# segfault in diff-delta.c on mac os x (commit 8433669) 4 messages from 2007-07-21 to 2007-07-22. Participants: Steffen Prohaska, Brian Gernhardt. Thread: https://gitlist.dev/t/9127 ## Steffen Prohaska, 2007-07-21 15:15 Subject: segfault in diff-delta.c on mac os x (commit 8433669) Message-ID: URL: https://gitlist.dev/e/C10CCDA5-6D65-445E-92F3-2D3E4DCA4F8B%40zib.de ``` 843366961cf14aad6490fbeb30f7b98f37f8833a may cause segfaults on Mac OS X. See backtrace below. I only observed the segfault with -O2 builds. I was not yet able to understand the reason causing the segfault. The situation is kind of strange. The for loop in line 302 shouldn't allow entry == 0 to ever happen. But maybe some more intricate corruption is taking place. Unfortunately I'm no longer able to reproduce the exact call stack because I wasn't aware of the details of when pruning takes place; and the repository changed in such a way that the segfault no longer happens. However, I experienced suspicious behaviour on other repositories during packing as well. I can probably create similar call stacks if needed. For now, I reverted 843366961cf14aad6490fbeb30f7b98f37f8833a for me. Steffen gcc --version i686-apple-darwin8-gcc-4.0.1 (GCC) 4.0.1 (Apple Computer, Inc. build 5250) Copyright (C) 2005 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. Counting objects: 7530 Done counting 56361 objects. Deltifying 56361 objects... 69% (38890/56361) done Program received signal EXC_BAD_ACCESS, Could not access memory. Reason: KERN_PROTECTION_FAILURE at address: 0x00000000 0x00048526 in create_delta (index=0x35d5000, trg_buf=0x35a0000, trg_size=214109, delta_size=0xbfffe83c, max_size=104893) at diff- delta.c:303 303 const unsigned char *ref = entry->ptr; (gdb) bt #0 0x00048526 in create_delta (index=0x35d5000, trg_buf=0x35a0000, trg_size=214109, delta_size=0xbfffe83c, max_size=104893) at diff- delta.c:303 #1 0x0002beb7 in prepare_pack (window=10, depth=50) at builtin-pack- objects.c:1293 #2 0x0002cd6e in cmd_pack_objects (argc=16, argv=0xbfffef78, prefix=0x0) at builtin-pack-objects.c:1709 #3 0x000020c9 in handle_internal_command (argc=16, argv=0xbfffef78, envp=0x84) at git.c:324 #4 0x00002669 in main (argc=16, argv=0xbfffef78, envp=0xbfffefbc) at git.c:393 (gdb) l 298 struct index_entry *entry; 299 val ^= U[data[-RABIN_WINDOW]]; 300 val = ((val << 8) | *data) ^ T[val >> RABIN_SHIFT]; 301 i = val & index->hash_mask; 302 for (entry = index->hash[i]; entry; entry = entry->next) { 303 const unsigned char *ref = entry->ptr; 304 const unsigned char *src = data; 305 unsigned int ref_size = ref_top - ref; 306 if (entry->val != val) 307 continue; (gdb) p entry $1 = (struct index_entry *) 0x0 ``` ## Brian Gernhardt, 2007-07-22 03:35 Subject: Re: segfault in diff-delta.c on mac os x (commit 8433669) Message-ID: <233B9D70-9D91-4527-9801-7E2463ABDDAA@silverinsanity.com> URL: https://gitlist.dev/e/233B9D70-9D91-4527-9801-7E2463ABDDAA%40silverinsanity.com In-Reply-To: ``` On Jul 21, 2007, at 11:15 AM, Steffen Prohaska wrote: > 843366961cf14aad6490fbeb30f7b98f37f8833a may cause segfaults on > Mac OS X. See backtrace below. I only observed the segfault with > -O2 builds. I have been using git on my OS X box for quite a while, and that commit appears to be nearly two months old. I have yet to see any packing errors in any of my repositories. (This is with -O2, which appears to be the default.) My gcc reports itself as build 5367 instead of 5250. Perhaps there is a compiler error in an older copy of the DevTools? Also, did this segfault occur with any publicly available repo or is it your own work? ~~ Brian ``` ## Steffen Prohaska, 2007-07-22 08:49 Subject: Re: segfault in diff-delta.c on mac os x (commit 8433669) Message-ID: <6A487E9A-27E5-4212-A7C9-EBB6528791FE@zib.de> URL: https://gitlist.dev/e/6A487E9A-27E5-4212-A7C9-EBB6528791FE%40zib.de In-Reply-To: <233B9D70-9D91-4527-9801-7E2463ABDDAA@silverinsanity.com> ``` On Jul 22, 2007, at 5:35 AM, Brian Gernhardt wrote: > > On Jul 21, 2007, at 11:15 AM, Steffen Prohaska wrote: > >> 843366961cf14aad6490fbeb30f7b98f37f8833a may cause segfaults on >> Mac OS X. See backtrace below. I only observed the segfault with >> -O2 builds. > > I have been using git on my OS X box for quite a while, and that > commit appears to be nearly two months old. I have yet to see any > packing errors in any of my repositories. (This is with -O2, which > appears to be the default.) > > My gcc reports itself as build 5367 instead of 5250. Perhaps there > is a compiler error in an older copy of the DevTools? This seems to be the case. I upgraded the compiler and tried again. The segfault didn't happen again. Note, this was not exactly the same situation as before because the git repository used for testing changed a bit since the first segfault. I'll do some more repacking over the day and will report my observations. > Also, did this segfault occur with any publicly available repo or > is it your own work? It occurred on repacking a clone of git://git.kernel.org/pub/scm/git/git.git. Steffen ``` ## Steffen Prohaska, 2007-07-22 12:59 Subject: Re: segfault in diff-delta.c on mac os x (commit 8433669) Message-ID: URL: https://gitlist.dev/e/B19AC964-3398-46AF-934B-BB2F06688F7B%40zib.de In-Reply-To: <6A487E9A-27E5-4212-A7C9-EBB6528791FE@zib.de> ``` On Jul 22, 2007, at 10:49 AM, Steffen Prohaska wrote: > > On Jul 22, 2007, at 5:35 AM, Brian Gernhardt wrote: > >> >> On Jul 21, 2007, at 11:15 AM, Steffen Prohaska wrote: >> >>> 843366961cf14aad6490fbeb30f7b98f37f8833a may cause segfaults on >>> Mac OS X. See backtrace below. I only observed the segfault with >>> -O2 builds. >> >> I have been using git on my OS X box for quite a while, and that >> commit appears to be nearly two months old. I have yet to see any >> packing errors in any of my repositories. (This is with -O2, >> which appears to be the default.) >> >> My gcc reports itself as build 5367 instead of 5250. Perhaps >> there is a compiler error in an older copy of the DevTools? > > This seems to be the case. I upgraded the compiler and > tried again. The segfault didn't happen again. Note, this > was not exactly the same situation as before because the > git repository used for testing changed a bit since the > first segfault. > > I'll do some more repacking over the day and will report > my observations. I did a lot more testing and am pretty convinced now that the problem is not present with the newer compiler. Using build 5367 of gcc seems to creating a working git executable while build 5250 creates a broken one. Steffen ```