[Qemu-arm] [PATCH 5/7] target/arm/translate-a64: Don't underdecode add/sub extended register

[Peter Maydell]

In the "add/subtract (extended register)" encoding group, the "opt"
field in bits [23:22] must be zero. Correctly UNDEF the unallocated
encodings where this field is not zero.

Reported-by: Laurent Desnogues <address@hidden>
Signed-off-by: Peter Maydell <address@hidden>
---
 target/arm/translate-a64.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/target/arm/translate-a64.c b/target/arm/translate-a64.c
index 2cade64ed25..efd2f6490b5 100644
--- a/target/arm/translate-a64.c
+++ b/target/arm/translate-a64.c
@@ -4204,12 +4204,13 @@ static void disas_add_sub_ext_reg(DisasContext *s, 
uint32_t insn)
     bool setflags = extract32(insn, 29, 1);
     bool sub_op = extract32(insn, 30, 1);
     bool sf = extract32(insn, 31, 1);
+    bool opt = extract32(insn, 22, 2);
 
     TCGv_i64 tcg_rm, tcg_rn; /* temps */
     TCGv_i64 tcg_rd;
     TCGv_i64 tcg_result;
 
-    if (imm3 > 4) {
+    if (imm3 > 4 || opt != 0) {
         unallocated_encoding(s);
         return;
     }
-- 
2.20.1