* Nicholas Piggin via Libc-alpha: > We may or may not be getting a new ABI that will use instructions not > supported by old processors. > > https://sourceware.org/legacy-ml/binutils/2019-05/msg00331.html > > Current ABI continues to work of course and be the default for some > time, but building for new one would give some opportunity to drop > such support for old procs, at least for glibc.
If I recall correctly, during last year's GNU Tools Cauldron, I think it was pretty clear that this was only to be used for intra-DSO ABIs, not cross-DSO optimization. Relocatable object files have an ABI, too, of course, so that's why there's a ABI documentation needed. For cross-DSO optimization, the link editor would look at the DSO being linked in, check if it uses the -mfuture ABI, and apply some shortcuts. But at that point, if the DSO is swapped back to a version built without -mfuture, it no longer works with those newly linked binaries against the -mfuture version. Such a thing is a clear ABI bump, and based what I remember from Cauldron, that is not the plan here. (I don't have any insider knowledge—I just don't want people to read this think: gosh, yet another POWER ABI bump. But the PCREL stuff *is* exciting!)
