Subject: [PATCH v2 3/5] parse_pack_header_option(): avoid unaligned memory writes

From: Jeff King <[email-masked]>
Date: Sun, 19 Jan 2025 08:23:44 -0500

In order to recreate a pack header in our in-memory buffer, we cast the
buffer to a "struct pack_header" and assign the individual fields. This
is reported to cause SIGBUS on sparc64 due to alignment issues.

We can work around this by using put_be32() which will write individual
bytes into the buffer.

Reported-by: Koakuma <[email-masked]>
Signed-off-by: Jeff King <[email-masked]>
---
Same as before.

 packfile.c | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/packfile.c b/packfile.c
index 2bf9e57330..2d80d80cb3 100644
--- a/packfile.c
+++ b/packfile.c
@@ -2318,17 +2318,20 @@ int is_promisor_object(struct repository *r, const struct object_id *oid)
 
 int parse_pack_header_option(const char *in, unsigned char *out, unsigned int *len)
 {
-	struct pack_header *hdr;
+	unsigned char *hdr;
 	char *c;
 
-	hdr = (struct pack_header *)out;
-	hdr->hdr_signature = htonl(PACK_SIGNATURE);
-	hdr->hdr_version = htonl(strtoul(in, &c, 10));
+	hdr = out;
+	put_be32(hdr, PACK_SIGNATURE);
+	hdr += 4;
+	put_be32(hdr, strtoul(in, &c, 10));
+	hdr += 4;
 	if (*c != ',')
 		return -1;
-	hdr->hdr_entries = htonl(strtoul(c + 1, &c, 10));
+	put_be32(hdr, strtoul(c + 1, &c, 10));
+	hdr += 4;
 	if (*c)
 		return -1;
-	*len = sizeof(*hdr);
+	*len = hdr - out;
 	return 0;
 }
-- 
2.48.1.466.g22b8cfd1fa