Re: [PATCH] x86-64: don't allow use of %axl as accumulator

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Mon, Nov 13, 2017 at 2:03 AM, Jan Beulich <JBeulich@suse.com> wrote:
>>>> On 10.11.17 at 14:27, <hjl.tools@gmail.com> wrote:
>> On Fri, Nov 10, 2017 at 4:50 AM, Jan Beulich <JBeulich@suse.com> wrote:
>>> Just like %cxl can't be used as shift count register. Otherwise for
>>> consistency %cxl would need to gain "ShiftCount" and use of both ought
>>> to properly cause REX prefixes to be emitted.
>>
>> There are no good testcases for
>>
>> axl, Reg8|Acc|Byte, RegRex64, 0, Dw2Inval, Dw2Inval
>> cxl, Reg8, RegRex64, 1, Dw2Inval, Dw2Inval
>> dxl, Reg8, RegRex64, 2, Dw2Inval, Dw2Inval
>> bxl, Reg8, RegRex64, 3, Dw2Inval, Dw2Inval
>> bpl, Reg8, RegRex64, 5, Dw2Inval, Dw2Inval
>
> Not sure I understand: I'm only changing %axl - why would I need
> to introduce tests for anything else?
>
>> I am not sure if the whole thing is handled correctly.  If we want to change
>> them, we should make sure that they work correctly.
>
> "They" being exactly what (and again in the context of what this
> patch does)? I'm not overly happy to introduce new unrelated
> tests, but I may be looking into adding some if I clearly knew
> what you're after. But even then I would submit that as a
> separate change, so you'd have to make up your mind on the
> change here independent of those anyway.
>

There are fake registers:

axl, Reg8|Acc|Byte, RegRex64, 0, Dw2Inval, Dw2Inval
cxl, Reg8, RegRex64, 1, Dw2Inval, Dw2Inval
dxl, Reg8, RegRex64, 2, Dw2Inval, Dw2Inval
bxl, Reg8, RegRex64, 3, Dw2Inval, Dw2Inval
spl, Reg8, RegRex64, 4, Dw2Inval, Dw2Inval
bpl, Reg8, RegRex64, 5, Dw2Inval, Dw2Inval
sil, Reg8, RegRex64, 6, Dw2Inval, Dw2Inval
dil, Reg8, RegRex64, 7, Dw2Inval, Dw2Inval

There should be at least one testcase to show they work
correctly.


-- 
H.J.