QA/Bibisect

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Introduction

Bibisect stands for "binary bisect". It's a procedure that helps identify commits that have caused regressions. Regressions are a most annoying artifact that unfortunately come with software development and QA. We want to deal with regressions quickly before time passes and they get harder and harder to triage and fix.

How does Bibisecting Work?

Each bibisect package is a git repository populated with hundreds or thousands of builds of LibreOffice. Added to the repository in chronological order, the builds provide a fast and simple way for us to test a bug against many different versions without having to compile LibreOffice each time we switch to a different version.

We can leverage the tools built into git for binary search through commits (e.g. git bisect) as well as benefit from the compression and de-duplication functions included in git. For example, in a series of builds that each might take up 500MB of disk space, through de-duplication we can potentially use only 25MB per additional build.

Watch Effective Bisection and Bibisection (Matthew Francis's talk at LibOCon 2015 on YouTube) for both an introduction, and practical details.

Details

A successful bibisect will leave developers with only a few commits to search through to find the 'culprit' commit that we believe introduced a regression. QA can go the additional step of fully bisecting (determining the exact commit) or can leave this to the developers. It's often easy to find the commit that caused the issue after bibisecting the bug.

With approximately 10 gigs, you'll have hundreds of builds to work with. A bibisect can take as little as 15 minutes.

Currently, bibisecting is possible on:

As can be seen from the Commits in range and Number of builds, depending upon the particular bibisect repository, this range might be on average 80 commits for old "43max" repository (reaching hundreds of source commits in some builds) to just 1 or 2 commits for newer repositories. (We also have some very 'coarse' bibisect repositories that use released versions + beta + RC builds, and these may have ranges spanning multiple hundreds of commits).

If build commit or range is found, bug is marked with keyword "bibisected", and if source commit is found, bug is additionally marked "bisected".

General Instructions

It might be a good idea for beginners to start by tracing the steps of a bibisect that was already completed successfully. For this purpose we have a bibisecting tutorial.

Note:
Each operating system is different, so please read the page that corresponds to your specific operating system (GNU/Linux, macOS or Windows) for more specific instructions, tips and troubleshooting.

Before bibisecting for the first time, you need to:

Set up your environment (possibly with extra software)
Download the relevant bibisect repository

Once set up, for each bug:

Bibisect the bug
Comment in the bug report with the results
Replace the keyword 'bibisectRequest' with 'bibisected'
If the precise commit causing the regression has been identified, also add the keyword 'bisected', add the developer as CC, and comment 'Adding Cc: to <developer's name>'

Note that you should only add the original author to the CC ("author" on git.libreoffice.org, or "owner" on gerrit), not any reviewers. If a developer has retired from the project (check the date of their last commits), there is no point in adding anyone to the CC. Rather in this case, you should bump the priority of the bug report.

Commit ranges

Some bibisect repositories have ranges of source commits folded into a single chunk. If after completing a bibisect you are presented with only a single one of these chunk commits, you can get the range by first copying the hash (note: not the source hash) and using it in a git log command like so:

git log c3f9dc54188b316a61dd871b63734d49b05f5d7f

Now you can copy the source hashes of the first and previous displayed commits and separate them with .. to construct a range query like so:

https://git.libreoffice.org/core/log/7c4d3ea6ba4d42b4dda5148a00c8c411b5d7703d..5b195fbcf7a441aeb193f6abd08b877e580938e0

This will allow you to skim commit messages looking for related subjects. For deeper scrutiny, see the section on detective work.

Finding the earliest version affected

If you have a local copy of the core repository, you can update the Version field in the bug report thanks to some git commands:

1. First, make sure you have all the tags:

git fetch --tag

2. Then, use `name-rev` to find the context (more precisely, by how many revisions it preceded the earliest tag that contains the commit):

git name-rev <commit>

3. If that didn't give a useful tag that matches a LibreOffice version, you can list all tags that contain the commit and have "libreoffice" in the name with:

git tag --contains <commit> | grep libreoffice

Limitations

Performing a bibisect is only possible if we have a repository available for the correct OS, covering the correct range of LibreOffice commits. We have very good coverage on GNU/Linux, and are improving our coverage on Windows and macOS.

Some regressions are difficult to reproduce, and may require multiple test runs for a bug to appear. As you may imagine, trying to bibisect such regressions is very difficult, and requires one to perform many test runs after each checkout of a new version of LibreOffice to give some security / statistics that the bug is indeed present or not present with the given version.

We do not currently have bibisect support for

LibreOffice for Android
BSDs (although the GNU/Linux bibisect packages may run, with minor tweaks)
LibreOffice Online
LibreOffice Vanilla for Mac (in the Mac App Store)

Versions

Versions are listed on each OS page. See #Details above.

Not Bibisectable

Some bugs are not bibisectable. These include

Bugs that don't show up on a supported platform (see #Limitations)
Bugs that predate our bibisect builds (We're working on extending the range covered)
Bugs that depend upon build options not enabled in the TDF builds (e.g. -kde)

If a bug with bibisectRequest Keyword is found to be not bibisectable, leave a comment on the bug explaining why we're not able to use bibisect to track down the introduction of this problem, and replace Keyword bibisectRequest with notBibisectable. If a bug predates bibisect builds, replace Keyword bibisectRequest with preBibisect.

Finding bugs

Finding bugs needing bibisect

The following bugs with keyword bibisectRequest are waiting for a bibisect:

In addition all unresolved regressions in LibreOffice might benefit from bibisecting.

Finding bugs already bibisected

For the links to bugzilla queries, please see here.

With the above info added to the bug a developer knows that the regression was introduced between the commits fb754a0df859e30255c25af8fa19bfaa75f257e7 (good) and 2d19e9bb07ccff3134f855812dddfda5c07b1fe4 (bad) on master.

git log fb754a0df859e30255c25af8fa19bfaa75f257e7..2d19e9bb07ccff3134f855812dddfda5c07b1fe4

The above command ran in the source repository will show the 128 commits including the one that introduced the bug, making it a lot easier for the developer to close in on the culprit. For more details, see:

Special situations

Bibisecting language-specific bugs

The TDF bibisect repositories provided do not include any lang-packs.

To bibisect bugs which work good with english UI, but bad with non-english UI (like CJKs): one should copy-paste the following files, from a release build which has your language, to the same location of the bibisect repo:

program/resource/<your_lang_tag>
share/registry/Langpack-<your_lang_tag>.xcd
share/registry/res/fcfg_langpack_<your_lang_tag>.xcd
share/registry/res/registry_<your_lang_tag>.xcd

The suggested language resources you should copy is the one for the same major branch. For example, for the bibisect-linux-64-6.0 repo, you can copy from 6.0.1.1 release.

Running with a separate user profile

To create separate profile directory in /tmp/ (which will be automatically removed during the next machine boot):

./opt/program/soffice -env:UserInstallation=file:///tmp/soffice-bisect

If you want to start fresh for each bisect iteration, you can add git commit hash to directory name. For example:

./opt/program/soffice \
-env:UserInstallation=file:///tmp/soffice-bisect-$(git rev-parse HEAD)

Finding a fix

Sometimes a bug is a collateral damage of another (possibly minor) bug, in a non obvious way. In such cases that other bug might be fixed on master, but was not backported to the release branch. To identify a problem-fixing commit you can use:

git bisect start --term-new=fixed --term-old=unfixed
git bisect fixed master
git bisect unfixed <some-old-sha> # you can use "git log --reverse" to detect the first revision in the bibisected package

As you test, say

git bisect fixed

or

git bisect unfixed

as appropriate.

If the fix is small and important enough, it likely can be easily backported to the release branch.

Checking out a specific commit based on source hash

Sometimes you already know a specific source commit has/does not have the bug you are hunting.

Copy the source hash from the LibreOffice git history and use it to grep in the bibisect repo log like so:

git log --all --grep='29a9f433c268414747d8ec7343fc2b5987971738'

Copy the commit hash of the bibisect repo and do a checkout for it to verify your assumption:

git checkout 38758b70f5278d4d8292a2e857e80a9a1130f38e

You can use the repo commit hash when determining the bad-good range to bisect:

git bisect start 38758b70f5278d4d8292a2e857e80a9a1130f38e oldest

Doing detective work inside a commit range

In case your bibisect result is a range of commits and you have trouble locating the offending commit, you might make your life easier by searching with a keyword.

An example for a case, where we know the problem is in Calc's Navigator view:

git log --stat --pretty=short --graph 169bd7718264b0e312052757f9bbd2321e1399c2...ff8b873936aa72b17309da4bfc2775573a5b1f55 | grep -B 10 -A 10 --color=always "sc/source/ui/navipi" | less -R

Adjust the -B and -A grep parameters to control how many lines before and after the hit you want to display. When piping to less, -R preserves the colouring of search results.

Bisect skip hell

Sometimes we get stuck in a miserable situation, where we have to use git bisect skip over and over again due to various reasons. There are ways of getting out of these infuriating messes and here we will show one of them.

Example bug: tdf#123095

Bug appeared in 4.0-4.1 range.

There are lots of commits, where the autofilter is not shown at all, so have to skip those.

We can use git bisect visualize to show us the remaining suspected commits:

git bisect visualize --oneline > /some/path/bisect-viz-123095.txt

The earliest bad results are at the top while the ones you have skipped are at the bottom. The commit below the bottom is the last known good one.

The top results included

  b842ac1 source-hash-7b4d76772ef76a8de852ed647ed0cad368f70189
  40ef04e source-hash-dc173b7f2a550185404aacbc6da744cb6d1880fc
  8e697de source-hash-eb96e4325278f31b9e6fbc1d5c6a01543204ded6

Doing git checkout b842ac1, test, continue with the next etc. it turns out the third one from the top was already a skippable commit.

A range query with the source hashes in the style bottomcommit..firstbadcommit can be made.

Searching for "filter" in the displayed results leads to a suspicious commit about sorting autofilter popup items.

If soffice is failing with a non-zero exit code - this probably means a crash - a solution under QA/Bibisect/Automation#Tidbits for efficiency offers a script to ease the pain of repeatedly skipping failed probes.

Especially in the older repositories, sometimes you can end up with a list of dozens of potential bad commits. The commits might not be in order, so it is not easy to construct a range query. You can save the list of commits to a text file and run git show for all of them, directing the output to a file:

while IFS="" read -r p || [ -n "$p" ]
do
  git show --no-patch "$p" >> /path/to/bisectlog.txt
done < /path/to/bisect_range.txt

The older repositories include the original commit message, so this resulting log file will be immediately useful. If the binary repository doesn't include the original messages, you have to first do a pass with git show --oneline --no-patch, tidy up the list of source hashes and then do the final looping against LibreOffice core repository.

Finding source commits from bibisect

If bibisect was done, but not likely to be correct or in a repository known to have large range of source commits, we can check the range by finding a previous build commit from the found one and then find the source range.

$ git log -1 1f14665c5624bc7a502738aa8f4f2bd70a211e72^
$ git log --oneline b6c016da23d309b4ac7d154bc33a22397974ed73..d85fd8a85501547d5bb87822d2589a07aed7f2d6

Troubleshooting

Please add your problems and how you solved them. This section covers issues that affect more than one OS. For OS-specific issues, please see the individual OS wiki pages.

Unable to extract files

If you can't extract files (you should get an error message). Try to rename the file from *.tar.lzma to *.tar.xz.

Installed LibreOffice became modified unexpectedly

Problem / Messages:

   error: Your local changes to the following files would be overwritten by checkout:
     opt/program/pythonloader.pyc
     opt/program/uno.pyc
     opt/program/unohelper.pyc
   Please, commit your changes or stash them before you can switch branches.
   Aborting

Solutions:

git checkout .

The above command will repair the problem. Afterwards you can start the next test run as usual with

git bisect good # or git bisect bad

If that does not solve the problem, you can try the following commands:

git clean -fd
git reset --hard

The ultimate repair is to delete everything except one hidden .git/ folder, and do

git checkout oldest

Unable to start soffice

Problem 1: Upon trying to run soffice within bibisect you receive the error "unexpected operator terminate called after throwing an instance of 'com::sun::star::uno::DeploymentException'

Solution: Reset your libreoffice profile located in ~/.config/libreoffice. Make sure to backup the folder if you have any settings you'd like to preserve for use with your stable libreoffice release. After you're done with bibisect you can try to return your backed up profile to it's original location (ie. delete the new profile folder and replace it with the backed up one)

Problem 2: Trying to run soffice within bibisect gives frequent errors such as "Application Error" and skipping via 'git bisect skip' is tedious.

Solution: Run a one-line script to skip commits on errors. The script will stop when soffice is successfully run and then you proceed with 'git bisect good' or 'git bisect bad'. If the error is repeated, the script can be run again.

while (git clean -f -X && git bisect skip && ! instdir/program/soffice); do : ; done

A version for PowerShell on Windows, additionally showing how to give arguments to soffice:

Do {
    git clean -f -X && git bisect skip
    $proc = Start-Process -PassThru -FilePath .\instdir\program\soffice -ArgumentList "--norestore C:\path\to\file.odt"
    Wait-Process -InputObject $proc
} until ($proc.ExitCode -eq 0)

Note that if the bug involves crashing, you have to get out of the skipping loop by quitting LibreOffice normally before testing.

How to bisect RTL bugs

In case you need to bisect a RTL ( Right-To-Left ) bug, please import this variable before calling LibreOffice:

SAL_RTL_ENABLED=1

How to bisect File Recovery bugs

In case you need to bisect File Recovery bugs ( e.g. tdf#129210 ), comment out line OOO_DISABLE_RECOVERY=1 in file instdir/program/ooenv

You may also use user control:

soffice --norestore file-that-recovers.ext

How to bisect file hanging / CPU or memory exhaustion bugs

In case you need to bisect file hanging/memory exhaustion bugs, you may limit memory or CPU or time execution.

In Linux, timeout utility can be used. To avoid confusion with built-in "timeout" command, here it's renamed to "tmt".

For example, if LibreOffice 'good' commit opens a file with 1 GB of memory, you may set soffice memory limit to 1.500.000 kilobytes to avoid 'bad' commit hanging your computer.

tmt -m 1500000 instdir/program/soffice

Or, to limit CPU+SYS time (where normal time is seen with successful run):

tmt -t 20 instdir/program/soffice

More advanced option is to use benchexec utility. User needs to be added to the appropriate group (benchexec). Runexec can be used to execute a single command while measuring its resource consumption, similarly to the tool "time" but with more reliable time measurements and with measurement of memory usage.

In Windows, process-governor utility can be used.

Further information

Automation

See the separate article on automating bisecting.

notes

For details on how the bibisect archives are generated:

QA/Bibisect/Implementation