Re: [PATCH 1/6] y2038: Use __clock_settime64 in deprecated stime function

[Lukasz Majewski <lukma at denx dot de>]

Hi Adhemerval,

> On 18/01/2020 04:20, Lukasz Majewski wrote:
> > Now, internally the deprecated stime uses __clock_settime64. This
> > patch is necessary for having architectures with __WORDSIZE == 32 &&
> > __TIMESIZE == 32 (like e.g. ARM32) Y2038 safe.
> > 
> > Build tests:
> > ./src/scripts/build-many-glibcs.py glibcs
> > ---
> >  time/stime.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/time/stime.c b/time/stime.c
> > index 576fa9c0c9..963902126b 100644
> > --- a/time/stime.c
> > +++ b/time/stime.c
> > @@ -27,11 +27,11 @@ int
> >  attribute_compat_text_section
> >  __stime (const time_t *when)
> >  {
> > -  struct timespec ts;
> > +  struct __timespec64 ts;
> >    ts.tv_sec = *when;
> >    ts.tv_nsec = 0;
> >  
> > -  return __clock_settime (CLOCK_REALTIME, &ts);
> > +  return __clock_settime64 (CLOCK_REALTIME, &ts);
> >  }
> >  
> >  compat_symbol (libc, __stime, stime, GLIBC_2_0);
> >   
> 
> For !__ASSUME_TIME64_SYSCALLS builds time_t will continue to be 32
> bits and stime will continue to be non Y2038 safe.

This patch is a preparatory work for introducing support of
-D_TIME_BITS=64 compilation flag when compiling programs with glibc [1].

Then the __USE_TIME_BITS64 is defined for exported glibc headers.
After this the time_t will become __time64_t on e.g. ARM32 bits
(__WORDSIZE==32 && __TIMESIZE==32).

As pointed out by Joseph [3], without such code we will not be able
atomically introduce _TIME_BITS=64 support.

>  Also, internally
> __clock_settime will first try to issue __NR_clock_settime64, so
> current code already accomplishes what this patch is aiming to do.

There is a use case when we do need to call __clock_settime64 though:

- ARM32 program is compiled with -D_TIME_BITS=64
- The clock_settime (or stime) internally uses __clock_settime() which
  in this case supports only 32 bit time API.

  To have this system Y2038 safe - one needs to call __clock_settime64
  explicitly to support passing arguments via struct __timespec64.

  This is true for all calls of __clock_settime/__clock_gettime
  (functions to be used internally by glibc, as we ought to switch to
  e.g. struct __timespec64).

Links:

[1] -
https://github.com/lmajewski/y2038_glibc/commit/e03c7188c72dd78d7141cf88f24dd2a5fd14c4f1#diff-a5ab6c74681eaf0569ed54f6bf0d7978R386

[2] -
https://github.com/lmajewski/y2038_glibc/commit/e03c7188c72dd78d7141cf88f24dd2a5fd14c4f1#diff-c051022b496f12bd9028edb46b8ec04dR7

[3] - https://sourceware.org/ml/libc-alpha/2020-01/msg00369.html

[4] -
https://github.com/lmajewski/y2038_glibc/blob/glibc_settimeofday_64bit_conversion_v1/sysdeps/unix/sysv/linux/clock_settime.c#L57



Best regards,

Lukasz Majewski

--

DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-59 Fax: (+49)-8142-66989-80 Email: lukma@denx.de

Attachment: pgpxiRdRA0L_I.pgp
Description: OpenPGP digital signature