git-bisect
(1)
Name
git-bisect - Find by binary search the change that
introduced a bug
Synopsis
git bisect <subcommand> <options>
Description
Git Manual GIT-BISECT(1)
NAME
git-bisect - Find by binary search the change that
introduced a bug
SYNOPSIS
git bisect <subcommand> <options>
DESCRIPTION
The command takes various subcommands, and different options
depending on the subcommand:
git bisect help
git bisect start [--no-checkout] [<bad> [<good>...]] [--] [<paths>...]
git bisect bad [<rev>]
git bisect good [<rev>...]
git bisect skip [(<rev>|<range>)...]
git bisect reset [<commit>]
git bisect visualize
git bisect replay <logfile>
git bisect log
git bisect run <cmd>...
This command uses git rev-list --bisect to help drive the
binary search process to find which change introduced a bug,
given an old "good" commit object name and a later "bad"
commit object name.
Getting help
Use "git bisect" to get a short usage description, and "git
bisect help" or "git bisect -h" to get a long usage
description.
Basic bisect commands: start, bad, good
Using the Linux kernel tree as an example, basic use of the
bisect command is as follows:
$ git bisect start
$ git bisect bad # Current version is bad
$ git bisect good v2.6.13-rc2 # v2.6.13-rc2 was the last version
# tested that was good
When you have specified at least one bad and one good
version, the command bisects the revision tree and outputs
something similar to the following:
Bisecting: 675 revisions left to test after this
The state in the middle of the set of revisions is then
checked out. You would now compile that kernel and boot it.
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If the booted kernel works correctly, you would then issue
the following command:
$ git bisect good # this one is good
The output of this command would be something similar to the
following:
Bisecting: 337 revisions left to test after this
You keep repeating this process, compiling the tree, testing
it, and depending on whether it is good or bad issuing the
command "git bisect good" or "git bisect bad" to ask for the
next bisection.
Eventually there will be no more revisions left to bisect,
and you will have been left with the first bad kernel
revision in "refs/bisect/bad".
Bisect reset
After a bisect session, to clean up the bisection state and
return to the original HEAD, issue the following command:
$ git bisect reset
By default, this will return your tree to the commit that
was checked out before git bisect start. (A new git bisect
start will also do that, as it cleans up the old bisection
state.)
With an optional argument, you can return to a different
commit instead:
$ git bisect reset <commit>
For example, git bisect reset HEAD will leave you on the
current bisection commit and avoid switching commits at all,
while git bisect reset bisect/bad will check out the first
bad revision.
Bisect visualize
To see the currently remaining suspects in gitk, issue the
following command during the bisection process:
$ git bisect visualize
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 instead. You can also give command line options such as
-p and --stat.
$ git bisect view --stat
Bisect log and bisect replay
After having marked revisions as good or bad, issue the
following command to show what has been done so far:
$ git bisect log
If you discover that you made a mistake in specifying the
status of a revision, 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
Avoiding testing a commit
If, in the middle of a bisect session, you know that the
next suggested revision 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 it does not have anything to do
with the bug you are chasing), you may want to find a nearby
commit and try that instead.
For example:
$ git bisect good/bad # previous round was good or bad.
Bisecting: 337 revisions left to test after this
$ git bisect visualize # oops, that is uninteresting.
$ git reset --hard HEAD~3 # try 3 revisions before what
# was suggested
Then compile and test the chosen revision, and afterwards
mark the revision as good or bad in the usual manner.
Bisect skip
Instead of choosing by yourself a nearby commit, you can ask
git to do it for you by issuing the command:
$ git bisect skip # Current version cannot be tested
But git may eventually be unable to tell the first bad
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commit among a bad commit and one or more skipped commits.
You can even skip a range of commits, instead of just one
commit, using the "<commit1>..<commit2>" notation. For
example:
$ git bisect skip v2.5..v2.6
This tells the bisect process that no commit after v2.5, up
to and including v2.6, should be tested.
Note that if you also want to skip the first commit of the
range you would issue the command:
$ git bisect skip v2.5 v2.5..v2.6
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
start
You 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 specifying path parameters when issuing
the bisect start command:
$ git bisect start -- arch/i386 include/asm-i386
If you know beforehand more than one good commit, you can
narrow the bisect space down by specifying all of the good
commits immediately after the bad commit when issuing the
bisect start command:
$ git bisect start v2.6.20-rc6 v2.6.20-rc4 v2.6.20-rc1 --
# v2.6.20-rc6 is bad
# v2.6.20-rc4 and v2.6.20-rc1 are good
Bisect run
If you have a script that can tell if the current source
code is good or bad, you can bisect by issuing the command:
$ git bisect run my_script arguments
Note that the script (my_script in the above example) should
exit with code 0 if the current source code is good, and
exit with a code between 1 and 127 (inclusive), except 125,
if the current source code is bad.
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Any other exit code will abort the bisect process. It should
be noted that a program that terminates via "exit(-1)"
leaves $? = 255, (see the exit(3) manual page), as the value
is chopped with "& 0377".
The special exit code 125 should be used when the current
source code cannot be tested. If the script exits with this
code, the current revision will be skipped (see git bisect
skip above). 125 was chosen as the highest sensible value to
use for this purpose, because 126 and 127 are used by POSIX
shells to signal specific error status (127 is for command
not found, 126 is for command found but not
executable---these details do not matter, as they are normal
errors in the script, as far as "bisect run" is concerned).
You may often find that during a bisect session you want to
have temporary modifications (e.g. s/#define DEBUG 0/#define
DEBUG 1/ in a header file, or "revision that does not have
this commit needs this patch applied to work around another
problem this bisection is not interested in") applied to the
revision being tested.
To cope with such a situation, after the inner git bisect
finds the next revision to test, the script can apply the
patch before compiling, run the real test, and afterwards
decide if the revision (possibly with the needed patch)
passed the test and then rewind the tree to the pristine
state. Finally the script should exit with the status of the
real test to let the "git bisect run" command loop determine
the eventual outcome of the bisect session.
OPTIONS
--no-checkout
Do not checkout the new working tree at each iteration
of the bisection process. Instead just update a special
reference named BISECT_HEAD to make it point to the
commit that should be tested.
This option may be useful when the test you would
perform in each step does not require a checked out
tree.
If the repository is bare, --no-checkout is assumed.
EXAMPLES
o Automatically bisect a broken build between v1.2 and
HEAD:
$ git bisect start HEAD v1.2 -- # HEAD is bad, v1.2 is good
$ git bisect run make # "make" builds the app
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o Automatically bisect a test failure between origin and
HEAD:
$ git bisect start HEAD origin -- # HEAD is bad, origin is good
$ git bisect run make test # "make test" builds and tests
o Automatically bisect a broken test case:
$ cat ~/test.sh
#!/bin/sh
make || exit 125 # this skips broken builds
~/check_test_case.sh # does the test case pass?
$ git bisect start HEAD HEAD~10 -- # culprit is among the last 10
$ git bisect run ~/test.sh
Here we use a "test.sh" custom script. In this script,
if "make" fails, we skip the current commit.
"check_test_case.sh" should "exit 0" if the test case
passes, and "exit 1" otherwise.
It is safer if both "test.sh" and "check_test_case.sh"
are outside the repository to prevent interactions
between the bisect, make and test processes and the
scripts.
o Automatically bisect with temporary modifications
(hot-fix):
$ cat ~/test.sh
#!/bin/sh
# tweak the working tree by merging the hot-fix branch
# and then attempt a build
if git merge --no-commit hot-fix &&
make
then
# run project specific test and report its status
~/check_test_case.sh
status=$?
else
# tell the caller this is untestable
status=125
fi
# undo the tweak to allow clean flipping to the next commit
git reset --hard
# return control
exit $status
This applies modifications from a hot-fix branch before
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each test run, e.g. in case your build or test
environment changed so that older revisions may need a
fix which newer ones have already. (Make sure the
hot-fix branch is based off a commit which is contained
in all revisions which you are bisecting, so that the
merge does not pull in too much, or use git cherry-pick
instead of git merge.)
o Automatically bisect a broken test case:
$ git bisect start HEAD HEAD~10 -- # culprit is among the last 10
$ git bisect run sh -c "make || exit 125; ~/check_test_case.sh"
This shows that you can do without a run script if you
write the test on a single line.
o Locate a good region of the object graph in a damaged
repository
$ git bisect start HEAD <known-good-commit> [ <boundary-commit> ... ] --no-checkout
$ git bisect run sh -c '
GOOD=$(git for-each-ref "--format=%(objectname)" refs/bisect/good-*) &&
git rev-list --objects BISECT_HEAD --not $GOOD >tmp.$$ &&
git pack-objects --stdout >/dev/null <tmp.$$
rc=$?
rm -f tmp.$$
test $rc = 0'
In this case, when git bisect run finishes, bisect/bad
will refer to a commit that has at least one parent
whose reachable graph is fully traversable in the sense
required by git pack objects.
ATTRIBUTES
See attributes(5) for descriptions of the following
attributes:
+---------------+--------------------------+
|ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+---------------+--------------------------+
|Availability | developer/versioning/git |
+---------------+--------------------------+
|Stability | Uncommitted |
+---------------+--------------------------+
SEE ALSO
Fighting regressions with git bisect[1], git-blame(1).
GIT
Part of the git(1) suite
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NOTES
1. Fighting regressions with git bisect
file:///home/junio/share/doc/git-doc/git-bisect-lk2009.html
This software was built from source available at
https://java.net/projects/solaris-userland. The original
community source was downloaded from http://git-
core.googlecode.com/files/git-1.7.9.2.tar.gz
Further information about this software can be found on the
open source community website at http://git-scm.com/.
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