Comment by kelnos
3 years ago
If what you're doing works for you, great, but in case it stops working at some point (or if for some reason you need to build on a current-gen distro version), you could also consider using this:
https://github.com/wheybags/glibc_version_header
It's a set of autogenerated headers that use symbol aliasing to allow you to build against your current version of glibc, but link to the proper older versioned symbols such that it will run on whatever oldest version of glibc you select.
glibc 2.34 has a hard break where you cannot compile with 2.34 and have it work with older glibc versions even if you use those version headers. It will always link __libc_start_main@GLIBC_2.34 (it's some kind of new security hardening measure, see https://sourceware.org/bugzilla/show_bug.cgi?id=23323).
Since additionally you also need to build all your dependencies with this same trick, including say libstdc++, it's really easiest to take GP's advice and build in a container with the old library versions. And nothing beats being able to actually test it on the old system.