Re: [PATCH 0/7] [gdb/build] Fix -std=c++20 issues

[Tom de Vries <tdevries@suse.de>]

On 8/16/23 20:27, Tom Tromey wrote:
>>>>>> "Tom" == Tom de Vries via Gdb-patches <gdb-patches@sourceware.org> writes:
> 
> Tom> I tried building gdb using -std=c++20, an ran into a few issues.
> Tom> This series contains fixes for most of them.
> 
> Thanks for doing this.  I read these & sent one comment.
> The rest look ok to me.
> 
> Tom> But the other one, in remote_target::thread_info_to_thread_handle remains
> Tom> unfixed:
> Tom> ...
> Tom> gdb::byte_vector
> Tom> remote_target::thread_info_to_thread_handle (struct thread_info *tp)
> Tom> {
> Tom>   remote_thread_info *priv = get_remote_thread_info (tp);
> Tom>   return priv->thread_handle;
> 
> First, I wonder if we even care about this copying.
> 

Well, I care because I run into a build error:
...
In file included from /usr/include/c++/12/ext/alloc_traits.h:34,
                  from /usr/include/c++/12/unordered_map:41,
                  from /usr/include/c++/12/functional:61,
                  from /data/vries/gdb/src/gdb/../gdbsupport/ptid.h:35,
                  from 
/data/vries/gdb/src/gdb/../gdbsupport/common-defs.h:206,
                  from /data/vries/gdb/src/gdb/defs.h:26,
                  from /data/vries/gdb/src/gdb/remote.c:22:
/usr/include/c++/12/bits/alloc_traits.h: In instantiation of ‘static 
constexpr _Alloc std::allocator_traits< <template-parameter-1-1> 
 >::select_on_container_copy_construction(const _Alloc&) [with _Alloc = 
gdb::default_init_allocator<unsigned char, 
std::pmr::polymorphic_allocator<unsigned char> >]’:
/usr/include/c++/12/ext/alloc_traits.h:98:63:   required from ‘static 
constexpr _Alloc __gnu_cxx::__alloc_traits<_Alloc, 
<template-parameter-1-2> >::_S_select_on_copy(const _Alloc&) [with 
_Alloc = gdb::default_init_allocator<unsigned char, 
std::pmr::polymorphic_allocator<unsigned char> >; 
<template-parameter-1-2> = unsigned char]’
/usr/include/c++/12/bits/stl_vector.h:598:34:   required from ‘constexpr 
std::vector<_Tp, _Alloc>::vector(const std::vector<_Tp, _Alloc>&) [with 
_Tp = unsigned char; _Alloc = gdb::default_init_allocator<unsigned char, 
std::pmr::polymorphic_allocator<unsigned char> >]’
/data/vries/gdb/src/gdb/remote.c:14557:16:   required from here
/usr/include/c++/12/bits/alloc_traits.h:402:25: error: could not convert 
‘std::allocator_traits<gdb::default_init_allocator<unsigned char, 
std::pmr::polymorphic_allocator<unsigned char> > >::_S_select<const 
gdb::default_init_allocator<unsigned char, 
std::pmr::polymorphic_allocator<unsigned char> > >((* & __rhs), 0)’ from 
‘std::pmr::polymorphic_allocator<unsigned char>’ to 
‘gdb::default_init_allocator<unsigned char, 
std::pmr::polymorphic_allocator<unsigned char> >’
   402 |       { return _S_select(__rhs, 0); }
       |                ~~~~~~~~~^~~~~~~~~~
       |                         |
       | 
std::pmr::polymorphic_allocator<unsigned char>
...

> But if we do, it could return a const reference and linux-thread-db
> could be modified to cache the byte_vector in thread_db_thread_info.

I've managed to get that working, submitted here ( 
https://sourceware.org/pipermail/gdb-patches/2023-August/201727.html ).

Thanks,
- Tom