Binary compatibility is also important to glibc, which is why they go to the trouble of carrying stubs that implement the older ABI for any functions that chang

Binary compatibility is also important to glibc, which is why they go to the trouble of carrying stubs that implement the older ABI for any functions that change ABI. Binaries linked against older library versions will continue to work with newer versions, through the magic of symbol versioning. This method will presumably be used to carry the old malloc implementation around for older emacs binaries that rely on it (whereas newly linked binaries will see the new API and ABI).