Merge pull request #9530 from kjbracey-arm/atomic_singletonptr

Use atomics for double-checked locks (SingletonPtr + __cxa_guard)

Author: Cruz Monrreal

platform/SingletonPtr.h

@@ -28,6 +28,7 @@
 #include <stdint.h>
 #include <new>
 #include "platform/mbed_assert.h"
+#include "platform/mbed_critical.h"
 #ifdef MBED_CONF_RTOS_PRESENT
 #include "cmsis_os2.h"
 #endif
@@ -92,17 +93,20 @@ struct SingletonPtr {
      */
     T *get() const
     {
-        if (NULL == _ptr) {
+        T *p = static_cast<T *>(core_util_atomic_load_ptr(&_ptr));
+        if (p == NULL) {
             singleton_lock();
-            if (NULL == _ptr) {
-                _ptr = new (_data) T();
+            p = static_cast<T *>(_ptr);
+            if (p == NULL) {
+                p = new (_data) T();
+                core_util_atomic_store_ptr(&_ptr, p);
             }
             singleton_unlock();
         }
         // _ptr was not zero initialized or was
         // corrupted if this assert is hit
-        MBED_ASSERT(_ptr == (T *)&_data);
-        return _ptr;
+        MBED_ASSERT(p == reinterpret_cast<T *>(&_data));
+        return p;
     }
 
     /** Get a pointer to the underlying singleton
@@ -126,7 +130,7 @@ struct SingletonPtr {
     }
 
     // This is zero initialized when in global scope
-    mutable T *_ptr;
+    mutable void *_ptr;
 #if __cplusplus >= 201103L
     // Align data appropriately
     alignas(T) mutable char _data[sizeof(T)];

platform/mbed_retarget.cpp

@@ -1417,7 +1417,7 @@ extern "C" void __env_unlock(struct _reent *_r)
 
 #endif
 
-#if defined (__GNUC__) || defined(__CC_ARM) || (defined (__ARMCC_VERSION) && (__ARMCC_VERSION >= 6010050))
+#if defined (__GNUC__) || defined (__ARMCC_VERSION)
 
 #define CXA_GUARD_INIT_DONE             (1 << 0)
 #define CXA_GUARD_INIT_IN_PROGRESS      (1 << 1)
@@ -1426,38 +1426,41 @@ extern "C" void __env_unlock(struct _reent *_r)
 extern "C" int __cxa_guard_acquire(int *guard_object_p)
 {
     uint8_t *guard_object = (uint8_t *)guard_object_p;
-    if (CXA_GUARD_INIT_DONE == (*guard_object & CXA_GUARD_MASK)) {
+    if ((core_util_atomic_load_u8(guard_object) & CXA_GUARD_MASK) == CXA_GUARD_INIT_DONE) {
         return 0;
     }
     singleton_lock();
-    if (CXA_GUARD_INIT_DONE == (*guard_object & CXA_GUARD_MASK)) {
+    uint8_t guard = *guard_object;
+    if ((guard & CXA_GUARD_MASK) == CXA_GUARD_INIT_DONE) {
         singleton_unlock();
         return 0;
     }
-    MBED_ASSERT(0 == (*guard_object & CXA_GUARD_MASK));
-    *guard_object = *guard_object | CXA_GUARD_INIT_IN_PROGRESS;
+    MBED_ASSERT((guard & CXA_GUARD_MASK) == 0);
+    core_util_atomic_store_u8(guard_object, guard | CXA_GUARD_INIT_IN_PROGRESS);
     return 1;
 }
 
 extern "C" void __cxa_guard_release(int *guard_object_p)
 {
     uint8_t *guard_object = (uint8_t *)guard_object_p;
-    MBED_ASSERT(CXA_GUARD_INIT_IN_PROGRESS == (*guard_object & CXA_GUARD_MASK));
-    *guard_object = (*guard_object & ~CXA_GUARD_MASK) | CXA_GUARD_INIT_DONE;
+    uint8_t guard = *guard_object;
+    MBED_ASSERT((guard & CXA_GUARD_MASK) == CXA_GUARD_INIT_IN_PROGRESS);
+    core_util_atomic_store_u8(guard_object, (guard & ~CXA_GUARD_MASK) | CXA_GUARD_INIT_DONE);
     singleton_unlock();
 }
 
 extern "C" void __cxa_guard_abort(int *guard_object_p)
 {
     uint8_t *guard_object = (uint8_t *)guard_object_p;
-    MBED_ASSERT(CXA_GUARD_INIT_IN_PROGRESS == (*guard_object & CXA_GUARD_MASK));
-    *guard_object = *guard_object & ~CXA_GUARD_INIT_IN_PROGRESS;
+    uint8_t guard = *guard_object;
+    MBED_ASSERT((guard & CXA_GUARD_MASK) == CXA_GUARD_INIT_IN_PROGRESS);
+    core_util_atomic_store_u8(guard_object, guard & ~CXA_GUARD_INIT_IN_PROGRESS);
     singleton_unlock();
 }
 
 #endif
 
-#if defined(MBED_MEM_TRACING_ENABLED) && (defined(__CC_ARM) || defined(__ICCARM__) || (defined (__ARMCC_VERSION) && (__ARMCC_VERSION >= 6010050)))
+#if defined(MBED_MEM_TRACING_ENABLED) && (defined(__ARMCC_VERSION) || defined(__ICCARM__))
 
 // If the memory tracing is enabled, the wrappers in mbed_alloc_wrappers.cpp
 // provide the implementation for these. Note: this needs to use the wrappers