Re: [Xen-devel] [PATCH v4 3/4] VMX: use proper instruction mnemonics if assembler supports them

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 26.08.13 at 17:07, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
> I was more referring to having a q in the instruction, yet an "r" in the
> parameter list.  I would suggest

So you perhaps mix up "q" as a constraint (meaning byte registers)
and "q" as an operand qualifier (meaning the 64-bit register
regardless of the operand size of the respective asm() operand)?

> INV{EPT,VPID} is strictly defined to take r64 as the "type" parameter in
> long mode.  Invalid/unsupported values found in this register can be
> detected based on the state of EFLAGS afterwards.
> 
> Therefore, I would suggest possibly changing "int type" to "unsigned
> long type" if we are going to the effort of getting this correct.  It
> shouldn't make a difference currently, as all calls use appropriate
> INVEPT_*_CONTEXT defines.

Yes, as already indicated. v5 is about to be on its way.

> As for the flags, should we be including "cc" to the clobber list as
> each of the VM*/INV* instructions explicitly sets the flags.  I would
> hope that the toolchain is pessimistic enough to not trust the state of
> the flags across some inline assembly, but I can't find any hard
> information one way or another.

Yes, on x86 at least it is never necessary to list cc explicitly.
Which at times is sad, but here's it's to our benefit.

Jan


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