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Re: [Qemu-devel] [RFC PATCH 1/3] target-i386: Add 486sx, old486, and old
From: |
H. Peter Anvin |
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 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130311 Thunderbird/17.0.4 |
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
- Re: [Qemu-devel] [RFC PATCH 1/3] target-i386: Add 486sx, old486, and old486sx CPU models, (continued)
- Re: [Qemu-devel] [RFC PATCH 1/3] target-i386: Add 486sx, old486, and old486sx CPU models, Igor Mammedov, 2013/03/25
- Re: [Qemu-devel] [RFC PATCH 1/3] target-i386: Add 486sx, old486, and old486sx CPU models, H. Peter Anvin, 2013/03/25
- Re: [Qemu-devel] [RFC PATCH 1/3] target-i386: Add 486sx, old486, and old486sx CPU models, Eduardo Habkost, 2013/03/25
- Re: [Qemu-devel] [RFC PATCH 1/3] target-i386: Add 486sx, old486, and old486sx CPU models, H. Peter Anvin, 2013/03/25
- Re: [Qemu-devel] [RFC PATCH 1/3] target-i386: Add 486sx, old486, and old486sx CPU models, Eduardo Habkost, 2013/03/25
- Re: [Qemu-devel] [RFC PATCH 1/3] target-i386: Add 486sx, old486, and old486sx CPU models, H. Peter Anvin, 2013/03/25
- Re: [Qemu-devel] [RFC PATCH 1/3] target-i386: Add 486sx, old486, and old486sx CPU models, H. Peter Anvin, 2013/03/25
- Re: [Qemu-devel] [RFC PATCH 1/3] target-i386: Add 486sx, old486, and old486sx CPU models, Eduardo Habkost, 2013/03/25
Re: [Qemu-devel] [RFC PATCH 1/3] target-i386: Add 486sx, old486, and old486sx CPU models, Aurelien Jarno, 2013/03/28