target-arm: Add debug check for mismatched cpreg resets

It's easy to accidentally define two cpregs which both try
to reset the same underlying state field (for instance a
clash between an AArch64 EL3 definition and an AArch32
banked register definition). if the two definitions disagree
about the reset value then the result is dependent on which
one happened to be reached last in the hashtable enumeration.

Add a consistency check to detect and assert in these cases:
after reset, we run a second pass where we check that the
reset operation doesn't change the value of the register.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
Message-id: 1436797559-20835-1-git-send-email-peter.maydell@linaro.org

target-arm/cpu.c

@@ -79,6 +79,27 @@ static void cp_reg_reset(gpointer key, gpointer value, gpointer opaque)
     }
 }
 
+static void cp_reg_check_reset(gpointer key, gpointer value,  gpointer opaque)
+{
+    /* Purely an assertion check: we've already done reset once,
+     * so now check that running the reset for the cpreg doesn't
+     * change its value. This traps bugs where two different cpregs
+     * both try to reset the same state field but to different values.
+     */
+    ARMCPRegInfo *ri = value;
+    ARMCPU *cpu = opaque;
+    uint64_t oldvalue, newvalue;
+
+    if (ri->type & (ARM_CP_SPECIAL | ARM_CP_ALIAS | ARM_CP_NO_RAW)) {
+        return;
+    }
+
+    oldvalue = read_raw_cp_reg(&cpu->env, ri);
+    cp_reg_reset(key, value, opaque);
+    newvalue = read_raw_cp_reg(&cpu->env, ri);
+    assert(oldvalue == newvalue);
+}
+
 /* CPUClass::reset() */
 static void arm_cpu_reset(CPUState *s)
 {
@@ -90,6 +111,8 @@ static void arm_cpu_reset(CPUState *s)
 
     memset(env, 0, offsetof(CPUARMState, features));
     g_hash_table_foreach(cpu->cp_regs, cp_reg_reset, cpu);
+    g_hash_table_foreach(cpu->cp_regs, cp_reg_check_reset, cpu);
+
     env->vfp.xregs[ARM_VFP_FPSID] = cpu->reset_fpsid;
     env->vfp.xregs[ARM_VFP_MVFR0] = cpu->mvfr0;
     env->vfp.xregs[ARM_VFP_MVFR1] = cpu->mvfr1;

target-arm/cpu.h

@@ -1448,6 +1448,9 @@ static inline bool cp_access_ok(int current_el,
     return (ri->access >> ((current_el * 2) + isread)) & 1;
 }
 
+/* Raw read of a coprocessor register (as needed for migration, etc) */
+uint64_t read_raw_cp_reg(CPUARMState *env, const ARMCPRegInfo *ri);
+
 /**
  * write_list_to_cpustate
  * @cpu: ARMCPU

target-arm/helper.c

@@ -144,7 +144,7 @@ static void *raw_ptr(CPUARMState *env, const ARMCPRegInfo *ri)
     return (char *)env + ri->fieldoffset;
 }
 
-static uint64_t read_raw_cp_reg(CPUARMState *env, const ARMCPRegInfo *ri)
+uint64_t read_raw_cp_reg(CPUARMState *env, const ARMCPRegInfo *ri)
 {
     /* Raw read of a coprocessor register (as needed for migration, etc). */
     if (ri->type & ARM_CP_CONST) {