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diff --git a/Documentation/git-bisect.txt b/Documentation/git-bisect.txt index 5f68ee1584..4cb52a7302 100644 --- a/Documentation/git-bisect.txt +++ b/Documentation/git-bisect.txt @@ -3,35 +3,45 @@ git-bisect(1) NAME ---- -git-bisect - Find the change that introduced a bug by binary search +git-bisect - Find by binary search the change that introduced a bug SYNOPSIS -------- -'git bisect' <subcommand> <options> +[verse] +'git bisect' <subcommand> <options> DESCRIPTION ----------- The command takes various subcommands, and different options depending on the subcommand: - git bisect start [<bad> [<good>...]] [--] [<paths>...] - git bisect bad <rev> - git bisect good <rev> - git bisect reset [<branch>] + 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' option to help drive the +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 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -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 @@ -40,115 +50,170 @@ $ git bisect good v2.6.13-rc2 # v2.6.13-rc2 was the last version # tested that was good ------------------------------------------------ -When you give at least one bad and one good versions, it will bisect -the revision tree and say something like: +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 ------------------------------------------------ -and check out the state in the middle. Now, compile that kernel, and -boot it. Now, let's say that this booted kernel works fine, then just -do +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 ------------------------------------------------ -which will now say +The output of this command would be something similar to the following: ------------------------------------------------ Bisecting: 337 revisions left to test after this ------------------------------------------------ -and you continue along, compiling that one, testing it, and depending -on whether it is good or bad, you say "git bisect good" or "git bisect -bad", and ask for the next bisection. +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. -Until you have no more left, and you'll have been left with the first -bad kernel rev in "refs/bisect/bad". +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 ~~~~~~~~~~~~ -Oh, and then after you want to reset to the original head, do a +After a bisect session, to clean up the bisection state and return to +the original HEAD (i.e., to quit bisecting), issue the following command: ------------------------------------------------ $ git bisect reset ------------------------------------------------ -to get back to the master branch, instead of being in one of the -bisection branches ("git bisect start" will do that for you too, -actually: it will reset the bisection state, and before it does that -it checks that you're not using some old bisection branch). +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 ~~~~~~~~~~~~~~~~ -During the bisection process, you can say +To see the currently remaining suspects in 'gitk', issue the following +command during the bisection process: ------------ $ git bisect visualize ------------ -to see the currently remaining suspects in `gitk`. +`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 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -The good/bad input is logged, and +After having marked revisions as good or bad, issue the following +command to show what has been done so far: ------------ $ git bisect log ------------ -shows what you have done so far. You can truncate its output somewhere -and save it in a file, and run +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 ------------ -if you find later you made a mistake telling good/bad about a -revision. - -Avoiding to test a commit +Avoiding testing a commit ~~~~~~~~~~~~~~~~~~~~~~~~~ -If in a middle of bisect session, you know what the bisect suggested -to try next is not a good one to test (e.g. the change the 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 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 this $ 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 ------------ -Then compile and test the one you chose to try. After that, tell -bisect what the result was as usual. +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 giving -paths parameters when you say `bisect start`, like this: +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 commits, you can narrow the -bisect space down without doing the whole tree checkout every time you -give good commits. You give the bad revision immediately after `start` -and then you give all the good revisions you have: +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 -- @@ -160,44 +225,166 @@ Bisect run ~~~~~~~~~~ If 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 arguments ------------ -Note that the "run" script (`my_script` in the above example) should -exit with code 0 in case the current source code is good and with a -code between 1 and 127 (included) in case the current source code is -bad. +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 +$ git bisect reset # quit the bisect session +------------ -Any other exit code will abort the automatic bisect process. (A -program that does "exit(-1)" leaves $? = 255, see exit(3) manual page, -the value is chopped with "& 0377".) +* Automatically bisect a test failure between origin and HEAD: ++ +------------ +$ git bisect start HEAD origin -- # HEAD is bad, origin is good +$ git bisect run make test # "make test" builds and tests +$ git bisect reset # quit the bisect session +------------ -You may often find that during bisect you want to have near-constant -tweaks (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 other problem this bisection is not interested in") -applied to the revision being tested. +* 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 +$ git bisect reset # quit the bisect session +------------ ++ +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" +$ git bisect reset # quit the bisect session +------------ ++ +This shows that you can do without a run script if you write the test +on a single line. -To cope with such a situation, after the inner git-bisect finds the -next revision to test, with the "run" script, you can apply that tweak -before compiling, run the real test, and after the test decides if the -revision (possibly with the needed tweaks) passed the test, rewind the -tree to the pristine state. Finally the "run" script can exit with -the status of the real test to let "git bisect run" command loop to -know the outcome. +* 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 $rc = 0' + +$ git bisect reset # quit the bisect session +------------ ++ +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'. -Author ------- -Written by Linus Torvalds <torvalds@osdl.org> -Documentation -------------- -Documentation by Junio C Hamano and the git-list <git@vger.kernel.org>. +SEE ALSO +-------- +link:git-bisect-lk2009.html[Fighting regressions with git bisect], +linkgit:git-blame[1]. GIT --- -Part of the gitlink:git[7] suite - +Part of the linkgit:git[1] suite |