Re: Bus Error- git merge

From: Johannes Schindelin <johannes.schindelin@gmx.de>
Date: Jan 30, 2009, 18:57 UTC
Message-ID: <alpine.DEB.1.00.0901301950100.3586@pacific.mpi-cbg.de>
In-Reply-To: <C5A883D0.E243%bmoran@onehub.com>

Hi,

On Fri, 30 Jan 2009, Brian Moran wrote:

> I am getting a bus error on a git merge, including the more recent versions.
> Following the instructions from a bug August, I got the latest sources,
> compiled them up, and executed the merge in the debugger to repro. Here¹s
> what I found:

Is it possible that your branch has submodules?

Show 29 quoted lines

> gdb ../git-1.6.1.2/git-merge
> GNU gdb 6.3.50-20050815 (Apple version gdb-768) (Tue Oct  2 04:07:49 UTC
> 2007)
> Copyright 2004 Free Software Foundation, Inc.
> GDB is free software, covered by the GNU General Public License, and you are
> welcome to change it and/or distribute copies of it under certain
> conditions.
> Type "show copying" to see the conditions.
> There is absolutely no warranty for GDB.  Type "show warranty" for details.
> This GDB was configured as "i386-apple-darwin"...Reading symbols for shared
> libraries ........ done
> 
> (gdb) set args -v v1-ftp-support
> (gdb) run
> Starting program: /Users/bmo/Documents/repo/git-1.6.1.2/git-merge -v
> v1-ftp-support
> Reading symbols for shared libraries +++++++. done
> 
> Program received signal EXC_BAD_ACCESS, Could not access memory.
> Reason: KERN_PROTECTION_FAILURE at address: 0x00000004
> 0x000863c3 in sha_eq (a=0x4 <Address 0x4 out of bounds>, b=0x7bf004 "<some
> random chars>") at cache.h:575
> 575        return memcmp(sha1, sha2, 20);
> 
> (gdb) backtrace
> #0  0x000863c3 in sha_eq (a=0x4 <Address 0x4 out of bounds>, b=0x7bf004
> "<some random chars>") at cache.h:575
> #1  0x00086dc6 in merge_trees (o=0xbfffedd4, head=0x7bf020, merge=0x7bf000,
> common=0x0, result=0xbfffed28) at merge-recursive.c:1164

common=0x0, that's the issue.

> #2  0x00088960 in merge_recursive (o=0xbfffedd4, h1=0x4f4060, h2=0x4f4000,
> ca=0x53cc20, result=0xbfffee2c) at merge-recursive.c:1294

However, here I read in my version of merge-recursive.c that "common" is the tree of merged_common_ancestor, which is either set to "pop_commit(&ca)", i.e. to one of the common ancestors, or to a virtual commit, that must have a tree.

So it would be good if you could debug this further, letting me know where the merged_common_ancestor came from, and why it does not have a tree.

Thanks, Dscho