Re: [Qemu-arm] [Qemu-devel] [PATCH] decodetree: Propagate return value from translate subroutines

[Richard Henderson]

On 03/01/2018 03:59 AM, Peter Maydell wrote:
> On 28 February 2018 at 16:48, Richard Henderson
> <address@hidden> wrote:
>> Allow the translate subroutines to return false for invalid insns.
>>
>> At present we can of course invoke an invalid insn exception from within
>> the translate subroutine, but in the short term this consolidates code.
>> In the long term it would allow the decodetree language to support
>> overlapping patterns for ISA extensions.
>>
>> Signed-off-by: Richard Henderson <address@hidden>
>> ---
>>
>> Since this makes an ABI change to the translate functions called by the
>> decode function, let's make it now before there are any in-tree users.
>>
>> My SVE branch over-decodes in quite a lot of cases -- e.g. things like
>> the 2-bit size field must be 1-3 for fp operands, and so size==0 is
>> unallocated.  Returning false for these cases allows the actual call
>> to unallocated_encoding to be done in one place instead of hundreds.
>>
>> Longer term, I'm thinking of how to handle decode of overlapping ISA
>> extensions.  One could allow (specific) overlapping patterns and
>> prioritize them in some way (e.g. first in file is first matched).
>> My thought is that trans_insn_a would check a cpu feature bit and
>> return false if not enabled.  Then trans_insn_b would be given its
>> chance to handle the insn.
> 
> Reviewed-by: Peter Maydell <address@hidden>
> 
> I'll put this into target-arm.next, unless you'd prefer it to go
> in via some other route.

That's fine.  Thanks!


r~