From 147269ed81d7d27cb1746cb62e8325066ff7a7cd Mon Sep 17 00:00:00 2001
From: Peter Maydell <peter.maydell@linaro.org>
Date: Sun, 3 Feb 2019 17:34:13 -0500
Subject: [PATCH] target/arm/translate-a64: Don't underdecode system
 instructions

The "system instructions" and "system register move" subcategories
of "branches, exception generating and system instructions" for A64
only apply if bits [23:22] are zero; other values are currently
unallocated. Correctly UNDEF these unallocated encodings.

Backports commit 08d5e3bde6b4ad32996bf69d93aa66ae43d3f3ff from qemu
---
 qemu/target/arm/translate-a64.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/qemu/target/arm/translate-a64.c b/qemu/target/arm/translate-a64.c
index 47ba5d49..52b35173 100644
--- a/qemu/target/arm/translate-a64.c
+++ b/qemu/target/arm/translate-a64.c
@@ -2221,7 +2221,11 @@ static void disas_b_exc_sys(DisasContext *s, uint32_t insn)
         break;
     case 0x6a: /* Exception generation / System */
         if (insn & (1 << 24)) {
-            disas_system(s, insn);
+            if (extract32(insn, 22, 2) == 0) {
+                disas_system(s, insn);
+            } else {
+                unallocated_encoding(s);
+            }
         } else {
             disas_exc(s, insn);
         }