From mboxrd@z Thu Jan  1 00:00:00 1970
From: ludo@gnu.org (Ludovic =?UTF-8?Q?Court=C3=A8s?=)
Subject: bug#30820: Chunked store references in compiled code break grafting
	(again)
Date: Mon, 19 Mar 2018 23:34:38 +0100
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References: <87o9jq7j7r.fsf@gnu.org> <87muz3dgy1.fsf@netris.org>
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To: Mark H Weaver <mhw@netris.org>
Cc: 30820@debbugs.gnu.org

Hi Mark,

Mark H Weaver <mhw@netris.org> skribis:

> ludo@gnu.org (Ludovic Court=C3=A8s) writes:
>
>> The recently added glibc grafts triggered issues that, in the end, show
>> the return of <http://bugs.gnu.org/24703> (=E2=80=9CStore references in =
8-byte
>> chunks in compiled code=E2=80=9D).
>
> I think that we should generalize our reference scanning and grafting
> code to support store references broken into pieces, as long as each
> piece containing part of the hash is at least 8 bytes long.
>
> Here's my preliminary proposal:
>
> (1) The reference scanner should recognize any 8-byte substring of a
>     hash as a valid reference to that hash.
>
> (2) To enable reliable grafting of chunked references, we should impose
>     the following new restrictions: (a) the store prefix must be at
>     least 6 bytes, (b) grafting can change only the hash, not the
>     readable part of the store name, and (c) the readable part of the
>     store name must be at least 6 bytes.
>
> (3) The grafter should recognize and replace any 8-byte subsequence of
>     the absolute store file name.

I=E2=80=99m quite reluctant because it would add complexity, it will probab=
ly
slow things down, and yet it may not handle all the cases, as Danny
suggests.

Mind you, the GCC patches are not perfect either, but they=E2=80=99re relat=
ively
easy to deal with (well, so far at least).  In theory we would need
similar patches for LLVM and maybe a couple other native compilers,
though, which is obviously a downside, although we haven=E2=80=99t had any
problems so far.

WDYT?

Ludo=E2=80=99.