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 start [<bad> [<good>...]] [--] [<paths>...]
  19  git bisect bad [<rev>]
  20  git bisect good [<rev>...]
  21  git bisect skip [<rev>...]
  22  git bisect reset [<branch>]
  23  git bisect visualize
  24  git bisect replay <logfile>
  25  git bisect log
  26  git bisect run <cmd>...
  27
  28 This command uses 'git-rev-list --bisect' option to help drive the
  29 binary search process to find which change introduced a bug, given an
  30 old "good" commit object name and a later "bad" commit object name.
  31
  32 Basic bisect commands: start, bad, good
  33 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  34
  35 The way you use it is:
  36
  37 ------------------------------------------------
  38 $ git bisect start
  39 $ git bisect bad                 # Current version is bad
  40 $ git bisect good v2.6.13-rc2    # v2.6.13-rc2 was the last version
  41                                  # tested that was good
  42 ------------------------------------------------
  43
  44 When you give at least one bad and one good versions, it will bisect
  45 the revision tree and say something like:
  46
  47 ------------------------------------------------
  48 Bisecting: 675 revisions left to test after this
  49 ------------------------------------------------
  50
  51 and check out the state in the middle. Now, compile that kernel, and
  52 boot it. Now, let's say that this booted kernel works fine, then just
  53 do
  54
  55 ------------------------------------------------
  56 $ git bisect good                       # this one is good
  57 ------------------------------------------------
  58
  59 which will now say
  60
  61 ------------------------------------------------
  62 Bisecting: 337 revisions left to test after this
  63 ------------------------------------------------
  64
  65 and you continue along, compiling that one, testing it, and depending
  66 on whether it is good or bad, you say "git bisect good" or "git bisect
  67 bad", and ask for the next bisection.
  68
  69 Until you have no more left, and you'll have been left with the first
  70 bad kernel rev in "refs/bisect/bad".
  71
  72 Bisect reset
  73 ~~~~~~~~~~~~
  74
  75 Oh, and then after you want to reset to the original head, do a
  76
  77 ------------------------------------------------
  78 $ git bisect reset
  79 ------------------------------------------------
  80
  81 to get back to the master branch, instead of being in one of the
  82 bisection branches ("git bisect start" will do that for you too,
  83 actually: it will reset the bisection state, and before it does that
  84 it checks that you're not using some old bisection branch).
  85
  86 Bisect visualize
  87 ~~~~~~~~~~~~~~~~
  88
  89 During the bisection process, you can say
  90
  91 ------------
  92 $ git bisect visualize
  93 ------------
  94
  95 to see the currently remaining suspects in `gitk`.
  96
  97 Bisect log and bisect replay
  98 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  99
 100 The good/bad input is logged, and
 101
 102 ------------
 103 $ git bisect log
 104 ------------
 105
 106 shows what you have done so far. You can truncate its output somewhere
 107 and save it in a file, and run
 108
 109 ------------
 110 $ git bisect replay that-file
 111 ------------
 112
 113 if you find later you made a mistake telling good/bad about a
 114 revision.
 115
 116 Avoiding to test a commit
 117 ~~~~~~~~~~~~~~~~~~~~~~~~~
 118
 119 If in a middle of bisect session, you know what the bisect suggested
 120 to try next is not a good one to test (e.g. the change the commit
 121 introduces is known not to work in your environment and you know it
 122 does not have anything to do with the bug you are chasing), you may
 123 want to find a near-by commit and try that instead.
 124
 125 It goes something like this:
 126
 127 ------------
 128 $ git bisect good/bad                   # previous round was good/bad.
 129 Bisecting: 337 revisions left to test after this
 130 $ git bisect visualize                  # oops, that is uninteresting.
 131 $ git reset --hard HEAD~3               # try 3 revs before what
 132                                         # was suggested
 133 ------------
 134
 135 Then compile and test the one you chose to try. After that, tell
 136 bisect what the result was as usual.
 137
 138 Bisect skip
 139 ~~~~~~~~~~~~
 140
 141 Instead of choosing by yourself a nearby commit, you may just want git
 142 to do it for you using:
 143
 144 ------------
 145 $ git bisect skip                 # Current version cannot be tested
 146 ------------
 147
 148 But computing the commit to test may be slower afterwards and git may
 149 eventually not be able to tell the first bad among a bad and one or
 150 more "skip"ped commits.
 151
 152 Cutting down bisection by giving more parameters to bisect start
 153 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 154
 155 You can further cut down the number of trials if you know what part of
 156 the tree is involved in the problem you are tracking down, by giving
 157 paths parameters when you say `bisect start`, like this:
 158
 159 ------------
 160 $ git bisect start -- arch/i386 include/asm-i386
 161 ------------
 162
 163 If you know beforehand more than one good commits, you can narrow the
 164 bisect space down without doing the whole tree checkout every time you
 165 give good commits. You give the bad revision immediately after `start`
 166 and then you give all the good revisions you have:
 167
 168 ------------
 169 $ git bisect start v2.6.20-rc6 v2.6.20-rc4 v2.6.20-rc1 --
 170                    # v2.6.20-rc6 is bad
 171                    # v2.6.20-rc4 and v2.6.20-rc1 are good
 172 ------------
 173
 174 Bisect run
 175 ~~~~~~~~~~
 176
 177 If you have a script that can tell if the current source code is good
 178 or bad, you can automatically bisect using:
 179
 180 ------------
 181 $ git bisect run my_script
 182 ------------
 183
 184 Note that the "run" script (`my_script` in the above example) should
 185 exit with code 0 in case the current source code is good.  Exit with a
 186 code between 1 and 127 (inclusive), except 125, if the current
 187 source code is bad.
 188
 189 Any other exit code will abort the automatic bisect process. (A
 190 program that does "exit(-1)" leaves $? = 255, see exit(3) manual page,
 191 the value is chopped with "& 0377".)
 192
 193 The special exit code 125 should be used when the current source code
 194 cannot be tested. If the "run" script exits with this code, the current
 195 revision will be skipped, see `git bisect skip` above.
 196
 197 You may often find that during bisect you want to have near-constant
 198 tweaks (e.g., s/#define DEBUG 0/#define DEBUG 1/ in a header file, or
 199 "revision that does not have this commit needs this patch applied to
 200 work around other problem this bisection is not interested in")
 201 applied to the revision being tested.
 202
 203 To cope with such a situation, after the inner git-bisect finds the
 204 next revision to test, with the "run" script, you can apply that tweak
 205 before compiling, run the real test, and after the test decides if the
 206 revision (possibly with the needed tweaks) passed the test, rewind the
 207 tree to the pristine state.  Finally the "run" script can exit with
 208 the status of the real test to let "git bisect run" command loop to
 209 know the outcome.
 210
 211 Author
 212 ------
 213 Written by Linus Torvalds <torvalds@osdl.org>
 214
 215 Documentation
 216 -------------
 217 Documentation by Junio C Hamano and the git-list <git@vger.kernel.org>.
 218
 219 GIT
 220 ---
 221 Part of the gitlink:git[7] suite