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

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

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.

-boris


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