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391 lines
12 KiB
Plaintext
391 lines
12 KiB
Plaintext
git-bisect(1)
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=============
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NAME
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----
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git-bisect - Find by binary search the change that introduced a bug
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SYNOPSIS
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--------
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[verse]
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'git bisect' <subcommand> <options>
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DESCRIPTION
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-----------
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The command takes various subcommands, and different options depending
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on the subcommand:
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git bisect help
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git bisect start [--no-checkout] [<bad> [<good>...]] [--] [<paths>...]
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git bisect bad [<rev>]
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git bisect good [<rev>...]
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git bisect skip [(<rev>|<range>)...]
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git bisect reset [<commit>]
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git bisect visualize
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git bisect replay <logfile>
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git bisect log
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git bisect run <cmd>...
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This command uses 'git rev-list --bisect' to help drive the
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binary search process to find which change introduced a bug, given an
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old "good" commit object name and a later "bad" commit object name.
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Getting help
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~~~~~~~~~~~~
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Use "git bisect" to get a short usage description, and "git bisect
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help" or "git bisect -h" to get a long usage description.
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Basic bisect commands: start, bad, good
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Using the Linux kernel tree as an example, basic use of the bisect
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command is as follows:
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------------------------------------------------
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$ git bisect start
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$ git bisect bad # Current version is bad
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$ git bisect good v2.6.13-rc2 # v2.6.13-rc2 was the last version
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# tested that was good
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------------------------------------------------
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When you have specified at least one bad and one good version, the
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command bisects the revision tree and outputs something similar to
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the following:
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------------------------------------------------
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Bisecting: 675 revisions left to test after this
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------------------------------------------------
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The state in the middle of the set of revisions is then checked out.
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You would now compile that kernel and boot it. If the booted kernel
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works correctly, you would then issue the following command:
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------------------------------------------------
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$ git bisect good # this one is good
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------------------------------------------------
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The output of this command would be something similar to the following:
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------------------------------------------------
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Bisecting: 337 revisions left to test after this
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------------------------------------------------
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You keep repeating this process, compiling the tree, testing it, and
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depending on whether it is good or bad issuing the command "git bisect good"
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or "git bisect bad" to ask for the next bisection.
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Eventually there will be no more revisions left to bisect, and you
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will have been left with the first bad kernel revision in "refs/bisect/bad".
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Bisect reset
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~~~~~~~~~~~~
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After a bisect session, to clean up the bisection state and return to
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the original HEAD (i.e., to quit bisecting), issue the following command:
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------------------------------------------------
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$ git bisect reset
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------------------------------------------------
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By default, this will return your tree to the commit that was checked
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out before `git bisect start`. (A new `git bisect start` will also do
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that, as it cleans up the old bisection state.)
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With an optional argument, you can return to a different commit
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instead:
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------------------------------------------------
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$ git bisect reset <commit>
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------------------------------------------------
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For example, `git bisect reset HEAD` will leave you on the current
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bisection commit and avoid switching commits at all, while `git bisect
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reset bisect/bad` will check out the first bad revision.
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Bisect visualize
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~~~~~~~~~~~~~~~~
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To see the currently remaining suspects in 'gitk', issue the following
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command during the bisection process:
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------------
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$ git bisect visualize
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------------
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`view` may also be used as a synonym for `visualize`.
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If the 'DISPLAY' environment variable is not set, 'git log' is used
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instead. You can also give command line options such as `-p` and
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`--stat`.
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------------
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$ git bisect view --stat
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------------
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Bisect log and bisect replay
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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After having marked revisions as good or bad, issue the following
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command to show what has been done so far:
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------------
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$ git bisect log
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------------
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If you discover that you made a mistake in specifying the status of a
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revision, you can save the output of this command to a file, edit it to
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remove the incorrect entries, and then issue the following commands to
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return to a corrected state:
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------------
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$ git bisect reset
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$ git bisect replay that-file
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------------
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Avoiding testing a commit
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~~~~~~~~~~~~~~~~~~~~~~~~~
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If, in the middle of a bisect session, you know that the next suggested
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revision is not a good one to test (e.g. the change the commit
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introduces is known not to work in your environment and you know it
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does not have anything to do with the bug you are chasing), you may
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want to find a nearby commit and try that instead.
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For example:
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------------
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$ git bisect good/bad # previous round was good or bad.
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Bisecting: 337 revisions left to test after this
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$ git bisect visualize # oops, that is uninteresting.
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$ git reset --hard HEAD~3 # try 3 revisions before what
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# was suggested
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------------
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Then compile and test the chosen revision, and afterwards mark
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the revision as good or bad in the usual manner.
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Bisect skip
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~~~~~~~~~~~~
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Instead of choosing by yourself a nearby commit, you can ask Git
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to do it for you by issuing the command:
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------------
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$ git bisect skip # Current version cannot be tested
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------------
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But Git may eventually be unable to tell the first bad commit among
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a bad commit and one or more skipped commits.
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You can even skip a range of commits, instead of just one commit,
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using the "'<commit1>'..'<commit2>'" notation. For example:
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------------
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$ git bisect skip v2.5..v2.6
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------------
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This tells the bisect process that no commit after `v2.5`, up to and
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including `v2.6`, should be tested.
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Note that if you also want to skip the first commit of the range you
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would issue the command:
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------------
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$ git bisect skip v2.5 v2.5..v2.6
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------------
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This tells the bisect process that the commits between `v2.5` included
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and `v2.6` included should be skipped.
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Cutting down bisection by giving more parameters to bisect start
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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You can further cut down the number of trials, if you know what part of
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the tree is involved in the problem you are tracking down, by specifying
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path parameters when issuing the `bisect start` command:
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------------
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$ git bisect start -- arch/i386 include/asm-i386
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------------
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If you know beforehand more than one good commit, you can narrow the
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bisect space down by specifying all of the good commits immediately after
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the bad commit when issuing the `bisect start` command:
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------------
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$ git bisect start v2.6.20-rc6 v2.6.20-rc4 v2.6.20-rc1 --
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# v2.6.20-rc6 is bad
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# v2.6.20-rc4 and v2.6.20-rc1 are good
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------------
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Bisect run
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~~~~~~~~~~
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If you have a script that can tell if the current source code is good
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or bad, you can bisect by issuing the command:
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------------
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$ git bisect run my_script arguments
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------------
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Note that the script (`my_script` in the above example) should
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exit with code 0 if the current source code is good, and exit with a
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code between 1 and 127 (inclusive), except 125, if the current
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source code is bad.
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Any other exit code will abort the bisect process. It should be noted
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that a program that terminates via "exit(-1)" leaves $? = 255, (see the
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exit(3) manual page), as the value is chopped with "& 0377".
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The special exit code 125 should be used when the current source code
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cannot be tested. If the script exits with this code, the current
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revision will be skipped (see `git bisect skip` above). 125 was chosen
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as the highest sensible value to use for this purpose, because 126 and 127
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are used by POSIX shells to signal specific error status (127 is for
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command not found, 126 is for command found but not executable---these
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details do not matter, as they are normal errors in the script, as far as
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"bisect run" is concerned).
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You may often find that during a bisect session you want to have
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temporary modifications (e.g. s/#define DEBUG 0/#define DEBUG 1/ in a
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header file, or "revision that does not have this commit needs this
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patch applied to work around another problem this bisection is not
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interested in") applied to the revision being tested.
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To cope with such a situation, after the inner 'git bisect' finds the
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next revision to test, the script can apply the patch
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before compiling, run the real test, and afterwards decide if the
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revision (possibly with the needed patch) passed the test and then
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rewind the tree to the pristine state. Finally the script should exit
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with the status of the real test to let the "git bisect run" command loop
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determine the eventual outcome of the bisect session.
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OPTIONS
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-------
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--no-checkout::
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+
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Do not checkout the new working tree at each iteration of the bisection
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process. Instead just update a special reference named 'BISECT_HEAD' to make
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it point to the commit that should be tested.
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+
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This option may be useful when the test you would perform in each step
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does not require a checked out tree.
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If the repository is bare, `--no-checkout` is assumed.
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EXAMPLES
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--------
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* Automatically bisect a broken build between v1.2 and HEAD:
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+
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------------
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$ git bisect start HEAD v1.2 -- # HEAD is bad, v1.2 is good
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$ git bisect run make # "make" builds the app
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$ git bisect reset # quit the bisect session
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------------
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* Automatically bisect a test failure between origin and HEAD:
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+
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------------
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$ git bisect start HEAD origin -- # HEAD is bad, origin is good
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$ git bisect run make test # "make test" builds and tests
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$ git bisect reset # quit the bisect session
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------------
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* Automatically bisect a broken test case:
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+
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------------
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$ cat ~/test.sh
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#!/bin/sh
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make || exit 125 # this skips broken builds
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~/check_test_case.sh # does the test case pass?
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$ git bisect start HEAD HEAD~10 -- # culprit is among the last 10
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$ git bisect run ~/test.sh
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$ git bisect reset # quit the bisect session
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------------
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+
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Here we use a "test.sh" custom script. In this script, if "make"
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fails, we skip the current commit.
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"check_test_case.sh" should "exit 0" if the test case passes,
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and "exit 1" otherwise.
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+
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It is safer if both "test.sh" and "check_test_case.sh" are
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outside the repository to prevent interactions between the bisect,
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make and test processes and the scripts.
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* Automatically bisect with temporary modifications (hot-fix):
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------------
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$ cat ~/test.sh
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#!/bin/sh
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# tweak the working tree by merging the hot-fix branch
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# and then attempt a build
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if git merge --no-commit hot-fix &&
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make
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then
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# run project specific test and report its status
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~/check_test_case.sh
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status=$?
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else
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# tell the caller this is untestable
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status=125
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fi
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# undo the tweak to allow clean flipping to the next commit
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git reset --hard
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# return control
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exit $status
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------------
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+
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This applies modifications from a hot-fix branch before each test run,
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e.g. in case your build or test environment changed so that older
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revisions may need a fix which newer ones have already. (Make sure the
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hot-fix branch is based off a commit which is contained in all revisions
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which you are bisecting, so that the merge does not pull in too much, or
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use `git cherry-pick` instead of `git merge`.)
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* Automatically bisect a broken test case:
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+
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------------
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$ git bisect start HEAD HEAD~10 -- # culprit is among the last 10
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$ git bisect run sh -c "make || exit 125; ~/check_test_case.sh"
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$ git bisect reset # quit the bisect session
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------------
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+
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This shows that you can do without a run script if you write the test
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on a single line.
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* Locate a good region of the object graph in a damaged repository
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+
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------------
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$ git bisect start HEAD <known-good-commit> [ <boundary-commit> ... ] --no-checkout
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$ git bisect run sh -c '
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GOOD=$(git for-each-ref "--format=%(objectname)" refs/bisect/good-*) &&
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git rev-list --objects BISECT_HEAD --not $GOOD >tmp.$$ &&
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git pack-objects --stdout >/dev/null <tmp.$$
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rc=$?
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rm -f tmp.$$
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test $rc = 0'
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$ git bisect reset # quit the bisect session
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------------
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+
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In this case, when 'git bisect run' finishes, bisect/bad will refer to a commit that
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has at least one parent whose reachable graph is fully traversable in the sense
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required by 'git pack objects'.
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SEE ALSO
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--------
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link:git-bisect-lk2009.html[Fighting regressions with git bisect],
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linkgit:git-blame[1].
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GIT
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---
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Part of the linkgit:git[1] suite
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