From: Michael Haggerty <mhagger@alum.mit.edu>
To: "Mantas Mikulėnas" <grawity@gmail.com>
Cc: git@vger.kernel.org
Subject: Re: Segfault in `git describe`
Date: Mon, 15 Jul 2013 15:03:51 +0200 [thread overview]
Message-ID: <51E3F337.8070708@alum.mit.edu> (raw)
In-Reply-To: <krrkk0$kri$1@ger.gmane.org>
On 07/13/2013 03:27 PM, Mantas Mikulėnas wrote:
> I have a clone of linux.git with various stuff added to it (remotes for
> 'stable' and 'next', a bunch of local tags, and historical repositories
> imported using `git replace`).
>
> Yesterday, I noticed that `git describe`, built from git.git master
> (v1.8.3.2-804-g0da7a53, gcc 4.8) would simply crash when run in that
> repository, with the following backtrace:
>
>> Program terminated with signal 11, Segmentation fault.
>> #0 0x00000000004c39dc in hashcpy (sha_src=0x1c <Address 0x1c out of bounds>,
>> sha_dst=0x7fffc0b4d610 "\242\271\301\366 \201&\346\337l\002B\214P\037\210ShX\022")
>> at cache.h:694
>> 694 memcpy(sha_dst, sha_src, 20);
>> (gdb) bt
>> #0 0x00000000004c39dc in hashcpy (sha_src=0x1c <Address 0x1c out of bounds>,
>> sha_dst=0x7fffc0b4d610 "\242\271\301\366 \201&\346\337l\002B\214P\037\210ShX\022")
>> at cache.h:694
>> #1 peel_ref (refname=refname@entry=0x1fe2d10 "refs/tags/next-20130607",
>> sha1=sha1@entry=0x7fffc0b4d610 "\242\271\301\366 \201&\346\337l\002B\214P\037\210ShX\022") at refs.c:1586
>> #2 0x0000000000424194 in get_name (path=0x1fe2d10 "refs/tags/next-20130607",
>> sha1=0x1fe2ce8 "\222V\356\276S5\tk\231Hi\264\r=\336\315\302\225\347\257\300N\376\327\064@\237ZDq[T\246\312\033T\260\314\362\025refs/tags/next-20130607", flag=<optimized out>,
>> cb_data=<optimized out>) at builtin/describe.c:156
>> #3 0x00000000004c1c21 in do_one_ref (entry=0x1fe2ce0, cb_data=0x7fffc0b4d7c0)
>> at refs.c:646
>> #4 0x00000000004c318d in do_for_each_entry_in_dir (dir=0x1fe1728,
>> offset=<optimized out>, fn=0x4c1bc0 <do_one_ref>, cb_data=0x7fffc0b4d7c0)
>> at refs.c:672
>> #5 0x00000000004c33d1 in do_for_each_entry_in_dirs (dir1=0x1fdf4d8, dir2=0x1fd6318,
>> cb_data=0x7fffc0b4d7c0, fn=0x4c1bc0 <do_one_ref>) at refs.c:716
>> #6 0x00000000004c33d1 in do_for_each_entry_in_dirs (dir1=0x1fdf1f8, dir2=0x1fd62d8,
>> cb_data=0x7fffc0b4d7c0, fn=0x4c1bc0 <do_one_ref>) at refs.c:716
>> #7 0x00000000004c3540 in do_for_each_entry (refs=refs@entry=0x7a2800 <ref_cache>,
>> base=base@entry=0x509cc6 "", cb_data=cb_data@entry=0x7fffc0b4d7c0,
>> fn=0x4c1bc0 <do_one_ref>) at refs.c:1689
>> #8 0x00000000004c3ff8 in do_for_each_ref (cb_data=cb_data@entry=0x0, flags=1, trim=0,
>> fn=fn@entry=0x424120 <get_name>, base=0x509cc6 "", refs=0x7a2800 <ref_cache>)
>> at refs.c:1724
>> #9 for_each_rawref (fn=fn@entry=0x424120 <get_name>, cb_data=cb_data@entry=0x0)
>> at refs.c:1873
>> #10 0x0000000000424f5b in cmd_describe (argc=0, argv=0x7fffc0b4ddc0, prefix=0x0)
>> at builtin/describe.c:466
>> #11 0x000000000040596d in run_builtin (argv=0x7fffc0b4ddc0, argc=1,
>> p=0x760b40 <commands.21352+576>) at git.c:291
>> #12 handle_internal_command (argc=1, argv=0x7fffc0b4ddc0) at git.c:453
>> #13 0x0000000000404d6e in run_argv (argv=0x7fffc0b4dc78, argcp=0x7fffc0b4dc5c)
>> at git.c:499
>> #14 main (argc=1, av=<optimized out>) at git.c:575
>> (gdb)
>
> According to `git bisect`, the first bad commit is:
>
> commit 9a489f3c17d6c974b18c47cf406404ca2a721c87
> Author: Michael Haggerty <mhagger@alum.mit.edu>
> Date: Mon Apr 22 21:52:22 2013 +0200
>
> refs: extract a function peel_entry()
>
> The crash happens only in repositories that have at least one replaced
> object in the branch's history. Running `git --no-replace-objects
> describe` avoids the crash.
>
> The crash happens only if there are any tags under .git/refs/tags/ that
> do not exist in .git/packed-refs, or if I remove all "peeled" lines from
> .git/packed-refs (including the '#' line; /^[#^]/d).
>
> A quick way to reproduce this with git.git master is:
>
> git tag -f test-tag HEAD~10
> git replace -f HEAD $(git --no-replace-objects cat-file commit HEAD \
> | sed 's/@/@test/' | git hash-object --stdin -t commit -w)
> ./git describe
Thanks for the bug report.
I think the cause of this bug is that peel_entry() is causing a nested
call to do_for_each_entry() to look up the replace reference, which
resets current_ref to NULL between the test and the dereference of
current_ref in peel_ref().
Unfortunately, I cannot reproduce the failure by following your recipe
(though I didn't have a lot of time yet for this). I suppose that my
repo starts out in a slightly different state than yours and therefore I
don't get the same results. If you could find a recipe to reproduce the
problem, starting either with an empty repo, or perhaps a fresh clone of
git.git, and double-check that you don't have any unusual config options
that might be affecting things, that would be very helpful.
I might have more time to look at this tonight.
Michael
--
Michael Haggerty
mhagger@alum.mit.edu
http://softwareswirl.blogspot.com/
next prev parent reply other threads:[~2013-07-15 13:04 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-07-13 13:27 Segfault in `git describe` Mantas Mikulėnas
2013-07-15 13:03 ` Michael Haggerty [this message]
2013-07-15 13:31 ` Mantas Mikulėnas
2013-07-15 15:24 ` [PATCH] do_one_ref(): save and restore value of current_ref Michael Haggerty
2013-07-18 4:03 ` Junio C Hamano
2013-07-19 17:43 ` Michael Haggerty
2013-07-19 19:34 ` Junio C Hamano
2013-07-24 14:35 ` Michael Haggerty
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