Re: [RFC] [gdb/build] Require c++17 compiler

[Pedro Alves <pedro@palves.net>]

On 2023-10-05 07:54, Tom de Vries via Gdb-patches wrote:

> Consequently, the NEWS item mentions gcc 9 as an example compiler to use.
> 
> My understanding of using gcc 5-8 is that it works as long as gdb doesn't use
> not yet available language features.  Of course the set of used language
> features may change in time, so what compiler still works may change.
> 
> Problems can arise when shared libs starts to have C++17 based APIs (or
> somehow expose instantiations of such classes).  If compiled with a compiler
> in which c++17 support was still experimental, it may be incompatible when
> linking with:
> - code compiled with a compiler with non-experimental c++17 support, or
> - code compiled with a different compiler with experimental c++17 support.
> 
> Looking at the current implementation of our only shared lib:
> libinproctrace.so, I couldn't spot any c++ usage in the API, so I'm assuming
> this problem is not likely to happen.

I think this concern goes beyond libinproctrace.co, and extends to APIs exposed
by libstdc++.  E.g., (and I haven't checked), say that the libstdc++ from GCC 6
implemented some C++17 library feature that we start using, but then the API/ABI of
that library feature changed in later GCCs.  Compiling GDB with GCC 6 and
expecting that it runs on a system with libstdc++ from GCC 9 may not work.  I don't
know whether there's some document or page or wiki or some such somewhere documenting
such ABI breakages.  +1 on requiring GCC 9, unless it proves troublesomely "too new"
in practice, which I hope not.