1GIT-BISECT(1) Git Manual GIT-BISECT(1)
2
6 git-bisect - Find by binary search the change that introduced a bug
7
9 git bisect <subcommand> <options>
10
13 The command takes various subcommands, and different options depending
14 on the subcommand:
15 git bisect help
17 git bisect start [--no-checkout] [<bad> [<good>...]] [--] [<paths>...]
18 git bisect bad [<rev>]
19 git bisect good [<rev>...]
20 git bisect skip [(<rev>|<range>)...]
21 git bisect reset [<commit>]
22 git bisect visualize
23 git bisect replay <logfile>
24 git bisect log
25 git bisect run <cmd>...
26 This command uses git rev-list --bisect to help drive the binary search
28 process to find which change introduced a bug, given an old "good"
29 commit object name and a later "bad" commit object name.
30 Getting help
32 Use "git bisect" to get a short usage description, and "git bisect
33 help" or "git bisect -h" to get a long usage description.
34 Basic bisect commands: start, bad, good
36 Using the Linux kernel tree as an example, basic use of the bisect
37 command is as follows:
38 $ git bisect start
40 $ git bisect bad # Current version is bad
41 $ git bisect good v2.6.13-rc2 # v2.6.13-rc2 was the last version
42 # tested that was good
43 When you have specified at least one bad and one good version, the
46 command bisects the revision tree and outputs something similar to the
47 following:
48 Bisecting: 675 revisions left to test after this
50 The state in the middle of the set of revisions is then checked out.
53 You would now compile that kernel and boot it. If the booted kernel
54 works correctly, you would then issue the following command:
55 $ git bisect good # this one is good
57 The output of this command would be something similar to the following:
60 Bisecting: 337 revisions left to test after this
62 You keep repeating this process, compiling the tree, testing it, and
65 depending on whether it is good or bad issuing the command "git bisect
66 good" or "git bisect bad" to ask for the next bisection.
67 Eventually there will be no more revisions left to bisect, and you will
69 have been left with the first bad kernel revision in "refs/bisect/bad".
70 Bisect reset
72 After a bisect session, to clean up the bisection state and return to
73 the original HEAD (i.e., to quit bisecting), issue the following
74 command:
75 $ git bisect reset
77 By default, this will return your tree to the commit that was checked
80 out before git bisect start. (A new git bisect start will also do that,
81 as it cleans up the old bisection state.)
82 With an optional argument, you can return to a different commit
84 instead:
85 $ git bisect reset <commit>
87 For example, git bisect reset HEAD will leave you on the current
90 bisection commit and avoid switching commits at all, while git bisect
91 reset bisect/bad will check out the first bad revision.
92 Bisect visualize
94 To see the currently remaining suspects in gitk, issue the following
95 command during the bisection process:
96 $ git bisect visualize
98 view may also be used as a synonym for visualize.
101 If the DISPLAY environment variable is not set, git log is used
103 instead. You can also give command line options such as -p and --stat.
104 $ git bisect view --stat
106 Bisect log and bisect replay
109 After having marked revisions as good or bad, issue the following
110 command to show what has been done so far:
111 $ git bisect log
113 If you discover that you made a mistake in specifying the status of a
116 revision, you can save the output of this command to a file, edit it to
117 remove the incorrect entries, and then issue the following commands to
118 return to a corrected state:
119 $ git bisect reset
121 $ git bisect replay that-file
122 Avoiding testing a commit
125 If, in the middle of a bisect session, you know that the next suggested
126 revision is not a good one to test (e.g. the change the commit
127 introduces is known not to work in your environment and you know it
128 does not have anything to do with the bug you are chasing), you may
129 want to find a nearby commit and try that instead.
130 For example:
132 $ git bisect good/bad # previous round was good or bad.
134 Bisecting: 337 revisions left to test after this
135 $ git bisect visualize # oops, that is uninteresting.
136 $ git reset --hard HEAD~3 # try 3 revisions before what
137 # was suggested
138 Then compile and test the chosen revision, and afterwards mark the
141 revision as good or bad in the usual manner.
142 Bisect skip
144 Instead of choosing by yourself a nearby commit, you can ask Git to do
145 it for you by issuing the command:
146 $ git bisect skip # Current version cannot be tested
148 But Git may eventually be unable to tell the first bad commit among a
151 bad commit and one or more skipped commits.
152 You can even skip a range of commits, instead of just one commit, using
154 the "<commit1>..<commit2>" notation. For example:
155 $ git bisect skip v2.5..v2.6
157 This tells the bisect process that no commit after v2.5, up to and
160 including v2.6, should be tested.
161 Note that if you also want to skip the first commit of the range you
163 would issue the command:
164 $ git bisect skip v2.5 v2.5..v2.6
166 This tells the bisect process that the commits between v2.5 included
169 and v2.6 included should be skipped.
170 Cutting down bisection by giving more parameters to bisect start
172 You can further cut down the number of trials, if you know what part of
173 the tree is involved in the problem you are tracking down, by
174 specifying path parameters when issuing the bisect start command:
175 $ git bisect start -- arch/i386 include/asm-i386
177 If you know beforehand more than one good commit, you can narrow the
180 bisect space down by specifying all of the good commits immediately
181 after the bad commit when issuing the bisect start command:
182 $ git bisect start v2.6.20-rc6 v2.6.20-rc4 v2.6.20-rc1 --
184 # v2.6.20-rc6 is bad
185 # v2.6.20-rc4 and v2.6.20-rc1 are good
186 Bisect run
189 If you have a script that can tell if the current source code is good
190 or bad, you can bisect by issuing the command:
191 $ git bisect run my_script arguments
193 Note that the script (my_script in the above example) should exit with
196 code 0 if the current source code is good, and exit with a code between
197 1 and 127 (inclusive), except 125, if the current source code is bad.
198 Any other exit code will abort the bisect process. It should be noted
200 that a program that terminates via "exit(-1)" leaves $? = 255, (see the
201 exit(3) manual page), as the value is chopped with "& 0377".
202 The special exit code 125 should be used when the current source code
204 cannot be tested. If the script exits with this code, the current
205 revision will be skipped (see git bisect skip above). 125 was chosen as
206 the highest sensible value to use for this purpose, because 126 and 127
207 are used by POSIX shells to signal specific error status (127 is for
208 command not found, 126 is for command found but not executable---these
209 details do not matter, as they are normal errors in the script, as far
210 as "bisect run" is concerned).
211 You may often find that during a bisect session you want to have
213 temporary modifications (e.g. s/#define DEBUG 0/#define DEBUG 1/ in a
214 header file, or "revision that does not have this commit needs this
215 patch applied to work around another problem this bisection is not
216 interested in") applied to the revision being tested.
217 To cope with such a situation, after the inner git bisect finds the
219 next revision to test, the script can apply the patch before compiling,
220 run the real test, and afterwards decide if the revision (possibly with
221 the needed patch) passed the test and then rewind the tree to the
222 pristine state. Finally the script should exit with the status of the
223 real test to let the "git bisect run" command loop determine the
224 eventual outcome of the bisect session.
225
227 --no-checkout
228 Do not checkout the new working tree at each iteration of the
229 bisection process. Instead just update a special reference named
230 BISECT_HEAD to make it point to the commit that should be tested.
231 This option may be useful when the test you would perform in each
233 step does not require a checked out tree.
234 If the repository is bare, --no-checkout is assumed.
236
238 · Automatically bisect a broken build between v1.2 and HEAD:
239 $ git bisect start HEAD v1.2 -- # HEAD is bad, v1.2 is good
241 $ git bisect run make # "make" builds the app
242 $ git bisect reset # quit the bisect session
243 · Automatically bisect a test failure between origin and HEAD:
246 $ git bisect start HEAD origin -- # HEAD is bad, origin is good
248 $ git bisect run make test # "make test" builds and tests
249 $ git bisect reset # quit the bisect session
250 · Automatically bisect a broken test case:
253 $ cat ~/test.sh
255 #!/bin/sh
256 make || exit 125 # this skips broken builds
257 ~/check_test_case.sh # does the test case pass?
258 $ git bisect start HEAD HEAD~10 -- # culprit is among the last 10
259 $ git bisect run ~/test.sh
260 $ git bisect reset # quit the bisect session
261 Here we use a "test.sh" custom script. In this script, if "make"
263 fails, we skip the current commit. "check_test_case.sh" should
264 "exit 0" if the test case passes, and "exit 1" otherwise.
265 It is safer if both "test.sh" and "check_test_case.sh" are outside
267 the repository to prevent interactions between the bisect, make and
268 test processes and the scripts.
269 · Automatically bisect with temporary modifications (hot-fix):
271 $ cat ~/test.sh
273 #!/bin/sh
274 # tweak the working tree by merging the hot-fix branch
276 # and then attempt a build
277 if git merge --no-commit hot-fix &&
278 make
279 then
280 # run project specific test and report its status
281 ~/check_test_case.sh
282 status=$?
283 else
284 # tell the caller this is untestable
285 status=125
286 fi
287 # undo the tweak to allow clean flipping to the next commit
289 git reset --hard
290 # return control
292 exit $status
293 This applies modifications from a hot-fix branch before each test
295 run, e.g. in case your build or test environment changed so that
296 older revisions may need a fix which newer ones have already. (Make
297 sure the hot-fix branch is based off a commit which is contained in
298 all revisions which you are bisecting, so that the merge does not
299 pull in too much, or use git cherry-pick instead of git merge.)
300 · Automatically bisect a broken test case:
302 $ git bisect start HEAD HEAD~10 -- # culprit is among the last 10
304 $ git bisect run sh -c "make || exit 125; ~/check_test_case.sh"
305 $ git bisect reset # quit the bisect session
306 This shows that you can do without a run script if you write the
308 test on a single line.
309 · Locate a good region of the object graph in a damaged repository
311 $ git bisect start HEAD <known-good-commit> [ <boundary-commit> ... ] --no-checkout
313 $ git bisect run sh -c '
314 GOOD=$(git for-each-ref "--format=%(objectname)" refs/bisect/good-*) &&
315 git rev-list --objects BISECT_HEAD --not $GOOD >tmp.$$ &&
316 git pack-objects --stdout >/dev/null <tmp.$$
317 rc=$?
318 rm -f tmp.$$
319 test $rc = 0'
320 $ git bisect reset # quit the bisect session
322 In this case, when git bisect run finishes, bisect/bad will refer
324 to a commit that has at least one parent whose reachable graph is
325 fully traversable in the sense required by git pack objects.
326
328 Fighting regressions with git bisect[1], git-blame(1).
329
331 Part of the git(1) suite
332
334 1. Fighting regressions with git bisect
335 file:///usr/share/doc/git-1.8.3.1/git-bisect-lk2009.html
336Git 1.8.3.1 11/19/2018 GIT-BISECT(1)