[Qemu-devel] [PATCH 09/10] target/arm: Get IL bit correct for v7 syndrome values

[Peter Maydell <peter.maydell@linaro.org>]

For the v7 version of the Arm architecture, the IL bit in
syndrome register values where the field is not valid was
defined to be UNK/SBZP. In v8 this is RES1, which is what
QEMU currently implements. Handle the desired v7 behaviour
by squashing the IL bit for the affected cases:
 * EC == EC_UNCATEGORIZED
 * prefetch aborts
 * data aborts where ISV is 0

(The fourth case listed in the v8 Arm ARM DDI 0487C.a in
section G7.2.70, "illegal state exception", can't happen
on a v7 CPU.)

This deals with a corner case noted in a comment.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
 target/arm/internals.h |  7 ++-----
 target/arm/helper.c    | 14 ++++++++++++++
 2 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/target/arm/internals.h b/target/arm/internals.h
index 516f9454e9b..cd8bc1ec3d4 100644
--- a/target/arm/internals.h
+++ b/target/arm/internals.h
@@ -286,11 +286,8 @@ static inline uint32_t syn_get_ec(uint32_t syn)
 /* Utility functions for constructing various kinds of syndrome value.
  * Note that in general we follow the AArch64 syndrome values; in a
  * few cases the value in HSR for exceptions taken to AArch32 Hyp
- * mode differs slightly, so if we ever implemented Hyp mode then the
- * syndrome value would need some massaging on exception entry.
- * (One example of this is that AArch64 defaults to IL bit set for
- * exceptions which don't specifically indicate information about the
- * trapping instruction, whereas AArch32 defaults to IL bit clear.)
+ * mode differs slightly, and we fix this up when populating HSR in
+ * arm_cpu_do_interrupt_aarch32_hyp().
  */
 static inline uint32_t syn_uncategorized(void)
 {
diff --git a/target/arm/helper.c b/target/arm/helper.c
index 0b89804961b..0b659171b07 100644
--- a/target/arm/helper.c
+++ b/target/arm/helper.c
@@ -8299,6 +8299,20 @@ static void arm_cpu_do_interrupt_aarch32_hyp(CPUState *cs)
     }
 
     if (cs->exception_index != EXCP_IRQ && cs->exception_index != EXCP_FIQ) {
+
+        if (!arm_feature(env, ARM_FEATURE_V8)) {
+            /*
+             * QEMU syndrome values are v8-style. v7 has the IL bit
+             * UNK/SBZP for "field not valid" cases, where v8 uses RES1.
+             * If this is a v7 CPU, squash the IL bit in those cases.
+             */
+            if (cs->exception_index == EXCP_PREFETCH_ABORT ||
+                (cs->exception_index == EXCP_DATA_ABORT &&
+                 !(env->exception.syndrome & ARM_EL_ISV)) ||
+                syn_get_ec(env->exception.syndrome) == EC_UNCATEGORIZED) {
+                env->exception.syndrome &= ~ARM_EL_IL;
+            }
+        }
         env->cp15.esr_el[2] = env->exception.syndrome;
     }
 
-- 
2.19.0