From: Junio C Hamano <gitster@pobox.com>
Date: Fri, 17 Jan 2025 22:45:04 GMT
Subject: Re: [PATCH 1/3] packfile: factor out --pack_header argument parsing
Message-ID: <xmqqo705hxfz.fsf@gitster.g>
In-Reply-To: <20250117125459.GA2893666@coredump.intra.peff.net>

Jeff King <peff@peff.net> writes:

>  			} else if (starts_with(arg, "--pack_header=")) {
> -				struct pack_header *hdr;
> -				char *c;
> -
> -				hdr = (struct pack_header *)input_buffer;
> -				hdr->hdr_signature = htonl(PACK_SIGNATURE);
> -				hdr->hdr_version = htonl(strtoul(arg + 14, &c, 10));

Interesting.  So the file-scope static input_buffer[] sits in the
BSS and happens to be well aligned not to cause the problem, but ...

> @@ -645,18 +646,9 @@ int cmd_unpack_objects(int argc,
>  				continue;
>  			}
>  			if (starts_with(arg, "--pack_header=")) {
> -				struct pack_header *hdr;
> -				char *c;
> -
> -				hdr = (struct pack_header *)buffer;
> -				hdr->hdr_signature = htonl(PACK_SIGNATURE);
> -				hdr->hdr_version = htonl(strtoul(arg + 14, &c, 10));

... the same file-scope static buffer[] that also sits in the BSS
was not well aligned by chance?

Otherwise these should be identical code.  Very interesting.

And of course the fix in the [2/3] is absolutely the right thing to
do.

Thanks.