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([2804:1b3:a7c1:7e99:6983:51e0:457e:734]) by smtp.gmail.com with ESMTPSA id s40-20020a05683043a800b00684a10970adsm2021124otv.16.2023.01.27.09.33.36 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 27 Jan 2023 09:33:37 -0800 (PST) Message-ID: <8333ae94-1730-da87-8483-624cbc63b9f2@linaro.org> Date: Fri, 27 Jan 2023 14:33:34 -0300 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.7.0 Subject: Re: time64 / Large File Support: 2) default time64 breaks legacy 32bit binaries Content-Language: en-US To: Sam James Cc: Libc-alpha References: <10857996.18pcnM708K@pinacolada> <7196595.N7aMVyhfb1@pinacolada> <7271eb94-b5d7-69d6-9be0-ca1afda29a50@cs.ucla.edu> <2342ab66-6ac6-17d8-3693-8e2fd93fc8a1@linaro.org> From: Adhemerval Zanella Netto Organization: Linaro In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Spam-Status: No, score=-6.2 required=5.0 tests=BAYES_00,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,NICE_REPLY_A,RCVD_IN_DNSWL_NONE,SPF_HELO_NONE,SPF_PASS,TXREP autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: On 26/01/23 20:35, Sam James wrote: > > >> On 26 Jan 2023, at 13:21, Adhemerval Zanella Netto via Libc-alpha wrote: >> >> >> >> On 26/01/23 01:13, Paul Eggert wrote: >>> On 1/25/23 15:59, Andreas K. Huettel via Libc-alpha wrote: >>> >>>> This was discussed already in the previous thread on this list [1], with reactions >>>> ranging from "need new triplet" via "need new libdir" to "meh".... >>>> [1] https://sourceware.org/pipermail/libc-alpha/2022-November/143386.html >>> >>> One thing new since that November email is that in bleeding-edge Autoconf we've scaled back AC_SYS_LARGEFILE so it no longer widens time_t by default. Instead, you need to pass a new option --enable-year2038 to 'configure' if you want 64-bit time_t on 32-bit glibc x86 and ARM platforms, which as I understand it are the only platforms that have this problem. If a package author wants --enable-year2038 to be the default, they need to use Autoconf's new AC_SYS_YEAR2038 macro. This change has also percolated into Gnulib so source packages using recent Gnulib will need to use the new Gnulib module year2038 if they want --enable-year2038 to be the default. >>> >>> This change was done out of concern that although AC_SYS_LARGEFILE has long tweaked blkcnt_t, dev_t, ino_t, fsblkcnt_t, fsfilcnt_t and rlim_t (in addition to off_t of course), having it also tweak time_t was a compatibility bridge too far. >>> >>>> Proposal: glibc gains two new build-time configure options: >>>> * --enable-hard-time64 >>>> * --enable-hard-lfs >>> >>> This sort of thing sounds like a good way to go. However, I suggest simplifying things, by having just one option (say, --enable-hard-sys-types64) that does both at once, because --enable-hard-time64 and --enable-hard-lfs would not be orthogonal and this would be confusing, and anyway nobody sane will want to use one option without also using the other - who wants the agony of *two* conversions? >> >> I agree a single option make sense, there is no good reason to add LFS-only >> with 64-bit support. It also simplify build systems that are not autoconf >> based. >> > > Single option is fine with me and I agree it makes more sense. > >> A minor problem, which is for all configure switch, it adds another build >> permutation that incur in more testing requirements and maintenance. >> >> However it does not help with the rest of plumbing that a system will need >> to do for correct set library selection, since ldconfig will see both 32 and >> 64 bit time_t shared library essentially being the same ABI. A mixed >> environment with legacy binaries/libraries will still incur in similar >> issue, albeit in a different direction. So to run old binaries one will >> need to either setup LD_PRELOAD/LD_LIBRARY_PATH/RUNPATH or run it in an >> isolated environment (which itself has its own issues). >> > > My feeling was that anyone who continues to need 32-bit time_t would just > run a system without such a glibc built and wouldn't contaminate it with > 64-bit time_t binaries. That is my expectations as well, however it requires just a single broken library in the loop to trigger a cascade of issues. I recall that we consider to mark the library using 64-bit time_t with an ABI mark, but it would be too troublesome to implement (with some corner cases as well). > >> And the configure switch also adds a kind of fragmentation, but it is also >> we already have when a projects enables time64_t anyway. >> > > Yeah, I think the ship has more-or-less sailed, but my hope is that we'd > all agree to do this as distros around the same time with new ABI > names to indicate it. > >> So although I am not quite against --enable-hard-sys-types64, I personally >> think we should do something more drastically (which not all other glibc >> developers agree) and flip the switch to enable 64-bit time_t *as default* >> and document 32-bit is opt-in. If Fedora or any distro wants to keep the >> *broken* non-LFS / 32 bit time_t, it is up to them to patch glibc to do so. > > Right, it seems RH has some needs due to supporting existing customers, > but I don't think this should unduly affect what glibc upstream does if there's > one clear technical path forward. Nobody seems to actually dispute that > the end-game here is a hard switch at some point. Just about when. > > But I'm a bit less bothered about this if we're saying that we only need > to wait 2 years or so. I could live with that if we really have to. Not ideal, > but my hands are full at the moment, so... I agree that a hard switch make sense if the idea is to keep providing 32 bit environments (which is the whole point of 64 bit time_t support). As Florian has hinted, RH will eventually phase out 32-bit support and thus we can might eventually move forward and make 64-bit time_t the default ABI.