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Reply-To:	Brian DOT Inglis AT SystematicSw DOT ab DOT ca
Subject:	Re: I sent in a bug report and never heard anything back
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To:	cygwin AT cygwin DOT com
From:	Brian Inglis <Brian DOT Inglis AT SystematicSw DOT ab DOT ca>
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Date:	Sun, 28 Aug 2016 01:18:00 -0600
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On 2016-08-27 22:57, Brian Inglis wrote:
> On 2016-08-27 10:27, jeff wrote:
>> Brian Inglis wrote:
>> Apparently it's a mobile Broadwell without AVX or AVX2,
>> which might be assumed present in gcc as compiled,
>> requiring a custom gcc build to run on that cpu.
>> My reply:
>> You are correct. The gcc people replied to my bug report with:
>> "So the problem is your GMP/MPFR are compiled for one type of CPU and cannot be
>> copied to other type."
>> They closed it as a resolved issue.
>> So the problem is that gcc now requires GMP, and GMP was compiled with options that
>> are not compatible with my CPU. I can fix the issue for myself by compiling everything
>> from scratch.
>> The bigger issue is can cygwin distribute a version of gcc that will work with all modern
>> processors, including mine, with it's weird lack of AVX and AVX2. Since I ran into the
>> issue, I suspect anyone else with a mobile processor like mine will run into the issue.
>> I don't know enough about how cygwin is built and installed to know how different versions
>> of the GMP library might be distributed for different Intel processors.
>> But the problem is not going to go away, and really should be addressed in order to make
>> cygwin run on all reasonable platforms.
>
> You could download devel sources for the MPC, MPFR, GMP, ISL, and
> CLOOG packages to check what options are used for the builds and
> whether AVX options are assumed on Broadwell cpus.
>
> GMP provides a build option, which could cause such a problem:
> "Fat binary, --enable-fat
>     Using --enable-fat selects a “fat binary” build on x86,
> where optimized low level subroutines are chosen at runtime according
> to the CPU detected.
> This means more code, but gives good performance on all x86 chips.
> (This option might become available for more architectures in the future.)"
>
> These libraries should be designed to run code either independent of,
> or dependent only on available, cpu features, but checks may not be
> sufficiently specific for newer variants.
>
> You may want to try searching for and filing bugs against GMP and/or
> MPFR with a link back to the GCC report, unless someone hereabouts
> can provide more specific info about a possible failure source.

See also https://gmplib.org/repo/gmp-6.1/rev/30c9cf97935a and
https://www.cygwin.com/ml/cygwin-apps/2015-11/msg00071.html
where GMP enabled avx support on all Broadwell cpus.

If you submit a GMP bug report with /proc/cpuinfo output and
a link to your gcc bug, they should be able to add a case to
support mobile Broadwells without AVX support in a fat binary.

-- 
Take care. Thanks, Brian Inglis, Calgary, Alberta, Canada

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