Re: [kvm-unit-tests PATCH v5 1/2] s390x: Add specification exception test

[Janosch Frank <frankja@linux.ibm.com>]

On 8/26/22 13:23, Janis Schoetterl-Glausch wrote:
> On Wed, 2022-08-24 at 11:35 +0200, Janosch Frank wrote:
>> On 7/20/22 16:25, Janis Schoetterl-Glausch wrote:
>>> Generate specification exceptions and check that they occur.
>>>
>>> Signed-off-by: Janis Schoetterl-Glausch <scgl@linux.ibm.com>
>>> ---
>>>    s390x/Makefile           |   1 +
>>>    lib/s390x/asm/arch_def.h |   5 ++
>>>    s390x/spec_ex.c          | 180 +++++++++++++++++++++++++++++++++++++++
>>>    s390x/unittests.cfg      |   3 +
>>>    4 files changed, 189 insertions(+)
>>>    create mode 100644 s390x/spec_ex.c
>>>
>>>
>>> +
>>> +/*
>>> + * Load possibly invalid psw, but setup fixup_psw before,
>>> + * so that fixup_invalid_psw() can bring us back onto the right track.

Not sure if the second line is needed as fixup_psw is a descriptive name 
already.

>>> + * Also acts as compiler barrier, -> none required in expect/check_invalid_psw
>>> + */
>>> +static void load_psw(struct psw psw)
>>> +{
>>> +	uint64_t scratch;
>>> +
> 
> [...]
> 
>> /*
>> Store a valid mask and the address of the nop into the fixup PSW.
>> Then load the possibly invalid PSW.
>> */
> 
> This seems a bit redundant given the function comment, but I can
> drop a comment in here describing how the fixup psw is computed.

Well, I skipped the function comment, got confused by the addr asm 
variable and then decided to propose the comment.

It's a bit confusing since you have the invalid PSW and the global fixup 
PSW in one function.

Maybe something like:
/* From here to the lpswe we're computing and setting the fixup PSW */

> 
>>
>>> +	fixup_psw.mask = extract_psw_mask();
>>> +	asm volatile ( "larl	%[scratch],0f\n"
>>> +		"	stg	%[scratch],%[addr]\n"
>>> +		"	lpswe	%[psw]\n"
>>> +		"0:	nop\n"
>>> +		: [scratch] "=&d"(scratch),
>>> +		  [addr] "=&T"(fixup_psw.addr)
>>
>> s/addr/psw_addr/ ?
>>
>>> +		: [psw] "Q"(psw)
>>> +		: "cc", "memory"
>>> +	);
>>> +}
>>> +
>>> +static void load_short_psw(struct short_psw psw)
>>> +{
>>> +	uint64_t scratch;
>>> +
>>> +	fixup_psw.mask = extract_psw_mask();
>>> +	asm volatile ( "larl	%[scratch],0f\n"
>>> +		"	stg	%[scratch],%[addr]\n"
>>> +		"	lpsw	%[psw]\n"
>>> +		"0:	nop\n"
>>> +		: [scratch] "=&d"(scratch),
>>> +		  [addr] "=&T"(fixup_psw.addr)
>>> +		: [psw] "Q"(psw)
>>> +		: "cc", "memory"
>>> +	);
>>
>> Same story.
> 
> Do you want me to repeat the comments here or just rename addr?

Just rename addr

> 
> [...]
> 
>>> +static int not_even(void)
>>> +{
>>> +	uint64_t quad[2] __attribute__((aligned(16))) = {0};
>>> +
>>> +	asm volatile (".insn	rxy,0xe3000000008f,%%r7,%[quad]" /* lpq %%r7,%[quad] */
>>> +		      : : [quad] "T"(quad)
>>
>> Is there a reason you never put a space after the constraint?
> 
> TBH I never noticed I'm unusual in that regard. I guess I tend to think
> of the operand and constraint as one entity.
> I'll add the spaces.
> 
>>
>>> +		      : "%r7", "%r8"
>>> +	);
>>> +	return 0;
>>> +}
>>> +
> 
> [...]