[PATCH v7.1 07/13] ARC: Linux Syscall Interface
Adhemerval Zanella
adhemerval.zanella at linaro.org
Tue Jul 7 15:24:09 EDT 2020
On 06/07/2020 22:25, Vineet Gupta wrote:
> On 7/6/20 6:20 AM, Adhemerval Zanella via Libc-alpha wrote:
>>>>> diff --git a/sysdeps/unix/sysv/linux/arc/clone.S b/sysdeps/unix/sysv/linux/arc/clone.S
>>>
>>>>> diff --git a/sysdeps/unix/sysv/linux/arc/fixup-asm-unistd.h b/sysdeps/unix/sysv/linux/arc/fixup-asm-unistd.h
>>>
>>>>> +
>>>>> +/* Adjustments to ARC asm-generic syscall ABI (3.9 kernel) for 64-bit time_t
>>>>> + support. */
>>>>> +
>>>>> +/* fstat64 and fstatat64 need to be replaced with statx. */
>>>>> +
>>>>> +#undef __NR_fstat64
>>>>> +#undef __NR_fstatat64
>>>
>>> This is certainly needed as they are present in ARC arch-syscall.h but we need to
>>> use statx.
>>>
>>>>> +/* Replace all other 32-bit time syscalls with 64-bit variants. */
>>>>> +
>>>>> +# undef __NR_clock_adjtime
>>>>> +# undef __NR_clock_getres
>>>>> +# undef __NR_futex
>>>>> +# undef __NR_mq_timedreceive
>>>>> +# undef __NR_mq_timedsend
>>>>> +# undef __NR_ppoll
>>>>> +# undef __NR_pselect6
>>>>> +# undef __NR_recvmmsg
>>>>> +# undef __NR_rt_sigtimedwait
>>>>> +# undef __NR_sched_rr_get_interval
>>>>> +# undef __NR_semtimedop
>>>>> +# undef __NR_timerfd_settime
>>>>> +# undef __NR_timerfd_gettime
>>>>> +# undef __NR_utimensat
>>>>
>>>> I am trying to understand why these are required since arc does not define
>>>> them in arch-syscall.h.
>>>
>>> arch-syscall.h doesn't define them precisely due to these being here. When
>>> update-syscalls is run, the 32-bit syscalls are generated for ARC (since kernel
>>> ABI provides these because that was v3.9 circa 2013). Adding them
>>> fixup-asm-unistd.h removes them (perhaps I need to add this in changelog to
>>> clarify - atleast for myself).
>>>
>>>> And the generic implementation should handle the time64 variant. If they
>>>> are not this is something we need to handle it.
>>>
>>> At the time we we doing this, arch-syscall.h generation was not yet in place,
>>> however I tried to undef in generic/sysdep.h for TIMESIZE==64. However I was asked
>>> me to add this to ARC specific fixup-asm-unistd.h
>>> https://sourceware.org/pipermail/libc-alpha/2020-March/112395.html
>>> https://sourceware.org/pipermail/libc-alpha/2020-April/112909.html
>>
>> My confusion here, I forgot that this header is only used glibcsyscalls.py
>> to actually generate arch-syscall.h.
>>
>> You changes does look correct.
>
> Actually we can add a few more entries here which have 64-bit variants.
>
> +# undef __NR_clock_gettime
> +# undef __NR_clock_nanosleep
> +# undef __NR_clock_settime
> +# undef __NR_timer_gettime
> +# undef __NR_timer_settime
It should not intefere since ARC also defines __ASSUME_TIME64_SYSCALLS
and the 32-bit fallback syscalls won't be used in this case.
As a side note, now that arch-syscall.h is based on latest kernel version
and all the 32-bit ABIs with old 32-bit time_t have upstream support for
64-bit time_t we can simplify a bit some implementation by assuming
the 64-bit time_t is always defined and adding a fallback only for
!define __ASSUME_TIME64_SYSCALLS.
>
>
>>>>> diff --git a/sysdeps/unix/sysv/linux/arc/kernel_stat.h b/sysdeps/unix/sysv/linux/arc/kernel_stat.h
>
>>> This specific one is actually dead code. I did post a patch to this effect and
>>> followed up with supporting data that enabling it on 64-bit arches doesn't lead to
>>> any changes in generated code.
>>>
>>> https://sourceware.org/pipermail/libc-alpha/2020-February/111259.html
>>> https://sourceware.org/pipermail/libc-alpha/2020-June/115217.html
>>>
>>
>> Ack.
>
> Thx. I'll repost this after things settle at bit.
>
>>>>> diff --git a/sysdeps/unix/sysv/linux/arc/sysdep.h b/sysdeps/unix/sysv/linux/arc/sysdep.h
>>>
>>> ...
>>>
>>>>> +/* 32-bit time syscalls are not available, but the redefines allow generic
>>>>> + wrappers to work. */
>>>>> +#define __NR_clock_adjtime __NR_clock_adjtime64
>>>>> +#define __NR_clock_getres __NR_clock_getres_time64
>>>>> +#define __NR_futex __NR_futex_time64
>>>>> +#define __NR_mq_timedreceive __NR_mq_timedreceive_time64
>>>>> +#define __NR_mq_timedsend __NR_mq_timedsend_time64
>>>>> +#define __NR_ppoll __NR_ppoll_time64
>>>>> +#define __NR_pselect6 __NR_pselect6_time64
>>>>> +#define __NR_recvmmsg __NR_recvmmsg_time64
>>>>> +#define __NR_rt_sigtimedwait __NR_rt_sigtimedwait_time64
>>>>> +#define __NR_sched_rr_get_interval __NR_sched_rr_get_interval_time64
>>>>> +#define __NR_semtimedop __NR_semtimedop_time64
>>>>> +#define __NR_timerfd_gettime __NR_timerfd_gettime64
>>>>> +#define __NR_timerfd_settime __NR_timerfd_settime64
>>>>> +#define __NR_utimensat __NR_utimensat_time64
>>>>
>>>> As for the fixup-asm-unistd.h, the generic implementation should handle it
>>>> without the requirement of the ABI to add such tricks.
>>>
>>> fixup-asm-unistd.h is different, but this could be avoided. I know for sure that
>>> ll code literally expects __NR_futex (atleast used to). But I can remove this and
>>> see what comes out.
>>>
>>>>
>>>> However it seems that we are still missing support for pselect
>>>> (__NR_pselect6_time64), recvmmsg (__NR_recvmmsg_time64), sigtimedwait
>>>> (__NR_rt_sigtimedwait_time64), and semtimeop (__NR_semtimedop_time64).
>>>>
>>>> I think we can add the redefine hack only the aforementioned symbols for
>>>> now and removed them once we implement the y2038 support on such symbols
>>>> (since the expected ABI won't change for ARC, only for old ABIs with
>>>> 32 time_t support).
>>>
>>> Sorry /me horribly confused here.
>>
>> Sorry for the confusion, I meant that some of these re-defines are superfluous
>> and I would like to have the minimum required re-define to enable the ARC
>> support,
>
> Right. The generic code needs a bit more work to eliminate the redefines altogether.
>
> 1. Following is not needed
>
> -#define __NR_clock_adjtime __NR_clock_adjtime64
> -#define __NR_sched_rr_get_interval __NR_sched_rr_get_interval_time64
> -#define __NR_mq_timedreceive __NR_mq_timedreceive_time64
> -#define __NR_mq_timedsend __NR_mq_timedsend_time64
> -#define __NR_timerfd_gettime __NR_timerfd_gettime64
> -#define __NR_timerfd_settime __NR_timerfd_settime64
Ok.
>
> 2. The minimum list needed for ARC (with annotations as to which generic file
> needs fixing).
>
> /* Fix sysdeps/unix/sysv/linux/clock_getcpuclockid.c. */
> #define __NR_clock_getres __NR_clock_getres_time64
It should be simple since there is no need to provide an extra symbol
for old ABIs, it would be to just use __NR_clock_getres_time64 if it
is defined.
> /* Fix sysdeps/nptl/lowlevellock-futex.h. */
> #define __NR_futex __NR_futex_time64
It seems Lukasz Majewski has sent a patchset to address it (I haven't
checked the detail yet).
> /* Fix sysdeps/unix/sysv/linux/pause.c. */
> #define __NR_ppoll __NR_ppoll_time64
This is another one similar to clock_getcpuclockid.
> /* Fix sysdeps/unix/sysv/linux/select.c. */
> #define __NR_pselect6 __NR_pselect6_time64
I have a patch for select [1], it a bit more complex because we need to
handle both the timeout and the microblaze lacking support of
pselect6.
> /* Fix sysdeps/unix/sysv/linux/recvmmsg.c. */
> #define __NR_recvmmsg __NR_recvmmsg_time64
I also have a patch for this [1], although it still does not have the
ancillary data from struct msghdr which might return SCM_TIMESTAMP
information (which returns struct timespec). The recvmsg also has
the same issue regarding ancillary data.
> /* Fix sysdeps/unix/sysv/linux/sigtimedwait.c. */
> #define __NR_rt_sigtimedwait __NR_rt_sigtimedwait_time64
The patch for is more straighfoward [1].
> /* Fix sysdeps/unix/sysv/linux/semtimedop.c. */
> #define __NR_semtimedop __NR_semtimedop_time64
The patch for is also straighfoward [1].
> /* Hack sysdeps/unix/sysv/linux/generic/utimes.c (need linux/utimes.c). */
> #define __NR_utimensat __NR_utimensat_time64
Lukasz Majewski also has a patchset for this, I will check this out.
>
>
>> so we can cleanup these later once we enable time64_t support on
>> old ABIs as well.
>
> IMO the cleanup applies to new ABIs too as generic code should handle those cases
> w/o these workarounds. But that would delay things further for new ports so I
> suggest we keep the workarounds and clean things up going fwd.
I agree, this can be worked in parallel.
>
> BTW, if one were to actually go about fixing those, whats the best approach.
> Consider the simplest case pause(). For !__NR_pause do we replicate the code for
> ppoll/ppoll64 handling or simply just call ppoll(). Later has a function call
> overhead) ? Or there is a paradigm to use __syscallxxx_helper() although that
> still has a function call overhead.
>
> Actually the pause case is really simple as there are no args, so just redefine
> __NR_xxx trick should suffice w/o going into all the explicit
> interworking/conversion etc.
>
> __libc_pause (void)
> {
> #ifdef __NR_pause
> return SYSCALL_CANCEL (pause);
> #else
>
> return SYSCALL_CANCEL (ppoll, NULL, 0, NULL, NULL);
> #endif
>
Each implementation has it ows requirements so I can't really say if
a helper function does make sense for all of them. For pause
specifically we can even simplify to since all architectures have
either ppoll or ppoll_time64:
int
__libc_pause (void)
{
#ifdef __NR_ppoll_time64
return SYSCALL_CANCEL (ppoll_time64, NULL, 0, NULL, NULL);
#else
return SYSCALL_CANCEL (ppoll, NULL, 0, NULL, NULL);
#endif
}
>
>>>>> +#undef SYS_ify
>>>>> +#define SYS_ify(syscall_name) __NR_##syscall_name
>>>>
>>>> The code mixes __NR_* and SYS_ify macro. This macro is really superflous
>>>> and I am preparing some patches to cleanup this up along with C asm
>>>> macros to generate syscall. So I would suggest to just use the __NR_*
>>>> way and drop this definition.
>>>
>>> I don't mind, but it seems that the wrapper was a simply way to avoid open-coding
>>> the macro concatenation. e.g.
>>>
>>> # define DO_CALL(syscall_name, args) \
>>> - mov r8, SYS_ify (syscall_name) ASM_LINE_SEP \
>>> + mov r8, __NR__##syscall_name ASM_LINE_SEP \
>>> ARC_TRAP_INSN
>>>
>>
>> My understand was in fact parametrized way to define syscall numbers when
>> glibc added support to future multiple Unix implementation (which never
>> actually happened). I don't have a strong opinion here in fact, any is
>> fine in the end.
>
> I open-coded the 2 calls to SYS_ify() in ARC code and deleted SYS_ify()...
>
> ... and 2 hrs later, after mysterious build failures, find that SYS_ify() needs to
> be retained (even if not used in ARC port) it is expected/used by generic
> make-syscalls.h :-(
Sigh, alright let keep it then.
[1] https://sourceware.org/git/?p=glibc.git;a=shortlog;h=refs/heads/azanella/y2038-fixes
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