@ -3,7 +3,7 @@ git-bisect(1)
NAMENAME
--------
git-bisect - Find the change that introduced a bug by binary searchgit-bisect - Find by binary search the change that introduced a bug
SYNOPSISSYNOPSIS
@ -39,7 +39,8 @@ help" or "git bisect -h" to get a long usage description.
Basic bisect commands: start, bad, goodBasic bisect commands: start, bad, good
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The way you use it is:Using the Linux kernel tree as an example, basic use of the bisect
command is as follows:
------------------------------------------------------------------------------------------------
$ git bisect start$ git bisect start
@ -48,61 +49,63 @@ $ git bisect good v2.6.13-rc2 # v2.6.13-rc2 was the last version
# tested that was good # tested that was good
------------------------------------------------------------------------------------------------
When you give at least one bad and one good versions, it will bisectWhen you have specified at least one bad and one good version, the
the revision tree and say something like:command bisects the revision tree and outputs something similar to
the following:
------------------------------------------------------------------------------------------------
Bisecting: 675 revisions left to test after thisBisecting: 675 revisions left to test after this
------------------------------------------------------------------------------------------------
and check out the state in the middle. Now, compile that kernel, andThe state in the middle of the set of revisions is then checked out.
boot it. Now, let's say that this booted kernel works fine, then justYou would now compile that kernel and boot it. If the booted kernel
doworks correctly, you would then issue the following command:
------------------------------------------------------------------------------------------------
$ git bisect good # this one is good$ git bisect good # this one is good
------------------------------------------------------------------------------------------------
which will now sayThe output of this command would be something similar to the following:
------------------------------------------------------------------------------------------------
Bisecting: 337 revisions left to test after thisBisecting: 337 revisions left to test after this
------------------------------------------------------------------------------------------------
and you continue along, compiling that one, testing it, and dependingYou keep repeating this process, compiling the tree, testing it, and
on whether it is good or bad, you say "git bisect good" or "git bisectdepending on whether it is good or bad issuing the command "git bisect good"
bad", and ask for the next bisection.or "git bisect bad" to ask for the next bisection.
Until you have no more left, and you'll have been left with the firstEventually there will be no more revisions left to bisect, and you
bad kernel rev in "refs/bisect/bad".will have been left with the first bad kernel revision in "refs/bisect/bad".
Bisect resetBisect reset
~~~~~~~~~~~~~~~~~~~~~~~~
Oh, and then after you want to reset to the original head, do aTo return to the original head after a bisect session, issue the
following command:
------------------------------------------------------------------------------------------------
$ git bisect reset$ git bisect reset
------------------------------------------------------------------------------------------------
to get back to the original branch, instead of being on the bisectionThis resets the tree to the original branch instead of being on the
commit ("git bisect start" will do that for you too, actually: it willbisection commit ("git bisect start" will also do that, as it resets
reset the bisection state).the bisection state).
Bisect visualizeBisect visualize
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
During the bisection process, you can sayTo see the currently remaining suspects in 'gitk', issue the following
command during the bisection process:
------------------------
$ git bisect visualize$ git bisect visualize
------------------------
to see the currently remaining suspects in 'gitk'. `visualize` is a bit`view` may also be used as a synonym for `visualize`.
too long to type and `view` is provided as a synonym.
If 'DISPLAY' environment variable is not set, 'git log' is usedIf the 'DISPLAY' environment variable is not set, 'git log' is used
instead. You can even give command line options such as `-p` andinstead. You can also give command line options such as `-p` and
`--stat`.`--stat`.
------------------------
@ -112,57 +115,58 @@ $ git bisect view --stat
Bisect log and bisect replayBisect log and bisect replay
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The good/bad input is logged, andAfter having marked revisions as good or bad, issue the following
command to show what has been done so far:
------------------------
$ git bisect log$ git bisect log
------------------------
shows what you have done so far. You can truncate its output somewhereIf you discover that you made a mistake in specifying the status of a
and save it in a file, and runrevision, you can save the output of this command to a file, edit it to
remove the incorrect entries, and then issue the following commands to
return to a corrected state:
------------------------
$ git bisect reset
$ git bisect replay that-file$ git bisect replay that-file
------------------------
if you find later you made a mistake telling good/bad about aAvoiding testing a commit
revision.
Avoiding to test a commit
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
If in a middle of bisect session, you know what the bisect suggestedIf, in the middle of a bisect session, you know that the next suggested
to try next is not a good one to test (e.g. the change the commitrevision is not a good one to test (e.g. the change the commit
introduces is known not to work in your environment and you know itintroduces is known not to work in your environment and you know it
does not have anything to do with the bug you are chasing), you maydoes not have anything to do with the bug you are chasing), you may
want to find a near-by commit and try that instead.want to find a nearby commit and try that instead.
It goes something like this:For example:
------------------------
$ git bisect good/bad # previous round was good/bad.$ git bisect good/bad # previous round was good or bad.
Bisecting: 337 revisions left to test after thisBisecting: 337 revisions left to test after this
$ git bisect visualize # oops, that is uninteresting.$ git bisect visualize # oops, that is uninteresting.
$ git reset --hard HEAD~3 # try 3 revs before what$ git reset --hard HEAD~3 # try 3 revisions before what
# was suggested # was suggested
------------------------
Then compile and test the one you chose to try. After that, tellThen compile and test the chosen revision, and afterwards mark
bisect what the result was as usual.the revision as good or bad in the usual manner.
Bisect skipBisect skip
~~~~~~~~~~~~~~~~~~~~~~~~
Instead of choosing by yourself a nearby commit, you may just want gitInstead of choosing by yourself a nearby commit, you can ask git
to do it for you using:to do it for you by issuing the command:
------------------------
$ git bisect skip # Current version cannot be tested$ git bisect skip # Current version cannot be tested
------------------------
But computing the commit to test may be slower afterwards and git mayBut computing the commit to test may be slower afterwards and git may
eventually not be able to tell the first bad among a bad and one oreventually not be able to tell the first bad commit among a bad commit
more "skip"ped commits.and one or more skipped commits.
You can even skip a range of commits, instead of just one commit,You can even skip a range of commits, instead of just one commit,
using the "'<commit1>'..'<commit2>'" notation. For example:using the "'<commit1>'..'<commit2>'" notation. For example:
@ -171,33 +175,34 @@ using the "'<commit1>'..'<commit2>'" notation. For example:
$ git bisect skip v2.5..v2.6$ git bisect skip v2.5..v2.6
------------------------
would mean that no commit between `v2.5` excluded and `v2.6` includedThis tells the bisect process that no commit after `v2.5`, up to and
can be tested.including `v2.6`, should be tested.
Note that if you want to also skip the first commit of a range you canNote that if you also want to skip the first commit of the range you
use something like:would issue the command:
------------------------
$ git bisect skip v2.5 v2.5..v2.6$ git bisect skip v2.5 v2.5..v2.6
------------------------
and the commit pointed to by `v2.5` will be skipped too.This tells the bisect process that the commits between `v2.5` included
and `v2.6` included should be skipped.
Cutting down bisection by giving more parameters to bisect startCutting down bisection by giving more parameters to bisect start
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
You can further cut down the number of trials if you know what part ofYou can further cut down the number of trials, if you know what part of
the tree is involved in the problem you are tracking down, by givingthe tree is involved in the problem you are tracking down, by specifying
paths parameters when you say `bisect start`, like this:path parameters when issuing the `bisect start` command:
------------------------
$ git bisect start -- arch/i386 include/asm-i386$ git bisect start -- arch/i386 include/asm-i386
------------------------
If you know beforehand more than one good commits, you can narrow theIf you know beforehand more than one good commit, you can narrow the
bisect space down without doing the whole tree checkout every time youbisect space down by specifying all of the good commits immediately after
give good commits. You give the bad revision immediately after `start`the bad commit when issuing the `bisect start` command:
and then you give all the good revisions you have:
------------------------
$ git bisect start v2.6.20-rc6 v2.6.20-rc4 v2.6.20-rc1 --$ git bisect start v2.6.20-rc6 v2.6.20-rc4 v2.6.20-rc1 --
@ -209,38 +214,38 @@ Bisect run
~~~~~~~~~~~~~~~~~~~~
If you have a script that can tell if the current source code is goodIf you have a script that can tell if the current source code is good
or bad, you can automatically bisect using:or bad, you can bisect by issuing the command:
------------------------
$ git bisect run my_script$ git bisect run my_script
------------------------
Note that the "run" script (`my_script` in the above example) shouldNote that the script (`my_script` in the above example) should
exit with code 0 in case the current source code is good. Exit with aexit with code 0 if the current source code is good, and exit with a
code between 1 and 127 (inclusive), except 125, if the currentcode between 1 and 127 (inclusive), except 125, if the current
source code is bad.source code is bad.
Any other exit code will abort the automatic bisect process. (AAny other exit code will abort the bisect process. It should be noted
program that does "exit(-1)" leaves $? = 255, see exit(3) manual page,that a program that terminates via "exit(-1)" leaves $? = 255, (see the
the value is chopped with "& 0377".)exit(3) manual page), as the value is chopped with "& 0377".
The special exit code 125 should be used when the current source codeThe special exit code 125 should be used when the current source code
cannot be tested. If the "run" script exits with this code, the currentcannot be tested. If the script exits with this code, the current
revision will be skipped, see `git bisect skip` above.revision will be skipped (see `git bisect skip` above).
You may often find that during bisect you want to have near-constantYou may often find that during a bisect session you want to have
tweaks (e.g., s/#define DEBUG 0/#define DEBUG 1/ in a header file, ortemporary modifications (e.g. s/#define DEBUG 0/#define DEBUG 1/ in a
"revision that does not have this commit needs this patch applied toheader file, or "revision that does not have this commit needs this
work around other problem this bisection is not interested in")patch applied to work around another problem this bisection is not
applied to the revision being tested.interested in") applied to the revision being tested.
To cope with such a situation, after the inner 'git bisect' finds theTo cope with such a situation, after the inner 'git bisect' finds the
next revision to test, with the "run" script, you can apply that tweaknext revision to test, the script can apply the patch
before compiling, run the real test, and after the test decides if thebefore compiling, run the real test, and afterwards decide if the
revision (possibly with the needed tweaks) passed the test, rewind therevision (possibly with the needed patch) passed the test and then
tree to the pristine state. Finally the "run" script can exit withrewind the tree to the pristine state. Finally the script should exit
the status of the real test to let the "git bisect run" command loop towith the status of the real test to let the "git bisect run" command loop
determine the outcome.determine the eventual outcome of the bisect session.
EXAMPLESEXAMPLES
----------------
@ -257,39 +262,39 @@ $ git bisect run make # "make" builds the app
------------------------
$ cat ~/test.sh$ cat ~/test.sh
#!/bin/sh#!/bin/sh
make || exit 125 # this "skip"s broken buildsmake || exit 125 # this skips broken builds
make test # "make test" runs the test suitemake test # "make test" runs the test suite
$ git bisect start v1.3 v1.1 -- # v1.3 is bad, v1.1 is good$ git bisect start v1.3 v1.1 -- # v1.3 is bad, v1.1 is good
$ git bisect run ~/test.sh$ git bisect run ~/test.sh
------------------------
++
Here we use a "test.sh" custom script. In this script, if "make"Here we use a "test.sh" custom script. In this script, if "make"
fails, we "skip" the current commit.fails, we skip the current commit.
++
It's safer to use a custom script outside the repo to preventIt is safer to use a custom script outside the repository to prevent
interactions between the bisect, make and test processes and theinteractions between the bisect, make and test processes and the
script.script.
++
And "make test" should "exit 0", if the test suite passes, and"make test" should "exit 0", if the test suite passes, and
"exit 1" (for example) otherwise."exit 1" otherwise.
* Automatically bisect a broken test case:* Automatically bisect a broken test case:
++
------------------------
$ cat ~/test.sh$ cat ~/test.sh
#!/bin/sh#!/bin/sh
make || exit 125 # this "skip"s broken buildsmake || exit 125 # this skips broken builds
~/check_test_case.sh # does the test case passes ?~/check_test_case.sh # does the test case passes ?
$ git bisect start HEAD HEAD~10 -- # culprit is among the last 10$ git bisect start HEAD HEAD~10 -- # culprit is among the last 10
$ git bisect run ~/test.sh$ git bisect run ~/test.sh
------------------------
++
Here "check_test_case.sh" should "exit 0", if the test case passes,Here "check_test_case.sh" should "exit 0" if the test case passes,
and "exit 1" (for example) otherwise.and "exit 1" otherwise.
++
It's safer if both "test.sh" and "check_test_case.sh" scripts areIt is safer if both "test.sh" and "check_test_case.sh" scripts are
outside the repo to prevent interactions between the bisect, make andoutside the repository to prevent interactions between the bisect,
test processes and the scripts.make and test processes and the scripts.
AuthorAuthor
------------
Junio C Hamano
16 years ago