LLD is (generally) used by default on Android, Fuchsia, Linux, and Windows nowadays, so it's no longer "experimental". We probably don't need to mention it at all here; just remove this paragraph. Bug: none Change-Id: I50a283b4ad4d9a3a7e56c2886759027c5c6c4f4f Reviewed-on: https://chromium-review.googlesource.com/c/1359517 Commit-Queue: Hans Wennborg <hans@chromium.org> Reviewed-by: Hans Wennborg <hans@chromium.org> Cr-Commit-Position: refs/heads/master@{#613467}
105 lines
3.4 KiB
Markdown
105 lines
3.4 KiB
Markdown
# Clang
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[Clang](http://clang.llvm.org/) is the main supported compiler when
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building Chromium on all platforms.
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Known [clang bugs and feature
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requests](http://code.google.com/p/chromium/issues/list?q=label:clang).
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[TOC]
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## Building with clang
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This happens by default, with clang binaries being fetched by gclient
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during the `gclient runhooks` phase. To fetch them manually, or build
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a local custom clang, use
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tools/clang/scripts/update.py
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Run `gn args` and make sure there is no `is_clang = false` in your args.gn file.
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Build: `ninja -C out/gn chrome`
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## Reverting to gcc on Linux or MSVC on Windows
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There are no bots that test this but `is_clang = false` will revert to
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gcc on Linux and to Visual Studio on Windows. There is no guarantee it
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will work.
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## Mailing List
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https://groups.google.com/a/chromium.org/group/clang/topics
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## Using plugins
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The
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[chromium style plugin](https://dev.chromium.org/developers/coding-style/chromium-style-checker-errors)
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is used by default when clang is used.
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If you're working on the plugin, you can build it locally like so:
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1. Run `./tools/clang/scripts/update.py --force-local-build --without-android`
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to build the plugin.
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1. Run `ninja -C third_party/llvm-build/Release+Asserts/` to build incrementally.
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1. Build with clang like described above, but, if you use goma, disable it.
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To test the FindBadConstructs plugin, run:
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(cd tools/clang/plugins/tests && \
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./test.py ../../../../third_party/llvm-build/Release+Asserts/bin/clang \
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../../../../third_party/llvm-build/Release+Asserts/lib/libFindBadConstructs.so)
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Since the plugin is rolled with clang changes, behavior changes to the plugin
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should be guarded by flags to make it easy to roll clang. A general outline:
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1. Implement new plugin behavior behind a flag.
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1. Wait for a compiler roll to bring in the flag.
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1. Start passing the new flag in `GN` and verify the new behavior.
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1. Enable the new plugin behavior unconditionally and update the plugin to
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ignore the flag.
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1. Wait for another compiler roll.
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1. Stop passing the flag from `GN`.
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1. Remove the flag completely.
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## Using the clang static analyzer
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See [clang_static_analyzer.md](clang_static_analyzer.md).
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## Windows
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Since October 2017, clang is the default compiler on Windows. It uses
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MSVC's linker and SDK, so you still need to have Visual Studio with
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C++ support installed.
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To use MSVC's compiler (if it still works), use `is_clang = false`.
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Current brokenness:
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* To get colored diagnostics, you need to be running
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[ansicon](https://github.com/adoxa/ansicon/releases).
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## Using a custom clang binary
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Set `clang_base_path` in your args.gn to the llvm build directory containing
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`bin/clang` (i.e. the directory you ran cmake). This [must][1] be an absolute
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path. You also need to disable chromium's clang plugin.
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Here's an example that also disables debug info and enables the component build
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(both not strictly necessary, but they will speed up your build):
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```
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clang_base_path = getenv("HOME") + "/src/llvm-build"
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clang_use_chrome_plugins = false
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is_debug = false
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symbol_level = 1
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is_component_build = true
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```
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You can then run `head out/gn/toolchain.ninja` and check that the first to
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lines set `cc` and `cxx` to your clang binary. If things look good, run `ninja
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-C out/gn` to build.
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If your clang revision is very different from the one currently used in chromium
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* Check `tools/clang/scripts/update.py` to find chromium's clang revision
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* You might have to tweak warning flags.
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