AppImageKit-checkrt/README.md

# The problem

Some projects require newer C++ standards to build them. To keep the glibc dependency low you can
build a newer GCC version on an older distro and use it to compile the project.
This project however will now require a newer version of the `libstdc++.so.6` library than available on that distro.
Bundling `libstdc++.so.6` however will in most cases break compatibility with distros that have a newer library
version installed into their system than the bundled one. So blindly bundling the library is not reliable.

By the way, while this is primarily an issue with `libstdc++.so.6` in some rare cases this might also occur with `libgcc_s.so.1`.
That's because both libraries are part of GCC.


# The solution

You would have to know the library version of the host system and decide whether to use a bundled library or not before the
application is started. This is exactly what the patched AppRun binary does.
It will search for `usr/optional/libstdc++/libstdc++.so.6` and `usr/optional/libgcc_s/libgcc_s.so.1` inside the AppImage or AppDir.
If found it will compare their internal versions with the ones found on the system and prepend their paths to `LD_LIBRARY_PATH` if necessary.
You should also put `exec.so` into `usr/optional`.