Have you ever hit a regression bug like this: "In chromium 85.0.4183.121, things were broken. Back in chromium 86.0.4240.193, it was fine."? A good way to attack bugs like this – where it's unclear what change could have caused the regression, but where you have a reliable repro – is to bisect.
tools/bisect-builds.py automates downloading builds of Chrome across a regression range, conducting a binary search for the problematic change.
If you don't have a chromium checkout, you can fetch just this script with the commands below:
curl -s --basic -n "https://chromium.googlesource.com/chromium/src/+/HEAD/tools/bisect-builds.py?format=TEXT" | base64 -d > bisect-builds.py
curl -s --basic -n "https://chromium.googlesource.com/chromium/src/+/HEAD/tools/bisect-builds.py?format=TEXT" | base64 -D > bisect-builds.py
Windows (no curl, base64) python3
python3 -c "import base64; import urllib.request; print(str(base64.b64decode(urllib.request.urlopen(\"https://chromium.googlesource.com/chromium/src/+/HEAD/tools/bisect-builds.py?format=TEXT\").read()),'utf-8'))" > bisect-builds.py
Run it like this:
python tools/bisect-builds.py -a platform -g good-revision -b bad-revision -- flags-for-chrome
python tools/bisect-builds.py -a mac -g 782793 -b 800218 --use-local-cache --verify-range -- --no-first-run --user-data-dir=/tmp http://example.com
Alternately, if bisecting between stable releases you can specify either end of the bisect range using milestone numbers, like this:
python tools/bisect-builds.py -a mac -g M85 -b M86 --use-local-cache --verify-range
Finally, you can specify either end of the bisect range using version numbers.
python tools/bisect-builds.py -a mac -g 85.0.4183.121 -b 86.0.4240.193 --use-local-cache --verify-range
The three range specifications above are equivalent. Note that in all cases the bisect is being done from trunk builds so merges to a release branch will not be bisected.
Valid archive types (the -a parameter) are
mac, mac64, win, win64, linux (not supported for builds after March 2016), linux64, linux-arm, and chromeos.
You can also use the
-p option to specify a profile. If no
--user-data-dir option is specified, a new profile will be created in a
temporary directory each time you are asked to try a build. If you specify a
profile folder, point to the directory that's a parent of Default/.
The script will download a build in the revision range and execute it. You must then manually check if the bug still repros. Quit Chromium, and the script will ask you if the bug reproduced or not. It will use your answer to drive a binary search, and after just a few steps it will tell you "this regression happened somewhere between revisions 793241 and 793248". From that list, it's usually easy to spot the offending CL. If you're adding the range as a comment to a bug, please always paste the output from bisect-builds.py, as this includes links to the chromium changes in the regression range.
View code changes in revision range with this useful URL (replacing SUCCESS_REV and FAILURE_REV with the range start and end):
Notes: For internal usage, we also enable bisect builds by commits. Please refer to internal doc for more information.
Getting an initial revision range
If you have two Chrome binaries, one which doesn't work, one which does, you can find their revision numbers as follows.
If your revision range is incorrect, or if something about your environment interferes with your reproduction of the bug, you will not get useful results from bisect-builds.py. If you would prefer to know this as soon as possible, rather than after downloading and checking O(log n) builds, pass the --verify-range option to bisect-builds.py. This will check the first and last builds in the range before starting the bisect.
You will have to locate a Flash binary from an official build. If you suspect a Chromium change causing the regression and the Flash version doesn't matter locate any binary on your machine. For instance:
./bisect-builds.py -f /opt/google/chrome/PepperFlash/libpepflashplayer.so -b 232915 -g 230425 -a linux64
python bisect-builds.py -f "C:\Program Files (x86)\Google\Chrome\Application\31.0.1650.39\PepperFlash\pepflashplayer.dll" -b 232915 -g 230425 -a win
./bisect-builds.py -f "/Applications/Google Chrome.app/Contents/Versions/33.0.1707.0/Google Chrome Framework.framework/Internet Plug-Ins/PepperFlash/PepperFlashPlayer.plugin" -b 232915 -g 230425 -a mac
API Keys and Chrome OS builds
Without API keys, Chrome OS won't allow you to log in as a specific user. To run a chromeos bisect on your Linux desktop, add the following variables to your environment (e.g., via .bashrc):
See https://www.chromium.org/developers/how-tos/api-keys for more info about API keys.
Bisecting Per-Revision Builds (Googlers Only)
The -o and -r options available in the internal version of the script allow tighter bisects. Google employees should visit go/bisect-builds for configuration instructions.