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diff --git a/Documentation/git-bisect.txt b/Documentation/git-bisect.txt new file mode 100644 index 0000000000..e4f46bc18d --- /dev/null +++ b/Documentation/git-bisect.txt @@ -0,0 +1,385 @@ +git-bisect(1) +============= + +NAME +---- +git-bisect - Find by binary search the change that introduced a bug + + +SYNOPSIS +-------- +[verse] +'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. 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`. + +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 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. + +Any other exit code will abort the bisect process. It should be noted +that a program that terminates via "exit(-1)" leaves $? = 255, (see the +exit(3) manual page), as the value is chopped with "& 0377". + +The special exit code 125 should be used when the current source code +cannot be tested. If the script exits with this code, the current +revision will be skipped (see `git bisect skip` above). 125 was chosen +as the highest sensible value to use for this purpose, because 126 and 127 +are used by POSIX shells to signal specific error status (127 is for +command not found, 126 is for command found but not executable---these +details do not matter, as they are normal errors in the script, as far as +"bisect run" is concerned). + +You may often find that during a bisect session you want to have +temporary modifications (e.g. s/#define DEBUG 0/#define DEBUG 1/ in a +header file, or "revision that does not have this commit needs this +patch applied to work around another problem this bisection is not +interested in") applied to the revision being tested. + +To cope with such a situation, after the inner 'git bisect' finds the +next revision to test, the script can apply the patch +before compiling, run the real test, and afterwards decide if the +revision (possibly with the needed patch) passed the test and then +rewind the tree to the pristine state. Finally the script should exit +with the status of the real test to let the "git bisect run" command loop +determine the eventual outcome of the bisect session. + +OPTIONS +------- +--no-checkout:: ++ +Do not checkout the new working tree at each iteration of the bisection +process. Instead just update a special reference named 'BISECT_HEAD' to make +it point to the commit that should be tested. ++ +This option may be useful when the test you would perform in each step +does not require a checked out tree. ++ +If the repository is bare, `--no-checkout` is assumed. + +EXAMPLES +-------- + +* Automatically bisect a broken build between v1.2 and HEAD: ++ +------------ +$ git bisect start HEAD v1.2 -- # HEAD is bad, v1.2 is good +$ git bisect run make # "make" builds the app +------------ + +* 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 +------------ + +* 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. + +* 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 $status +------------ ++ +This applies modifications from a hot-fix branch before each test run, +e.g. in case your build or test environment changed so that older +revisions may need a fix which newer ones have already. (Make sure the +hot-fix branch is based off a commit which is contained in all revisions +which you are bisecting, so that the merge does not pull in too much, or +use `git cherry-pick` instead of `git merge`.) + +* Automatically bisect a broken test case: ++ +------------ +$ 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. + +* 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'. + + +SEE ALSO +-------- +link:git-bisect-lk2009.html[Fighting regressions with git bisect], +linkgit:git-blame[1]. + +GIT +--- +Part of the linkgit:git[1] suite |