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

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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@xxxxxxxxxxxxx>
---
  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@xxxxxxxxxx>
   */
  #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




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