Re: [Qemu-devel] [PATCH 09/13] target-s390x: implement TRANSLATE EXTENDED instruction

[Richard Henderson <rth@twiddle.net>]

On 06/02/2015 12:05 PM, Aurelien Jarno wrote:
>> But why don't we just pass and return (most) of the data to the helper?  Like
>>
>>   C(0xb2a5, TRE,     RRE,   Z,   0, r2, r1_P, 0, tre, 0)
>>
>>   potential_page_fault(s);
>>   gen_helper_tre(o->out, cpu_env, o->out, o->out2, o->in2);
>>   return_low128(o->out2);
>>   set_cc_static(s);
> 
> My point was that we need to pass 4 values (reg0, r1, r1+1 and r2) and
> return 3 values (r1, r1+1 and cc), so it's probably better to pass all
> of them the same way. It's the strategy chosen for other similar
> instructions (e.g mvcl), except for cc.
> 
> I'll change that in the next version.

The reg0 and cc data is at a fixed location, and are
therefore more amenable to passing implicitly.

It's r1, r1+1, and r2 that are in varying locations,
and therefore you either have to pass their register
number or their contents.

For mvcl, there are 5 return values, so we're pretty
much stuck passing register numbers.


r~