[v2] y2038: linux: Provide __time64 implementation

  In the glibc the time function can use vDSO (on power and x86 the
USE_IFUNC_TIME is defined), time syscall or 'default' time() from
./time/time.c (as a fallback).

In this patch the last function (time) has been refactored and moved
to ./sysdeps/unix/sysv/linux/time.c to be Linux specific.

The new __time64 explicit 64 bit function for providing 64 bit value of
seconds after epoch (by internally calling __clock_gettime64) has been
introduced.

Moreover, a 32 bit version - __time has been refactored to internally
use __time64.

The __time is now supposed to be used on systems still supporting 32 bit
time (__TIMESIZE != 64) - hence the necessary check for time_t potential
overflow.

The iFUNC vDSO direct call optimization has been removed from both i686 and
powerpc32 (USE_IFUNC_TIME is not defined for those architectures
anymore). The Linux kernel does not provide a y2038 safe implementation of
time neither it plans to provide it in the future, __clock_gettime64
should be used instead. Keeping support for this optimization would require
to handle another build permutation (!__ASSUME_TIME64_SYSCALLS &&
USE_IFUNC_TIME which adds more complexity and has limited use (since the
idea is to eventually have a y2038 safe glibc build).

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 __time64 and __time.

---
Changes for v2:
- Add guards #ifdef __x86_64__ and #ifdef __powerpc64__ to avoid using time
vDSO on 32 bit powerpc and x86
- Remove comment about time syscall conversion to 64 bit
- Avoid implicit checks on timer (shall be timer != NULL)
- Add comment about disabling vDSO optimization on powerpc32 and x86
---
 include/time.h                         |  7 +++++
 sysdeps/unix/sysv/linux/powerpc/time.c |  4 ++-
 sysdeps/unix/sysv/linux/time.c         | 37 +++++++++++++++++++++++++-
 sysdeps/unix/sysv/linux/x86/time.c     |  4 ++-
 4 files changed, 49 insertions(+), 3 deletions(-)
  

On 16/10/2020 10:32, Lukasz Majewski wrote:
> In the glibc the time function can use vDSO (on power and x86 the
> USE_IFUNC_TIME is defined), time syscall or 'default' time() from
> ./time/time.c (as a fallback).
> 
> In this patch the last function (time) has been refactored and moved
> to ./sysdeps/unix/sysv/linux/time.c to be Linux specific.
> 
> The new __time64 explicit 64 bit function for providing 64 bit value of
> seconds after epoch (by internally calling __clock_gettime64) has been
> introduced.
> 
> Moreover, a 32 bit version - __time has been refactored to internally
> use __time64.
> 
> The __time is now supposed to be used on systems still supporting 32 bit
> time (__TIMESIZE != 64) - hence the necessary check for time_t potential
> overflow.
> 
> The iFUNC vDSO direct call optimization has been removed from both i686 and
> powerpc32 (USE_IFUNC_TIME is not defined for those architectures
> anymore). The Linux kernel does not provide a y2038 safe implementation of
> time neither it plans to provide it in the future, __clock_gettime64
> should be used instead. Keeping support for this optimization would require
> to handle another build permutation (!__ASSUME_TIME64_SYSCALLS &&
> USE_IFUNC_TIME which adds more complexity and has limited use (since the
> idea is to eventually have a y2038 safe glibc build).
> 
> 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 __time64 and __time.

LGTM, thanks.

Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org> 

> 
> ---
> Changes for v2:
> - Add guards #ifdef __x86_64__ and #ifdef __powerpc64__ to avoid using time
> vDSO on 32 bit powerpc and x86
> - Remove comment about time syscall conversion to 64 bit
> - Avoid implicit checks on timer (shall be timer != NULL)
> - Add comment about disabling vDSO optimization on powerpc32 and x86
> ---
>  include/time.h                         |  7 +++++
>  sysdeps/unix/sysv/linux/powerpc/time.c |  4 ++-
>  sysdeps/unix/sysv/linux/time.c         | 37 +++++++++++++++++++++++++-
>  sysdeps/unix/sysv/linux/x86/time.c     |  4 ++-
>  4 files changed, 49 insertions(+), 3 deletions(-)
> 
> diff --git a/include/time.h b/include/time.h
> index edf6cdf829..caf2af5e74 100644
> --- a/include/time.h
> +++ b/include/time.h
> @@ -317,6 +317,13 @@ extern int __timespec_get64 (struct __timespec64 *ts, int base);
>  libc_hidden_proto (__timespec_get64)
>  #endif
>  
> +#if __TIMESIZE == 64
> +# define __time64 __time
> +#else
> +extern __time64_t __time64 (__time64_t *timer);
> +libc_hidden_proto (__time64)
> +#endif
> +
>  /* Use in the clock_* functions.  Size of the field representing the
>     actual clock ID.  */
>  #define CLOCK_IDFIELD_SIZE	3

Ok.

> diff --git a/sysdeps/unix/sysv/linux/powerpc/time.c b/sysdeps/unix/sysv/linux/powerpc/time.c
> index d10f449c5c..4fd5e138a3 100644
> --- a/sysdeps/unix/sysv/linux/powerpc/time.c
> +++ b/sysdeps/unix/sysv/linux/powerpc/time.c
> @@ -16,5 +16,7 @@
>     License along with the GNU C Library; if not, see
>     <https://www.gnu.org/licenses/>.  */
>  
> -#define USE_IFUNC_TIME
> +#ifdef __powerpc64__
> +# define USE_IFUNC_TIME
> +#endif
>  #include <sysdeps/unix/sysv/linux/time.c>

Ok.

> diff --git a/sysdeps/unix/sysv/linux/time.c b/sysdeps/unix/sysv/linux/time.c
> index 9d8e573c0a..80641d9ca4 100644
> --- a/sysdeps/unix/sysv/linux/time.c
> +++ b/sysdeps/unix/sysv/linux/time.c
> @@ -47,5 +47,40 @@ time (time_t *t)
>  }
>  # endif /* !SHARED */
>  #else /* USE_IFUNC_TIME  */
> -# include <time/time.c>
> +# include <time.h>
> +# include <time-clockid.h>
> +# include <errno.h>
> +/* Return the time now, and store it in *TIMER if not NULL.  */
> +

I would add a new line between the includes and the comment.

> +__time64_t
> +__time64 (__time64_t *timer)
> +{
> +  struct __timespec64 ts;
> +  __clock_gettime64 (TIME_CLOCK_GETTIME_CLOCKID, &ts);
> +
> +  if (timer != NULL)
> +    *timer = ts.tv_sec;
> +  return ts.tv_sec;
> +}
> +
> +# if __TIMESIZE != 64
> +libc_hidden_def (__time64)
> +
> +time_t
> +__time (time_t *timer)
> +{
> +  __time64_t t = __time64 (NULL);
> +
> +  if (! in_time_t_range (t))
> +    {
> +      __set_errno (EOVERFLOW);
> +      return -1;
> +    }
> +
> +  if (timer != NULL)
> +    *timer = t;
> +  return t;
> +}
> +# endif
> +weak_alias (__time, time)
>  #endif

Ok.

> diff --git a/sysdeps/unix/sysv/linux/x86/time.c b/sysdeps/unix/sysv/linux/x86/time.c
> index 1d158e443c..ed2c5f5dbb 100644
> --- a/sysdeps/unix/sysv/linux/x86/time.c
> +++ b/sysdeps/unix/sysv/linux/x86/time.c
> @@ -16,5 +16,7 @@
>     License along with the GNU C Library; if not, see
>     <https://www.gnu.org/licenses/>.  */
>  
> -#define USE_IFUNC_TIME
> +#ifdef __x86_64__
> +# define USE_IFUNC_TIME
> +#endif
>  #include <sysdeps/unix/sysv/linux/time.c>
> 

Ok.