> I've read GLIBC docs, and it _seems_ like "mission impossible", > to replace existing LIBC in the system - too many things (like ld) > depend on it. It is possible to have 2 versions of glibc coexisting, I have done that in the past in order to mainitin or reinstall old software, when for whatever reason compiling a new version was not suitable. You just have to be careful arranging that such applications as use incompatible library features 'see' the correct library version. I gues the same ideas would apply to installing a new version too. Then in principal you could build each tool that you need to use, so that it's linked to the other glibc, having two versions carefully organized until you've done them all! I am not sure at what point that differs from building a whole new gnu/linux installation, these source-based distros like gentoo or linux-from-scratch seem to have good webpages on doing this sort of thing (like what order you should do in, which you might only figure out the hard way on your own) even if you don't use the tools provided by the distribution. In fact distribution-documentation seems like the right place for finding out how different tools interact , rather than the documentation for just the library or just the compiler.
