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

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

[olologin]

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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.

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

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

[Jonathan Wakely]

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.