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[Qemu-devel] [Bug 1828867] Re: QEmu translation is incorrect when using
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From: |
Alex Bennée |
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Subject: |
[Qemu-devel] [Bug 1828867] Re: QEmu translation is incorrect when using REX in combination with LAHF/SAHF |
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Date: |
Mon, 13 May 2019 20:24:28 -0000 |
** Tags added: tcg testcase x86
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https://bugs.launchpad.net/bugs/1828867
Title:
QEmu translation is incorrect when using REX in combination with
LAHF/SAHF
Status in QEMU:
New
Bug description:
When translating code that is using LAHF and SAHF in combination with the REX
prefix then qemu translates incorrectly.
These two instructions only ever use the AH register. Contrary to other
instructions where if you use REX + high bit offsets then it'll pull in rsp and
a few other registers.
On hardware the REX prefix doesn't effect behaviour of these instructions at
all.
QEMU incorrectly selects RSP as the register of choice here due to this
combination of REX + AH register usage.
I've attached a patch that is super terrible just so I can work around
the issue locally and to sort of show off how it is to be "fixed"
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