Author: ericwf Date: Wed Oct 5 17:55:10 2016 New Revision: 283408 URL: http://llvm.org/viewvc/llvm-project?rev=283408&view=rev Log: Fix strict-aliasing violation in typeinfo::hash_code()
Summary: The current implementation of `hash_code()` for uniqued RTTI strings violates strict aliasing by dereferencing a type-punned pointer. Specifically it generates a `const char**` pointer from the address of the `__name` member before casting it to `const size_t*` and dereferencing it to get the hash. This is really just a complex and incorrect way of writing `reinterpret_cast<size_t>(__name)`. This patch changes the conversion sequence so that it no longer contains UB. Reviewers: howard.hinnant, mclow.lists Subscribers: rjmccall, cfe-commits Differential Revision: https://reviews.llvm.org/D24012 Modified: libcxx/trunk/include/__config libcxx/trunk/include/typeinfo Modified: libcxx/trunk/include/__config URL: http://llvm.org/viewvc/llvm-project/libcxx/trunk/include/__config?rev=283408&r1=283407&r2=283408&view=diff ============================================================================== --- libcxx/trunk/include/__config (original) +++ libcxx/trunk/include/__config Wed Oct 5 17:55:10 2016 @@ -694,12 +694,6 @@ template <unsigned> struct __static_asse #define _NOALIAS #endif -#ifdef __GNUC__ -#define _LIBCPP_MAY_ALIAS __attribute__((__may_alias__)) -#else -#define _LIBCPP_MAY_ALIAS -#endif - #if __has_feature(cxx_explicit_conversions) || defined(__IBMCPP__) # define _LIBCPP_EXPLICIT explicit #else Modified: libcxx/trunk/include/typeinfo URL: http://llvm.org/viewvc/llvm-project/libcxx/trunk/include/typeinfo?rev=283408&r1=283407&r2=283408&view=diff ============================================================================== --- libcxx/trunk/include/typeinfo (original) +++ libcxx/trunk/include/typeinfo Wed Oct 5 17:55:10 2016 @@ -77,8 +77,6 @@ class _LIBCPP_EXCEPTION_ABI type_info type_info& operator=(const type_info&); type_info(const type_info&); - typedef size_t _LIBCPP_MAY_ALIAS _ASizeT; // Avoid strict-aliasing issues. - protected: #ifndef _LIBCPP_NONUNIQUE_RTTI_BIT const char* __type_name; @@ -119,7 +117,7 @@ public: _LIBCPP_INLINE_VISIBILITY size_t hash_code() const _NOEXCEPT #ifndef _LIBCPP_NONUNIQUE_RTTI_BIT - {return *reinterpret_cast<const _ASizeT *>(&__type_name);} + {return reinterpret_cast<size_t>(__type_name);} #else {if (!(__type_name & _LIBCPP_NONUNIQUE_RTTI_BIT)) return __type_name; const char *__ptr = name(); _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
