# [PATCH] pack-bitmap: Don't perform unaligned memory access 3 messages from 2017-06-26 to 2017-06-27. Participants: James Clarke, Junio C Hamano, Jonathan Nieder. Thread: https://gitlist.dev/t/46262 ## James Clarke, 2017-06-26 15:16 Subject: [PATCH] pack-bitmap: Don't perform unaligned memory access Message-ID: <20170626151612.64019-1-jrtc27@jrtc27.com> URL: https://gitlist.dev/e/20170626151612.64019-1-jrtc27%40jrtc27.com ``` The preceding bitmap entries have a 1-byte XOR-offset and 1-byte flags, so their size is not a multiple of 4. Thus the name-hash cache is only guaranteed to be 2-byte aligned and so we must use get_be32 rather than indexing the array directly. Signed-off-by: James Clarke --- This was noticed thanks to the recent tests added to t5310-pack-bitmaps.sh, which were crashing with SIGBUS on Debian sparc64. All tests (excluding those marked with known breakage) now pass again. pack-bitmap.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/pack-bitmap.c b/pack-bitmap.c index a3ac3dccd..327634cd7 100644 --- a/pack-bitmap.c +++ b/pack-bitmap.c @@ -627,7 +627,7 @@ static void show_objects_for_type( sha1 = nth_packed_object_sha1(bitmap_git.pack, entry->nr); if (bitmap_git.hashes) - hash = ntohl(bitmap_git.hashes[entry->nr]); + hash = get_be32(bitmap_git.hashes + entry->nr); show_reach(sha1, object_type, 0, hash, bitmap_git.pack, entry->offset); } -- 2.13.2 ``` ## Junio C Hamano, 2017-06-26 19:30 Subject: Re: [PATCH] pack-bitmap: Don't perform unaligned memory access Message-ID: URL: https://gitlist.dev/e/xmqqr2y64kdj.fsf%40gitster.mtv.corp.google.com In-Reply-To: <20170626151612.64019-1-jrtc27@jrtc27.com> ``` James Clarke writes: > The preceding bitmap entries have a 1-byte XOR-offset and 1-byte flags, > so their size is not a multiple of 4. Thus the name-hash cache is only > guaranteed to be 2-byte aligned and so we must use get_be32 rather than > indexing the array directly. > > Signed-off-by: James Clarke > --- > > This was noticed thanks to the recent tests added to t5310-pack-bitmaps.sh, > which were crashing with SIGBUS on Debian sparc64. All tests (excluding those > marked with known breakage) now pass again. Thanks. > > pack-bitmap.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/pack-bitmap.c b/pack-bitmap.c > index a3ac3dccd..327634cd7 100644 > --- a/pack-bitmap.c > +++ b/pack-bitmap.c > @@ -627,7 +627,7 @@ static void show_objects_for_type( > sha1 = nth_packed_object_sha1(bitmap_git.pack, entry->nr); > > if (bitmap_git.hashes) > - hash = ntohl(bitmap_git.hashes[entry->nr]); > + hash = get_be32(bitmap_git.hashes + entry->nr); > > show_reach(sha1, object_type, 0, hash, bitmap_git.pack, entry->offset); > } > -- > 2.13.2 ``` ## Jonathan Nieder, 2017-06-27 00:06 Subject: Re: [PATCH] pack-bitmap: Don't perform unaligned memory access Message-ID: <20170627000600.GD161648@aiede.mtv.corp.google.com> URL: https://gitlist.dev/e/20170627000600.GD161648%40aiede.mtv.corp.google.com In-Reply-To: <20170626151612.64019-1-jrtc27@jrtc27.com> ``` James Clarke wrote: > The preceding bitmap entries have a 1-byte XOR-offset and 1-byte flags, > so their size is not a multiple of 4. Thus the name-hash cache is only > guaranteed to be 2-byte aligned and so we must use get_be32 rather than > indexing the array directly. > > Signed-off-by: James Clarke > --- > pack-bitmap.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) Reviewed-by: Jonathan Nieder Failing build log: https://buildd.debian.org/status/fetch.php?pkg=git&arch=sparc64&ver=1%3A2.13.2-2&stamp=1498520310&raw=0 Thanks for tracking down and fixing it. ```