Unlike most of the other issues I reported today, this one doesn't seem so harmless, or is it? How can I avoid it; should I just disable this warning? Removing the shared_ptr makes it go away, even though the shared_ptr is completely unused (in this code -- I need it in my actual code). % cat test.cpp #include <vector> #include <memory> struct D { const char *s = "a"; std::shared_ptr <int> p; D (std::shared_ptr <int> p_ = { }): p (p_) { } }; struct T { std::vector <char> v; T () { D d; v.insert (v.end (), d.s, d.s + 1); } }; int main () { T t; } % g++ -c -std=c++20 -Wall -Wextra -O2 test.cpp In file included from /usr/include/c++/12/vector:60, from test.cpp:1: In static member function ‘static constexpr _Tp* std::__copy_move<_IsMove, true, std::random_access_iterator_tag>::__copy_m(const _Tp*, const _Tp*, _Tp*) [with _Tp = char; bool _IsMove = true]’, inlined from ‘constexpr _OI std::__copy_move_a2(_II, _II, _OI) [with bool _IsMove = true; _II = char*; _OI = char*]’ at /usr/include/c++/12/bits/stl_algobase.h:495:30, inlined from ‘constexpr _OI std::__copy_move_a1(_II, _II, _OI) [with bool _IsMove = true; _II = char*; _OI = char*]’ at /usr/include/c++/12/bits/stl_algobase.h:522:42, inlined from ‘constexpr _OI std::__copy_move_a(_II, _II, _OI) [with bool _IsMove = true; _II = char*; _OI = char*]’ at /usr/include/c++/12/bits/stl_algobase.h:529:31, inlined from ‘constexpr _OI std::copy(_II, _II, _OI) [with _II = move_iterator<char*>; _OI = char*]’ at /usr/include/c++/12/bits/stl_algobase.h:620:7, inlined from ‘static _ForwardIterator std::__uninitialized_copy<true>::__uninit_copy(_InputIterator, _InputIterator, _ForwardIterator) [with _InputIterator = std::move_iterator<char*>; _ForwardIterator = char*]’ at /usr/include/c++/12/bits/stl_uninitialized.h:147:27, inlined from ‘_ForwardIterator std::uninitialized_copy(_InputIterator, _InputIterator, _ForwardIterator) [with _InputIterator = move_iterator<char*>; _ForwardIterator = char*]’ at /usr/include/c++/12/bits/stl_uninitialized.h:185:15, inlined from ‘constexpr _ForwardIterator std::__uninitialized_copy_a(_InputIterator, _InputIterator, _ForwardIterator, allocator<_Tp>&) [with _InputIterator = move_iterator<char*>; _ForwardIterator = char*; _Tp = char]’ at /usr/include/c++/12/bits/stl_uninitialized.h:372:37, inlined from ‘constexpr _ForwardIterator std::__uninitialized_move_if_noexcept_a(_InputIterator, _InputIterator, _ForwardIterator, _Allocator&) [with _InputIterator = char*; _ForwardIterator = char*; _Allocator = allocator<char>]’ at /usr/include/c++/12/bits/stl_uninitialized.h:397:2, inlined from ‘constexpr void std::vector<_Tp, _Alloc>::_M_range_insert(iterator, _ForwardIterator, _ForwardIterator, std::forward_iterator_tag) [with _ForwardIterator = const char*; _Tp = char; _Alloc = std::allocator<char>]’ at /usr/include/c++/12/bits/vector.tcc:801:9, inlined from ‘constexpr void std::vector<_Tp, _Alloc>::_M_insert_dispatch(iterator, _InputIterator, _InputIterator, std::__false_type) [with _InputIterator = const char*; _Tp = char; _Alloc = std::allocator<char>]’ at /usr/include/c++/12/bits/stl_vector.h:1779:19, inlined from ‘constexpr std::vector<_Tp, _Alloc>::iterator std::vector<_Tp, _Alloc>::insert(const_iterator, _InputIterator, _InputIterator) [with _InputIterator = const char*; <template-parameter-2-2> = void; _Tp = char; _Alloc = std::allocator<char>]’ at /usr/include/c++/12/bits/stl_vector.h:1481:22, inlined from ‘T::T()’ at test.cpp:17:14: /usr/include/c++/12/bits/stl_algobase.h:431:30: warning: ‘void* __builtin_memmove(void*, const void*, long unsigned int)’ writing 1 or more bytes into a region of size 0 overflows the destination [-Wstringop-overflow=] 431 | __builtin_memmove(__result, __first, sizeof(_Tp) * _Num); | ~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ In file included from /usr/include/x86_64-linux-gnu/c++/12/bits/c++allocator.h:33, from /usr/include/c++/12/bits/allocator.h:46, from /usr/include/c++/12/vector:61: In member function ‘_Tp* std::__new_allocator<_Tp>::allocate(size_type, const void*) [with _Tp = char]’, inlined from ‘constexpr _Tp* std::allocator< <template-parameter-1-1> >::allocate(std::size_t) [with _Tp = char]’ at /usr/include/c++/12/bits/allocator.h:188:40, inlined from ‘static constexpr _Tp* std::allocator_traits<std::allocator<_Up> >::allocate(allocator_type&, size_type) [with _Tp = char]’ at /usr/include/c++/12/bits/alloc_traits.h:464:28, inlined from ‘constexpr std::_Vector_base<_Tp, _Alloc>::pointer std::_Vector_base<_Tp, _Alloc>::_M_allocate(std::size_t) [with _Tp = char; _Alloc = std::allocator<char>]’ at /usr/include/c++/12/bits/stl_vector.h:378:33, inlined from ‘constexpr std::_Vector_base<_Tp, _Alloc>::pointer std::_Vector_base<_Tp, _Alloc>::_M_allocate(std::size_t) [with _Tp = char; _Alloc = std::allocator<char>]’ at /usr/include/c++/12/bits/stl_vector.h:375:7, inlined from ‘constexpr void std::vector<_Tp, _Alloc>::_M_range_insert(iterator, _ForwardIterator, _ForwardIterator, std::forward_iterator_tag) [with _ForwardIterator = const char*; _Tp = char; _Alloc = std::allocator<char>]’ at /usr/include/c++/12/bits/vector.tcc:787:40, inlined from ‘constexpr void std::vector<_Tp, _Alloc>::_M_insert_dispatch(iterator, _InputIterator, _InputIterator, std::__false_type) [with _InputIterator = const char*; _Tp = char; _Alloc = std::allocator<char>]’ at /usr/include/c++/12/bits/stl_vector.h:1779:19, inlined from ‘constexpr std::vector<_Tp, _Alloc>::iterator std::vector<_Tp, _Alloc>::insert(const_iterator, _InputIterator, _InputIterator) [with _InputIterator = const char*; <template-parameter-2-2> = void; _Tp = char; _Alloc = std::allocator<char>]’ at /usr/include/c++/12/bits/stl_vector.h:1481:22, inlined from ‘T::T()’ at test.cpp:17:14: /usr/include/c++/12/bits/new_allocator.h:137:55: note: at offset 1 into destination object of size 1 allocated by ‘operator new’ 137 | return static_cast<_Tp*>(_GLIBCXX_OPERATOR_NEW(__n * sizeof(_Tp))); | ^ In static member function ‘static constexpr _Tp* std::__copy_move<_IsMove, true, std::random_access_iterator_tag>::__copy_m(const _Tp*, const _Tp*, _Tp*) [with _Tp = char; bool _IsMove = true]’, inlined from ‘constexpr _OI std::__copy_move_a2(_II, _II, _OI) [with bool _IsMove = true; _II = char*; _OI = char*]’ at /usr/include/c++/12/bits/stl_algobase.h:495:30, inlined from ‘constexpr _OI std::__copy_move_a1(_II, _II, _OI) [with bool _IsMove = true; _II = char*; _OI = char*]’ at /usr/include/c++/12/bits/stl_algobase.h:522:42, inlined from ‘constexpr _OI std::__copy_move_a(_II, _II, _OI) [with bool _IsMove = true; _II = char*; _OI = char*]’ at /usr/include/c++/12/bits/stl_algobase.h:529:31, inlined from ‘constexpr _OI std::copy(_II, _II, _OI) [with _II = move_iterator<char*>; _OI = char*]’ at /usr/include/c++/12/bits/stl_algobase.h:620:7, inlined from ‘static _ForwardIterator std::__uninitialized_copy<true>::__uninit_copy(_InputIterator, _InputIterator, _ForwardIterator) [with _InputIterator = std::move_iterator<char*>; _ForwardIterator = char*]’ at /usr/include/c++/12/bits/stl_uninitialized.h:147:27, inlined from ‘_ForwardIterator std::uninitialized_copy(_InputIterator, _InputIterator, _ForwardIterator) [with _InputIterator = move_iterator<char*>; _ForwardIterator = char*]’ at /usr/include/c++/12/bits/stl_uninitialized.h:185:15, inlined from ‘constexpr _ForwardIterator std::__uninitialized_copy_a(_InputIterator, _InputIterator, _ForwardIterator, allocator<_Tp>&) [with _InputIterator = move_iterator<char*>; _ForwardIterator = char*; _Tp = char]’ at /usr/include/c++/12/bits/stl_uninitialized.h:372:37, inlined from ‘constexpr _ForwardIterator std::__uninitialized_move_if_noexcept_a(_InputIterator, _InputIterator, _ForwardIterator, _Allocator&) [with _InputIterator = char*; _ForwardIterator = char*; _Allocator = allocator<char>]’ at /usr/include/c++/12/bits/stl_uninitialized.h:397:2, inlined from ‘constexpr void std::vector<_Tp, _Alloc>::_M_range_insert(iterator, _ForwardIterator, _ForwardIterator, std::forward_iterator_tag) [with _ForwardIterator = const char*; _Tp = char; _Alloc = std::allocator<char>]’ at /usr/include/c++/12/bits/vector.tcc:801:9, inlined from ‘constexpr void std::vector<_Tp, _Alloc>::_M_insert_dispatch(iterator, _InputIterator, _InputIterator, std::__false_type) [with _InputIterator = const char*; _Tp = char; _Alloc = std::allocator<char>]’ at /usr/include/c++/12/bits/stl_vector.h:1779:19, inlined from ‘constexpr std::vector<_Tp, _Alloc>::iterator std::vector<_Tp, _Alloc>::insert(const_iterator, _InputIterator, _InputIterator) [with _InputIterator = const char*; <template-parameter-2-2> = void; _Tp = char; _Alloc = std::allocator<char>]’ at /usr/include/c++/12/bits/stl_vector.h:1481:22, inlined from ‘T::T()’ at test.cpp:17:14: /usr/include/c++/12/bits/stl_algobase.h:431:30: warning: ‘void* __builtin_memmove(void*, const void*, long unsigned int)’ writing 1 or more bytes into a region of size 0 overflows the destination [-Wstringop-overflow=] 431 | __builtin_memmove(__result, __first, sizeof(_Tp) * _Num); | ~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ In member function ‘_Tp* std::__new_allocator<_Tp>::allocate(size_type, const void*) [with _Tp = char]’, inlined from ‘constexpr _Tp* std::allocator< <template-parameter-1-1> >::allocate(std::size_t) [with _Tp = char]’ at /usr/include/c++/12/bits/allocator.h:188:40, inlined from ‘static constexpr _Tp* std::allocator_traits<std::allocator<_Up> >::allocate(allocator_type&, size_type) [with _Tp = char]’ at /usr/include/c++/12/bits/alloc_traits.h:464:28, inlined from ‘constexpr std::_Vector_base<_Tp, _Alloc>::pointer std::_Vector_base<_Tp, _Alloc>::_M_allocate(std::size_t) [with _Tp = char; _Alloc = std::allocator<char>]’ at /usr/include/c++/12/bits/stl_vector.h:378:33, inlined from ‘constexpr std::_Vector_base<_Tp, _Alloc>::pointer std::_Vector_base<_Tp, _Alloc>::_M_allocate(std::size_t) [with _Tp = char; _Alloc = std::allocator<char>]’ at /usr/include/c++/12/bits/stl_vector.h:375:7, inlined from ‘constexpr void std::vector<_Tp, _Alloc>::_M_range_insert(iterator, _ForwardIterator, _ForwardIterator, std::forward_iterator_tag) [with _ForwardIterator = const char*; _Tp = char; _Alloc = std::allocator<char>]’ at /usr/include/c++/12/bits/vector.tcc:787:40, inlined from ‘constexpr void std::vector<_Tp, _Alloc>::_M_insert_dispatch(iterator, _InputIterator, _InputIterator, std::__false_type) [with _InputIterator = const char*; _Tp = char; _Alloc = std::allocator<char>]’ at /usr/include/c++/12/bits/stl_vector.h:1779:19, inlined from ‘constexpr std::vector<_Tp, _Alloc>::iterator std::vector<_Tp, _Alloc>::insert(const_iterator, _InputIterator, _InputIterator) [with _InputIterator = const char*; <template-parameter-2-2> = void; _Tp = char; _Alloc = std::allocator<char>]’ at /usr/include/c++/12/bits/stl_vector.h:1481:22, inlined from ‘T::T()’ at test.cpp:17:14: /usr/include/c++/12/bits/new_allocator.h:137:55: note: at offset 1 into destination object of size 1 allocated by ‘operator new’ 137 | return static_cast<_Tp*>(_GLIBCXX_OPERATOR_NEW(__n * sizeof(_Tp)));
At least I found a work-around (for now): Moving, rather than copying the (emtpy) shared_ptr parameter to the (unused) shared_ptr member avoids the warning. Still, I'd like to know if this is an actual bug, or another false positive.
I think it's a false positive, GCC 13 no longer diagnoses this so it's likely a duplicate of another bug. Might be either suppressed in libstdc++ or avoided in the diagnostic code.
Fixed by r13-4393-gcca06f0d6d76b0
Thanks. I just got another similar one, this time with string.insert. But I guess it's pointless to dissect this one, or do you need more examples for your test suite?
So it's a dup of one of these: PR libstdc++/107852 PR libstdc++/106199 PR libstdc++/100366
(In reply to Frank Heckenbach from comment #4) > Thanks. > > I just got another similar one, this time with string.insert. But I guess > it's pointless to dissect this one, or do you need more examples for your > test suite? Actually, on a closer look, this one is a bit different. Do you need an example for that, or should it also be fixed in trunk? In static member function 'static constexpr std::char_traits<char>::char_type* std::char_traits<char>::copy(char_type*, const char_type*, std::size_t)', inlined from 'static constexpr void std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::_S_copy(_CharT*, const _CharT*, size_type) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]' at /usr/include/c++/12/bits/basic_string.h:423:21, inlined from 'constexpr std::__cxx11::basic_string<_CharT, _Traits, _Allocator>& std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::_M_replace(size_type, size_type, const _CharT*, size_type) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]' at /usr/include/c++/12/bits/basic_string.tcc:532:22, inlined from 'constexpr std::__cxx11::basic_string<_CharT, _Traits, _Alloc>& std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::replace(size_type, size_type, const _CharT*, size_type) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]' at /usr/include/c++/12/bits/basic_string.h:2171:19, inlined from 'constexpr std::__cxx11::basic_string<_CharT, _Traits, _Alloc>& std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::insert(size_type, const _CharT*) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]' at /usr/include/c++/12/bits/basic_string.h:1928:22, inlined from 'std::string mpf_to_string(mpf_class, size_t)' at pi.cpp:102:12: /usr/include/c++/12/bits/char_traits.h:431:56: error: 'void* __builtin_memcpy(void*, const void*, long unsigned int)' accessing 9223372036854775810 or more bytes at offsets -4611686018427387902 and [-4611686018427387903, 4611686018427387904] may overlap up to 9223372036854775813 bytes at offset -3 [-Werror=restrict] 431 | return static_cast<char_type*>(__builtin_memcpy(__s1, __s2, __n)); | ~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~
Probably either PR 105329 or PR 105651