target-arm: A64: add support for BR, BLR and RET insns

Implement BR, BLR and RET. This is all of the 'unconditional
branch (register)' instruction category except for ERET
and DPRS (which are system mode only).
Signed-off-by: NAlexander Graf <agraf@suse.de>
[claudio: reimplemented on top of new decoder structure]
Signed-off-by: NClaudio Fontana <claudio.fontana@linaro.org>
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Reviewed-by: NRichard Henderson <rth@twiddle.net>

target-arm/translate-a64.c

@@ -384,10 +384,49 @@ static void disas_exc(DisasContext *s, uint32_t insn)
     unsupported_encoding(s, insn);
 }
 
-/* Unconditional branch (register) */
+/* C3.2.7 Unconditional branch (register)
+ *  31           25 24   21 20   16 15   10 9    5 4     0
+ * +---------------+-------+-------+-------+------+-------+
+ * | 1 1 0 1 0 1 1 |  opc  |  op2  |  op3  |  Rn  |  op4  |
+ * +---------------+-------+-------+-------+------+-------+
+ */
 static void disas_uncond_b_reg(DisasContext *s, uint32_t insn)
 {
-    unsupported_encoding(s, insn);
+    unsigned int opc, op2, op3, rn, op4;
+
+    opc = extract32(insn, 21, 4);
+    op2 = extract32(insn, 16, 5);
+    op3 = extract32(insn, 10, 6);
+    rn = extract32(insn, 5, 5);
+    op4 = extract32(insn, 0, 5);
+
+    if (op4 != 0x0 || op3 != 0x0 || op2 != 0x1f) {
+        unallocated_encoding(s);
+        return;
+    }
+
+    switch (opc) {
+    case 0: /* BR */
+    case 2: /* RET */
+        break;
+    case 1: /* BLR */
+        tcg_gen_movi_i64(cpu_reg(s, 30), s->pc);
+        break;
+    case 4: /* ERET */
+    case 5: /* DRPS */
+        if (rn != 0x1f) {
+            unallocated_encoding(s);
+        } else {
+            unsupported_encoding(s, insn);
+        }
+        return;
+    default:
+        unallocated_encoding(s);
+        return;
+    }
+
+    tcg_gen_mov_i64(cpu_pc, cpu_reg(s, rn));
+    s->is_jmp = DISAS_JUMP;
 }
 
 /* C3.2 Branches, exception generating and system instructions */