A little mystery - crash caused by empty commit message.

From: Tor Arvid Lund <torarvid@gmail.com>
Date: Feb 10, 2009, 11:15 UTC
Message-ID: <1a6be5fa0902100315q554dc457j8c8476d3f59a314f@mail.gmail.com>

Hi, all.

So - I started noticing a problem where for instance "git log" or "git branch -av" would crash in one of my repositories. My environment is Windows Vista x64, using msysgit. I have compiled several versions of git, but I think I had version 1.6.0.3 then this problem arose. When the crash occurred, Windows would just pop up a dialog window saying "git.exe has stopped working". So I tried running it with gdb, which told me there was a segfault in strchr() but no more. Git is built with debug symbols (-g), so I am guessing this may be a problem with my msysgit environment (maybe in conjunction with 64-bit Vista) or something. But I don't really know what I'm talking about, and it is another topic anyway...

Then I tried copying the repository to a linux box and tried gdb there. Much better. strchr(line, '\n') is called in pretty.c in the get_header function. For one of the commits, the 'line' parameter was NULL, so I managed to make it not crash with this little patch:

diff --git a/pretty.c b/pretty.c
index 8d4dbc9..1b2d097 100644
--- a/pretty.c
+++ b/pretty.c
@@ -230,6 +230,8 @@ static char *get_header(const struct commit
*commit, const char *key)
       const char *line = commit->buffer;

       for (;;) {
+               if (line == NULL)
+                       return NULL;
               const char *eol = strchr(line, '\n'), *next;

               if (line == eol)



The result from "git log" for me is then:

...
commit 6a1ac5bc05b2cdd276c7f8a39565681f9d8017d7
<normal output>

commit f67f77edf06bbcebabf430735c751245a4b70f14
Author: Tor Arvid Lund <toral@qsystems.no>
Date:   Thu Feb 5 17:47:09 2009 +0100

commit 6d109492008c68d28af821b96b82f807f338caf6
<normal output>
...

That is - a handful of commits that are output "normally", followed by
one commit where the message is just blank, and then more "normal"
output... By the way - I tried running git fsck --full --strict, and
it did not report any errors (just the "common" list of dangling blobs
and such...

But the question is then - how did I manage to get my repository in
this state? The commit in question was made by me - I know I entered a
message when I committed it. I can even find the commit *with* the
original commit message in another branch... I am sorry to say that my
memory fails me, so I cannot remember all the times I may have moved
commits around, rebased, etc. I do such things often, as I use git-p4
to communicate with the "official company repo" (and because its so
nice :)). I don't know the core git code well, but when I'm in the
mood for speculation, I feel like a rebase or a cherry-pick must have
been the reason for this to have happened...

Well - I just thought I should tell you all about it. My simple little
patch makes it "not crash", but it should maybe report an error or
warning to the user - as something is most likely wrong somewhere.

-Tor Arvid-