target/arm: Clear exclusive monitor on v7M reset, exception entry/exit

For M profile we must clear the exclusive monitor on reset, exception
entry and exception exit.  We weren't doing any of these things; fix
this bug.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Alistair Francis <alistair.francis@xilinx.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 1505137930-13255-3-git-send-email-peter.maydell@linaro.org

target/arm/cpu.c

@@ -235,6 +235,12 @@ static void arm_cpu_reset(CPUState *s)
         env->regs[15] = 0xFFFF0000;
     }
 
+    /* M profile requires that reset clears the exclusive monitor;
+     * A profile does not, but clearing it makes more sense than having it
+     * set with an exclusive access on address zero.
+     */
+    arm_clear_exclusive(env);
+
     env->vfp.xregs[ARM_VFP_FPEXC] = 0;
 #endif
 

target/arm/helper.c

@@ -6175,6 +6175,7 @@ static void v7m_exception_taken(ARMCPU *cpu, uint32_t lr)
 
     armv7m_nvic_acknowledge_irq(env->nvic);
     switch_v7m_sp(env, 0);
+    arm_clear_exclusive(env);
     /* Clear IT bits */
     env->condexec_bits = 0;
     env->regs[14] = lr;
@@ -6354,6 +6355,7 @@ static void do_v7m_exception_exit(ARMCPU *cpu)
     }
 
     /* Otherwise, we have a successful exception exit. */
+    arm_clear_exclusive(env);
     qemu_log_mask(CPU_LOG_INT, "...successful exception return\n");
 }
 

target/arm/internals.h

@@ -443,6 +443,16 @@ bool arm_is_psci_call(ARMCPU *cpu, int excp_type);
 void arm_handle_psci_call(ARMCPU *cpu);
 #endif
 
+/**
+ * arm_clear_exclusive: clear the exclusive monitor
+ * @env: CPU env
+ * Clear the CPU's exclusive monitor, like the guest CLREX instruction.
+ */
+static inline void arm_clear_exclusive(CPUARMState *env)
+{
+    env->exclusive_addr = -1;
+}
+
 /**
  * ARMMMUFaultInfo: Information describing an ARM MMU Fault
  * @s2addr: Address that caused a fault at stage 2

target/arm/op_helper.c

@@ -1022,7 +1022,7 @@ void HELPER(exception_return)(CPUARMState *env)
 
     aarch64_save_sp(env, cur_el);
 
-    env->exclusive_addr = -1;
+    arm_clear_exclusive(env);
 
     /* We must squash the PSTATE.SS bit to zero unless both of the
      * following hold: