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v8-updates.md

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V8 Updates

To update the version of V8 used by workerd, the steps are:

  1. Check https://chromiumdash.appspot.com/ and identify the latest version of V8 used by the beta versions of Chrome beta.

  2. Install depot_tools if it is not already present on your machine.

    https://commondatastorage.googleapis.com/chrome-infra-docs/flat/depot_tools/docs/html/depot_tools_tutorial.html#_setting_up

  3. Fetch a local copy of V8:

    mkdir v8
cd v8
fetch v8

  4. Sync the local copy of V8 to the version used by workerd.

    First find, the tag of the V8 http_archive (name = "v8") in the workerd WORKSPACE file.

    Then sync your fetched version v8 based on the tag.

    cd <path_to_v8>/v8
git checkout <tag>
gclient sync

  5. Create a V8 branch for workerd's V8 patches in your local copy of V8.

    git checkout -b workerd-patches
git am <path_to_workerd>/patches/v8/*

  6. Rebase the workerd V8 changes onto the new version of V8. For example, assuming we are updating to 11.4.183.8 and there are 19 workerd patches for V8, the command would be:

    git rebase --onto 11.4.183.8 HEAD~19

    Note that HEAD~19, here and elsewhere, could be replaced with $(git describe --tags --abbrev=0), which prints the name of the tag on which the branch is based.

    There is usually some minor patch editing required during a rebase.

    Ideally at this stage, you should be able to build and test the local V8 with the patches applied. See the V8 Testing page.

  7. Re-generate workerd's V8 patches. Assuming there are 19 workerd patches for V8, the command would be:

    git format-patch --full-index -k --no-signature --no-stat --zero-commit HEAD~19

  8. Remove the existing patches from workerd/patches/v8 and copy over the latest generated patches from the V8 directory.

  9. Update the http_archive for V8 in the workerd/WORKSPACE file.

    The list of patches should be refreshed if new patches are being added or existing patches are being removed.

    strip_prefix and url in the http_archive for V8 should be updated based on the new V8 version/tag.

    The integrity check needs to be updated to the new value. You can get the new value in bazel's preferred format just by looking into the mismatch error while trying to compile workerd using the newer V8 version or by running openssl dgst -sha256 -binary <tarball_filename> | openssl base64 -A

    See V8 http_archive in WORKSPACE

  10. Update V8's dependencies in workerd/WORKSPACE.

    You can find the commit versions for V8's dependencies under v8/DEPS and the ones that are carried through to workerd in the workerd/WORKSPACE file.

    These currently include zlib and com_googlesource_chromium_icu. Typically you'll get a build failure if the projects are out of sync. Copy the commit versions from v8/DEPS to the WORKSPACE file.

  11. Check workerd's tests pass with the updated V8.

    bazel test //...

  12. Commit your workerd changes and push them for review.