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Justin Bogner <m...@justinbogner.com> writes: > 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. > > This does waste some space in the 32-bit case. It wouldn't be too hard > to make the size of this struct dependent on the host machine if > that's an issue. WDYT? > > commit 1f1d41a60f5106e9e89fbc917bfc0826b5caad02 > Author: Justin Bogner <m...@justinbogner.com> > Date: Mon Jun 22 16:02:17 2015 -0700 > > 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. > > diff --git a/lib/CodeGen/CodeGenFunction.h b/lib/CodeGen/CodeGenFunction.h > index 45475d1..0891b5d 100644 > --- a/lib/CodeGen/CodeGenFunction.h > +++ b/lib/CodeGen/CodeGenFunction.h > @@ -283,12 +283,12 @@ 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. > @@ -388,6 +388,8 @@ 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...); _______________________________________________ cfe-commits mailing list cfe-commits@cs.uiuc.edu http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits