Re: [kvm-unit-tests PATCH v2 2/3] s390x/spec_ex: Add test introducing odd address into PSW

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

On Tue, 21 Feb 2023 18:48:21 +0100
Nina Schoetterl-Glausch <nsg@linux.ibm.com> wrote:

> Instructions on s390 must be halfword aligned.
> Introducing an odd instruction address into the PSW leads to a
> specification exception when attempting to execute the instruction at
> the odd address.
> Add a test for this.
> 
> Signed-off-by: Nina Schoetterl-Glausch <nsg@linux.ibm.com>
> ---
>  s390x/spec_ex.c | 50 ++++++++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 49 insertions(+), 1 deletion(-)
> 
> diff --git a/s390x/spec_ex.c b/s390x/spec_ex.c
> index 2adc5996..a26c56aa 100644
> --- a/s390x/spec_ex.c
> +++ b/s390x/spec_ex.c
> @@ -88,12 +88,23 @@ static void expect_invalid_psw(struct psw psw)
>  	invalid_psw_expected = true;
>  }
>  
> +static void clear_invalid_psw(void)
> +{
> +	expected_psw = PSW(0, 0);
> +	invalid_psw_expected = false;
> +}
> +
>  static int check_invalid_psw(void)
>  {
>  	/* Since the fixup sets this to false we check for false here. */
>  	if (!invalid_psw_expected) {
> +		/*
> +		 * Early exception recognition: pgm_int_id == 0.
> +		 * Late exception recognition: psw address has been
> +		 *	incremented by pgm_int_id (unpredictable value)
> +		 */
>  		if (expected_psw.mask == invalid_psw.mask &&
> -		    expected_psw.addr == invalid_psw.addr)
> +		    expected_psw.addr == invalid_psw.addr - lowcore.pgm_int_id)
>  			return 0;
>  		report_fail("Wrong invalid PSW");
>  	} else {
> @@ -112,6 +123,42 @@ static int psw_bit_12_is_1(void)
>  	return check_invalid_psw();
>  }
>  
> +extern char misaligned_code[];
> +asm (  ".balign	2\n"

which section will this end up in?

> +"	. = . + 1\n"
> +"misaligned_code:\n"
> +"	larl	%r0,0\n"
> +"	bcr	0xf,%r1\n"

you should just use
        br %r1
it's shorter and easier to understand

> +);
> +
> +static int psw_odd_address(void)
> +{
> +	struct psw odd = PSW_WITH_CUR_MASK((uint64_t)&misaligned_code);
> +	uint64_t executed_addr;
> +
> +	expect_invalid_psw(odd);
> +	fixup_psw.mask = extract_psw_mask();
> +	asm volatile ( "xr	%%r0,%%r0\n"
> +		"	larl	%%r1,0f\n"
> +		"	stg	%%r1,%[fixup_addr]\n"
> +		"	lpswe	%[odd_psw]\n"
> +		"0:	lr	%[executed_addr],%%r0\n"
> +	: [fixup_addr] "=&T" (fixup_psw.addr),
> +	  [executed_addr] "=d" (executed_addr)
> +	: [odd_psw] "Q" (odd)
> +	: "cc", "%r0", "%r1"
> +	);
> +
> +	if (!executed_addr) {
> +		return check_invalid_psw();
> +	} else {
> +		assert(executed_addr == odd.addr);
> +		clear_invalid_psw();
> +		report_fail("did not execute unaligned instructions");
> +		return 1;
> +	}
> +}
> +
>  /* A short PSW needs to have bit 12 set to be valid. */
>  static int short_psw_bit_12_is_0(void)
>  {
> @@ -170,6 +217,7 @@ struct spec_ex_trigger {
>  static const struct spec_ex_trigger spec_ex_triggers[] = {
>  	{ "psw_bit_12_is_1", &psw_bit_12_is_1, false, &fixup_invalid_psw },
>  	{ "short_psw_bit_12_is_0", &short_psw_bit_12_is_0, false, &fixup_invalid_psw },
> +	{ "psw_odd_address", &psw_odd_address, false, &fixup_invalid_psw },
>  	{ "bad_alignment", &bad_alignment, true, NULL },
>  	{ "not_even", &not_even, true, NULL },
>  	{ NULL, NULL, false, NULL },