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Re: kern/50332: AVX instructions don't work but OSXSAVE flag is set
The following reply was made to PR kern/50332; it has been noted by GNATS.
From: Manuel Bouyer <bouyer%antioche.eu.org@localhost>
To: =?iso-8859-1?Q?Torbj=F6rn?= Granlund <tg%gmplib.org@localhost>
Cc: gnats-bugs%netbsd.org@localhost, kern-bug-people%netbsd.org@localhost, gnats-admin%netbsd.org@localhost,
Subject: Re: kern/50332: AVX instructions don't work but OSXSAVE flag is set
Date: Tue, 20 Oct 2015 21:23:48 +0200
On Tue, Oct 20, 2015 at 06:41:54PM +0200, Torbjörn Granlund wrote:
> David Laight <david%l8s.co.uk@localhost> writes:
> No, there is no reason why you can't have a cpu (and os) that supports xsave
> (etc) but doesn't support avx.
> You have to look at the bitmap of supported extensions.
> IIRC Only the x87 fpu registers are mandatory.
> Note that my updated test case tests both flags to make this a moot
> However that probably isn't the issue here.
> More likely is that something in xen should stop avx being used,
> or xen needs to do something different from bare-metal to support avx.
> Please note that non-NetBSD guest systems have no problem. Also, NetBSD
> with no Xen around works fine.
> That makes me suspect Xen is innocent and that NetBSD gets this wrong
> when run with Xen.
> My complaint is not that AVX does not work under Xen+NetBSD, but that it
> doesn't work in spite of that NetBSD sets OSXSAVE.
AFAIK NetBSD is not setting OSXSAVE. This comes from the cpuid instruction,
and I don't think the OS can change what cpuid repports.
Manuel Bouyer <bouyer%antioche.eu.org@localhost>
NetBSD: 26 ans d'experience feront toujours la difference
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