target/arm: Assert thumb pc is aligned

Misaligned thumb PC is architecturally impossible.
Assert is better than proceeding, in case we've missed
something somewhere.

Expand a comment about aligning the pc in gdbstub.
Fail an incoming migrate if a thumb pc is misaligned.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

1 files changed, 10 insertions, 0 deletions

diff --git a/target/arm/machine.c b/target/arm/machine.c
index c74d8c3f4b..135d2420b5 100644
--- a/target/arm/machine.c
+++ b/target/arm/machine.c
@@ -794,6 +794,16 @@ static int cpu_post_load(void *opaque, int version_id)
             return -1;
         }
     }
+
+    /*
+     * Misaligned thumb pc is architecturally impossible.
+     * We have an assert in thumb_tr_translate_insn to verify this.
+     * Fail an incoming migrate to avoid this assert.
+     */
+    if (!is_a64(env) && env->thumb && (env->regs[15] & 1)) {
+        return -1;
+    }
+
     if (!kvm_enabled()) {
         pmu_op_finish(&cpu->env);
     }