Re: [kvm-unit-tests PATCH v3 1/2] s390x: Add specification exception test

[Claudio Imbrenda <imbrenda@linux.ibm.com>]

On Tue, 26 Oct 2021 14:00:31 +0200
Janis Schoetterl-Glausch <scgl@linux.vnet.ibm.com> wrote:

[...]

> I don't think that would work, the compiler might inline the function,
> duplicating the label.

__attribute__((noinline))

:)

> I suppose I could replace the stg with an assignment in C, not sure if that's nicer.
> 
> >> +	fixup_psw.mask = extract_psw_mask();  
> > 
> > then you could add this here:
> > 	fixup_psw.addr = after_lpswe;
> >   
> >> +	asm volatile (
> >> +		"	larl	%[scratch],nop%=\n"
> >> +		"	stg	%[scratch],%[addr]\n"  
> > 	^ those two lines are no longer needed ^  
> >> +		"	lpswe	%[psw]\n"
> >> +		"nop%=:	nop\n"  
> > 	".global after_lpswe \n"
> > 	"after_lpswe:	nop"  
> >> +		: [scratch] "=&r"(scratch),
> >> +		  [addr] "=&T"(fixup_psw.addr)
> >> +		: [psw] "Q"(psw)
> >> +		: "cc", "memory"
> >> +	);
> >> +}

[...]
 
> That's nicer indeed.
> >   
> >> +	asm volatile ("lpq %0,%2"
> >> +		      : "=r"(r1), "=r"(r2)  
> > 
> > since you're ignoring the return value, can't you hardcode r6, and mark
> > it (and r7) as clobbered? like:
> > 		"lpq 6, %[bad]"
> > 		: : [bad] "T"(words[1])
> > 		: "%r6", "%r7" 
> >   
> Ok, btw. is there a reason bare register numbers seem to be more common
> compared to %%rN ?

I don't know, I guess laziness?

> 
> >> +		      : "T"(*bad_aligned)
> >> +	);
> >> +}
> >> +
> >> +static void not_even(void)
> >> +{
> >> +	uint64_t quad[2];
> >> +
> >> +	register uint64_t r1 asm("7");
> >> +	register uint64_t r2 asm("8");
> >> +	asm volatile (".insn	rxy,0xe3000000008f,%0,%2" //lpq
> >> %0,%2  
> > 
> > this is even uglier. I guess you had already tried this?
> >   
> Yes, the assembler won't let you do that.

yeah I thought so

> 
> > 		"lpq 7, %[good]"
> > 			: : [good] "T"(quad)
> > 			: "%r7", "%r8"
> > 
> > if that doesn't work, then the same but with .insn

I guess you can still try this ^ ?

> >   
> >> +		      : "=r"(r1), "=r"(r2)
> >> +		      : "T"(quad)
> >> +	);
> >> +}
> >> +
> >> +struct spec_ex_trigger {
> >> +	const char *name;
> >> +	void (*func)(void);
> >> +	void (*fixup)(void);
> >> +};
> >> +
> >> +static const struct spec_ex_trigger spec_ex_triggers[] = {
> >> +	{ "psw_bit_12_is_1", &psw_bit_12_is_1, &fixup_invalid_psw},
> >> +	{ "bad_alignment", &bad_alignment, NULL},
> >> +	{ "not_even", &not_even, NULL},
> >> +	{ NULL, NULL, NULL},
> >> +};
> >> +  
> > 
> > this is a lot of infrastructure for 3 tests... (or even for 5 tests,
> > since you will add the transactions in the next patch)  
> 
> Is it? I think we'd want a test for a "normal" specification exception,
> and one for an invalid PSW at least. Even for just those two, I don't
> think it would be nice to duplicate the test_spec_ex harness.

usually we do duplicate code for simple tests, so that reviewers have
an easier time understanding what's going on, on the other hand..

> > 
> > are you planning to significantly extend this test in the future?  
> 
> Not really, but I thought having it be easily extensible might be nice.

..fair enough

this way it will be easier to extend this in the future, even though we
don't have any immediate plans to do so

maybe add some words in the patch description, and some comments, to
explain what's going on, to make it easier for others to understand
this code

> >   
> >> +struct args {
> >> +	uint64_t iterations;
> >> +};
> >> +
> >> +static void test_spec_ex(struct args *args,
> >> +			 const struct spec_ex_trigger *trigger)
> >> +{
> >> +	uint16_t expected_pgm = PGM_INT_CODE_SPECIFICATION;
> >> +	uint16_t pgm;
> >> +	unsigned int i;
> >> +
> >> +	for (i = 0; i < args->iterations; i++) {
> >> +		expect_pgm_int();
> >> +		register_pgm_cleanup_func(trigger->fixup);
> >> +		trigger->func();
> >> +		register_pgm_cleanup_func(NULL);
> >> +		pgm = clear_pgm_int();
> >> +		if (pgm != expected_pgm) {
> >> +			report_fail("Program interrupt: expected(%d)
> >> == received(%d)",
> >> +				    expected_pgm,
> >> +				    pgm);
> >> +			return;
> >> +		}
> >> +	}
> >> +	report_pass("Program interrupt: always expected(%d) ==
> >> received(%d)",
> >> +		    expected_pgm,
> >> +		    expected_pgm);
> >> +}
> >> +
> >> +static struct args parse_args(int argc, char **argv)  
> > 
> > do we _really_ need commandline arguments?
> >   
> No, but they can be useful.
> The iterations argument can be used to check if interpretation happens.
> The transaction arguments can be useful while developing a test case.
> 
> > is it really so important to be able to control these parameters?
> > 
> > can you find some values for the parameters so that the test works (as
> > in, it actually tests what it's supposed to) and also so that the whole
> > unit test ends in less than 30 seconds?  
> 
> I think the defaults are fine for that, no?

ok so they are only for convenience in case things go wrong?

> >   
> >> +{
> >> +	struct args args = {
> >> +		.iterations = 1,
> >> +	};
> >> +	unsigned int i;
> >> +	long arg;
> >> +	bool no_arg;
> >> +	char *end;
> >> +
> >> +	for (i = 1; i < argc; i++) {
> >> +		no_arg = true;
> >> +		if (i < argc - 1) {
> >> +			no_arg = *argv[i + 1] == '\0';
> >> +			arg = strtol(argv[i + 1], &end, 10);
> >> +			no_arg |= *end != '\0';
> >> +			no_arg |= arg < 0;
> >> +		}
> >> +
> >> +		if (!strcmp("--iterations", argv[i])) {
> >> +			if (no_arg)
> >> +				report_abort("--iterations needs a
> >> positive parameter");
> >> +			args.iterations = arg;
> >> +			++i;
> >> +		} else {
> >> +			report_abort("Unsupported parameter '%s'",
> >> +				     argv[i]);
> >> +		}
> >> +	}

I wonder if we can factor out the parameter parsing

> >> +	return args;
> >> +}
> >> +
> >> +int main(int argc, char **argv)
> >> +{
> >> +	unsigned int i;
> >> +
> >> +	struct args args = parse_args(argc, argv);
> >> +
> >> +	report_prefix_push("specification exception");
> >> +	for (i = 0; spec_ex_triggers[i].name; i++) {
> >> +		report_prefix_push(spec_ex_triggers[i].name);
> >> +		test_spec_ex(&args, &spec_ex_triggers[i]);
> >> +		report_prefix_pop();
> >> +	}
> >> +	report_prefix_pop();
> >> +
> >> +	return report_summary();
> >> +}
> >> diff --git a/s390x/unittests.cfg b/s390x/unittests.cfg
> >> index 9e1802f..5f43d52 100644
> >> --- a/s390x/unittests.cfg
> >> +++ b/s390x/unittests.cfg
> >> @@ -109,3 +109,6 @@ file = edat.elf
> >>  
> >>  [mvpg-sie]
> >>  file = mvpg-sie.elf
> >> +
> >> +[spec_ex]
> >> +file = spec_ex.elf  
> >   
>