Updating the Windows .order files

The chrome/build/*.orderfile files are used to specify the order in which the linker should lay out symbols in the binary it‘s producing. By ordering functions in the order they’re typically executed during start-up, the start-up time can be reduced slightly.

The order files are used automatically when building with Clang for Windows with the gn flag is_official_build set to true.

To update the order files:

  1. Build with instrumentation enabled:

    The instrumentation will capture the couple of million function calls in a binary as it runs and write them to a file in the \src\tmp directory. Make sure this directory exists.

    gn gen out\instrument --args="is_debug=false is_official_build=true generate_order_files=true symbol_level=1"
    ninja -C out\instrument chrome

    (If you have access to Goma, add use_goma=true to the gn args and -j500 to the Ninja invocation.)

  2. Run the instrumented binaries:

    (Some binaries such as mksnapshot, yasm, and protoc already ran with instrumentation during the build process. The instrumentation output should be available under \src\tmp.)

    Open the Task Manager's Details tab or Process Explorer to be able to see the Process IDs of running programs.

    Run Chrome:


    Note the Process ID of the browser process.

    Check in \src\tmp\ for instrumentation output from the process, for example cygprofile_14652.txt. The files are only written once a certain number of function calls have been made, so sometimes you need to browse a bit for the file to be produced.

  3. If the file appears to have sensible contents (a long list of function names that eventually seem related to what the browser should do), copy it into chrome\build\:

    copy \src\tmp\cygprofile_25392.txt chrome\build\chrome.x64.orderfile
  4. Re-build the chrome target. This will re-link chrome.dll using the new order file and surface any link errors if the order file is broken.

    ninja -C out\instrument chrome
  5. Repeat the previous steps with a 32-bit build, i.e. passing target_cpu="x86" to gn and storing the file as .x86.orderfile.

  6. Upload the order files to Google Cloud Storage. They will get downloaded by a gclient hook based on the contents of the .orderfile.sha1 files.

    You need to have write access to the chromium-browser-clang GCS bucket for this step.

    cd chrome\build\
    upload_to_google_storage.py -b chromium-browser-clang/orderfiles -z orderfile chrome.x64.orderfile chrome.x86.orderfile
    gsutil.py setacl public-read gs://chromium-browser-clang/orderfiles/*
  7. Check in the .sha1 files corresponding to the orderfiles created by the previous step.