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

[Alexander Graf <agraf@suse.de>]

On 10/01/2013 05:52 PM, Richard Henderson wrote:
> On 10/01/2013 08:48 AM, Alexander Graf wrote:
>> 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  I know there's some amount of out-of-date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 :).
> Can we leave that for a separate patch series then?

Just make sure you actually check for feature bits on every instruction 
(which I think you do, but the current code is way too magical to me to 
really understand it anymore) so that we can always implement a z900 cpu 
type later on.

>
>>>>> -    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 :).
> Fair enough.  I'll rearrange the order of the patches so that we can
> update STFL to use the DisasContext data.

Thanks :)


Alex