include/qemu/atomic: add compile time asserts

To be safely portable no atomic access should be trying to do more than
the natural word width of the host. The most common abuse is trying to
atomically access 64 bit values on a 32 bit host.

This patch adds some QEMU_BUILD_BUG_ON to the __atomic instrinsic paths
to create a build failure if (sizeof(*ptr) > sizeof(void *)).

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <1459780549-12942-3-git-send-email-alex.bennee@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/include/qemu/atomic.h b/include/qemu/atomic.h
index 8f1d8d927dca0229f746a5229bf691c38487ba4c..5bc4d6cc476000a2ed45aac71dae7de946b37b6c 100644 (file)
--- a/include/qemu/atomic.h
+++ b/include/qemu/atomic.h
@@ -42,30 +42,34 @@
  * loads/stores past the atomic operation load/store. However there is
  * no explicit memory barrier for the processor.
  */
-#define atomic_read(ptr)                          \
-    ({                                            \
-    typeof(*ptr) _val;                            \
-     __atomic_load(ptr, &_val, __ATOMIC_RELAXED); \
-    _val;                                         \
+#define atomic_read(ptr)                              \
+    ({                                                \
+    QEMU_BUILD_BUG_ON(sizeof(*ptr) > sizeof(void *)); \
+    typeof(*ptr) _val;                                \
+     __atomic_load(ptr, &_val, __ATOMIC_RELAXED);     \
+    _val;                                             \
     })
 
-#define atomic_set(ptr, i)  do {                  \
-    typeof(*ptr) _val = (i);                      \
-    __atomic_store(ptr, &_val, __ATOMIC_RELAXED); \
+#define atomic_set(ptr, i)  do {                      \
+    QEMU_BUILD_BUG_ON(sizeof(*ptr) > sizeof(void *)); \
+    typeof(*ptr) _val = (i);                          \
+    __atomic_store(ptr, &_val, __ATOMIC_RELAXED);     \
 } while(0)
 
 /* Atomic RCU operations imply weak memory barriers */
 
-#define atomic_rcu_read(ptr)                      \
-    ({                                            \
-    typeof(*ptr) _val;                            \
-     __atomic_load(ptr, &_val, __ATOMIC_CONSUME); \
-    _val;                                         \
+#define atomic_rcu_read(ptr)                          \
+    ({                                                \
+    QEMU_BUILD_BUG_ON(sizeof(*ptr) > sizeof(void *)); \
+    typeof(*ptr) _val;                                \
+    __atomic_load(ptr, &_val, __ATOMIC_CONSUME);      \
+    _val;                                             \
     })
 
-#define atomic_rcu_set(ptr, i)  do {                    \
-    typeof(*ptr) _val = (i);                            \
-    __atomic_store(ptr, &_val, __ATOMIC_RELEASE);       \
+#define atomic_rcu_set(ptr, i) do {                   \
+    QEMU_BUILD_BUG_ON(sizeof(*ptr) > sizeof(void *)); \
+    typeof(*ptr) _val = (i);                          \
+    __atomic_store(ptr, &_val, __ATOMIC_RELEASE);     \
 } while(0)
 
 /* atomic_mb_read/set semantics map Java volatile variables. They are
@@ -79,6 +83,7 @@
 #if defined(_ARCH_PPC)
 #define atomic_mb_read(ptr)                             \
     ({                                                  \
+    QEMU_BUILD_BUG_ON(sizeof(*ptr) > sizeof(void *));   \
     typeof(*ptr) _val;                                  \
      __atomic_load(ptr, &_val, __ATOMIC_RELAXED);       \
      smp_rmb();                                         \
@@ -86,22 +91,25 @@
     })
 
 #define atomic_mb_set(ptr, i)  do {                     \
+    QEMU_BUILD_BUG_ON(sizeof(*ptr) > sizeof(void *));   \
     typeof(*ptr) _val = (i);                            \
     smp_wmb();                                          \
     __atomic_store(ptr, &_val, __ATOMIC_RELAXED);       \
     smp_mb();                                           \
 } while(0)
 #else
-#define atomic_mb_read(ptr)                       \
-    ({                                            \
-    typeof(*ptr) _val;                            \
-     __atomic_load(ptr, &_val, __ATOMIC_SEQ_CST); \
-    _val;                                         \
+#define atomic_mb_read(ptr)                             \
+    ({                                                  \
+    QEMU_BUILD_BUG_ON(sizeof(*ptr) > sizeof(void *));   \
+    typeof(*ptr) _val;                                  \
+    __atomic_load(ptr, &_val, __ATOMIC_SEQ_CST);        \
+    _val;                                               \
     })
 
-#define atomic_mb_set(ptr, i)  do {               \
-    typeof(*ptr) _val = (i);                      \
-    __atomic_store(ptr, &_val, __ATOMIC_SEQ_CST); \
+#define atomic_mb_set(ptr, i)  do {                     \
+    QEMU_BUILD_BUG_ON(sizeof(*ptr) > sizeof(void *));   \
+    typeof(*ptr) _val = (i);                            \
+    __atomic_store(ptr, &_val, __ATOMIC_SEQ_CST);       \
 } while(0)
 #endif
 
@@ -109,6 +117,7 @@
 /* All the remaining operations are fully sequentially consistent */
 
 #define atomic_xchg(ptr, i)    ({                           \
+    QEMU_BUILD_BUG_ON(sizeof(*ptr) > sizeof(void *));       \
     typeof(*ptr) _new = (i), _old;                          \
     __atomic_exchange(ptr, &_new, &_old, __ATOMIC_SEQ_CST); \
     _old;                                                   \
@@ -117,6 +126,7 @@
 /* Returns the eventual value, failed or not */
 #define atomic_cmpxchg(ptr, old, new)                                   \
     ({                                                                  \
+    QEMU_BUILD_BUG_ON(sizeof(*ptr) > sizeof(void *));                   \
     typeof(*ptr) _old = (old), _new = (new);                            \
     __atomic_compare_exchange(ptr, &_old, &_new, false,                 \
                               __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST);      \