arm: Don't decode MRS(banked) or MSR(banked) for M profile

M profile doesn't have the MSR(banked) and MRS(banked) instructions
and uses the encodings for different kinds of M-profile MRS/MSR.
Guard the relevant bits of the decode logic to make sure we don't
accidentally fall into them by accident on M-profile.

(The bit being checked for this (bit 5) is part of the SYSm field on
M-profile, but since no currently allocated system registers have
encodings with bit 5 of SYSm set, this hasn't been a problem in
practice.)

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Message-id: 1487616072-9226-3-git-send-email-peter.maydell@linaro.org

target/arm/translate.c

@@ -10500,7 +10500,8 @@ static int disas_thumb2_insn(CPUARMState *env, DisasContext *s, uint16_t insn_hw
                         gen_exception_return(s, tmp);
                         break;
                     case 6: /* MRS */
-                        if (extract32(insn, 5, 1)) {
+                        if (extract32(insn, 5, 1) &&
+                            !arm_dc_feature(s, ARM_FEATURE_M)) {
                             /* MRS (banked) */
                             int sysm = extract32(insn, 16, 4) |
                                 (extract32(insn, 4, 1) << 4);
@@ -10521,7 +10522,8 @@ static int disas_thumb2_insn(CPUARMState *env, DisasContext *s, uint16_t insn_hw
                         store_reg(s, rd, tmp);
                         break;
                     case 7: /* MRS */
-                        if (extract32(insn, 5, 1)) {
+                        if (extract32(insn, 5, 1) &&
+                            !arm_dc_feature(s, ARM_FEATURE_M)) {
                             /* MRS (banked) */
                             int sysm = extract32(insn, 16, 4) |
                                 (extract32(insn, 4, 1) << 4);