We distribute prebuilt packages of LLVM binaries, including clang and lld, that all developers and bots pull at
gclient runhooks time. These binaries are just regular LLVM binaries built at a fixed upstream revision. This document describes how to build a package at a newer revision and update Chromium to it. An archive of all packages built so far is at https://is.gd/chromeclang
tools/clang/scripts/upload_revision.pywith a recent upstream LLVM commit hash as the argument. After the
*_upload_clangtrybots are successfully finished, run go/chrome-promote-clang on the new Clang package name.
Cq-Include-Trybots:lines for all needed bots, so it's sufficient to just run
git cl try(or hit “CQ DRY RUN” on gerrit).
After doing a clang roll, you may get a performance bug assigned to you (example). Some performance noise is expected while doing a clang roll.
You can check all performance data for a clang roll via
XXXXXX is the revision number, e.g.
778090 for the example bug (look in the first message of the performance bug to find this). Click the checkboxes to display graphs. Hover over points in the graph to see the value and error.
Serious regressions require bisecting upstream commits (TODO: how to repro?). If the regressions look insignificant and there is green as well as red, you can close the bug as “WontFix” with an explanation.
The clang package is downloaded unconditionally by all bots and devs. It's called “clang” for historical reasons, but nowadays also contains other mission-critical toolchain pieces besides clang.
We try to limit the contents of the clang package. They should meet these criteria:
If you want to add something to the clang package that doesn‘t (yet?) meet these criteria, you can make package.py upload it to a separate zip file and then download it on an opt-in basis by using update.py’s --package option.
If you‘re adding a new feature that you expect will meet the inclusion criteria eventually but doesn’t yet, start by having your things in a separate zip and move it to the main zip once the criteria are met.