Re: [Qemu-devel] [PATCH 01/10] target-s390: Move facilities bits to env

[Alexander Graf <agraf@suse.de>]

On 09/30/2013 09:15 PM, Richard Henderson wrote:
> On 09/30/2013 11:03 AM, Alexander Graf wrote:
>> On 09/23/2013 04:04 PM, Richard Henderson wrote:
>>> Rather than simply hard-coding them in STFL instruction.
>>>
>>> Signed-off-by: Richard Henderson<rth@twiddle.net>
>>> ---
>>>    target-s390x/cpu.c       |  3 +++
>>>    target-s390x/cpu.h       |  1 +
>>>    target-s390x/translate.c | 10 +++++-----
>>>    3 files changed, 9 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/target-s390x/cpu.c b/target-s390x/cpu.c
>>> index 3c89f8a..ff691df 100644
>>> --- a/target-s390x/cpu.c
>>> +++ b/target-s390x/cpu.c
>>> @@ -181,6 +181,9 @@ static void s390_cpu_initfn(Object *obj)
>>>        env->cpu_num = cpu_num++;
>>>        env->ext_index = -1;
>>>
>>> +    env->facilities[0] = 0xc000000000000000ull;
>>> +    env->facilities[1] = 0;
>> Could we add CPU definitions along the way here? I'm fine with making z9 the
>> default CPU type, but we should make this explicit :).
> Certainly that's what we should do.  I just hadn't yet researched the
> currently correct way to do that.  I know there's some amount of out-of-date
> examples in the current source base.

I'll leave the answer to that to Andreas :).

>
> Pointers?
>
>>>    static ExitStatus op_stfl(DisasContext *s, DisasOps *o)
>>>    {
>>> -    TCGv_i64 f, a;
>>> -    /* We really ought to have more complete indication of facilities
>>> -       that we implement.  Address this when STFLE is implemented.  */
>>> +    TCGv_i64 f = tcg_temp_new_i64();
>>> +    TCGv_i64 a = tcg_const_i64(200);
>>> +
>>>        check_privileged(s);
>>> -    f = tcg_const_i64(0xc0000000);
>>> -    a = tcg_const_i64(200);
>>> +    tcg_gen_ld_i64(f, cpu_env, offsetof(CPUS390XState, facilities[0]));
>>> +    tcg_gen_shri_i64(f, f, 32);
>> IMHO the facility list should be stored in DisasContext. That way we can check
>> whether we're generating code against the correct target.
> See patch 4.
>
> As for the code we generate here, does it really matter if we load the value
> from env, or have it encoded as a constant?  It still has to get stored to
> memory, so it's not like the TCG optimizer is going to do anything with the
> constant.

No, it only seemed more straight forward to me from a "single source of 
information" point of view. But it really doesn't matter. Shifting in C 
seems to be easier to read :).


Alex