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libstdc++: More fixes for null pointers used with std::char_traits

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The std::char_traits member functions require that [p,p+n) is a valid
range, which is true for p==nullptr iff n==0. But we must not call
memcpy, memset etc, in that case, as they require non-null pointers even
when n==0.

This std::char_traits<char> and std::char_traits<wchar_t> explicit
specializations are already correct, but the primary template has some
bugs.

libstdc++-v3/ChangeLog:

	* include/bits/char_traits.h (char_traits::copy): Return without
	using memcpy if n==0.
	(char_traits::assign): Likewise for memset.
This commit is contained in:
Jonathan Wakely 2023-03-28 11:12:58 +01:00
parent bf78b43873
commit cb6f663f9d
1 changed files with 8 additions and 4 deletions
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12
libstdc++-v3/include/bits/char_traits.h
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@ -263,6 +263,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
char_traits<_CharT>::
copy(char_type* __s1, const char_type* __s2, std::size_t __n)
{
if (__n == 0)
return __s1;
#if __cplusplus >= 202002L
if (std::__is_constant_evaluated())
{
@ -271,7 +273,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
return __s1;
}
#endif
__builtin_memcpy(__s1, __s2, __n * sizeof(char_type));
return __s1;
}
@ -293,9 +294,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
if _GLIBCXX17_CONSTEXPR (sizeof(_CharT) == 1 && __is_trivial(_CharT))
{
unsigned char __c;
__builtin_memcpy(&__c, __builtin_addressof(__a), 1);
__builtin_memset(__s, __c, __n);
if (__n)
{
unsigned char __c;
__builtin_memcpy(&__c, __builtin_addressof(__a), 1);
__builtin_memset(__s, __c, __n);
}
}
else
{