Re: [PATCH v2 2/7] y2038: Introduce __ASSUME_64BIT_TIME define

[Lukasz Majewski <lukma at denx dot de>]

Hi Stepan,

> 06.05.2019 в 23:14:44 +0200 Lukasz Majewski написал:
> > For ARM, x86 there shall be call to clock_settime64 syscall
> > 
> > For x32 there shall be call to clock_settime syscall (which is
> > supporting 64 bit anyway - despite the ignoring possible padding
> > clearing issue).  
> 
> > I rather thought about something like:
> > 
> > __clock_settime64 (clockid_t clock_id, const struct __timespec64
> > *tp) {
> >   <overflow check>
> > 
> > #ifdef __ASSUME_TIME64_SYSCALLS
> > # ifdef __NR_clock_settime64
> >   int ret = INLINE_SYSCALL_CALL (clock_settime64, clock_id, tp);
> >   if (ret == 0 || errno != ENOSYS)
> > 	return ret;
> > # endif
> >   /* Fall back to syscall supporting 32bit struct timespec.  */
> >   struct timespec ts32;
> >   valid_timespec64_to_timespec (tp, &ts32);
> >   return INLINE_SYSCALL_CALL (clock_settime, clock_id, &ts32);
> > #else
> >   /* 64 bit machines + x32 */
> >   return INLINE_SYSCALL_CALL (clock_settime, clock_id, tp);
> > #endif
> > }
> > 
> > In the above pseudo code we assume that __ASSUME_TIME64_SYSCALLS is
> > #undef'ed for x32 (so it is treated as a 'special case' - in the
> > same way as x86_64).  
> 
> Usually the point of __ASSUME_* macros is to avoid compiling old
> compatibility code when it's not needed.  That means there should be
> no fallback to 32-bit clock_settime when __ASSUME_TIME64_SYSCALLS is
> defined.  Even when it's defined on 32-bit arm or x86.
> 
> And with your current use of __ASSUME_TIME64_SYSCALLS
> __NR_clock_settime64 won't be used on any existing architecture.
> Because __ASSUME_TIME64_SYSCALLS won't be defined until Linux 5.0 is
> no longer supported.

It will be used when the minimal supported kernel reaches 5.1. (now it
is 3.2.)

For testing I do use --enable-kernel="5.1.0" passed to configure.

> 
> If you replace
> 
> #ifdef __ASSUME_TIME64_SYSCALLS
> 
> with
> 
> #ifdef __NR_clock_settime64
> 
> result would make more sense than what you have now.




Best regards,

Lukasz Majewski

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