From: Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>
To: Sam James <sam@gentoo.org>
Cc: Libc-alpha <libc-alpha@sourceware.org>
Subject: Re: time64 / Large File Support: 2) default time64 breaks legacy 32bit binaries
Date: Fri, 27 Jan 2023 14:33:34 -0300 [thread overview]
Message-ID: <8333ae94-1730-da87-8483-624cbc63b9f2@linaro.org> (raw)
In-Reply-To: <C16AB11D-7CCD-48CC-AD08-888D70479174@gentoo.org>
On 26/01/23 20:35, Sam James wrote:
>
>
>> On 26 Jan 2023, at 13:21, Adhemerval Zanella Netto via Libc-alpha <libc-alpha@sourceware.org> 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.
next prev parent reply other threads:[~2023-01-27 17:33 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-25 23:57 The time64 and Large File Support mess Andreas K. Huettel
2023-01-25 23:58 ` time64 / Large File Support: 1) [2.28 Regression]: New getdents{64} implementation breaks qemu-user Andreas K. Huettel
2023-01-26 12:21 ` Adhemerval Zanella Netto
2023-01-27 20:08 ` Andreas K. Huettel
2023-01-25 23:59 ` time64 / Large File Support: 2) default time64 breaks legacy 32bit binaries Andreas K. Huettel
2023-01-26 4:13 ` Paul Eggert
2023-01-26 13:21 ` Adhemerval Zanella Netto
2023-01-26 23:35 ` Sam James
2023-01-27 17:33 ` Adhemerval Zanella Netto [this message]
2023-02-01 16:26 ` Florian Weimer
2023-02-01 19:47 ` Sam James
2023-02-01 19:54 ` Sam James
2023-02-03 17:52 ` Florian Weimer
2023-02-01 22:22 ` Michael Hudson-Doyle
2023-02-03 14:17 ` Adhemerval Zanella Netto
2023-02-03 18:56 ` Florian Weimer
2023-01-27 2:38 ` Paul Eggert
2023-01-27 17:40 ` Adhemerval Zanella Netto
2023-01-27 23:51 ` Paul Eggert
2023-01-27 23:58 ` Joseph Myers
2023-02-01 12:27 ` Adhemerval Zanella Netto
2023-01-26 10:43 ` Florian Weimer
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