Re: [PATCH v4 1/2] y2038: linux: Provide __timerfd_gettime64 implementation

[Lukasz Majewski <lukma@denx.de>]

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Hi Adhemerval,

> 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, 

So then we will build against the newest kernel (like 5.4 now). As it
was noted in the other thread - this would simplify the
build-many-glibcs.py

> which might simplify the logic to use some kernel 
> features.

I must admit that I do not see such simplification... Could you give an
example?

> 
> 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.

Thanks.


Best regards,

Lukasz Majewski

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