target/arm: Define new TBFLAG for v8M stack checking

The Arm v8M architecture includes hardware stack limit checking.
When certain instructions update the stack pointer, if the new
value of SP is below the limit set in the associated limit register
then an exception is taken. Add a TB flag that tracks whether
the limit-checking code needs to be emitted.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-id: 20181002163556.10279-2-peter.maydell@linaro.org

1 files changed, 10 insertions, 0 deletions

diff --git a/target/arm/helper.c b/target/arm/helper.c
index efe42f9e07..0807173eac 100644
--- a/target/arm/helper.c
+++ b/target/arm/helper.c
@@ -12686,6 +12686,16 @@ void cpu_get_tb_cpu_state(CPUARMState *env, target_ulong *pc,
         flags |= ARM_TBFLAG_HANDLER_MASK;
     }
 
+    /* v8M always applies stack limit checks unless CCR.STKOFHFNMIGN is
+     * suppressing them because the requested execution priority is less than 0.
+     */
+    if (arm_feature(env, ARM_FEATURE_V8) &&
+        arm_feature(env, ARM_FEATURE_M) &&
+        !((mmu_idx  & ARM_MMU_IDX_M_NEGPRI) &&
+          (env->v7m.ccr[env->v7m.secure] & R_V7M_CCR_STKOFHFNMIGN_MASK))) {
+        flags |= ARM_TBFLAG_STACKCHECK_MASK;
+    }
+
     *pflags = flags;
     *cs_base = 0;
 }