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From: Junio C Hamano <>
To: Jeff King <>
Cc: Victoria Dye <>,
	Derrick Stolee <>,
Subject: Re: fails with SANITIZE=undefined
Date: Thu, 22 Sep 2022 15:56:21 -0700	[thread overview]
Message-ID: <xmqq7d1vxbl6.fsf@gitster.g> (raw)
In-Reply-To: <> (Jeff King's message of "Thu, 22 Sep 2022 18:27:19 -0400")

Jeff King <> writes:

> I also wondered why other versions do not have a similar problem. After
> all, cache entries contain pathnames which are going to be of varying
> lengths. But this seems telling:
>   $ git grep -m1 -B1 -A2 align_padding_size
>   read-cache.c-/* These are only used for v3 or lower */
>   read-cache.c:#define align_padding_size(size, len) ((size + (len) + 8) & ~7) - (size + len)
>   read-cache.c-#define align_flex_name(STRUCT,len) ((offsetof(struct STRUCT,data) + (len) + 8) & ~7)
>   read-cache.c-#define ondisk_cache_entry_size(len) align_flex_name(ondisk_cache_entry,len)
> So we actually pad the entries in earlier versions to align them, but
> don't in v4. I'm not sure if that was a conscious choice to save space,
> or an unintended consequence (though it is mentioned in the docs, I
> think that came after the code).

I think we didn't even have on-disk vs in-core distinction in the
early index code.  The active_cache[] array used to be an array of
pointers into the (read-only) mmapped memory, peeking into on-disk
index we just "read".  Back when v4 was introduced, that arrangement
was (thought to be) long gone---we iterated over the mmapped memory
and used create_from_disk() to munge the on-disk representation into
a machine native form.  At that point, there was no point in having
the padding---we are supposed to be using get_beXX() and stuff
without having to worry about alignment requirements.

      reply	other threads:[~2022-09-22 22:56 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-09-22 10:04 fails with SANITIZE=undefined Jeff King
2022-09-22 12:35 ` Derrick Stolee
2022-09-22 19:12   ` Jeff King
2022-09-22 22:09     ` Victoria Dye
2022-09-22 22:27       ` Jeff King
2022-09-22 22:56         ` Junio C Hamano [this message]

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