https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109299
Bug ID: 109299
Summary: wrong warning on std::wstring with -O2 -std=c++20
-D_FORTIFY_SOURCE=2
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: benni.buch at gmail dot com
Target Milestone: ---
I run into this by using googletest with CMake in release mode.
```
#include <string>
static std::wstring foo(std::wstring text = {}) {
text.resize(42);
return text;
}
int main() {
foo();
}
```
```
$ g++ -O2 -std=c++20 -D_FORTIFY_SOURCE=2 main.cpp
In file included from /usr/include/features.h:486,
from
/usr/include/x86_64-linux-gnu/c++/12/bits/os_defines.h:39,
from
/usr/include/x86_64-linux-gnu/c++/12/bits/c++config.h:655,
from /usr/include/c++/12/string:38,
from main.cpp:1:
In function ‘wchar_t* wmemcpy(wchar_t*, const wchar_t*, size_t)’,
inlined from ‘static constexpr std::char_traits<wchar_t>::char_type*
std::char_traits<wchar_t>::copy(char_type*, const char_type*, std::size_t)’ at
/usr/include/c++/12/bits/char_traits.h:558:16,
inlined from ‘constexpr std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>::basic_string(std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&&)
[with _CharT = wchar_t; _Traits = std::char_traits<wchar_t>; _Alloc =
std::allocator<wchar_t>]’ at /usr/include/c++/12/bits/basic_string.h:675:23,
inlined from ‘std::wstring foo(std::wstring)’ at main.cpp:5:12,
inlined from ‘int main()’ at main.cpp:9:8:
/usr/include/x86_64-linux-gnu/bits/wchar2.h:42:10: warning: call to
‘__wmemcpy_chk_warn’ declared with attribute warning: wmemcpy called with
length bigger than size of destination buffer [-Wattribute-warning]
42 | return __glibc_fortify_n (wmemcpy, __n, sizeof (wchar_t),
| ^~~~~~~~~~~~~~~~~
```
On stackoverflow.com you can already find a few discussion about it:
- https://stackoverflow.com/questions/75689057
user17732522 reduced it to:
```
#include <wchar.h>
wchar_t* _M_dataplus;
int _M_string_length;
wchar_t _M_local_buf[4];
wchar_t _M_local_buf2[4];
void g();
void f() {
g();
_M_string_length = 4;
if (_M_dataplus == _M_local_buf)
wmemcpy(_M_local_buf2, _M_local_buf, _M_string_length + 1);
}
```
```
$ g++ -O1 -D_FORTIFY_SOURCE=2 -c main.cpp
In file included from /usr/include/features.h:486,
from
/usr/include/x86_64-linux-gnu/bits/libc-header-start.h:33,
from /usr/include/wchar.h:27,
from main.cpp:1:
In function ‘wchar_t* wmemcpy(wchar_t*, const wchar_t*, size_t)’,
inlined from ‘void f()’ at main.cpp:15:16:
/usr/include/x86_64-linux-gnu/bits/wchar2.h:42:10: warning: call to
‘__wmemcpy_chk_warn’ declared with attribute warning: wmemcpy called with
length bigger than size of destination buffer [-Wattribute-warning]
42 | return __glibc_fortify_n (wmemcpy, __n, sizeof (wchar_t),
| ^~~~~~~~~~~~~~~~~
```
