4eeedf7979
Bug: none Change-Id: If369a5b8880c8412da00118a00fd08d84c6a78ad Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6177037 Reviewed-by: Nico Weber <thakis@chromium.org> Auto-Submit: Hans Wennborg <hans@chromium.org> Commit-Queue: Nico Weber <thakis@chromium.org> Cr-Commit-Position: refs/heads/main@{#1407861}
108 lines
3.7 KiB
Markdown
108 lines
3.7 KiB
Markdown
# Clang
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Chromium ships a prebuilt [clang](http://clang.llvm.org) binary.
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It's just upstream clang built at a known-good revision that we
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bump every two weeks or so.
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This is the only supported compiler for building Chromium.
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[TOC]
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## Using gcc on Linux
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`is_clang = false` will make the build use system gcc on Linux. There are no
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bots that test this and there is no guarantee it will work, but we accept
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patches for this configuration.
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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/build.py --without-android --without-fuchsia`
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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 reclient, 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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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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clang is the default compiler on Windows. It uses MSVC's SDK, so you still need
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to have Visual Studio with C++ support installed.
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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 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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On Windows, for `clang_base_path` use something like this instead:
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```
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clang_base_path = "c:/src/llvm-build"
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```
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You can then look in `out/gn/toolchain.ninja` and check that the `rule cc` and
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`rule cxx` commands run your clang binary. If things look good, run `ninja
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-C out/gn` to build.
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Chromium tries to be buildable with its currently pinned clang, and with clang
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trunk. Set `llvm_force_head_revision = true` in your args.gn if the clang you're
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trying to build with is closer to clang trunk than to Chromium's pinned clang
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(which `tools/clang/scripts/update.py --print-revision` prints).
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## Related documents
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* [Toolchain support](toolchain_support.md) gives an overview of clang
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rolls, and documents when to revert clang rolls and how to file good
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toolchain bugs.
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* [Updating clang](updating_clang.md) documents the mechanics of updating clang,
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and which files are included in the default clang package.
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* [Clang Sheriffing](clang_sheriffing.md) contains instructions for how to debug
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compiler bugs, for clang sheriffs.
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* [Clang Tool Refactoring](clang_tool_refactoring.md) has notes on how to build
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and run refactoring tools based on clang's libraries.
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* [Updating Clang format binaries](updating_clang_format_binaries.md) has notes
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on how to update clang-format.
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