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[UCRT] Fix __crt_fast_encode_pointer

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GCC was optimizing away the xor with __security_cookie when passing nullptr_t, because the return value was also nullptr_t, assuming it must be nullptr.
This commit is contained in:
Timo Kreuzer 2025-07-22 14:18:58 +03:00
parent 6891f03119
commit e2deec8235
1 changed files with 22 additions and 6 deletions
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28
sdk/lib/vcruntime/inc/internal_shared.h
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@ -185,18 +185,34 @@ template<typename T>
__forceinline
T __crt_fast_encode_pointer(T ptr)
{
union { T Ptr; uintptr_t Uint; } u = { ptr };
u.Uint ^= __security_cookie;
return u.Ptr;
return reinterpret_cast<T>(
reinterpret_cast<uintptr_t>(ptr) ^ __security_cookie);
}
// Workaround for nullptr encoding.
// Casting nullptr_t to uinttptr_t is not allowed in C++. Using a union compiles,
// but GCC will optimize it to a constant zero, which is not what we want.
class encoded_nullptr_t
{
void* m_ptr;
public:
inline encoded_nullptr_t(void* P) : m_ptr(P) { };
template<typename T> operator T*() { return (T*)m_ptr; }
};
__forceinline
encoded_nullptr_t __crt_fast_encode_pointer(decltype(nullptr) ptr)
{
void* encoded_null = __crt_fast_encode_pointer((void*)ptr);
return encoded_nullptr_t(encoded_null);
}
template<typename T>
__forceinline
T __crt_fast_decode_pointer(T ptr)
{
union { T Ptr; uintptr_t Uint; } u = { ptr };
u.Uint ^= __security_cookie;
return u.Ptr;
return reinterpret_cast<T>(
reinterpret_cast<uintptr_t>(ptr) ^ __security_cookie);
}
template<typename T>