On 10/12/2016 10:17 AM, John David Anglin wrote: > On 2016-10-12 9:48 AM, Jason Merrill wrote: >> On Wed, Oct 12, 2016 at 4:02 AM, Jakub Jelinek <ja...@redhat.com> wrote: >>> On Wed, Oct 12, 2016 at 09:52:04AM +0200, Florian Weimer wrote: >>>> dropping the alignment means that the padding before the lock member >>>> vanishes. Consequently, we have just created a silent ABI change in >>>> application code, which is a big no-no. >>> Sure, it would be an ABI change, but how many users would it affect? >>> >>>> Since this is PA-RISC, which is essentially dead (neither HPE nor Debian >>>> ship it anymore), I stand by my suggestion to bump the fundamental >>>> alignment >>> Or just drop support for a dead arch? >>> >>>> instead. Sure, it is a bit inefficient, but this will only affect PA-RISC >>>> users. It does not even cause work for PA-RISC porters. Conversely, if we >>>> work on this to come up with a different fix, many more people will be >>>> affected (because they don't get all the nice things we could work on >>>> instead), and we may need to maintain a special GCC kludge for the >>>> alternative solution, impacting GCC developers in particular. >>> But sure, bumping malloc alignment is probably easiest. And people who want >>> performance have better options than to stay on 32-bit PA-RISC anyway. >> Or we could do nothing and tell people to ignore the harmless warning. > The warning is an issue because of -Werror. However, it appears easy to > suppress it in the PA > backend. I have a patch that I'm testing. > > We are discussing offline regarding the glibc issue. It easy to bump the > alignment of malloc > but I take Jakub's point and maybe we should break the ABI. Debian unstable > churns > quickly, and I think we would be better off being consistent with the current > max_align_t > and 8-byte aligned malloc.
I am against breaking the ABI. I would rather see us bump malloc alignment up to 16-bytes. The last time I changed this alignment it _immediately_ broken libstdc++ boostrap because it's using exactly the kind of embedded pthread_mutext_t we're talking about breaking. So in that case the debian builds in unstable broke right away, and I had to revert the change. We'd have to BinNMU a bunch of things to get this working again. Again I think our two options are, in my order of preference: - Disable the warning via a PA backend change. - Bump malloc alignment. I am sensitive to the first change being something that carries with it extra maintenance burden, so I'm happy to see the second solution chosen if that's what everyone wants (Florian's suggestion). -- Cheers, Carlos.