This optional behavior was removed from the ISA in v3.0, see
Summary of Changes preface:

  Data Storage Interrupt Status Register for Alignment Interrupt:
  Simplifies the Alignment interrupt by remov- ing the Data Storage
  Interrupt Status Register (DSISR) from the set of registers modified
  by the Alignment interrupt.

Reviewed-by: Fabiano Rosas <farosas@suse.de>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
Since v2: no change.

 target/ppc/excp_helper.c | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/target/ppc/excp_helper.c b/target/ppc/excp_helper.c
index bc2be4a726..453750a9d6 100644
--- a/target/ppc/excp_helper.c
+++ b/target/ppc/excp_helper.c
@@ -1449,13 +1449,16 @@ static void powerpc_excp_books(PowerPCCPU *cpu, int excp)
         break;
     }
     case POWERPC_EXCP_ALIGN:     /* Alignment exception                      */
-        /* Get rS/rD and rA from faulting opcode */
-        /*
-         * Note: the opcode fields will not be set properly for a
-         * direct store load/store, but nobody cares as nobody
-         * actually uses direct store segments.
-         */
-        env->spr[SPR_DSISR] |= (env->error_code & 0x03FF0000) >> 16;
+        /* Optional DSISR update was removed from ISA v3.0 */
+        if (!(env->insns_flags2 & PPC2_ISA300)) {
+            /* Get rS/rD and rA from faulting opcode */
+            /*
+             * Note: the opcode fields will not be set properly for a
+             * direct store load/store, but nobody cares as nobody
+             * actually uses direct store segments.
+             */
+            env->spr[SPR_DSISR] |= (env->error_code & 0x03FF0000) >> 16;
+        }
         break;
     case POWERPC_EXCP_PROGRAM:   /* Program exception                        */
         switch (env->error_code & ~0xF) {
-- 
2.40.1