[Bug 1828867] Re: QEmu translation is incorrect when using REX in combination with LAHF/SAHF

[Thomas Huth]

This is an automated cleanup. This bug report has been moved to QEMU's
new bug tracker on gitlab.com and thus gets marked as 'expired' now.
Please continue with the discussion here:

 https://gitlab.com/qemu-project/qemu/-/issues/130


** Changed in: qemu
       Status: New => Expired

** Bug watch added: gitlab.com/qemu-project/qemu/-/issues #130
   https://gitlab.com/qemu-project/qemu/-/issues/130

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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:
  Expired

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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