> On 12 Nov 2022, at 04:20, Wookey <wookey@xxxxxxxxxxxx> wrote: > > On 2022-11-11 10:19 +0100, Florian Weimer wrote: > > Hi. I've started looking into the 64-bit time_t transition for 32-bit armhf > in Debian. We are currently doing a preliminary bootstrap to see what > breaks. We strongly suspect that only a wholesale rebuild for the new > ABI (i.e a new Debian architecture) is practical, but have not yet > entirely ruled out attempting a migration within the existing armhf > arch. > > [snip] > >> * Sam James >> >>> In Gentoo, we've been planning out what we should do for time64 on >>> glibc [0] and concluded that we need some support in glibc for a newer >>> option. I'll outline why below. >>> >>> Proposal: glibc gains two new build-time configure options: >>> * --enable-hard-time64 >>> * --enable-hard-lfs > > I don't quite follow the logic of this. glibc already has build-time macros to set these two things: > _TIME_BITS=64 > _FILE_OFFSET_BITS=64 > > why do we need configure options too? How do you make sure that every program built uses it? Not every program respects CPPFLAGS and even in CFLAGS, it's a bit of a nuisance. If you patch GCC, you don't cover Clang. If you patch system compilers, that's messy but also doesn't help with custom-built programs. Of course, we could just patch glibc and cheerily jam it in the headers, but we run into the kind of problems that Joseph Myers mentions then, I think (basically I'd want to make sure we do it right.) > >>> We're now (possibly) on the eve of an autoconf 2.72 release which contains two changes >>> of note [2][3] >>> 1. addition of a new AC_SYS_YEAR2038 macro; >>> 2. making AC_SYS_LARGEFILE change behaviour to imply AC_SYS_YEAR2038. > > Which is the opposite way round to glibc, where _TIME_BITS=64 requires > _FILE_OFFSET_BITS=64, but not the other way round > (_FILE_OFFSET_BITS=64, can be set on its own). Am I misunderstanding something here? > I wonder the same. I don't think it's obvious, and it may not be obvious to people writing software using autoconf either... > It doesn't seem right to me that AC_SYS_LARGEFILE should imply > AC_SYS_YEAR2038. What is the reasoning behind that? > >> I really wish the rest of GNU would talk to glibc maintainers before >> overriding glibc maintainer decisions. If we cannot revert this in >> autoconf (and gnulib), this will very much endanger the Fedora i386 >> port. Debian will probably be impacted in the same way. > > I need to read around all this as I have only just become aware that > the LFS thing is entangled with the timet_64 thing. Is there a good > place to read _why_ one implies the other? It definitely complicates > matters. time64 has to imply LFS because of some structures like stat including both off_t (LFS) and st_atim (time64), I think. Some of it is internal too. Or do you mean LFS => time64? I have no idea for why that's entangled in autoconf and gnulib. > >>> On reflection and after extensive discussion within Gentoo (although >>> I don't seek to speak for everybody there) - with special thanks to >>> David Seifert and Arsen Arsenović for tolerating my bikesheds on this, >>> we don't think it's feasible to handle this in a piecemeal fashion - >>> at the very least not without spending a significant & for some, >>> undesirable amount of time on supporting "obsolete" 32-bit platforms. > > Distros need to co-ordinate on this. If there are going to be new > triplets for the 'LFS and 64_bit timet' ABI(s) then we should agree on > them and use them. If distros are happy to migrate to these ABIs > within the existing arm-linux-gnueabihf and i386-linux-gnu (or > i686-linux-gnu) then we should do that. > > If half the distros migrate within the existing triplet and the rest use > a new one, that sounds like a recipie for much confusion. > 100%. And also on sharing patches and known problems and experience with the migration. All of it! > I could write more, but I'll swot up a bit first :-) It's not easy to find much about all of this! I almost felt like I was missing something at first. :) Best, sam
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