Re: How to make sure GCC links only with old runtime that is supplied with the system

[Jonathan Wakely <jwakely.gcc@gmail.com>]

On Thu, 20 Oct 2022 at 11:35, olologin via Gcc-help
<gcc-help@gcc.gnu.org> wrote:
>
> Hi everyone,
> I am kind of new to cross-compiling (if we can call my task like this), so
> maybe my question is kind of stupid.
>
> I need to build my project for old runtimes (libstdc++, libgcc_s, etc) that
> came with GCC 6, but I can build my sourcecode only with newest C++
> features, so I chose GCC 12 for this.
> Of course my API is old enough to support GCC 6. And of course I am aware
> of potential risks (like some implementations that can be missing in the
> old runtime).
>
> Currently I am doing this in a very hacky way, and build my project in a
> container that looks like this:
> https://gist.github.com/olologin/b4ba2db91fc5c526d625715b39ac4579
> As you can see, starting from line 73 it gets hacky because I could not
> find a better way to make sure GCC 12 links my code with GCC 6 runtime
> instead of GCC 12.
> So I decided that I should just get rid of all *.so, *.a and *.o files in
> GCC12 install directory, and later when I build my project I point GCC12 on
> GCC6 runtime with -Wl,-L.

This is very undefined and unsupported.

>
> Is there a better way to do this? Maybe I am missing something.
> Thanks in advance.

The GCC Developer Toolset on RHEL and CentOS solves this properly. The
new GCC in the toolset links to libstdc++_nonshared.a which provides
all the new symbols not present in the base version of libstdc++.so.6
from the system compiler. The new additions are statically linked, and
everything that's already present in the base libstdc++.so.6 gets used
from there.

Or you can just statically link your whole project.