Re: Segfault with merge-tree on multiple Git versions

From: John Keeping <john@keeping.me.uk>
Date: Mar 27, 2013, 15:58 UTC
Message-ID: <20130327155850.GN2286@serenity.lan>
In-Reply-To: <87boa47saw.fsf@linux-k42r.v.cablecom.net>

On Wed, Mar 27, 2013 at 04:53:27PM +0100, thomas wrote:

Show 43 quoted lines

> Charlie Smurthwaite <charlie@atechmedia.com> writes:
> 
> > I am experiencing a segmentation fault in various versions of Git using
> > different repositories. Specifically, I have reproduced it using a
> > public repo and the latest stable Git version. Other repos trigger the
> > error on different versions.
> >
> > Full info can be found below. Thanks,
> >
> > Charlie
> >
> >
> > Test repository:
> > https://github.com/atech/mail
> >
> > Test Command
> > git merge-tree 26bb22a052fef9f74063afd4fc6fc11fe200b19f
> > 8d6bdf012941d876b2279994e02f1bb0d5c26e7d
> > d5ef97ac407d945f231cd7c8fb1cfe48b3a12083
> 
> I happened to walk past on IRC and found I could easily reproduce it, so
> I bisected:
> 
>   35ffe7583108ab236dcf81226690388491d9962f is the first bad commit
>   commit 35ffe7583108ab236dcf81226690388491d9962f
>   Author: Junio C Hamano <gitster@pobox.com>
>   Date:   Thu Dec 13 15:51:29 2012 -0800
> 
>       merge-tree: fix d/f conflicts
>       
>       The previous commit documented two known breakages revolving around
>       a case where one side flips a tree into a blob (or vice versa),
>       where the original code simply gets confused and feeds a mixture of
>       trees and blobs into either the recursive merge-tree (and recursing
>       into the blob will fail) or three-way merge (and merging tree contents
>       together with blobs will fail).
>       
>       Fix it by feeding trees (and only trees) into the recursive
>       merge-tree machinery and blobs (and only blobs) into the three-way
>       content level merge machinery separately; when this happens, the
>       entire merge has to be marked as conflicting at the structure level.
>       
>       Signed-off-by: Junio C Hamano <gitster@pobox.com>

Looks like a simple typo in merge-tree.c::unresolved:

-- >8 -- merge-tree: fix typo in merge-tree.c::unresolved

When calculating whether there is a d/f conflict, the calculation of whether both sides are directories generates an incorrect references mask because it does not use the loop index to set the correct bit. Fix this typo.

Signed-off-by: John Keeping <john@keeping.me.uk>

diff --git a/builtin/merge-tree.c b/builtin/merge-tree.c
index e0d0b7d..bc912e3 100644
--- a/builtin/merge-tree.c
+++ b/builtin/merge-tree.c
@@ -245,7 +245,7 @@ static void unresolved(const struct traverse_info *info, struct name_entry n[3])
 	unsigned dirmask = 0, mask = 0;
 
 	for (i = 0; i < 3; i++) {
-		mask |= (1 << 1);
+		mask |= (1 << i);
 		if (n[i].mode && S_ISDIR(n[i].mode))
 			dirmask |= (1 << i);
 	}