[Qemu-devel] [Bug 1828867] [NEW] QEmu translation is incorrect when using REX in combination with LAHF/SAHF

[Qemu-devel] [Bug 1828867] [NEW] QEmu translation is incorrect when using REX in combination with LAHF/SAHF

[Sonicadvance1]

Public bug reported:

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"

** Affects: qemu
     Importance: Undecided
         Status: New

** Patch added: "Terrible terrible patch"
   https://bugs.launchpad.net/bugs/1828867/+attachment/5263494/+files/lahf_sahf.diff

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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"

To manage notifications about this bug go to:
https://bugs.launchpad.net/qemu/+bug/1828867/+subscriptions

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

[Sonicadvance1]

Here's also a basic test that can be run on hardware and have rflags and
rsp inspected after each instruction just to see how hardware doesn't
effect it.

** Attachment added: "a.cpp"
   https://bugs.launchpad.net/qemu/+bug/1828867/+attachment/5263495/+files/a.cpp

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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"

To manage notifications about this bug go to:
https://bugs.launchpad.net/qemu/+bug/1828867/+subscriptions

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

[Alex Bennée]

** 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"

To manage notifications about this bug go to:
https://bugs.launchpad.net/qemu/+bug/1828867/+subscriptions

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

[Thomas Huth]

The QEMU project is currently considering to move its bug tracking to
another system. For this we need to know which bugs are still valid
and which could be closed already. Thus we are setting older bugs to
"Incomplete" now.

If you still think this bug report here is valid, then please switch
the state back to "New" within the next 60 days, otherwise this report
will be marked as "Expired". Or please mark it as "Fix Released" if
the problem has been solved with a newer version of QEMU already.

Thank you and sorry for the inconvenience.

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

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Title:
  QEmu translation is incorrect when using REX in combination with
  LAHF/SAHF

Status in QEMU:
  Incomplete

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"

To manage notifications about this bug go to:
https://bugs.launchpad.net/qemu/+bug/1828867/+subscriptions

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

[Ryan Houdek]

This is still relevant.

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

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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"

To manage notifications about this bug go to:
https://bugs.launchpad.net/qemu/+bug/1828867/+subscriptions

[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"

To manage notifications about this bug go to:
https://bugs.launchpad.net/qemu/+bug/1828867/+subscriptions