GNU bug report logs - #22533
Non-determinism in python-3 ".pyc" bytecode

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From: Gábor Boskovits <boskovits <at> gmail.com>
To: Ricardo Wurmus <rekado <at> elephly.net>
Cc: Marius Bakke <mbakke <at> fastmail.com>, 22533 <at> debbugs.gnu.org
Subject: bug#22533: Python bytecode reproducibility
Date: Sun, 4 Mar 2018 10:21:17 +0100

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2018-03-03 23:37 GMT+01:00 Ricardo Wurmus <rekado <at> elephly.net>:

> Hi Guix,
>
> Marius Bakke <mbakke <at> fastmail.com> writes:
>
> > It would be great to revive this longstanding bug!
>
> Indeed.
>
> Here’s another attempt.  As far as I understand, the timestamp in the
> pyc files only affects the header.
>
> Up until Python 3.6 (incl) the header looks like this:
>
>   magic | timestamp | size
>
> Since Python 3.7 the header may either contain a timestamp or a hash:
>
>   magic | 00000000000000000000000000000000 | timestamp | size
>   magic | 00000000000000000000000000000001 | hash      | size
>
> This means we likely won’t have this problem any more with Python 3.7.
> For Python 3.6 I guess we could add a final build phase that overwrites
> the timestamp in the *binary*.  This needs to happen before any of the
> compiled files are wrapped up in a wheel.
>
> Should we just wait for Python 3.7 which is expected to be released in
> June 2018?  We’d still have to deal with this problem in Python 2,
> though.
>
> Is it a bad idea to override the timestamps in the generated binaries?
> I think that we could avoid the recency check then, which was an
> obstacle to resetting the timestamps of the source files.

--
> Ricardo
>
> GPG: BCA6 89B6 3655 3801 C3C6  2150 197A 5888 235F ACAC
> https://elephly.net
>
>
Nix had this issue, it seems they have a python 3.5 solution, which
should be easy to adopt: https://github.com/NixOS/nixpkgs/issues/22570.
WDYT?

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