CodeGen: Resize LifetimeExtendedCleanupHeader to avoid alignment issues

The LifetimeExtendedCleanupHeader is carefully fit into 32 bytes,
meaning that cleanups on the LifetimeExtendedCleanupStack are *always*
allocated at a misaligned address and cause undefined behaviour.

There are two ways to solve this - add padding after the header when
we allocated our cleanups, or just simplify the header and let it use
64 bits in the first place. I've opted for the latter, and added a
static assert to avoid the issue in the future.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@241133 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/CodeGenFunction.h b/lib/CodeGen/CodeGenFunction.h
index 8cf87a3933d00aa7f4eb40fbcc2a15dd76cd5155..d98c7ae6318c0b54d98fd2450190e7bdb028a861 100644 (file)
--- a/lib/CodeGen/CodeGenFunction.h
+++ b/lib/CodeGen/CodeGenFunction.h
@@ -297,12 +297,12 @@ public:
   /// Header for data within LifetimeExtendedCleanupStack.
   struct LifetimeExtendedCleanupHeader {
     /// The size of the following cleanup object.
-    unsigned Size : 29;
+    unsigned Size;
     /// The kind of cleanup to push: a value from the CleanupKind enumeration.
-    unsigned Kind : 3;
+    CleanupKind Kind;
 
-    size_t getSize() const { return size_t(Size); }
-    CleanupKind getKind() const { return static_cast<CleanupKind>(Kind); }
+    size_t getSize() const { return Size; }
+    CleanupKind getKind() const { return Kind; }
   };
 
   /// i32s containing the indexes of the cleanup destinations.
@@ -402,6 +402,8 @@ public:
     LifetimeExtendedCleanupStack.resize(
         LifetimeExtendedCleanupStack.size() + sizeof(Header) + Header.Size);
 
+    static_assert(sizeof(Header) % llvm::AlignOf<T>::Alignment == 0,
+                  "Cleanup will be allocated on misaligned address");
     char *Buffer = &LifetimeExtendedCleanupStack[OldSize];
     new (Buffer) LifetimeExtendedCleanupHeader(Header);
     new (Buffer + sizeof(Header)) T(A...);