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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

llvm-svn: 283408
This commit is contained in:
Eric Fiselier 2016-10-05 22:55:10 +00:00
parent 5d0fbbbca1
commit ae34c56ee7
2 changed files with 1 additions and 9 deletions
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6
libcxx/include/__config
View File

@ -694,12 +694,6 @@ template <unsigned> struct __static_assert_check {};
#define _NOALIAS #define _NOALIAS
#endif #endif
#ifdef __GNUC__
#define _LIBCPP_MAY_ALIAS __attribute__((__may_alias__))
#else
#define _LIBCPP_MAY_ALIAS
#endif
#if __has_feature(cxx_explicit_conversions) || defined(__IBMCPP__) #if __has_feature(cxx_explicit_conversions) || defined(__IBMCPP__)
# define _LIBCPP_EXPLICIT explicit # define _LIBCPP_EXPLICIT explicit
#else #else

4
libcxx/include/typeinfo
View File

@ -77,8 +77,6 @@ class _LIBCPP_EXCEPTION_ABI type_info
type_info& operator=(const type_info&); type_info& operator=(const type_info&);
type_info(const type_info&); type_info(const type_info&);
typedef size_t _LIBCPP_MAY_ALIAS _ASizeT; // Avoid strict-aliasing issues.
protected: protected:
#ifndef _LIBCPP_NONUNIQUE_RTTI_BIT #ifndef _LIBCPP_NONUNIQUE_RTTI_BIT
const char* __type_name; const char* __type_name;
@ -119,7 +117,7 @@ public:
_LIBCPP_INLINE_VISIBILITY _LIBCPP_INLINE_VISIBILITY
size_t hash_code() const _NOEXCEPT size_t hash_code() const _NOEXCEPT
#ifndef _LIBCPP_NONUNIQUE_RTTI_BIT #ifndef _LIBCPP_NONUNIQUE_RTTI_BIT
{return *reinterpret_cast<const _ASizeT *>(&__type_name);} {return reinterpret_cast<size_t>(__type_name);}
#else #else
{if (!(__type_name & _LIBCPP_NONUNIQUE_RTTI_BIT)) return __type_name; {if (!(__type_name & _LIBCPP_NONUNIQUE_RTTI_BIT)) return __type_name;
const char *__ptr = name(); const char *__ptr = name();