Re: [Xen-devel] [PATCH] xen/x86: Fix up rules when forcing -mno-sse

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 12/08/15 17:03, Doug Goldstein wrote:
> On Wed, Aug 12, 2015 at 10:38 AM, Jan Beulich <JBeulich@xxxxxxxx> wrote:
>>>>> On 12.08.15 at 17:23, <cardoe@xxxxxxxxxx> wrote:
>>> From: Nathan Rossi <nathan.rossi@xxxxxxxxxx>
>>>
>>> * When forcing -mno-sse specify -mfpmath=387 to avoid the fallback
>>>   warning
>> "the fallback warning" being what? I've never seen any, and I don't
>> think I've ever heard anyone else say there was one.
>>
>> Apart from that I don't think -mfpmath=387 is what we want - we'd
>> better tell the compiler to not use x87 registers at all.

Agreed.

However, a git grep shows:

crypto/vmac.c:1098:    double cpb;
crypto/vmac.c:1158:             
((double)CLOCKS_PER_SEC*speed_lengths[i]*speed_iters[i]));

which I suspect might need fixing.

>>
>> Jan
>>
> I guess I jumped the gun a bit. When targeting a corei7 based chip, Yocto uses
> the following CFLAGS for the packages it builds:
>
> -march=corei7 -mtune=corei7 -mfpmath=sse -msse4.2
>
> The issue is the -mfpmath value.
>

It seems wrong to set -mfpmath=387, as that implies that floating point
maths is ok.

I cant however find an obvious "no fpmath" option.

Perhaps Xen should specifically filter options such as those out from
the environmental CFLAGS

~Andrew

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