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Merge branch 'ps/commit-graph-overflow-fix'

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Fix a regression in writing the commit-graph where commits with dates
exceeding 34 bits (beyond year 2514) could cause an underflow and
crash Git during the generation data overflow chunk writing.

* ps/commit-graph-overflow-fix:
  commit-graph: fix writing generations with dates exceeding 34 bits
This commit is contained in:
Junio C Hamano
2026-04-07 14:59:25 -07:00
parent 716b9db0d3 04c9c5e8d2
commit d88c8ba70b
2 changed files with 54 additions and 3 deletions
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37
commit-graph.c
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@@ -1319,6 +1319,37 @@ static int write_graph_chunk_data(struct hashfile *f,
return 0;
}
/*
* Compute the generation offset between the commit date and its generation.
* This is what's ultimately stored as generation number in the commit graph.
*
* Note that the computation of the commit date is more involved than you might
* think. Instead of using the full commit date, we're in fact masking bits so
* that only the 34 lowest bits are considered. This results from the fact that
* commit graphs themselves only ever store 34 bits of the commit date
* themselves.
*
* This means that if we have a commit date that exceeds 34 bits we'll end up
* in situations where depending on whether the commit has been parsed from the
* object database or the commit graph we'll have different dates, where the
* ones parsed from the object database would have full 64 bit precision.
*
* But ultimately, we only ever want the offset to be relative to what we
* actually end up storing on disk, and hence we have to mask all the other
* bits.
*/
static timestamp_t compute_generation_offset(struct commit *c)
{
timestamp_t masked_date;
if (sizeof(timestamp_t) > 4)
masked_date = c->date & (((timestamp_t) 1 << 34) - 1);
else
masked_date = c->date;
return commit_graph_data_at(c)->generation - masked_date;
}
static int write_graph_chunk_generation_data(struct hashfile *f,
void *data)
{
@@ -1329,7 +1360,7 @@ static int write_graph_chunk_generation_data(struct hashfile *f,
struct commit *c = ctx->commits.items[i];
timestamp_t offset;
repo_parse_commit(ctx->r, c);
offset = commit_graph_data_at(c)->generation - c->date;
offset = compute_generation_offset(c);
display_progress(ctx->progress, ++ctx->progress_cnt);
if (offset > GENERATION_NUMBER_V2_OFFSET_MAX) {
@@ -1350,7 +1381,7 @@ static int write_graph_chunk_generation_data_overflow(struct hashfile *f,
int i;
for (i = 0; i < ctx->commits.nr; i++) {
struct commit *c = ctx->commits.items[i];
timestamp_t offset = commit_graph_data_at(c)->generation - c->date;
timestamp_t offset = compute_generation_offset(c);
display_progress(ctx->progress, ++ctx->progress_cnt);
if (offset > GENERATION_NUMBER_V2_OFFSET_MAX) {
@@ -1741,7 +1772,7 @@ static void compute_generation_numbers(struct write_commit_graph_context *ctx)
for (i = 0; i < ctx->commits.nr; i++) {
struct commit *c = ctx->commits.items[i];
timestamp_t offset = commit_graph_data_at(c)->generation - c->date;
timestamp_t offset = compute_generation_offset(c);
if (offset > GENERATION_NUMBER_V2_OFFSET_MAX)
ctx->num_generation_data_overflows++;
}