[PATCH v2] X86: disambiguate unqualified btr, bts

[Jim Grosbach]

On Jul 17, 2013, at 9:13 AM, Tim Northover <t.p.northover at gmail.com> wrote:

> On Wed, Jul 17, 2013 at 4:54 PM, James Molloy <james at jamesmolloy.co.uk> wrote:
>> Wouldn't this be a viable use of the third disassembler return value
>> "SoftFail"? The only difference between its use here and how it is used in
>> the ARM backend is that the Intel manuals explicitly define the behaviour in
>> the out of range case, but you could easily reappropriate SoftFail for the
>> x86 architecture to mean "It's defined, but I'm going to warn about it".
> 
> I think that's going too far; these instructions appear to be
> sanctioned in the manual unlike the ARM ones. But there's a
> CommentStream available during disassembly. They could probably be
> annotated as "non-standard encoding ..." or something more pithy if we
> decide to go down that route.
> 
> I think this is the approach armasm takes to at least some of the
> similar ARM issues.
> 

A fair point. Also note that issuing a diagnostic doesn’t mean we have to reject the instruction. We could use a warning rather than a hard error.

-Jim
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