Re: [PATCH v7.1 07/13] ARC: Linux Syscall Interface

[Adhemerval Zanella <adhemerval.zanella@linaro.org>]

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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