apic: Fix access to non-existent APIC

When running with -M isapc, there is no env->apic_state. Fix
cpu_get/set_apic_* helpers to handle this corner case gracefully.
Signed-off-by: NJan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: NAurelien Jarno <aurelien@aurel32.net>

git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@7048 c046a42c-6fe2-441c-8c8c-71466251a162

hw/apic.c

@@ -280,6 +280,8 @@ void cpu_set_apic_base(CPUState *env, uint64_t val)
 #ifdef DEBUG_APIC
     printf("cpu_set_apic_base: %016" PRIx64 "\n", val);
 #endif
+    if (!s)
+        return;
     s->apicbase = (val & 0xfffff000) |
         (s->apicbase & (MSR_IA32_APICBASE_BSP | MSR_IA32_APICBASE_ENABLE));
     /* if disabled, cannot be enabled again */
@@ -294,14 +296,17 @@ uint64_t cpu_get_apic_base(CPUState *env)
 {
     APICState *s = env->apic_state;
 #ifdef DEBUG_APIC
-    printf("cpu_get_apic_base: %016" PRIx64 "\n", (uint64_t)s->apicbase);
+    printf("cpu_get_apic_base: %016" PRIx64 "\n",
+           s ? (uint64_t)s->apicbase: 0);
 #endif
-    return s->apicbase;
+    return s ? s->apicbase : 0;
 }
 
 void cpu_set_apic_tpr(CPUX86State *env, uint8_t val)
 {
     APICState *s = env->apic_state;
+    if (!s)
+        return;
     s->tpr = (val & 0x0f) << 4;
     apic_update_irq(s);
 }
@@ -309,7 +314,7 @@ void cpu_set_apic_tpr(CPUX86State *env, uint8_t val)
 uint8_t cpu_get_apic_tpr(CPUX86State *env)
 {
     APICState *s = env->apic_state;
-    return s->tpr >> 4;
+    return s ? s->tpr >> 4 : 0;
 }
 
 /* return -1 if no bit is set */