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

[Vineet Gupta]

On 7/2/20 7:47 PM, Adhemerval Zanella via Libc-alpha wrote:
> 
> 
> On 30/06/2020 21:08, Vineet Gupta via Libc-alpha wrote:
>> ---
>>    Changes since v7:
>>      - used long int (iso int) in sysdep.h/syscall_error for handling registers
> 
> Patch looks ok, but I have question on the __NR_* undef/define. 
> 

>> diff --git a/sysdeps/unix/sysv/linux/arc/arch-syscall.h b/sysdeps/unix/sysv/linux/arc/arch-syscall.h
...
>> +#define __NR_write 64
>> +#define __NR_writev 66
> 
> Looks good. As side note I think an improvement would be to add
> an annotation on update-syscall-lists.py to specify which kernel
> version it used.

Very good idea indeed. I've asked myself the very question atleast once.


>> diff --git a/sysdeps/unix/sysv/linux/arc/clone.S b/sysdeps/unix/sysv/linux/arc/clone.S
..
>> +
>> +	; adjust libc args for syscall
> 
> Use the C comment style for constency with rest of the file.

Done.

>> 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

>> diff --git a/sysdeps/unix/sysv/linux/arc/kernel_stat.h b/sysdeps/unix/sysv/linux/arc/kernel_stat.h
...
>> +#define STATFS_IS_STATFS64 0
> 
> Ok.

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


>> 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.

>> +
>> +#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