Re: [kvm-unit-tests PATCH v6 3/4] s390x: lib: add SPX and STPX instruction wrapper

[Thomas Huth <thuth@redhat.com>]

On 09/01/2020 17.50, Claudio Imbrenda wrote:
> On Thu, 9 Jan 2020 17:43:55 +0100
> Thomas Huth <thuth@redhat.com> wrote:
> 
>> On 09/01/2020 17.16, Claudio Imbrenda wrote:
>>> Add a wrapper for the SET PREFIX and STORE PREFIX instructions, and
>>> use it instead of using inline assembly everywhere.
>>>
>>> Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
>>> ---
>>>  lib/s390x/asm/arch_def.h | 10 ++++++++++
>>>  s390x/intercept.c        | 33 +++++++++++++--------------------
>>>  2 files changed, 23 insertions(+), 20 deletions(-)
>>>
>>> diff --git a/lib/s390x/asm/arch_def.h b/lib/s390x/asm/arch_def.h
>>> index 1a5e3c6..465fe0f 100644
>>> --- a/lib/s390x/asm/arch_def.h
>>> +++ b/lib/s390x/asm/arch_def.h
>>> @@ -284,4 +284,14 @@ static inline int servc(uint32_t command,
>>> unsigned long sccb) return cc;
>>>  }
>>>  
>>> +static inline void spx(uint32_t *new_prefix)  
>>
>> Looking at this a second time ... why is new_prefix a pointer? A
>> normal value should be sufficient here, shouldn't it?
> 
> no. if you look at the code in the same patch, intercept.c at some
> points needs to pass "wrong" pointers to spx and stpx in order to test
> them, so this needs to be a pointer
> 
> the instructions themselves expect pointers (base register + offset)

Ah, you're right, that "Q" constraint always confuses me... I guess you
could do it without pointers when using the "r" constraint, but it's
likely better to do it the same way as stpx, so your patch should be fine.

>>> +{
>>> +	asm volatile("spx %0" : : "Q" (*new_prefix) : "memory");
>>> +}
>>> +
>>> +static inline void stpx(uint32_t *current_prefix)
>>> +{
>>> +	asm volatile("stpx %0" : "=Q" (*current_prefix));
>>> +}
>>> +  

Reviewed-by: Thomas Huth <thuth@redhat.com>