Re: [Xen-devel] [PATCH v3] SVM: use generic instruction decoding

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 09/30/2016 10:56 AM, Jan Beulich wrote:
>>>> On 30.09.16 at 16:54, <boris.ostrovsky@xxxxxxxxxx> wrote:
>> On 09/30/2016 10:44 AM, Jan Beulich wrote:
>>>>> +int
>>>>> +x86_insn_modrm(const struct x86_emulate_state *state,
>>>>> +               unsigned int *rm, unsigned int *reg)
>>>>> +{
>>>>> +    check_state(state);
>>>>> +
>>>>> +    if ( !(state->desc & ModRM) )
>>>>> +        return -EINVAL;
>>>>> +
>>>>> +    if ( rm )
>>>>> +        *rm = state->modrm_rm;
>>>>> +    if ( reg )
>>>>> +        *reg = state->modrm_reg;
>>>>> +
>>>>> +    return state->modrm_mod;
>>>>> +}
>>>> Can this return struct modrm (which would then become visible outside of
>>>> svm.c)? And then x86_emulate_state can include the same struct instead
>>>> of the three separate fields.
>>> I'd prefer not to, to leave it to callers which parts they actually care
>>> about. No need for them to put the whole structure on stack when
>>> all they want is e.g. mod.
>> But isn't the whole struct one byte long so you'd not be increasing
>> amount of data on stack? This will also make comparison at least in
>> __get_instruction_length_from_list() (and possibly other places) simpler.
> See the other reply (as well as Andrew's): We'd be making available
> incomplete information if we did it that way.


Yes, I saw them after I sent my reply.

Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>

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