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index-pack --verify: read anomalous offsets from v2 idx file

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A pack v2 .idx file usually records offset using 64-bit representation
only when the offset does not fit within 31-bit, but you can handcraft
your .idx file to record smaller offset using 64-bit, storing all zero
in the upper 4-byte.  By inspecting the original idx file when running
index-pack --verify, encode such low offsets that do not need to be in
64-bit but are encoded using 64-bit just like the original idx file so
that we can still validate the pack/idx pair by comparing the idx file
recomputed with the original.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Junio C Hamano
2011-02-25 16:55:26 -08:00
parent fb956c1f44
commit 3c9fc074c2
4 changed files with 74 additions and 2 deletions
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48
builtin/index-pack.c
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@ -891,6 +891,51 @@ static int git_index_pack_config(const char *k, const char *v, void *cb)
return git_default_config(k, v, cb);
}
static int cmp_uint32(const void *a_, const void *b_)
{
uint32_t a = *((uint32_t *)a_);
uint32_t b = *((uint32_t *)b_);
return (a < b) ? -1 : (a != b);
}
static void read_v2_anomalous_offsets(struct packed_git *p,
struct pack_idx_option *opts)
{
const uint32_t *idx1, *idx2;
uint32_t i;
/* The address of the 4-byte offset table */
idx1 = (((const uint32_t *)p->index_data)
+ 2 /* 8-byte header */
+ 256 /* fan out */
+ 5 * p->num_objects /* 20-byte SHA-1 table */
+ p->num_objects /* CRC32 table */
);
/* The address of the 8-byte offset table */
idx2 = idx1 + p->num_objects;
for (i = 0; i < p->num_objects; i++) {
uint32_t off = ntohl(idx1[i]);
if (!(off & 0x80000000))
continue;
off = off & 0x7fffffff;
if (idx2[off * 2])
continue;
/*
* The real offset is ntohl(idx2[off * 2]) in high 4
* octets, and ntohl(idx2[off * 2 + 1]) in low 4
* octets. But idx2[off * 2] is Zero!!!
*/
ALLOC_GROW(opts->anomaly, opts->anomaly_nr + 1, opts->anomaly_alloc);
opts->anomaly[opts->anomaly_nr++] = ntohl(idx2[off * 2 + 1]);
}
if (1 < opts->anomaly_nr)
qsort(opts->anomaly, opts->anomaly_nr, sizeof(uint32_t), cmp_uint32);
}
static void read_idx_option(struct pack_idx_option *opts, const char *pack_name)
{
struct packed_git *p = add_packed_git(pack_name, strlen(pack_name), 1);
@ -903,6 +948,9 @@ static void read_idx_option(struct pack_idx_option *opts, const char *pack_name)
/* Read the attributes from the existing idx file */
opts->version = p->index_version;
if (opts->version == 2)
read_v2_anomalous_offsets(p, opts);
/*
* Get rid of the idx file as we do not need it anymore.
* NEEDSWORK: extract this bit from free_pack_by_name() in