Bug#742409: [Sereal] 2.06 fails to build on some architectures: (#47)

[Niko Tyni]

(Cc'ing Yves instead of the scary github address as he
 explicitly asked for that in the upstream ticket.)

On Wed, Jul 16, 2014 at 05:06:29PM +0200, gregor herrmann wrote:
> On Tue, 15 Jul 2014 13:03:56 -0700, Yves Orton wrote:

> > This is so frustrating. Is there anyone in the Debian community that knows
> > these platforms that can help?
> 
> Hm, probably but I'm not sure who knows about all of them.
> Cc'ing the Debian bug report.

Hi, I looked at the Sereal-Encoder problems briefly. The current state
with Debian libsereal-encoder-perl 3.002-1 (unpatched 3.002) is that it
only fails on 64-bit big-endian architectures (s390x and powerpc64).

The failures are all in t/700_roundtrip/ with the snappy tests, and
involve array refs and long strings. I was able to reduce at least one
of them to this:

  #!/usr/bin/perl -w
  use blib;
  use Sereal::Decoder;
  use Sereal::Encoder;
  my $opt = { snappy => 1, use_protocol_v1 => 1};
  
  my $len = shift || 509;
  
  my $s="A"x$len;
  my $e =  Sereal::Encoder->new($opt)->encode([$s, $s]);
  my $d =  Sereal::Decoder->new($opt)->decode($e);
  
  # print $e;
  print "" . ($d->[0] eq $s ? "" : "not ") . "ok 1 first element\n";
  print "" . ($d->[1] eq $s ? "" : "not ") . "ok 2 second element\n";
 
which gives "not ok 2" on s390x when the length is 509 or greater.

The problem is with the encoder: amd64 and s390x encoded contents differ,
and feeding the amd64 encoded output to an s390x decoder works fine.
The second element of the decoded array is just the string "3" in the
incorrect case.

I see the length of the encoded output shortens dramatically at the 508 ->
509 step, looks like some compression kicks in.

I'm attaching the binary output from both s390x (incorrect) and amd64
(correct) for reference for length==509. Hope they make it through,
the md5sums should be

 8787f3dd9a3bfa23bd91eb08c40f3716  509.amd64
 276cbe59ce957915cc92b52fb0b7b51c  509.s390x

All this makes me think that the problem is in snappy/csnappy_compress.c,
but I haven't really delved into it yet.

Hope this helps. Yves, please let me know if I can help in any way.
-- 
Niko Tyni   ntyni at debian.org
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