hw/intc/armv7m_nvic: Support v8.1M CCR.TRD bit

v8.1M introduces a new TRD flag in the CCR register, which enables
checking for stack frame integrity signatures on SG instructions.
This bit is not banked, and is always RAZ/WI to Non-secure code.
Adjust the code for handling CCR reads and writes to handle this.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20201119215617.29887-23-peter.maydell@linaro.org

hw/intc/armv7m_nvic.c

@@ -1095,8 +1095,9 @@ static uint32_t nvic_readl(NVICState *s, uint32_t offset, MemTxAttrs attrs)
         }
         return cpu->env.v7m.scr[attrs.secure];
     case 0xd14: /* Configuration Control.  */
-        /* The BFHFNMIGN bit is the only non-banked bit; we
-         * keep it in the non-secure copy of the register.
+        /*
+         * Non-banked bits: BFHFNMIGN (stored in the NS copy of the register)
+         * and TRD (stored in the S copy of the register)
          */
         val = cpu->env.v7m.ccr[attrs.secure];
         val |= cpu->env.v7m.ccr[M_REG_NS] & R_V7M_CCR_BFHFNMIGN_MASK;
@@ -1639,17 +1640,25 @@ static void nvic_writel(NVICState *s, uint32_t offset, uint32_t value,
         cpu->env.v7m.scr[attrs.secure] = value;
         break;
     case 0xd14: /* Configuration Control.  */
+    {
+        uint32_t mask;
+
         if (!arm_feature(&cpu->env, ARM_FEATURE_M_MAIN)) {
             goto bad_offset;
         }
 
         /* Enforce RAZ/WI on reserved and must-RAZ/WI bits */
-        value &= (R_V7M_CCR_STKALIGN_MASK |
-                  R_V7M_CCR_BFHFNMIGN_MASK |
-                  R_V7M_CCR_DIV_0_TRP_MASK |
-                  R_V7M_CCR_UNALIGN_TRP_MASK |
-                  R_V7M_CCR_USERSETMPEND_MASK |
-                  R_V7M_CCR_NONBASETHRDENA_MASK);
+        mask = R_V7M_CCR_STKALIGN_MASK |
+            R_V7M_CCR_BFHFNMIGN_MASK |
+            R_V7M_CCR_DIV_0_TRP_MASK |
+            R_V7M_CCR_UNALIGN_TRP_MASK |
+            R_V7M_CCR_USERSETMPEND_MASK |
+            R_V7M_CCR_NONBASETHRDENA_MASK;
+        if (arm_feature(&cpu->env, ARM_FEATURE_V8_1M) && attrs.secure) {
+            /* TRD is always RAZ/WI from NS */
+            mask |= R_V7M_CCR_TRD_MASK;
+        }
+        value &= mask;
 
         if (arm_feature(&cpu->env, ARM_FEATURE_V8)) {
             /* v8M makes NONBASETHRDENA and STKALIGN be RES1 */
@@ -1666,6 +1675,7 @@ static void nvic_writel(NVICState *s, uint32_t offset, uint32_t value,
 
         cpu->env.v7m.ccr[attrs.secure] = value;
         break;
+    }
     case 0xd24: /* System Handler Control and State (SHCSR) */
         if (!arm_feature(&cpu->env, ARM_FEATURE_V7)) {
             goto bad_offset;

target/arm/cpu.h

@@ -1611,6 +1611,8 @@ FIELD(V7M_CCR, STKOFHFNMIGN, 10, 1)
 FIELD(V7M_CCR, DC, 16, 1)
 FIELD(V7M_CCR, IC, 17, 1)
 FIELD(V7M_CCR, BP, 18, 1)
+FIELD(V7M_CCR, LOB, 19, 1)
+FIELD(V7M_CCR, TRD, 20, 1)
 
 /* V7M SCR bits */
 FIELD(V7M_SCR, SLEEPONEXIT, 1, 1)