From: "H. Peter Anvin" <hpa@zytor.com>
To: Aurelien Jarno <aurelien@aurel32.net>
Cc: qemu-devel@nongnu.org
Subject: Re: [Qemu-devel] [RFC PATCH 1/3] target-i386: Add 486sx, old486, and old486sx CPU models
Date: Thu, 28 Mar 2013 13:12:11 -0700 [thread overview]
Message-ID: <5154A41B.2030609@zytor.com> (raw)
In-Reply-To: <20130328191533.GA23069@ohm.aurel32.net>
On 03/28/2013 12:15 PM, Aurelien Jarno wrote:
>
> This really looks like Linux kernel specific. I haven't been able to
> test on a real machine, but the documentation I have found suggest that
> without and x87 FPU, the FPU instructions are simply ignored. The common
> way to detect an FPU is therefore to initialize registers to a given
> value, run fnstsw and fnstcw instructions with the register in arguments
> and see if they have been modified.
>
> The Linux kernel indeed set the initial value of these registers to
> 0xffff, but I am not sure all codes are doing the same.
>
> For me it looks like better to skip such instructions directly in
> translate.c. As a bonus it seems easy to do that for all FPU
> instructions.
>
It might have been (and this is from memory, so don't take it for
anything) that the register form receives 0xffff, but the memory form is
ignored.
-hpa
next prev parent reply other threads:[~2013-03-28 20:12 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <1362017554-1260-1-git-send-email-hpa@zytor.com>
2013-03-24 5:06 ` [Qemu-devel] [RFC PATCH 1/3] target-i386: Add 486sx, old486, and old486sx CPU models H. Peter Anvin
2013-03-25 9:06 ` Paolo Bonzini
2013-03-25 9:23 ` Andreas Färber
[not found] ` <1362017554-1260-3-git-send-email-hpa@zytor.com>
2013-03-25 9:05 ` [Qemu-devel] [RFC PATCH 3/3] mc146818rtc: export the timezone information Paolo Bonzini
2013-03-25 15:47 ` H. Peter Anvin
2013-03-25 15:51 ` Paolo Bonzini
2013-03-25 9:39 ` [Qemu-devel] [RFC PATCH 1/3] target-i386: Add 486sx, old486, and old486sx CPU models Andreas Färber
2013-03-25 15:15 ` Igor Mammedov
2013-03-25 18:44 ` H. Peter Anvin
2013-03-25 19:05 ` Eduardo Habkost
2013-03-25 20:45 ` H. Peter Anvin
2013-03-25 20:56 ` Eduardo Habkost
2013-03-25 20:56 ` H. Peter Anvin
2014-01-07 5:53 ` H. Peter Anvin
2014-01-07 9:08 ` Igor Mammedov
2013-03-25 20:47 ` H. Peter Anvin
2013-03-25 19:01 ` Eduardo Habkost
[not found] ` <1362017554-1260-2-git-send-email-hpa@zytor.com>
2013-03-28 19:15 ` [Qemu-devel] [RFC PATCH 2/3] target-i386: Raise #UD on accessing non-existent control registers Aurelien Jarno
2013-03-28 19:15 ` [Qemu-devel] [RFC PATCH 1/3] target-i386: Add 486sx, old486, and old486sx CPU models Aurelien Jarno
2013-03-28 20:02 ` H. Peter Anvin
2013-03-28 20:12 ` H. Peter Anvin [this message]
2013-03-29 5:10 ` Rob Landley
2013-03-29 5:25 ` H. Peter Anvin
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