Changeset 15334

Timestamp:

Jun 11, 2014, 9:50:38 PM (9 years ago)

Author:

philip

Message:

Fix TestHeaderless failure on GCC 4.9.

Once 'delete' is called on an object, that object no longer exists, and accessing its member variables is undefined behaviour. GCC 4.9's optimiser recognises this, and eliminates any writes to member variables inside the destructor, since it knows they cannot legally be read later.

BoundaryTagManager relied on ~FreedBlock resetting its memory to 0, so this optimisation broke it. Replace the placement new/delete with plain non-magic Setup/Reset functions, to avoid the optimisation.

Fixes #2481.

File:

• ps/trunk/source/lib/allocators/headerless.cpp (modified) (3 diffs)

ps/trunk/source/lib/allocators/headerless.cpp

@@ -55 +55 @@
     }
 
-    FreedBlock(uintptr_t id, size_t size)
-        :  m_magic(s_magic), m_size(size), m_id(id)
-    {
-    }
-
-    ~FreedBlock()
+    void Setup(uintptr_t id, size_t size)
+    {
+        m_magic = s_magic;
+        m_size = size;
+        m_id = id;
+    }
+
+    void Reset()
     {
         // clear all fields to prevent accidental reuse
@@ -411 +413 @@
     FreedBlock* WriteTags(u8* p, size_t size)
     {
-        FreedBlock* freedBlock = new(p) FreedBlock(s_headerId, size);
-        (void)new(Footer(freedBlock)) FreedBlock(s_footerId, size);
+        FreedBlock* freedBlock = (FreedBlock*)p;
+        freedBlock->Setup(s_headerId, size);
+        Footer(freedBlock)->Setup(s_footerId, size);
 
         m_freeBlocks++;
@@ -431 +434 @@
 
         FreedBlock* footer = Footer(freedBlock);
-        freedBlock->~FreedBlock();
-        footer->~FreedBlock();
+        freedBlock->Reset();
+        footer->Reset();
     }