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Re: [perl #130133] [PATCH] Configure leaves garbage in$Config{longdblinfbytes}

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From:
Niko Tyni
Date:
November 19, 2016 08:30
Subject:
Re: [perl #130133] [PATCH] Configure leaves garbage in$Config{longdblinfbytes}
Message ID:
20161119083030.n3ou6lx663p6eiwq@estella.local.invalid
In-Reply-To: <rt-4.0.24-6473-1479505426-193.130133-94-0@perl.org>

On Fri, Nov 18, 2016 at 01:43:46PM -0800, James E Keenan via RT wrote:

> Do you expect that the impact of this will only show up if someone is using 'gcc' rather than, say, g++ or clang?

I realize I probably didn't answer your question. Sorry.

I've only tried with gcc 5 and 6 from Debian unstable. I'd expect g++
to be the same. No idea about clang.

As for seeing the impact: with gcc 6 on Debian unstable/amd64 (=x86_64),
where the randomness started to show up here, manually running the
unpatched probe extracted from Configure gives:

 % for i in $(seq 1 5); do ./a.out 3; done
 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x80, 0xff, 0x7f, 0x82, 0x83, 0x53, 0x56, 0x00, 0x00
 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x80, 0xff, 0x7f, 0x8c, 0xe8, 0x9f, 0x55, 0x00, 0x00
 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x80, 0xff, 0x7f, 0x0f, 0x99, 0x8f, 0x55, 0x00, 0x00
 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x80, 0xff, 0x7f, 0xe9, 0x86, 0x8f, 0x55, 0x00, 0x00
 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x80, 0xff, 0x7f, 0xcd, 0x64, 0xb3, 0x55, 0x00, 0x00

while the patched one consistently gives
 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x80, 0xff, 0x7f, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00

I'm attaching the (buggy) probe program for convenience.

gcc is 'gcc version 6.2.0 20161103 (Debian 6.2.0-11)'.
-- 
Niko Tyni   ntyni@debian.org

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