Re: [PATCH v3 2/2] sysdeps/clock_gettime: Use clock_gettime64 if avaliable

[Alistair Francis <alistair23 at gmail dot com>]

On Wed, Dec 4, 2019 at 9:24 AM Adhemerval Zanella
<adhemerval.zanella@linaro.org> wrote:
>
>
>
> On 03/12/2019 16:29, Adhemerval Zanella wrote:
> >
> >
> > On 23/11/2019 19:27, Alistair Francis wrote:
> >> With the clock_gettime64 call we prefer to use vDSO. There is no call
> >> to clock_gettime64 on glibc with older headers and kernel 5.1+ if it
> >> doesn't support vDSO.
> >
> > Ok with the fix below regarding HAVE_CLOCK_GETTIME64_VSYSCALL.
>
> As [1] I think we can handle both the cases:
>
>   8.  Define both __NR_clock_gettime64, provide a 64-bit vDSO, define
>       __NR_clock_gettime, and provide a 32-bit vDSO.
>       - i.e: some 32-bits ports built against kernel header equal or newer
>         then v5.1 (i386, arm, and mips).
>
>   9.  Define both __NR_clock_gettime64, provide a 64-bit vDSO, and
>       define __NR_clock_gettime (unlikely, but possible)..
>
> With my vDSO refactor to use relro data structures.
>
> This patch is ok.
>
> Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>

Thanks :)

I'll apply these two patches later today unless there are any other comments.

Alistair

>
> [1] https://sourceware.org/ml/libc-alpha/2019-12/msg00142.html
>
> >
> >> ---
> >> This was patch was runtime tested with RV32 and RV64
> >> It was build tested using the ./scripts/build-many-glibcs.py script.
> >>
> >> I also ran:
> >> $ make ; make install ; make check
> >> tests on native ARM (32-bit) with the following three confiugrations:
> >>  - 4.19 Kernel and 4.19 Headers
> >>  - 5.2 Kernel and 4.19 Headers
> >>  - 5.2 Kernel and 5.2 Headers
> >> and didn't see any regressions
> >>
> >> v3:
> >>  - Assume HAVE_CLOCK_GETTIME64_VSYSCALL means we have __NR_clock_gettime64
> >>  - Change code style to be more glibc-ish
> >> v2:
> >>  - Add commit message
> >>  - Change ret_64 to int
> >>
> >>  include/time.h                          |  3 ++
> >>  sysdeps/unix/sysv/linux/clock_gettime.c | 44 ++++++++++++++++++++++++-
> >>  2 files changed, 46 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/include/time.h b/include/time.h
> >> index d7800eb30f..c19c73ae09 100644
> >> --- a/include/time.h
> >> +++ b/include/time.h
> >> @@ -211,11 +211,14 @@ extern double __difftime (time_t time1, time_t time0);
> >>
> >>  #if __TIMESIZE == 64
> >>  # define __clock_nanosleep_time64 __clock_nanosleep
> >> +# define __clock_gettime64 __clock_gettime
> >>  #else
> >>  extern int __clock_nanosleep_time64 (clockid_t clock_id,
> >>                                       int flags, const struct __timespec64 *req,
> >>                                       struct __timespec64 *rem);
> >>  libc_hidden_proto (__clock_nanosleep_time64)
> >> +extern int __clock_gettime64 (clockid_t clock_id, struct __timespec64 *tp);
> >> +libc_hidden_proto (__clock_gettime64)
> >>  #endif
> >>
> >>  /* Use in the clock_* functions.  Size of the field representing the
> >> diff --git a/sysdeps/unix/sysv/linux/clock_gettime.c b/sysdeps/unix/sysv/linux/clock_gettime.c
> >> index ca40983f6c..875c4fe905 100644
> >> --- a/sysdeps/unix/sysv/linux/clock_gettime.c
> >> +++ b/sysdeps/unix/sysv/linux/clock_gettime.c
> >> @@ -17,6 +17,7 @@
> >>     <https://www.gnu.org/licenses/>.  */
> >>
> >>  #include <sysdep.h>
> >> +#include <kernel-features.h>
> >>  #include <errno.h>
> >>  #include <time.h>
> >>  #include "kernel-posix-cpu-timers.h"
> >> @@ -30,10 +31,51 @@
> >>
> >>  /* Get current value of CLOCK and store it in TP.  */
> >>  int
> >> +__clock_gettime64 (clockid_t clock_id, struct __timespec64 *tp)
> >> +{
> >> +#ifdef __ASSUME_TIME64_SYSCALLS
> >> +# ifndef __NR_clock_gettime64
> >> +#  define __NR_clock_gettime64   __NR_clock_gettime
> >> +#  define __vdso_clock_gettime64 __vdso_clock_gettime
> >> +# endif
> >> +   return INLINE_VSYSCALL (clock_gettime64, 2, clock_id, tp);
> >
> > Ok, in this case either __vdso_clock_gettime/__NR_clock_gettime or
> > __vdso_clock_gettime64/__NR_clock_gettime64 will be called.
> >
> >> +#else
> >> +# if defined HAVE_CLOCK_GETTIME64_VSYSCALL
> >> +  int ret64 = INLINE_VSYSCALL (clock_gettime64, 2, clock_id, tp);
> >> +  if (ret64 == 0 || errno != ENOSYS)
> >> +    return ret64;
> >> +# endif
> > This should be:
> >
> > #if defined __NR_clock_gettime64
> >   int ret64 = INLINE_VSYSCALL (clock_gettime64, ...)
> >   [...]
> >
> > And before sysdep-vdso.h it should be.
> >
> > #if defined HAVE_CLOCK_GETTIME_VSYSCALL || defined HAVE_CLOCK_GETTIME64_VSYSCALL
> > # define HAVE_SYSCALL
> > #endif
> >
> > If !HAVE_SYSCALL the INLINE_VSYSCALL is defined as INLINE_SYCALL.
> > It means that if an architecture does provide __NR_clock_gettime64
> > but not provide HAVE_CLOCK_GETTIME64_VSYSCALL, it will still use
> > the syscall. This code only uses the syscall if the vDSO is still
> > present.
> >
> > I hope I can get my vDSO refactor, which would simplify a bit this
> > code.
> >
> >> +  struct timespec tp32;
> >> +  int ret = INLINE_VSYSCALL (clock_gettime, 2, clock_id, &tp32);
> >> +  if (ret == 0)
> >> +    *tp = valid_timespec_to_timespec64 (tp32);
> >> +  return ret;
> >> +#endif
> >> +}
> >
> > Ok, old fallback to time32 vdso/syscall.
> >
> >> +
> >> +#if __TIMESIZE != 64
> >> +int
> >>  __clock_gettime (clockid_t clock_id, struct timespec *tp)
> >>  {
> >> -  return INLINE_VSYSCALL (clock_gettime, 2, clock_id, tp);
> >> +  int ret;
> >> +  struct __timespec64 tp64;
> >> +
> >> +  ret = __clock_gettime64 (clock_id, &tp64);
> >> +
> >> +  if (ret == 0)
> >> +    {
> >> +      if (! in_time_t_range (tp64.tv_sec))
> >> +        {
> >> +          __set_errno (EOVERFLOW);
> >> +          return -1;
> >> +        }
> >> +
> >> +      *tp = valid_timespec64_to_timespec (tp64);
> >> +    }
> >> +
> >> +  return ret;
> >>  }
> >> +#endif
> >>  libc_hidden_def (__clock_gettime)
> >>
> >>  versioned_symbol (libc, __clock_gettime, clock_gettime, GLIBC_2_17);
> >>
> >
> > Ok.
> >