pack-bitmap: do not use gcc packed attribute

The "__attribute__" flag may be a noop on some compilers.
That's OK as long as the code is correct without the
attribute, but in this case it is not. We would typically
end up with a struct that is 2 bytes too long due to struct
padding, breaking both reading and writing of bitmaps.

Instead of marshalling the data in a struct, let's just
provide helpers for reading and writing the appropriate
types. Besides being correct on all platforms, the result is
more efficient and simpler to read.

Signed-off-by: Karsten Blees <blees@dcon.de>
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 15 insertions, 7 deletions

diff --git a/pack-bitmap.c b/pack-bitmap.c
index 91e410153..9f8b90981 100644
--- a/pack-bitmap.c
+++ b/pack-bitmap.c
@@ -197,13 +197,24 @@ static struct stored_bitmap *store_bitmap(struct bitmap_index *index,
 	return stored;
 }
 
+static inline uint32_t read_be32(const unsigned char *buffer, size_t *pos)
+{
+	uint32_t result = get_be32(buffer + *pos);
+	(*pos) += sizeof(result);
+	return result;
+}
+
+static inline uint8_t read_u8(const unsigned char *buffer, size_t *pos)
+{
+	return buffer[(*pos)++];
+}
+
 static int load_bitmap_entries_v1(struct bitmap_index *index)
 {
 	static const size_t MAX_XOR_OFFSET = 160;
 
 	uint32_t i;
 	struct stored_bitmap **recent_bitmaps;
-	struct bitmap_disk_entry *entry;
 
 	recent_bitmaps = xcalloc(MAX_XOR_OFFSET, sizeof(struct stored_bitmap));
 
@@ -214,15 +225,12 @@ static int load_bitmap_entries_v1(struct bitmap_index *index)
 		uint32_t commit_idx_pos;
 		const unsigned char *sha1;
 
-		entry = (struct bitmap_disk_entry *)(index->map + index->map_pos);
-		index->map_pos += sizeof(struct bitmap_disk_entry);
+		commit_idx_pos = read_be32(index->map, &index->map_pos);
+		xor_offset = read_u8(index->map, &index->map_pos);
+		flags = read_u8(index->map, &index->map_pos);
 
-		commit_idx_pos = ntohl(entry->object_pos);
 		sha1 = nth_packed_object_sha1(index->pack, commit_idx_pos);
 
-		xor_offset = (int)entry->xor_offset;
-		flags = (int)entry->flags;
-
 		bitmap = read_bitmap_1(index);
 		if (!bitmap)
 			return -1;