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Re: [Qemu-devel] Bug report about x86 'bt' insn
From: |
malc |
Subject: |
Re: [Qemu-devel] Bug report about x86 'bt' insn |
Date: |
Sat, 6 Nov 2010 20:16:13 +0300 (MSK) |
User-agent: |
Alpine 2.00 (LNX 1167 2008-08-23) |
On Sat, 6 Nov 2010, Torbjorn Granlund wrote:
> [This is a bug report, reported here since I was redirected to some
> corporate site when attempting to follow the recommended bug report
> practice. If I am really required to register an account with a
> corporation in order to report a qemu bug, and that bug reports are not
> accepted here, then please accept my apology; I suggest that you simply
> ignore this bug report.]
>
> Bug report:
>
> Qemu version: 0.13.0 (installed via FreeBSD's ports system).
>
> Host: FreeBSD 8.1 amd64 (without any relevant kernel modules)
>
> Guest environments where problem has been reproduced: (1) Debian GNU/Linux
> 5, (2) Debian GNU/kFreeBSD snapshot, (3) FreeBSD 8.1
>
> Problem: The bt insn works incorrectly under qemu. It incorrectly sets
> the Z flag. The bt insn should only affect the carry flag. (This
> causes the GMP library to work incorrectly.)
>
> Test code snippet:
>
> .text
> .globl main
> main: mov $1, %eax
> and %eax, %eax
> bt $0, %eax
> jz 1f
> xor %eax, %eax
> 1: ret
>
> Assembly and execute. Correct behaviour is to exit(0). Under qemu it
> it exits with value 1.
ZF is undefined according to AMD's 24594.pdf page 69.
>
> (I thought qemu wouldn't interfere with plain user mode instructions
> when the host system can handle all the guest systems's instructions,
> and that they would execute natively and at full speed. This bug
> suggests that buggy emulation is taking place.)
>
>
--
mailto:address@hidden
- [Qemu-devel] Bug report about x86 'bt' insn, Torbjorn Granlund, 2010/11/06
- Re: [Qemu-devel] Bug report about x86 'bt' insn,
malc <=
- Re: [Qemu-devel] Bug report about x86 'bt' insn, Torbjorn Granlund, 2010/11/06
- Re: [Qemu-devel] Bug report about x86 'bt' insn, malc, 2010/11/06
- Re: [Qemu-devel] Bug report about x86 'bt' insn, Nathan Froyd, 2010/11/06
- Re: [Qemu-devel] Bug report about x86 'bt' insn, malc, 2010/11/06
- Re: [Qemu-devel] Bug report about x86 'bt' insn, malc, 2010/11/06
- Re: [Qemu-devel] Bug report about x86 'bt' insn, Torbjorn Granlund, 2010/11/10
- Re: [Qemu-devel] Bug report about x86 'bt' insn, malc, 2010/11/10
- Re: [Qemu-devel] Bug report about x86 'bt' insn, Torbjorn Granlund, 2010/11/10
- Re: [Qemu-devel] Bug report about x86 'bt' insn, malc, 2010/11/10
- Re: [Qemu-devel] Bug report about x86 'bt' insn, malc, 2010/11/10