Re: [PATCH v6] y2038: linux: Provide __gettimeofday64 implementation

[Lukasz Majewski <lukma@denx.de>]

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Hi Adhemerval,

Thank you for the review.

> On 12/02/2020 05:45, Lukasz Majewski wrote:
> > In the glibc the gettimeofday can use vDSO (on power and x86 the
> > USE_IFUNC_GETTIMEOFDAY is defined), gettimeofday syscall or
> > 'default' ___gettimeofday() from ./time/gettime.c (as a fallback).
> > 
> > In this patch the last function (___gettimeofday) has been
> > refactored and moved to ./sysdeps/unix/sysv/linux/gettimeofday.c to
> > be Linux specific.  
> 
> In fact the function implementation is replicated on Linux version.
> Once this patch is upstream I plan to make a generic implementation
> and refactor alpha, Linux, and generic implementation to avoid code
> duplication.

Ok. I shall apply this patch till the end of the day.

> 
> > 
> > The new __gettimeofday64 explicit 64 bit function for getting 64
> > bit time from the kernel (by internally calling __clock_gettime64)
> > has been introduced.
> > 
> > Moreover, a 32 bit version - __gettimeofday has been refactored to
> > internally use __gettimeofday64.
> > 
> > The __gettimeofday is now supposed to be used on systems still
> > supporting 32 bit time (__TIMESIZE != 64) - hence the necessary
> > check for time_t potential overflow and conversion of struct
> > __timeval64 to 32 bit struct timespec.
> > 
> > The alpha port is a bit problematic for this change - it supports
> > 64 bit time and can safely use gettimeofday implementation from
> > ./time/gettimeofday.c as it has
> > ./sysdeps/unix/sysv/linux/alpha/gettimeofday.c, which includes
> > ./time/gettimeofday.c, so the Linux specific one can be avoided.
> > For that reason the code to set default gettimeofday symbol has not
> > been moved to ./sysdeps/unix/sysv/linux/gettimeofday.c as only
> > alpha defines VERSION_gettimeofday.  
> 
> You can remove this part about alpha from commit message, this
> patch does not change anything about alpha behaviour.

Ok.

> 
> > 
> > The USE_IFUNC_GETTIMEOFDAY for powerpc and i686 has been undefined
> > on purpose. Due to that the support for gettimeofday vDSO on them
> > has been traded for Y2038 safeness (as this syscall is going to be
> > obsolete).  
> 
> I think it would be useful to extend a bit why this optimization was
> removed from i686 and powerpc32.  Maybe add:
> 
>   The iFUNC vDSO direct call optimization has been removed from both
>   i686 and powerpc32 (USE_IFUNC_GETTIMEOFDAY is not defined for the
>   architectures anymore).  The Linux kernel does not provide a y2038
>   safe implementation of gettimeofday neither it plans to provide it
>   in the future, clock_gettime64 should be use instead.  It meant to
>   keep support for this optimization it would require to handle
> another build permutation (!__ASSUME_TIME64_SYSCALLS &&
> USE_IFUNC_GETTIMEOFDAY) with adds more complexity and has limited use
> (since the idea is to eventually have a y2038 safe glibc build).
> 

Ok. I will add this description.

> > 
> > Build tests:
> > ./src/scripts/build-many-glibcs.py glibcs
> > 
> > Run-time tests:
> > - Run specific tests on ARM/x86 32bit systems (qemu):
> >   https://github.com/lmajewski/meta-y2038 and run tests:
> >   https://github.com/lmajewski/y2038-tests/commits/master
> > 
> > Above tests were performed with Y2038 redirection applied as well
> > as without to test proper usage of both __gettimeofday64 and
> > __gettimeofday.  
> 
> LGTM with the suggested commit message changes.
> 
> Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>

Thanks. 

Could you also review following patch set:
https://patchwork.ozlabs.org/cover/1234918/

(It seems to be straightforward and has been posted to the mailing list
some time ago).

Thanks in advance.

> 
> > 
> > ---
> > Changes for v6:
> > - Do not check if tv pointer is NULL as in generic implementation of
> >   ./time/gettimeofday.c. Moreover, prototype for this function has
> >   __nonnull GCC attribute for this parameter.
> > 
> > Changes for v5:
> > - Replace '___gettimeofday64' with '__gettimeofday64' in the
> > subject of the patch
> > 
> > Changes for v4:
> > - Rename ___gettimeofday{64} to __gettimeofday{64} as '___' prefix
> > is not needed for our implementation
> > - Correctly handle the case when tv is NULL (also in
> > __gettimeofday).
> > - Do not define USE_IFUNC_GETTIMEOFDAY for 32 bit archs - namely
> > powerpc and i686.
> > 
> > Changes for v3:
> > - New patch
> > ---
> >  include/time.h                                |  4 ++
> >  sysdeps/unix/sysv/linux/gettimeofday.c        | 40
> > ++++++++++++++++++- .../unix/sysv/linux/powerpc/gettimeofday.c    |
> >  4 +- sysdeps/unix/sysv/linux/x86/gettimeofday.c    |  4 +-
> >  4 files changed, 49 insertions(+), 3 deletions(-)
> > 
> > diff --git a/include/time.h b/include/time.h
> > index 73f66277ac..61806658e7 100644
> > --- a/include/time.h
> > +++ b/include/time.h
> > @@ -227,10 +227,14 @@ libc_hidden_proto (__sched_rr_get_interval64);
> >  
> >  #if __TIMESIZE == 64
> >  # define __settimeofday64 __settimeofday
> > +# define __gettimeofday64 __gettimeofday
> >  #else
> >  extern int __settimeofday64 (const struct __timeval64 *tv,
> >                               const struct timezone *tz);
> >  libc_hidden_proto (__settimeofday64)
> > +extern int __gettimeofday64 (struct __timeval64 *restrict tv,
> > +                             void *restrict tz);
> > +libc_hidden_proto (__gettimeofday64)
> >  #endif
> >  
> >  /* Compute the `struct tm' representation of T,  
> 
> Ok.
> 
> > diff --git a/sysdeps/unix/sysv/linux/gettimeofday.c
> > b/sysdeps/unix/sysv/linux/gettimeofday.c index
> > d5cdb22495..cb57bc9cf2 100644 ---
> > a/sysdeps/unix/sysv/linux/gettimeofday.c +++
> > b/sysdeps/unix/sysv/linux/gettimeofday.c @@ -54,5 +54,43 @@
> > __gettimeofday (struct timeval *restrict tv, void *restrict tz) #
> > endif weak_alias (__gettimeofday, gettimeofday)
> >  #else /* USE_IFUNC_GETTIMEOFDAY  */
> > -# include <time/gettimeofday.c>
> > +/* Conversion of gettimeofday function to support 64 bit time on
> > archs
> > +   with __WORDSIZE == 32 and __TIMESIZE == 32/64  */
> > +#include <errno.h>
> > +
> > +int
> > +__gettimeofday64 (struct __timeval64 *restrict tv, void *restrict
> > tz) +{
> > +  if (__glibc_unlikely (tz != 0))
> > +    memset (tz, 0, sizeof (struct timezone));
> > +
> > +  struct __timespec64 ts64;
> > +  if (__clock_gettime64 (CLOCK_REALTIME, &ts64))
> > +	  return -1;
> > +
> > +  *tv = timespec64_to_timeval64 (ts64);
> > +  return 0;
> > +}
> > +
> > +# if __TIMESIZE != 64
> > +libc_hidden_def (__gettimeofday64)
> > +
> > +int
> > +__gettimeofday (struct timeval *restrict tv, void *restrict tz)
> > +{
> > +  struct __timeval64 tv64;
> > +  if (__gettimeofday64 (&tv64, tz))
> > +	  return -1;
> > +
> > +  if (! in_time_t_range (tv64.tv_sec))
> > +    {
> > +      __set_errno (EOVERFLOW);
> > +      return -1;
> > +    }
> > +
> > +  *tv = valid_timeval64_to_timeval (tv64);
> > +  return 0;
> > +}
> > +# endif
> > +weak_alias (__gettimeofday, gettimeofday)
> >  #endif  
> 
> Ok.
> 
> > diff --git a/sysdeps/unix/sysv/linux/powerpc/gettimeofday.c
> > b/sysdeps/unix/sysv/linux/powerpc/gettimeofday.c index
> > 183fb0ac70..2d6978f333 100644 ---
> > a/sysdeps/unix/sysv/linux/powerpc/gettimeofday.c +++
> > b/sysdeps/unix/sysv/linux/powerpc/gettimeofday.c @@ -15,5 +15,7 @@
> >     License along with the GNU C Library; if not, see
> >     <https://www.gnu.org/licenses/>.  */
> >  
> > -#define USE_IFUNC_GETTIMEOFDAY
> > +#ifdef __powerpc64__
> > +# define USE_IFUNC_GETTIMEOFDAY
> > +#endif
> >  #include <sysdeps/unix/sysv/linux/gettimeofday.c>  
> 
> Ok.
> 
> > diff --git a/sysdeps/unix/sysv/linux/x86/gettimeofday.c
> > b/sysdeps/unix/sysv/linux/x86/gettimeofday.c index
> > 1b7aa880a2..0c1779dc83 100644 ---
> > a/sysdeps/unix/sysv/linux/x86/gettimeofday.c +++
> > b/sysdeps/unix/sysv/linux/x86/gettimeofday.c @@ -16,5 +16,7 @@
> >     License along with the GNU C Library; if not, see
> >     <https://www.gnu.org/licenses/>.  */
> >  
> > -#define USE_IFUNC_GETTIMEOFDAY
> > +#ifdef __x86_64__
> > +# define USE_IFUNC_GETTIMEOFDAY
> > +#endif
> >  #include <sysdeps/unix/sysv/linux/gettimeofday.c>
> >   
> 
> Ok.




Best regards,

Lukasz Majewski

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