Re: [kvm-unit-tests PATCH 4/8] lib: s390x: Start using bitops instead of magic constants

[Thomas Huth <thuth@redhat.com>]

On 13/08/2021 09.36, Janosch Frank wrote:
> TEID data is specified in the Principles of Operation as bits so it
> makes more sens to test the bits instead of anding the mask.
> 
> We need to set -Wno-address-of-packed-member since for test bit we
> take an address of a struct lowcore member.
> 
> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
> ---
>   lib/s390x/interrupt.c | 5 +++--
>   s390x/Makefile        | 1 +
>   2 files changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/lib/s390x/interrupt.c b/lib/s390x/interrupt.c
> index 1248bceb..e05c212e 100644
> --- a/lib/s390x/interrupt.c
> +++ b/lib/s390x/interrupt.c
> @@ -8,6 +8,7 @@
>    *  David Hildenbrand <david@redhat.com>
>    */
>   #include <libcflat.h>
> +#include <bitops.h>
>   #include <asm/barrier.h>
>   #include <sclp.h>
>   #include <interrupt.h>
> @@ -77,8 +78,8 @@ static void fixup_pgm_int(struct stack_frame_int *stack)
>   		break;
>   	case PGM_INT_CODE_PROTECTION:
>   		/* Handling for iep.c test case. */
> -		if (lc->trans_exc_id & 0x80UL && lc->trans_exc_id & 0x04UL &&
> -		    !(lc->trans_exc_id & 0x08UL))
> +		if (test_bit_inv(56, &lc->trans_exc_id) && test_bit_inv(61, &lc->trans_exc_id) &&
> +		    !test_bit_inv(60, &lc->trans_exc_id))

I'd rather prefer:

	if ((lc->trans_exc_id & 0x8c) == 0x84)

... or maybe you could add a helper function for these checks a la:

bool check_teid_prot_cause(uint64_t teid, bool bit56, bool bit60,
                            bool bit61)

then you could replace the if statement with:

	if (check_teid_prot_cause(lc->trans_exc_id, 1, 0, 1))

which would be way more readable, IMHO.

>   			/*
>   			 * We branched to the instruction that caused
>   			 * the exception so we can use the return
> diff --git a/s390x/Makefile b/s390x/Makefile
> index ef8041a6..d260b336 100644
> --- a/s390x/Makefile
> +++ b/s390x/Makefile
> @@ -45,6 +45,7 @@ CFLAGS += -O2
>   CFLAGS += -march=zEC12
>   CFLAGS += -mbackchain
>   CFLAGS += -fno-delete-null-pointer-checks
> +CFLAGS += -Wno-address-of-packed-member

I think we should avoid this since this also affects the common code, 
doesn't it? And in common code, we might need to deal with this.

  Thomas