Re: [RFC v3 02/23] sysdeps/gettimeofday: Use clock_gettime64 if avaliable

[Florian Weimer <fweimer at redhat dot com>]

* Alistair Francis:

> diff --git a/sysdeps/unix/sysv/linux/gettimeofday.c b/sysdeps/unix/sysv/linux/gettimeofday.c
> index a74f03825a..151b1e606c 100644
> --- a/sysdeps/unix/sysv/linux/gettimeofday.c
> +++ b/sysdeps/unix/sysv/linux/gettimeofday.c
> @@ -32,7 +32,35 @@
>  int
>  __gettimeofday (struct timeval *tv, struct timezone *tz)
>  {
> +#ifdef __ASSUME_TIME64_SYSCALLS
> +  int ret;
> +  struct __timespec64 now;
> +
> +  ret = INLINE_VSYSCALL (clock_gettime64, 2, CLOCK_REALTIME,
> +                         &now);
> +
> +  /* Convert from timespec to timeval */
> +  tv->tv_sec = now.tv_sec;
> +  tv->tv_usec = now.tv_nsec / 1000;
> +
> +  return ret;
> +#else
> +# ifdef __NR_clock_gettime64
> +  long int ret;
> +  struct __timespec64 now;
> +
> +  ret = INLINE_VSYSCALL (clock_gettime64, 2, CLOCK_REALTIME,
> +                         &now);
> +
> +  /* Convert from timespec to timeval */
> +  tv->tv_sec = now.tv_sec;
> +  tv->tv_usec = now.tv_nsec / 1000;
> +
> +  if (ret == 0 || errno != ENOSYS)
> +    return ret;
> +# endif
>    return INLINE_VSYSCALL (gettimeofday, 2, tv, tz);
> +#endif
>  }

This loses vDSO acceleration if glibc is compiled with kernel headers
which define __NR_clock_gettime64, but the run-time kernel does not have
clock_gettime64 in the vDSO.

And the kernel folks really want us to call clock_gettime when the user
calls the 32-bit function, for tracability of legacy processes.

Thanks,
Florian