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Chromium for arm Macs

Apple is planning on selling Macs with arm chips by the end of 2020. This document describes the state of native binaries for these Macs.

There's a bot that builds for arm. It cross-builds on an Intel machine.

There's also a tester bot that continuously runs tests. Most tests pass.

Building for arm Macs

You can build Chrome for arm macs on an Intel Mac. To build for arm64, you have to do 2 things:

  1. use the MacOSX11.0.sdk that comes with Xcode 12.2. If you're on Google's corporate network, this SDK is part of the hermetic toolchain and will be used automatically. Otherwise, manually download and install this version of Xcode and, if necessary, make it the active Xcode with xcode-select.

  2. Add target_cpu = "arm64" to your args.gn.

Then build normally.

To run a built Chromium, you need to copy it to your arm mac. If you don't do a component build (e.g. a regular is_debug=false build), you can just copy over Chromium.app from your build directory. If you copy it using macOS's "Shared Folder" feature and Finder, Chromium.app should be directly runnable. If you zip, upload Chromium.app to some web service and download it on the DTK, browsers will set the com.apple.quarantine bit, which will cause Finder to say "Chromium" is damanged and can't be opened. You should move it to the Trash.". In Console.app, the kernel will log kernel: Security policy would not allow process: 2204, /Users/you/Downloads/Chromium.app/Contents/MacOS/Chromium and amfid will log amfid: /Users/you/Downloads/Chromium.app/Contents/MacOS/Chromium signature not valid: -67050. To fix this, open a terminal and run

% cd ~/Downloads && xattr -rc Chromium.app

After that, it should start fine.

As an alternative to building locally, changes can be submitted to the opt-in mac-arm64-rel trybot. A small number of swarming bots are also available for Googlers to run tests on.

You can follow the Mac-ARM64 label to get updates on progress.

Universal Builds

A “universal” (or “fat”) .app can be created from distinct x86_64 and arm64 builds produced from the same source version. Chromium has a universalizer.py tool that can then be used to merge the two builds into a single universal .app.

% ninja -C out/release_x86_64 chrome
% ninja -C out/release_arm64 chrome
% mkdir out/release_universal
% chrome/installer/mac/universalizer.py \
      out/release_x86_64/Chromium.app \
      out/release_arm64/Chromium.app \
      out/release_universal/Chromium.app

The universal build is produced in this way rather than having a single all-encompassing gn configuration because:

  • Chromium builds tend to take a long time, even maximizing the parallelism capabilities of a single machine. This split allows an additional dimension of parallelism by delegating the x86_64 and arm64 build tasks to different machines.
  • During the mac-arm64 bring-up, the x86_64 and arm64 versions were built using different SDK and toolchain versions. When using the hermetic SDK and toolchain, a single version of this package must be shared by an entire source tree, because it’s managed by gclient, not gn. However, as of November 2020, Chromium builds for the two architectures converged and are expected to remain on the same version indefinitely, so this is now more of a historical artifact.

Building on arm Macs

Building on arm Macs means that all the tools we use to build chrome need to either work under Rosetta or have a native arm binary.

We think it makes sense to use arch-specific binaries for stuff that's downloaded in a hook (things pulled from cipd and elsewhere in gclient hooks -- I think this includes clang, gn, clang-format, python3 in depot_tools, ...), and fat binaries for things where we'd end up downloading both binaries anyways (mostly ninja-mac in depot_tools). There's a tracking bug for eventually making native arm binaries available for everything.

Go does not yet support building binaries for arm macs, so all our go tooling needs to run under Rosetta for now.

cipd defaults to downloading Intel binaries on arm macs for now, so that they can run under Rosetta.

If a binary runs under Rosetta, the subprocesses it spawns by default also run under rosetta, even if they have a native slice. The arch tool can be used to prevent this (example cl), which can be useful to work around Rosetta bugs.

As of today, it's possible to install depot_tools and then run fetch chromium, and it will download Chromium and its dependencies, but it will die in runhooks.

ninja, gn, and gomacc all work fine under Rosetta.