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Re: [PATCH v4 1/2] y2038: linux: Provide __timerfd_gettime64 implementation
- From: Adhemerval Zanella <adhemerval dot zanella at linaro dot org>
- To: Lukasz Majewski <lukma at denx dot de>
- Cc: Joseph Myers <joseph at codesourcery dot com>, Paul Eggert <eggert at cs dot ucla dot edu>, Andreas Schwab <schwab at suse dot de>, Alistair Francis <alistair23 at gmail dot com>, Alistair Francis <alistair dot francis at wdc dot com>, GNU C Library <libc-alpha at sourceware dot org>, Siddhesh Poyarekar <siddhesh at gotplt dot org>, Florian Weimer <fweimer at redhat dot com>, Florian Weimer <fw at deneb dot enyo dot de>, Zack Weinberg <zackw at panix dot com>, Carlos O'Donell <carlos at redhat dot com>, Arnd Bergmann <arnd at arndb dot de>
- Date: Tue, 7 Jan 2020 17:16:42 -0300
- Subject: Re: [PATCH v4 1/2] y2038: linux: Provide __timerfd_gettime64 implementation
- References: <20200106121742.1628-1-lukma@denx.de> <ea1ea005-6dee-f8dd-f205-d0a47a952904@linaro.org> <20200107102752.396f7f6f@jawa> <b09ec981-7cf4-19e8-74b9-74c558ba0e75@linaro.org> <20200107152521.7416d5f3@jawa>
On 07/01/2020 11:25, Lukasz Majewski wrote:
> Hi Adhemerval,
>
>> On 07/01/2020 06:27, Lukasz Majewski wrote:
>>
>>>> As a side note, now that arch-syscall patch is upstream should we
>>>> assume that for !__ASSUME_TIME64_SYSCALLS the
>>>> __NR_timerfd_gettime64 should be defined (meaning that Linux
>>>> supports time64 for all 32-bit architectures)?
>>>
>>> Only Linux version >= 5.1 supports 64 bit time on archs with
>>> __WORDSIZE = 32. I do guess (but I may be wrong here) that the
>>> arch-syscall is supposed to reflect the exact syscalls provided by
>>> kernel headers used for building (to help with validation of Y2038
>>> patches).
>>
>> The arch-syscall is now autogenerated from the latest kernel release
>> defined in build-many-glibcs.py. So the question is whether Linux
>> support and enforces time64 support on all and future 32-bit
>> architectures or if there is still some missing ones (as it has
>> happen on some syscall additions, where some architecture lag
>> behind some releases).
>
> This question would be best answered by Arnd (CC'ed) IMHO. From what I
> know all 32 bit architectures gained syscalls covered by
> __ASSUME_TIME64_SYSCALLS from Linux 5.1+.
>
> The arch-syscall seems to me like a mean to test for example the time
> related syscalls which use different versions (32bit time vs 64 bit) on
> different archs. Notable example - clock_gettime(). Am I right?
The arch-syscall is a way to decouple the build from the kernel header
used on build, which might simplify the logic to use some kernel
features.
On the clock_gettime, for instance, as Arnd has indicated we can
assume that __NR_clock_gettime64 will be always presented for
!__ASSUME_TIME64_SYSCALLS.
It would be interesting if kernel also could enforce that new
generic syscalls would be wire-up, or at least the syscall number
reserved; once a new generic syscall is introduced. It would
simplify the __ASSUME_* macro, not requiring the arch-specific
overrides on some architectures.
>
> The __clock_gettime64 is going to be exported (as clock_gettime
> redirection) on 32 bit archs which are going to be Y2038 safe (with 64
> bit time_t).
>
>> clock_gettime64 would be suffice (with a {weak,strong}_alias).
>>
>
> The internal in-glibc usage (calling) of clock_gettime() shall be
> replaced by either __clock_gettime64 or clock_gettime64. I would prefer
> the former as it reflects that it is internal function (with __ prefix).
It required to be the former because we also need to take in consideration
linking namespace pollution.
>
>> However I do think we should fix it to avoid such confusion why there
>> is a hidden_proto and not a hidden_def.
>
> +1.
Ack, I will send a patch.