Documentation/git-bisect.txt

   1 git-bisect(1)
   2 =============
   3
   4 NAME
   5 ----
   6 git-bisect - Find the change that introduced a bug by binary search
   7
   8
   9 SYNOPSIS
  10 --------
  11 'git bisect' <subcommand> <options>
  12
  13 DESCRIPTION
  14 -----------
  15 The command takes various subcommands, and different options depending
  16 on the subcommand:
  17
  18  git bisect help
  19  git bisect start [<bad> [<good>...]] [--] [<paths>...]
  20  git bisect bad [<rev>]
  21  git bisect good [<rev>...]
  22  git bisect skip [<rev>...]
  23  git bisect reset [<branch>]
  24  git bisect visualize
  25  git bisect replay <logfile>
  26  git bisect log
  27  git bisect run <cmd>...
  28
  29 This command uses 'git-rev-list --bisect' option to help drive the
  30 binary search process to find which change introduced a bug, given an
  31 old "good" commit object name and a later "bad" commit object name.
  32
  33 Getting help
  34 ~~~~~~~~~~~~
  35
  36 Use "git bisect" to get a short usage description, and "git bisect
  37 help" or "git bisect -h" to get a long usage description.
  38
  39 Basic bisect commands: start, bad, good
  40 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  41
  42 The way you use it is:
  43
  44 ------------------------------------------------
  45 $ git bisect start
  46 $ git bisect bad                 # Current version is bad
  47 $ git bisect good v2.6.13-rc2    # v2.6.13-rc2 was the last version
  48                                  # tested that was good
  49 ------------------------------------------------
  50
  51 When you give at least one bad and one good versions, it will bisect
  52 the revision tree and say something like:
  53
  54 ------------------------------------------------
  55 Bisecting: 675 revisions left to test after this
  56 ------------------------------------------------
  57
  58 and check out the state in the middle. Now, compile that kernel, and
  59 boot it. Now, let's say that this booted kernel works fine, then just
  60 do
  61
  62 ------------------------------------------------
  63 $ git bisect good                       # this one is good
  64 ------------------------------------------------
  65
  66 which will now say
  67
  68 ------------------------------------------------
  69 Bisecting: 337 revisions left to test after this
  70 ------------------------------------------------
  71
  72 and you continue along, compiling that one, testing it, and depending
  73 on whether it is good or bad, you say "git bisect good" or "git bisect
  74 bad", and ask for the next bisection.
  75
  76 Until you have no more left, and you'll have been left with the first
  77 bad kernel rev in "refs/bisect/bad".
  78
  79 Bisect reset
  80 ~~~~~~~~~~~~
  81
  82 Oh, and then after you want to reset to the original head, do a
  83
  84 ------------------------------------------------
  85 $ git bisect reset
  86 ------------------------------------------------
  87
  88 to get back to the original branch, instead of being in one of the
  89 bisection branches ("git bisect start" will do that for you too,
  90 actually: it will reset the bisection state, and before it does that
  91 it checks that you're not using some old bisection branch).
  92
  93 Bisect visualize
  94 ~~~~~~~~~~~~~~~~
  95
  96 During the bisection process, you can say
  97
  98 ------------
  99 $ git bisect visualize
 100 ------------
 101
 102 to see the currently remaining suspects in `gitk`.  `visualize` is a bit
 103 too long to type and `view` is provided as a synonym.
 104
 105 If `DISPLAY` environment variable is not set, `git log` is used
 106 instead.  You can even give command line options such as `-p` and
 107 `--stat`.
 108
 109 ------------
 110 $ git bisect view --stat
 111 ------------
 112
 113 Bisect log and bisect replay
 114 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 115
 116 The good/bad input is logged, and
 117
 118 ------------
 119 $ git bisect log
 120 ------------
 121
 122 shows what you have done so far. You can truncate its output somewhere
 123 and save it in a file, and run
 124
 125 ------------
 126 $ git bisect replay that-file
 127 ------------
 128
 129 if you find later you made a mistake telling good/bad about a
 130 revision.
 131
 132 Avoiding to test a commit
 133 ~~~~~~~~~~~~~~~~~~~~~~~~~
 134
 135 If in a middle of bisect session, you know what the bisect suggested
 136 to try next is not a good one to test (e.g. the change the commit
 137 introduces is known not to work in your environment and you know it
 138 does not have anything to do with the bug you are chasing), you may
 139 want to find a near-by commit and try that instead.
 140
 141 It goes something like this:
 142
 143 ------------
 144 $ git bisect good/bad                   # previous round was good/bad.
 145 Bisecting: 337 revisions left to test after this
 146 $ git bisect visualize                  # oops, that is uninteresting.
 147 $ git reset --hard HEAD~3               # try 3 revs before what
 148                                         # was suggested
 149 ------------
 150
 151 Then compile and test the one you chose to try. After that, tell
 152 bisect what the result was as usual.
 153
 154 Bisect skip
 155 ~~~~~~~~~~~~
 156
 157 Instead of choosing by yourself a nearby commit, you may just want git
 158 to do it for you using:
 159
 160 ------------
 161 $ git bisect skip                 # Current version cannot be tested
 162 ------------
 163
 164 But computing the commit to test may be slower afterwards and git may
 165 eventually not be able to tell the first bad among a bad and one or
 166 more "skip"ped commits.
 167
 168 Cutting down bisection by giving more parameters to bisect start
 169 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 170
 171 You can further cut down the number of trials if you know what part of
 172 the tree is involved in the problem you are tracking down, by giving
 173 paths parameters when you say `bisect start`, like this:
 174
 175 ------------
 176 $ git bisect start -- arch/i386 include/asm-i386
 177 ------------
 178
 179 If you know beforehand more than one good commits, you can narrow the
 180 bisect space down without doing the whole tree checkout every time you
 181 give good commits. You give the bad revision immediately after `start`
 182 and then you give all the good revisions you have:
 183
 184 ------------
 185 $ git bisect start v2.6.20-rc6 v2.6.20-rc4 v2.6.20-rc1 --
 186                    # v2.6.20-rc6 is bad
 187                    # v2.6.20-rc4 and v2.6.20-rc1 are good
 188 ------------
 189
 190 Bisect run
 191 ~~~~~~~~~~
 192
 193 If you have a script that can tell if the current source code is good
 194 or bad, you can automatically bisect using:
 195
 196 ------------
 197 $ git bisect run my_script
 198 ------------
 199
 200 Note that the "run" script (`my_script` in the above example) should
 201 exit with code 0 in case the current source code is good.  Exit with a
 202 code between 1 and 127 (inclusive), except 125, if the current
 203 source code is bad.
 204
 205 Any other exit code will abort the automatic bisect process. (A
 206 program that does "exit(-1)" leaves $? = 255, see exit(3) manual page,
 207 the value is chopped with "& 0377".)
 208
 209 The special exit code 125 should be used when the current source code
 210 cannot be tested. If the "run" script exits with this code, the current
 211 revision will be skipped, see `git bisect skip` above.
 212
 213 You may often find that during bisect you want to have near-constant
 214 tweaks (e.g., s/#define DEBUG 0/#define DEBUG 1/ in a header file, or
 215 "revision that does not have this commit needs this patch applied to
 216 work around other problem this bisection is not interested in")
 217 applied to the revision being tested.
 218
 219 To cope with such a situation, after the inner git-bisect finds the
 220 next revision to test, with the "run" script, you can apply that tweak
 221 before compiling, run the real test, and after the test decides if the
 222 revision (possibly with the needed tweaks) passed the test, rewind the
 223 tree to the pristine state.  Finally the "run" script can exit with
 224 the status of the real test to let "git bisect run" command loop to
 225 know the outcome.
 226
 227 EXAMPLES
 228 --------
 229
 230 * Automatically bisect a broken build between v1.2 and HEAD:
 231 +
 232 ------------
 233 $ git bisect start HEAD v1.2 --      # HEAD is bad, v1.2 is good
 234 $ git bisect run make                # "make" builds the app
 235 ------------
 236
 237 * Automatically bisect a broken test suite:
 238 +
 239 ------------
 240 $ cat ~/test.sh
 241 #!/bin/sh
 242 make || exit 125                   # this "skip"s broken builds
 243 make test                          # "make test" runs the test suite
 244 $ git bisect start v1.3 v1.1 --    # v1.3 is bad, v1.1 is good
 245 $ git bisect run ~/test.sh
 246 ------------
 247 +
 248 Here we use a "test.sh" custom script. In this script, if "make"
 249 fails, we "skip" the current commit.
 250 +
 251 It's safer to use a custom script outside the repo to prevent
 252 interactions between the bisect, make and test processes and the
 253 script.
 254 +
 255 And "make test" should "exit 0", if the test suite passes, and
 256 "exit 1" (for example) otherwise.
 257
 258 * Automatically bisect a broken test case:
 259 +
 260 ------------
 261 $ cat ~/test.sh
 262 #!/bin/sh
 263 make || exit 125                     # this "skip"s broken builds
 264 ~/check_test_case.sh                 # does the test case passes ?
 265 $ git bisect start HEAD HEAD~10 --   # culprit is among the last 10
 266 $ git bisect run ~/test.sh
 267 ------------
 268 +
 269 Here "check_test_case.sh" should "exit 0", if the test case passes,
 270 and "exit 1" (for example) otherwise.
 271 +
 272 It's safer if both "test.sh" and "check_test_case.sh" scripts are
 273 outside the repo to prevent interactions between the bisect, make and
 274 test processes and the scripts.
 275
 276 Author
 277 ------
 278 Written by Linus Torvalds <torvalds@osdl.org>
 279
 280 Documentation
 281 -------------
 282 Documentation by Junio C Hamano and the git-list <git@vger.kernel.org>.
 283
 284 GIT
 285 ---
 286 Part of the linkgit:git[1] suite