GNU bug report logs - #30820
Chunked store references in compiled code break grafting (again)

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Message #21 received at 30820 <at> debbugs.gnu.org (full text, mbox):

From: Mark H Weaver <mhw <at> netris.org>
To: ludo <at> gnu.org (Ludovic Courtès)
Cc: 30820 <at> debbugs.gnu.org
Subject: Re: bug#30820: Chunked store references in compiled code break
 grafting (again)
Date: Mon, 19 Mar 2018 15:16:30 -0400

Mark H Weaver <mhw <at> netris.org> writes:

> ludo <at> gnu.org (Ludovic Courtès) writes:
>
>> The recently added glibc grafts triggered issues that, in the end, show
>> the return of <http://bugs.gnu.org/24703> (“Store references in 8-byte
>> chunks in compiled code”).
>
> 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.

To facilitate the transition: to support older versions of the Guix
daemon (or Nix daemon), we could add a final phase to gnu-build-system
which would "unhide" these references as follows: It would scan each
output directory for 8-byte substrings of hashes.  If it finds any
references that the old scanner is unable to see, it would install a
file to the output directory containing the full store names of the
hidden references.

This only works for output directories, though.  I don't know what to do
about output files containing hidden references.  I guess the final
phase should raise an error in this case, and hopefully it rarely
happens.

      Mark

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