Verified Commit 9e079476 authored by Tyson Smith's avatar Tyson Smith Committed by ma1
Browse files

Bug 2035963 - Add MOZ_EMPTY_BASES to Maybe<T> to fix UBSan on Windows. r=sergesanspaille 

Without __declspec(empty_bases), the MSVC ABI doesn't apply empty base
optimization for multiple inheritance. Maybe<T>'s empty base
(Maybe_CopyMove_Enabler<T>) gets a unique 1-byte slot past the storage, and
UBSan fires "insufficient space" when operator= adjusts `this` to that subobject.

Differential Revision: https://phabricator.services.mozilla.com/D299791
parent 67f1d5da

mfbt/Maybe.h

+3 −3
Original line number Diff line number Diff line
@@ -360,8 +360,8 @@ constexpr Maybe<U> Some(T&& aValue); 
 *     functions |Some()| and |Nothing()|.

 */

template <class T>

class MOZ_INHERIT_TYPE_ANNOTATIONS_FROM_TEMPLATE_ARGS MOZ_GSL_OWNER Maybe

    : private detail::MaybeStorage<T>,

class MOZ_INHERIT_TYPE_ANNOTATIONS_FROM_TEMPLATE_ARGS MOZ_GSL_OWNER

    MOZ_EMPTY_BASES Maybe : private detail::MaybeStorage<T>,

                            public detail::Maybe_CopyMove_Enabler<T> {

  template <typename, bool, bool, bool>

  friend class detail::Maybe_CopyMove_Enabler;