tcg: Introduce set/clear_helper_retaddr

At present we have a potential error in that helper_retaddr contains
data for handle_cpu_signal, but we have not ensured that those stores
will be scheduled properly before the operation that may fault.

It might be that these races are not in practice observable, due to
our use of -fno-strict-aliasing, but better safe than sorry.

Adjust all of the setters of helper_retaddr.

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

1 files changed, 6 insertions, 5 deletions

diff --git a/accel/tcg/user-exec.c b/accel/tcg/user-exec.c
index cb5f4b19c5..4384b59a4d 100644
--- a/accel/tcg/user-exec.c
+++ b/accel/tcg/user-exec.c
@@ -134,7 +134,7 @@ static inline int handle_cpu_signal(uintptr_t pc, siginfo_t *info,
              * currently executing TB was modified and must be exited
              * immediately.  Clear helper_retaddr for next execution.
              */
-            helper_retaddr = 0;
+            clear_helper_retaddr();
             cpu_exit_tb_from_sighandler(cpu, old_set);
             /* NORETURN */
 
@@ -152,7 +152,7 @@ static inline int handle_cpu_signal(uintptr_t pc, siginfo_t *info,
      * an exception.  Undo signal and retaddr state prior to longjmp.
      */
     sigprocmask(SIG_SETMASK, old_set, NULL);
-    helper_retaddr = 0;
+    clear_helper_retaddr();
 
     cc = CPU_GET_CLASS(cpu);
     access_type = is_write ? MMU_DATA_STORE : MMU_DATA_LOAD;
@@ -682,14 +682,15 @@ static void *atomic_mmu_lookup(CPUArchState *env, target_ulong addr,
     if (unlikely(addr & (size - 1))) {
         cpu_loop_exit_atomic(env_cpu(env), retaddr);
     }
-    helper_retaddr = retaddr;
-    return g2h(addr);
+    void *ret = g2h(addr);
+    set_helper_retaddr(retaddr);
+    return ret;
 }
 
 /* Macro to call the above, with local variables from the use context.  */
 #define ATOMIC_MMU_DECLS do {} while (0)
 #define ATOMIC_MMU_LOOKUP  atomic_mmu_lookup(env, addr, DATA_SIZE, GETPC())
-#define ATOMIC_MMU_CLEANUP do { helper_retaddr = 0; } while (0)
+#define ATOMIC_MMU_CLEANUP do { clear_helper_retaddr(); } while (0)
 
 #define ATOMIC_NAME(X)   HELPER(glue(glue(atomic_ ## X, SUFFIX), END))
 #define EXTRA_ARGS