build error --std=c++17 vs --std=c++23 -Wrestrict "may overlap up to 9223372036854775813 bytes at offset -3"

build error --std=c++17 vs --std=c++23 -Wrestrict "may overlap up to 9223372036854775813 bytes at offset -3"

[Jonny Grant]

Hello

Anyone else seeing an issue when using c++23 ?
gcc (Ubuntu 12.2.0-3ubuntu1) 12.2.0

The only change is to use --std=c++23

-Wrestrict is enabled by -Wall


#include <string>

typedef struct a_bc
{
    std::string a;
    std::string b;
} a_t;

void f()
{
    a_t c;

    c.a = " sdfsdf fsdfsdf fdfsfdsdf ";   // seems to need this long string to reproduce, down to 8 bytes it didn't
    c.b = "E";
}








$ g++ -O3 --std=c++23 -Wall -c -o gcc_err3 src/gcc_err3.cpp
In file included from /usr/include/c++/12/string:40,
                 from src/gcc_err3.cpp:4:
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>::assign(const _CharT*) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]’ at /usr/include/c++/12/bits/basic_string.h:1647:19,
    inlined from ‘constexpr std::__cxx11::basic_string<_CharT, _Traits, _Alloc>& std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::operator=(const _CharT*) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]’ at /usr/include/c++/12/bits/basic_string.h:815:28,
    inlined from ‘void f(const std::string&, bool, bool)’ at src/gcc_err3.cpp:17:13:
/usr/include/c++/12/bits/char_traits.h:431:56: warning: ‘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 [-Wrestrict]
  431 |         return static_cast<char_type*>(__builtin_memcpy(__s1, __s2, __n));
      |                                        ~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~

Re: build error --std=c++17 vs --std=c++23 -Wrestrict "may overlap up to 9223372036854775813 bytes at offset -3"

[Jonny Grant]

I saw there are quite a few similar issues reported.

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=Wrestrict

Maybe it is similar to this one

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105651

Jonny


On 11/02/2023 23:38, Jonny Grant wrote:
> Hello
> 
> Anyone else seeing an issue when using c++23 ?
> gcc (Ubuntu 12.2.0-3ubuntu1) 12.2.0
> 
> The only change is to use --std=c++23
> 
> -Wrestrict is enabled by -Wall
> 
> 
> #include <string>
> 
> typedef struct a_bc
> {
>     std::string a;
>     std::string b;
> } a_t;
> 
> void f()
> {
>     a_t c;
> 
>     c.a = " sdfsdf fsdfsdf fdfsfdsdf ";   // seems to need this long string to reproduce, down to 8 bytes it didn't
>     c.b = "E";
> }
> 
> 
> 
> 
> 
> 
> 
> 
> $ g++ -O3 --std=c++23 -Wall -c -o gcc_err3 src/gcc_err3.cpp
> In file included from /usr/include/c++/12/string:40,
>                  from src/gcc_err3.cpp:4:
> 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>::assign(const _CharT*) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]’ at /usr/include/c++/12/bits/basic_string.h:1647:19,
>     inlined from ‘constexpr std::__cxx11::basic_string<_CharT, _Traits, _Alloc>& std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::operator=(const _CharT*) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]’ at /usr/include/c++/12/bits/basic_string.h:815:28,
>     inlined from ‘void f(const std::string&, bool, bool)’ at src/gcc_err3.cpp:17:13:
> /usr/include/c++/12/bits/char_traits.h:431:56: warning: ‘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 [-Wrestrict]
>   431 |         return static_cast<char_type*>(__builtin_memcpy(__s1, __s2, __n));
>       |                                        ~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~

Re: build error --std=c++17 vs --std=c++23 -Wrestrict "may overlap up to 9223372036854775813 bytes at offset -3"

[Jonathan Wakely]

[-- Attachment #1: Type: text/plain, Size: 2914 bytes --]

On Sat, 11 Feb 2023, 23:38 Jonny Grant, <jg@jguk.org> wrote:

> Hello
>
> Anyone else seeing an issue when using c++23 ?
> gcc (Ubuntu 12.2.0-3ubuntu1) 12.2.0
>
> The only change is to use --std=c++23
>

With C++17 std::string is instantiated in the library, not in your code.
With C++20 your code instantiates it. That's the only reason the -std
option matters here.





> -Wrestrict is enabled by -Wall
>
>
> #include <string>
>
> typedef struct a_bc
> {
>     std::string a;
>     std::string b;
> } a_t;
>
> void f()
> {
>     a_t c;
>
>     c.a = " sdfsdf fsdfsdf fdfsfdsdf ";   // seems to need this long
> string to reproduce, down to 8 bytes it didn't
>     c.b = "E";
> }
>
>
>
>
>
>
>
>
> $ g++ -O3 --std=c++23 -Wall -c -o gcc_err3 src/gcc_err3.cpp
> In file included from /usr/include/c++/12/string:40,
>                  from src/gcc_err3.cpp:4:
> 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>::assign(const
> _CharT*) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc =
> std::allocator<char>]’ at /usr/include/c++/12/bits/basic_string.h:1647:19,
>     inlined from ‘constexpr std::__cxx11::basic_string<_CharT, _Traits,
> _Alloc>& std::__cxx11::basic_string<_CharT, _Traits,
> _Alloc>::operator=(const _CharT*) [with _CharT = char; _Traits =
> std::char_traits<char>; _Alloc = std::allocator<char>]’ at
> /usr/include/c++/12/bits/basic_string.h:815:28,
>     inlined from ‘void f(const std::string&, bool, bool)’ at
> src/gcc_err3.cpp:17:13:
> /usr/include/c++/12/bits/char_traits.h:431:56: warning: ‘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 [-Wrestrict]
>   431 |         return static_cast<char_type*>(__builtin_memcpy(__s1,
> __s2, __n));
>       |
> ~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~
>

Re: build error --std=c++17 vs --std=c++23 -Wrestrict "may overlap up to 9223372036854775813 bytes at offset -3"

[Jonny Grant]

On 12/02/2023 01:33, Jonathan Wakely wrote:
> 
> 
> On Sat, 11 Feb 2023, 23:38 Jonny Grant, <jg@jguk.org <mailto:jg@jguk.org>> wrote:
> 
>     Hello
> 
>     Anyone else seeing an issue when using c++23 ?
>     gcc (Ubuntu 12.2.0-3ubuntu1) 12.2.0
> 
>     The only change is to use --std=c++23
> 
> 
> With C++17 std::string is instantiated in the library, not in your code. With C++20 your code instantiates it. That's the only reason the -std option matters here.

Ok I see.

Re: build error --std=c++17 vs --std=c++23 -Wrestrict "may overlap up to 9223372036854775813 bytes at offset -3"

[Saifi Khan]

>  -------Original Message-------
>  From: Jonathan Wakely via Gcc-help <gcc-help@gcc.gnu.org>
>  To: Saifi Khan <saifi.khan@nishan.io>
>  Cc: gcc-help@gcc.gnu.org <gcc-help@gcc.gnu.org>
>  Subject: Re: build error --std=c++17 vs --std=c++23 -Wrestrict "may overlap up to 9223372036854775813 bytes at offset -3"
>  Sent: 2023-02-23 16:33
>  
>  On Thu, 23 Feb 2023 at 14:10, Saifi Khan wrote:
>  >
>  > Hi:
>  >
>  > Tried Jonny Grant's example
>  > g++ -O3 --std=c++23 -Wall -c repro_jg01.cc
>  
>  Context please - which example is that? 

#include <string>

typedef struct a_bc
{
    std::string a;
    std::string b;
} a_t;

void f()
{
    a_t c;

    c.a = " sdfsdf fsdfsdf fdfsfdsdf ";   // seems to need this long string to reproduce, down to 8 bytes it didn't
    c.b = "E";
}

Here is a verbatim copy of the the sample code, in which the OP encountered build error(s) with gcc 12.2.x

warm regards
Saifi.

Re: build error --std=c++17 vs --std=c++23 -Wrestrict "may overlap up to 9223372036854775813 bytes at offset -3"

[Jonathan Wakely]

On Thu, 23 Feb 2023 at 14:10, Saifi Khan wrote:
>
> Hi:
>
> Tried Jonny Grant's example
> g++ -O3 --std=c++23 -Wall -c repro_jg01.cc

Context please - which example is that? He's posted several and I'm
not going to go digging through them all.


>
> With the mainline build, the code compiles without any error.
>
> Environment
> - Linux  6.1.0-3-amd64 x86_64 GNU/Linux
> - Debian GLIBC 2.36-8) 2.36
> - gcc version 13.0.1 20230215 (experimental) (GCC)
>
> Curious to know, what changed in the mainline code ? Anyone knows the commit hash ?

If you don't tell us what you're compiling, we can't guess anything about it.

Re: build error --std=c++17 vs --std=c++23 -Wrestrict "may overlap up to 9223372036854775813 bytes at offset -3"

[Saifi Khan]

Hi:

Tried Jonny Grant's example
g++ -O3 --std=c++23 -Wall -c repro_jg01.cc

With the mainline build, the code compiles without any error.

Environment
- Linux  6.1.0-3-amd64 x86_64 GNU/Linux
- Debian GLIBC 2.36-8) 2.36
- gcc version 13.0.1 20230215 (experimental) (GCC)

Curious to know, what changed in the mainline code ? Anyone knows the commit hash ?


warm regards
Saifi.