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

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From:
James E Keenan via RT
Date:
November 18, 2016 21:43
Subject:
[perl #130133] [PATCH] Configure leaves garbage in$Config{longdblinfbytes}
Message ID:
rt-4.0.24-6473-1479505426-1461.130133-15-0@perl.org
On Fri, 18 Nov 2016 19:18:07 GMT, ntyni@debian.org wrote:
> This is a bug report for perl from Niko Tyni <ntyni@debian.org>,
> generated with the help of perlbug 1.40 running under perl 5.25.7.
> 
> 
> -----------------------------------------------------------------
> [Please describe your issue here]
> 
> The Configure test for long double implementation details probes the
> contents of "long double inf", and they get stored in the Config
> module:
> 
> % perl -V:longdblinfbytes
> longdblinfbytes='0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x80, 0xff,
> 0x7f, 0x40, 0x00, 0x00, 0x00, 0x00, 0x00';
> 
> Some of these bytes are currently essentially random and vary between
> builds on at least amd64 and i386, because their long doubles are only
> 80-bit and the remaining six bytes stay uninitialized.
> 
> The relevant Configure probe tries to initialize these bytes, but has
> several bugs that defeat the purpose. Patch attached.
> 
> The randomness seems to only have started to show on Debian with GCC-6
> for one reason or another; the bytes are zeroed out on at least GCC-5.
> 

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

I ask because I suspect we'll have to hunt up people to test this on multiple versions of multiple C compilers.

Thank you very much.

-- 
James E Keenan (jkeenan@cpan.org)

---
via perlbug:  queue: perl5 status: new
https://rt.perl.org/Ticket/Display.html?id=130133

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