armv7m: Raise correct kind of UsageFault for attempts to execute ARM code

M profile doesn't implement ARM, and the architecturally required
behaviour for attempts to execute with the Thumb bit clear is to
generate a UsageFault with the CFSR INVSTATE bit set.  We were
incorrectly implementing this as generating an UNDEFINSTR UsageFault;
fix this.
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Reviewed-by: NAlex Bennée <alex.bennee@linaro.org>

linux-user/main.c

@@ -574,6 +574,7 @@ void cpu_loop(CPUARMState *env)
         switch(trapnr) {
         case EXCP_UDEF:
         case EXCP_NOCP:
+        case EXCP_INVSTATE:
             {
                 TaskState *ts = cs->opaque;
                 uint32_t opcode;

target/arm/cpu.h

@@ -57,6 +57,7 @@
 #define EXCP_VFIQ           15
 #define EXCP_SEMIHOST       16   /* semihosting call */
 #define EXCP_NOCP           17   /* v7M NOCP UsageFault */
+#define EXCP_INVSTATE       18   /* v7M INVSTATE UsageFault */
 
 #define ARMV7M_EXCP_RESET   1
 #define ARMV7M_EXCP_NMI     2

target/arm/helper.c

@@ -6245,6 +6245,10 @@ void arm_v7m_cpu_do_interrupt(CPUState *cs)
         armv7m_nvic_set_pending(env->nvic, ARMV7M_EXCP_USAGE);
         env->v7m.cfsr |= R_V7M_CFSR_NOCP_MASK;
         break;
+    case EXCP_INVSTATE:
+        armv7m_nvic_set_pending(env->nvic, ARMV7M_EXCP_USAGE);
+        env->v7m.cfsr |= R_V7M_CFSR_INVSTATE_MASK;
+        break;
     case EXCP_SWI:
         /* The PC already points to the next instruction.  */
         armv7m_nvic_set_pending(env->nvic, ARMV7M_EXCP_SVC);

target/arm/translate.c

@@ -7990,9 +7990,13 @@ static void disas_arm_insn(DisasContext *s, unsigned int insn)
     TCGv_i32 addr;
     TCGv_i64 tmp64;
 
-    /* M variants do not implement ARM mode.  */
+    /* M variants do not implement ARM mode; this must raise the INVSTATE
+     * UsageFault exception.
+     */
     if (arm_dc_feature(s, ARM_FEATURE_M)) {
-        goto illegal_op;
+        gen_exception_insn(s, 4, EXCP_INVSTATE, syn_uncategorized(),
+                           default_exception_el(s));
+        return;
     }
     cond = insn >> 28;
     if (cond == 0xf){