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

[Lukasz Majewski]

Hi Adhemerval,

> On 20/01/2020 14:58, Lukasz Majewski wrote:
> > 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.  
> 
> The _TIME_BITS=64 is a redirection for programs build against the
> glibc provided headers, not for glibc build *itself*. Otherwise we
> will change the ABI depending of the minimum supported kernel (which
> might define __ASSUME_TIME64_SYSCALLS).
> 
> In this compatibility case we need to always assure the internal
> time_t is 32 bits to architecture that provided such interface.
> 
> 
> >   
> >>  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.  
> 
> Arm programs linked against old glibc will need to continue to call
> stime with time_t being 32-bits.  The stime won't be exported for
> -D_TIME_BITS=64, neither a stime64 will be implemented.

Ok.

> 
> > 
> >   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).  
> 
> The idea of deprecate and make stime a compat symbol is exactly to
> avoid need to provide a Y2038 version of it. Newer programs that aim
> to be Y2038 safe will need to use clock_settime instead.

I've noted that stime is marked as "deprecated". If we can agree that
it will be removed from glibc soon (or at least before Y2038 :-)) or we
explicitly state that it will NOT be Y2038 safe, then indeed this patch
is not needed.

> 
> 
> > 
> > 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 
>  


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
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 488 bytes
Desc: OpenPGP digital signature
URL: <http://sourceware.org/pipermail/libc-alpha/attachments/20200121/ab44fd67/attachment.sig>