Re: x86_decode_insn succeeds with GroupMask flags when it should fail

[Avi Kivity <avi@redhat.com>]

On 01/07/2012 12:37 PM, Stefan Hajnoczi wrote:
> The unimplemented movdqa (66 0f 7f 07) instruction triggers a bug in
> the x86 emulator.  The emulator should fail since the instruction is
> unimplemented.   However the emulator thinks it is succeeding but we
> keep re-executing the same instruction over and over.  top shows 100%
> CPU utilization and perf top shows we're constantly running through
> the x86 emulator in kvm.ko.
>
> The problem is that ctxt->d != 0 even though the instruction is
> unimplemented (N):
>
> while (ctxt->d & GroupMask) {
>     switch (ctxt->d & GroupMask) {
>     ...  <-- opcode zeroed if instruction is unimplemented
>     }
>
>     ctxt->d &= ~(u64)GroupMask;  <-- only clears GroupMask
>     ctxt->d |= opcode.flags;     <-- opcode.flags == 0, ctxt->d != 0
> }
>
> ...
>
> /* Unrecognised? */
> if (ctxt->d == 0 || (ctxt->d & Undefined))  <-- always false
>     return EMULATION_FAILED;
>

#define N D(Undefined)

should fix it.

-- 
error compiling committee.c: too many arguments to function