Make the qatomic classes work in ARMv5 OABI.

The function testAndSetOrdered is not atomic.
The context of a thread may be interrupted inside testAndSetOrdered
and then if another thread calls fetchAndStoreOrdered, _q_value may be
overwritten. After that _q_value will contain random value
depending on where testAndSetOrdered was interrupted.
It should not be possible for the atomic classes.

Since the commit 8a7b5aca7b6575013a4e4ee9b99808d25edf6fdf
introduced new implementation of QMutex for linux
the bug causes deadlock.

Change-Id: Ib9ffcf0e26d3be36a0e158fd12a363b97177dcbf
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 16 insertions, 0 deletions

diff --git a/src/corelib/arch/qatomic_armv5.h b/src/corelib/arch/qatomic_armv5.h
index 20d6b1bb06..58af4138ca 100644
--- a/src/corelib/arch/qatomic_armv5.h
+++ b/src/corelib/arch/qatomic_armv5.h
@@ -226,10 +226,18 @@ inline bool QBasicAtomicInt::testAndSetRelease(int expectedValue, int newValue)
 inline int QBasicAtomicInt::fetchAndStoreOrdered(int newValue)
 {
     int originalValue;
+#ifndef QT_NO_ARM_EABI
     asm volatile("swp %0,%2,[%3]"
                  : "=&r"(originalValue), "=m" (_q_value)
                  : "r"(newValue), "r"(&_q_value)
                  : "cc", "memory");
+#else
+    while (q_atomic_swp(&q_atomic_lock, ~0) != 0)
+        qt_atomic_yield(&count);
+    originalValue=_q_value;
+    _q_value = newValue;
+    q_atomic_swp(&q_atomic_lock, 0);
+#endif
     return originalValue;
 }
 
@@ -355,10 +363,18 @@ template <typename T>
 Q_INLINE_TEMPLATE T *QBasicAtomicPointer<T>::fetchAndStoreOrdered(T *newValue)
 {
     T *originalValue;
+#ifndef QT_NO_ARM_EABI
     asm volatile("swp %0,%2,[%3]"
                  : "=&r"(originalValue), "=m" (_q_value)
                  : "r"(newValue), "r"(&_q_value)
                  : "cc", "memory");
+#else
+    while (q_atomic_swp(&q_atomic_lock, ~0) != 0)
+        qt_atomic_yield(&count);
+    originalValue=_q_value;
+    _q_value = newValue;
+    q_atomic_swp(&q_atomic_lock, 0);
+#endif
     return originalValue;
 }