target/arm: Define new TBFLAG for v8M stack checking

The Arm v8M architecture includes hardware stack limit checking.
When certain instructions update the stack pointer, if the new
value of SP is below the limit set in the associated limit register
then an exception is taken. Add a TB flag that tracks whether
the limit-checking code needs to be emitted.
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Reviewed-by: NRichard Henderson <richard.henderson@linaro.org>
Reviewed-by: NPhilippe Mathieu-Daudé <philmd@redhat.com>
Message-id: 20181002163556.10279-2-peter.maydell@linaro.org

target/arm/cpu.h

@@ -1344,8 +1344,10 @@ FIELD(V7M_CCR, UNALIGN_TRP, 3, 1)
 FIELD(V7M_CCR, DIV_0_TRP, 4, 1)
 FIELD(V7M_CCR, BFHFNMIGN, 8, 1)
 FIELD(V7M_CCR, STKALIGN, 9, 1)
+FIELD(V7M_CCR, STKOFHFNMIGN, 10, 1)
 FIELD(V7M_CCR, DC, 16, 1)
 FIELD(V7M_CCR, IC, 17, 1)
+FIELD(V7M_CCR, BP, 18, 1)
 
 /* V7M SCR bits */
 FIELD(V7M_SCR, SLEEPONEXIT, 1, 1)
@@ -2850,6 +2852,9 @@ static inline bool arm_cpu_data_is_big_endian(CPUARMState *env)
 /* For M profile only, Handler (ie not Thread) mode */
 #define ARM_TBFLAG_HANDLER_SHIFT    21
 #define ARM_TBFLAG_HANDLER_MASK     (1 << ARM_TBFLAG_HANDLER_SHIFT)
+/* For M profile only, whether we should generate stack-limit checks */
+#define ARM_TBFLAG_STACKCHECK_SHIFT 22
+#define ARM_TBFLAG_STACKCHECK_MASK  (1 << ARM_TBFLAG_STACKCHECK_SHIFT)
 
 /* Bit usage when in AArch64 state */
 #define ARM_TBFLAG_TBI0_SHIFT 0        /* TBI0 for EL0/1 or TBI for EL2/3 */
@@ -2892,6 +2897,8 @@ static inline bool arm_cpu_data_is_big_endian(CPUARMState *env)
     (((F) & ARM_TBFLAG_BE_DATA_MASK) >> ARM_TBFLAG_BE_DATA_SHIFT)
 #define ARM_TBFLAG_HANDLER(F) \
     (((F) & ARM_TBFLAG_HANDLER_MASK) >> ARM_TBFLAG_HANDLER_SHIFT)
+#define ARM_TBFLAG_STACKCHECK(F) \
+    (((F) & ARM_TBFLAG_STACKCHECK_MASK) >> ARM_TBFLAG_STACKCHECK_SHIFT)
 #define ARM_TBFLAG_TBI0(F) \
     (((F) & ARM_TBFLAG_TBI0_MASK) >> ARM_TBFLAG_TBI0_SHIFT)
 #define ARM_TBFLAG_TBI1(F) \

target/arm/helper.c

@@ -12686,6 +12686,16 @@ void cpu_get_tb_cpu_state(CPUARMState *env, target_ulong *pc,
         flags |= ARM_TBFLAG_HANDLER_MASK;
     }
 
+    /* v8M always applies stack limit checks unless CCR.STKOFHFNMIGN is
+     * suppressing them because the requested execution priority is less than 0.
+     */
+    if (arm_feature(env, ARM_FEATURE_V8) &&
+        arm_feature(env, ARM_FEATURE_M) &&
+        !((mmu_idx  & ARM_MMU_IDX_M_NEGPRI) &&
+          (env->v7m.ccr[env->v7m.secure] & R_V7M_CCR_STKOFHFNMIGN_MASK))) {
+        flags |= ARM_TBFLAG_STACKCHECK_MASK;
+    }
+
     *pflags = flags;
     *cs_base = 0;
 }

target/arm/translate.c

@@ -12451,6 +12451,7 @@ static void arm_tr_init_disas_context(DisasContextBase *dcbase, CPUState *cs)
     dc->v7m_handler_mode = ARM_TBFLAG_HANDLER(dc->base.tb->flags);
     dc->v8m_secure = arm_feature(env, ARM_FEATURE_M_SECURITY) &&
         regime_is_secure(env, dc->mmu_idx);
+    dc->v8m_stackcheck = ARM_TBFLAG_STACKCHECK(dc->base.tb->flags);
     dc->cp_regs = cpu->cp_regs;
     dc->features = env->features;
 

target/arm/translate.h

@@ -38,6 +38,7 @@ typedef struct DisasContext {
     int vec_stride;
     bool v7m_handler_mode;
     bool v8m_secure; /* true if v8M and we're in Secure mode */
+    bool v8m_stackcheck; /* true if we need to perform v8M stack limit checks */
     /* Immediate value in AArch32 SVC insn; must be set if is_jmp == DISAS_SWI
      * so that top level loop can generate correct syndrome information.
      */