Sparc: fix non-faulting unassigned memory accesses

Commit b14ef7c9
introduced cpu_unassigned_access() function. On Sparc,
the function does not restore AREG0 used for global CPUState
on function exit, causing bugs with non-faulting unassigned
memory accesses. Alpha, Microblaze and MIPS are not affected.

Fix by restoring AREG0 on exit. Remove excess saving by
do_unassigned_access() functions.

Also ignore unassigned accesses outside of CPU context.
Reported-by: NBob Breuer <breuerr@mc.net>
Tested-by: NBob Breuer <breuerr@mc.net>
Signed-off-by: NBlue Swirl <blauwirbel@gmail.com>

target-sparc/op_helper.c

@@ -4252,13 +4252,8 @@ void tlb_fill(target_ulong addr, int is_write, int mmu_idx, void *retaddr)
 static void do_unassigned_access(target_phys_addr_t addr, int is_write,
                                  int is_exec, int is_asi, int size)
 {
-    CPUState *saved_env;
     int fault_type;
 
-    /* XXX: hack to restore env in all cases, even if not called from
-       generated code */
-    saved_env = env;
-    env = cpu_single_env;
 #ifdef DEBUG_UNASSIGNED
     if (is_asi)
         printf("Unassigned mem %s access of %d byte%s to " TARGET_FMT_plx
@@ -4306,8 +4301,6 @@ static void do_unassigned_access(target_phys_addr_t addr, int is_write,
     if (env->mmuregs[0] & MMU_NF) {
         tlb_flush(env, 1);
     }
-
-    env = saved_env;
 }
 #endif
 #else
@@ -4319,13 +4312,6 @@ static void do_unassigned_access(target_phys_addr_t addr, int is_write,
                                  int is_exec, int is_asi, int size)
 #endif
 {
-    CPUState *saved_env;
-
-    /* XXX: hack to restore env in all cases, even if not called from
-       generated code */
-    saved_env = env;
-    env = cpu_single_env;
-
 #ifdef DEBUG_UNASSIGNED
     printf("Unassigned mem access to " TARGET_FMT_plx " from " TARGET_FMT_lx
            "\n", addr, env->pc);
@@ -4335,8 +4321,6 @@ static void do_unassigned_access(target_phys_addr_t addr, int is_write,
         raise_exception(TT_CODE_ACCESS);
     else
         raise_exception(TT_DATA_ACCESS);
-
-    env = saved_env;
 }
 #endif
 
@@ -4370,7 +4354,14 @@ void helper_tick_set_limit(void *opaque, uint64_t limit)
 void cpu_unassigned_access(CPUState *env1, target_phys_addr_t addr,
                            int is_write, int is_exec, int is_asi, int size)
 {
+    CPUState *saved_env;
+
+    saved_env = env;
     env = env1;
-    do_unassigned_access(addr, is_write, is_exec, is_asi, size);
+    /* Ignore unassigned accesses outside of CPU context */
+    if (env1) {
+        do_unassigned_access(addr, is_write, is_exec, is_asi, size);
+    }
+    env = saved_env;
 }
 #endif