[PATCH 3/3] khashl: fix ensemble lookups on empty table

From: Eric Wong <e@80x24.org>
Date: Mar 28, 2024, 10:13 UTC
Message-ID: <20240328101356.300374-4-e@80x24.org>
In-Reply-To: <20240328101356.300374-1-e@80x24.org>

The ->bits field of regular khashl structs is invalid when the ->keys array is NULL. Thus the ensemble *_getp implementation must follow existing *_get and *_getp usage conventions and check the iterator against kh_end().

This fixes a fast-import crash on t3427-rebase-subtree.sh in an abandoned commit to use the ensemble implementation for oid_map and oid_pos. I've abandoned the aforementioned commit for now since it was more intrusive, more expensive for small tables, and realloc(3) on glibc is already optimized using mremap(2) for large hash resizes.

Signed-off-by: Eric Wong <e@80x24.org>
---
 khashl.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/khashl.h b/khashl.h
index 1e724bbf88..30f85dc5e2 100644
--- a/khashl.h
+++ b/khashl.h
@@ -265,7 +265,7 @@ typedef struct {
 		low = hash & ((1U<<g->bits) - 1); \
 		h = &g->sub[low]; \
 		ret = prefix##_sub_getp_core(h, key, hash); \
-		if (ret == 1U<<h->bits) r.sub = low, r.pos = (khint_t)-1; \
+		if (ret >= kh_end(h)) r.sub = low, r.pos = (khint_t)-1; \
 		else r.sub = low, r.pos = ret; \
 		return r; \
 	} \