Commit d60c49c (read-cache.c: allow unaligned mapping of the
index file, 2012-04-03) introduced helpers to access
unaligned data. However, we already have get_be32, which has
a few advantages:
1. It's already written, so we avoid duplication.
2. It's probably faster, since it does the endian
conversion and the alignment fix at the same time.
3. The get_be32 code is well-tested, having been in
block-sha1 for a long time. By contrast, our custom
helpers were probably almost never used, since the user
needed to manually define a macro to enable them.
We have to add a get_be16 implementation to the existing
get_be32, but that is very simple to do.
Signed-off-by: Jeff King <p...@peff.net>
---
This _might_ still suffer from the issue fixed in 5f6a112 (block-sha1:
avoid pointer conversion that violates alignment constraints,
2012-07-22), as we are taking the pointer of a uint32 in a struct. But
if that is the case, then the original did, as well. It's not clear to
me if the casting get_be32 does is sufficient, or if a sufficiently
clever compiler might make assumptions based on the original pointer
type.
I'm inclined to leave it for now, as we haven't made anything worse, and
nobody has reported a problem.
compat/bswap.h | 4 ++++
read-cache.c | 44 ++++++++++++--------------------------------
2 files changed, 16 insertions(+), 32 deletions(-)
diff --git a/compat/bswap.h b/compat/bswap.h
index 7d17953..120c6c1 100644
--- a/compat/bswap.h
+++ b/compat/bswap.h
@@ -136,11 +136,15 @@ static inline uint64_t git_bswap64(uint64_t x)
defined(__powerpc__) || defined(__powerpc64__) || \
defined(__s390__) || defined(__s390x__)
+#define get_be16(p) ntohs(*(unsigned short *)(p))
#define get_be32(p) ntohl(*(unsigned int *)(p))
#define put_be32(p, v) do { *(unsigned int *)(p) = htonl(v); } while (0)
#else
+#define get_be16(p) ( \
+ (*((unsigned char *)(p) + 0) << 8) | \
+ (*((unsigned char *)(p) + 1) << 0) )
#define get_be32(p) ( \
(*((unsigned char *)(p) + 0) << 24) | \
(*((unsigned char *)(p) + 1) << 16) | \
diff --git a/read-cache.c b/read-cache.c
index 33dd676..4221872 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -1313,26 +1313,6 @@ int read_index(struct index_state *istate)
return read_index_from(istate, get_index_file());
}
-#ifndef NEEDS_ALIGNED_ACCESS
-#define ntoh_s(var) ntohs(var)
-#define ntoh_l(var) ntohl(var)
-#else
-static inline uint16_t ntoh_s_force_align(void *p)
-{
- uint16_t x;
- memcpy(&x, p, sizeof(x));
- return ntohs(x);
-}
-static inline uint32_t ntoh_l_force_align(void *p)
-{
- uint32_t x;
- memcpy(&x, p, sizeof(x));
- return ntohl(x);
-}
-#define ntoh_s(var) ntoh_s_force_align(&(var))
-#define ntoh_l(var) ntoh_l_force_align(&(var))
-#endif
-
static struct cache_entry *cache_entry_from_ondisk(struct ondisk_cache_entry
*ondisk,
unsigned int flags,
const char *name,
@@ -1340,16 +1320,16 @@ static struct cache_entry
*cache_entry_from_ondisk(struct ondisk_cache_entry *on
{
struct cache_entry *ce = xmalloc(cache_entry_size(len));
- ce->ce_stat_data.sd_ctime.sec = ntoh_l(ondisk->ctime.sec);
- ce->ce_stat_data.sd_mtime.sec = ntoh_l(ondisk->mtime.sec);
- ce->ce_stat_data.sd_ctime.nsec = ntoh_l(ondisk->ctime.nsec);
- ce->ce_stat_data.sd_mtime.nsec = ntoh_l(ondisk->mtime.nsec);
- ce->ce_stat_data.sd_dev = ntoh_l(ondisk->dev);
- ce->ce_stat_data.sd_ino = ntoh_l(ondisk->ino);
- ce->ce_mode = ntoh_l(ondisk->mode);
- ce->ce_stat_data.sd_uid = ntoh_l(ondisk->uid);
- ce->ce_stat_data.sd_gid = ntoh_l(ondisk->gid);
- ce->ce_stat_data.sd_size = ntoh_l(ondisk->size);
+ ce->ce_stat_data.sd_ctime.sec = get_be32(&ondisk->ctime.sec);
+ ce->ce_stat_data.sd_mtime.sec = get_be32(&ondisk->mtime.sec);
+ ce->ce_stat_data.sd_ctime.nsec = get_be32(&ondisk->ctime.nsec);
+ ce->ce_stat_data.sd_mtime.nsec = get_be32(&ondisk->mtime.nsec);
+ ce->ce_stat_data.sd_dev = get_be32(&ondisk->dev);
+ ce->ce_stat_data.sd_ino = get_be32(&ondisk->ino);
+ ce->ce_mode = get_be32(&ondisk->mode);
+ ce->ce_stat_data.sd_uid = get_be32(&ondisk->uid);
+ ce->ce_stat_data.sd_gid = get_be32(&ondisk->gid);
+ ce->ce_stat_data.sd_size = get_be32(&ondisk->size);
ce->ce_flags = flags & ~CE_NAMEMASK;
ce->ce_namelen = len;
hashcpy(ce->sha1, ondisk->sha1);
@@ -1389,14 +1369,14 @@ static struct cache_entry *create_from_disk(struct
ondisk_cache_entry *ondisk,
unsigned int flags;
/* On-disk flags are just 16 bits */
- flags = ntoh_s(ondisk->flags);
+ flags = get_be16(&ondisk->flags);
len = flags & CE_NAMEMASK;
if (flags & CE_EXTENDED) {
struct ondisk_cache_entry_extended *ondisk2;
int extended_flags;
ondisk2 = (struct ondisk_cache_entry_extended *)ondisk;
- extended_flags = ntoh_s(ondisk2->flags2) << 16;
+ extended_flags = get_be16(&ondisk2->flags2) << 16;
/* We do not yet understand any bit out of CE_EXTENDED_FLAGS */
if (extended_flags & ~CE_EXTENDED_FLAGS)
die("Unknown index entry format %08x", extended_flags);
--
1.8.5.2.500.g8060133
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