a8722a5979
Be more specific about "reasonably green". Add instructions on how to roll your own Clang. Change-Id: If5fd297e41f9a66c7c6e736903c14e911fe5819f Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2373265 Reviewed-by: Hans Wennborg <hans@chromium.org> Commit-Queue: Arthur Eubanks <aeubanks@google.com> Cr-Commit-Position: refs/heads/master@{#801436}
73 lines
3.7 KiB
Markdown
73 lines
3.7 KiB
Markdown
# Updating clang
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We distribute prebuilt packages of LLVM binaries, including clang and lld, that
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all developers and bots pull at `gclient runhooks` time. These binaries are
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just regular LLVM binaries built at a fixed upstream revision. This document
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describes how to build a package at a newer revision and update Chromium to it.
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An archive of all packages built so far is at https://is.gd/chromeclang
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1. Check that https://ci.chromium.org/p/chromium/g/chromium.clang/console
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looks reasonably green. Red bots with seemingly normal test failures are
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usually ok, that likely means the test is broken with the stable Clang as
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well.
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1. Sync your Chromium tree to the latest revision to pick up any plugin
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changes.
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1. Run [go/chrome-push-clang-to-goma](https://goto.google.com/chrome-push-clang-to-goma).
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This takes a recent dry run CL to update clang, and if the trybots were
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successful it will copy the binaries from the staging bucket to the
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production one. Writing to this bucket requires special permissions. File a
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bug at g.co/bugatrooper if you don't have these already (e.g.,
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https://crbug.com/1034081). Then it will push the packages to goma. If you
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do not have the necessary credentials to do the upload, ask
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clang@chromium.org to find someone who does.
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* Alternatively, to create your own roll CL, you can manually run
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`tools/clang/scripts/upload_revision.py` with a recent upstream LLVM
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commit hash as the argument. After the `*_upload_clang` trybots are
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successfully finished, run
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[go/chrome-promote-clang](https://goto.google.com/chrome-promote-clang)
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on the new Clang package name.
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1. Run an exhaustive set of try jobs to test the new compiler. The CL
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description created previously by upload_revision.py includes
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`Cq-Include-Trybots:` lines for all needed bots, so it's sufficient to just
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run `git cl try` (or hit "CQ DRY RUN" on gerrit).
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1. Commit the roll CL from the previous step.
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1. The bots will now pull the prebuilt binary, and goma will have a matching
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binary, too.
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## Performance regressions
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After doing a clang roll, you may get a performance bug assigned to you
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([example](https://crbug.com/1094671)). Some performance noise is expected
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while doing a clang roll.
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You can check all performance data for a clang roll via
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`https://chromeperf.appspot.com/group_report?rev=XXXXXX`, where `XXXXXX` is the
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revision number, e.g. `778090` for the example bug (look in the first message
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of the performance bug to find this). Click the checkboxes to display graphs.
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Hover over points in the graph to see the value and error.
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Serious regressions require bisecting upstream commits (TODO: how to repro?).
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If the regressions look insignificant and there is green as well as red, you
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can close the bug as "WontFix" with an explanation.
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## Adding files to the clang package
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The clang package is downloaded unconditionally by all bots and devs. It's
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called "clang" for historical reasons, but nowadays also contains other
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mission-critical toolchain pieces besides clang.
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We try to limit the contents of the clang package. They should meet these
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criteria:
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- things that are used by most developers use most of the time (e.g. a
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compiler, a linker, sanitizer runtimes)
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- things needed for doing official builds
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If you want to add something to the clang package that doesn't (yet?) meet
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these criteria, you can make package.py upload it to a separate zip file
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and then download it on an opt-in basis by using update.py's --package option.
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If you're adding a new feature that you expect will meet the inclusion criteria
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eventually but doesn't yet, start by having your things in a separate zip
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and move it to the main zip once the criteria are met.
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