R – Linking against a specific shared library version in linux

You do not have to use PIC code in shared objects (as you have discovered you can use the -mimpure-text option to allow that).

That said, non-PIC code in shared objects are more heavyweight. With PIC code, the text pages in memory are just direct memory mappings of the text pages on disk. This means that if multiple processes are using the shared object, they can share the memory page.

But if you do not have PIC code, when the runtime linker loads the shared object, it will have to apply fixups to the text pages. This means that every processes that uses the shared object will have it's own unique version of any text page that has a fixup on it (even if the shared object is loaded at the same address as copy-on-write only notices that the page was modified and not that it was modified in the same way).

To me, the important issue is whether you will simultaneously have multiple processes running that each load the shared object. If you do, it is definitely worth making sure all the code within the SO is PIC.

But if that is not the case and only a single process has the shared object loaded, it's not nearly as critical.

I think this is very annoying, and I think it is arrogant to call a feature "useless" because it has problems dealing with certain use cases. The biggest problem with the glibc approach is that it hard-codes paths to system libraries (gconv as well as nss), and thus it breaks when people try to run a static binary on a Linux distribution different from the one it was built for.

Anyway, you can work around the gconv issue by setting GCONV_PATH to point to the appropriate location, this allowed me to take binaries built on Ubuntu and run them on Red Hat.