Re: [PATCH v5] sysdeps/clock_nanosleep: Use clock_nanosleep_time64 if avaliable

[Lukasz Majewski <lukma at denx dot de>]

Hi Alistair,

Please find my comments regarding checking of NULL pointers.

> The clock_nanosleep syscall is not supported on newer 32-bit
> platforms (such as RV32). To fix this issue let's use
> clock_nanosleep_time64 if it is avaliable.
> ---
> 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
> 
> v5:
>  - Fix clock_nanosleep syscall
>  - Rebase on master
> 
> v4:
>  - Rebase on master
>  - Use __clock_nanosleep to avoid duplicate implementations
>  - Fix the error handling when a syscall fails
> v2:
>  - Explicitly include `#include <kernel-features.h>`
> 
>  include/time.h                            | 20 +++++++
>  sysdeps/unix/sysv/linux/clock_nanosleep.c | 66
> +++++++++++++++++++++-- 2 files changed, 81 insertions(+), 5
> deletions(-)
> 
> diff --git a/include/time.h b/include/time.h
> index b3e635395db..03389bda290 100644
> --- a/include/time.h
> +++ b/include/time.h
> @@ -209,6 +209,26 @@ libc_hidden_proto (__difftime64)
>  
>  extern double __difftime (time_t time1, time_t time0);
>  
> +#if __TIMESIZE == 64
> +# define __thrd_sleep_time64 thrd_sleep
> +# define __clock_nanosleep_time64 __clock_nanosleep
> +# define __nanosleep_time64 __nanosleep
> +# define __nanosleep_nocancel_time64 __nanosleep_nocancel
> +#else
> +extern int __thrd_sleep_time64 (const struct __timespec64*
> time_point,
> +                                struct __timespec64* remaining);
> +libc_hidden_proto (__thrd_sleep_time64)
> +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 __nanosleep_time64 (const struct __timespec64
> *requested_time,
> +                                struct __timespec64 *remaining);
> +libc_hidden_proto (__nanosleep_time64)
> +extern int __nanosleep_nocancel_time64 (const struct __timespec64
> *requested_time,
> +                                        struct __timespec64
> *remaining); +libc_hidden_proto (__nanosleep_nocancel_time64)
> +#endif
>  
>  /* Use in the clock_* functions.  Size of the field representing the
>     actual clock ID.  */
> diff --git a/sysdeps/unix/sysv/linux/clock_nanosleep.c
> b/sysdeps/unix/sysv/linux/clock_nanosleep.c index
> f3c6fd2d5f7..7212dcf9c6d 100644 ---
> a/sysdeps/unix/sysv/linux/clock_nanosleep.c +++
> b/sysdeps/unix/sysv/linux/clock_nanosleep.c @@ -16,6 +16,7 @@
>     <https://www.gnu.org/licenses/>.  */
>  
>  #include <time.h>
> +#include <kernel-features.h>
>  #include <errno.h>
>  
>  #include <sysdep-cancel.h>
> @@ -26,9 +27,11 @@
>  /* We can simply use the syscall.  The CPU clocks are not supported
>     with this function.  */
>  int
> -__clock_nanosleep (clockid_t clock_id, int flags, const struct
> timespec *req,
> -		   struct timespec *rem)
> +__clock_nanosleep_time64 (clockid_t clock_id, int flags, const
> struct __timespec64 *req,
> +                          struct __timespec64 *rem)
>  {
> +  int r;
> +
>    if (clock_id == CLOCK_THREAD_CPUTIME_ID)
>      return EINVAL;
>    if (clock_id == CLOCK_PROCESS_CPUTIME_ID)
> @@ -37,11 +40,64 @@ __clock_nanosleep (clockid_t clock_id, int flags,
> const struct timespec *req, /* If the call is interrupted by a signal
> handler or encounters an error, it returns a positive value similar
> to errno.  */ INTERNAL_SYSCALL_DECL (err);
> -  int r = INTERNAL_SYSCALL_CANCEL (clock_nanosleep, err, clock_id,
> flags,
> -				   req, rem);
> +
> +#ifdef __ASSUME_TIME64_SYSCALLS
> +# ifndef __NR_clock_nanosleep_time64
> +#  define __NR_clock_nanosleep_time64 __NR_clock_nanosleep
> +# endif
> +  r = INTERNAL_SYSCALL_CANCEL (clock_nanosleep_time64, err, clock_id,
> +                               flags, req, rem);
> +#else
> +# ifdef __NR_clock_nanosleep_time64
> +  r = INTERNAL_SYSCALL_CANCEL (clock_nanosleep_time64, err, clock_id,
> +                               flags, req, rem);
> +
> +  if (r == 0 || errno != ENOSYS)
> +    {
> +      return (INTERNAL_SYSCALL_ERROR_P (r, err)
> +              ? INTERNAL_SYSCALL_ERRNO (r, err) : 0);
> +    }
> +# endif /* __NR_clock_nanosleep_time64 */
> +  struct timespec ts32, tr32;
> +
> +  if (! in_time_t_range (req->tv_sec))
> +    {
> +      __set_errno (EOVERFLOW);
> +      return -1;
> +    }
> +
> +  ts32 = valid_timespec64_to_timespec (*req);

Here we don't need to check req == NULL, as we will go into this piece
of code only for 32 bit systems (and kernel < 5.1) with glibc's local
copy of struct __timespec64.

> +  r =  INTERNAL_SYSCALL_CANCEL (clock_nanosleep, err, clock_id,
> flags,
> +                                &ts32, &tr32);
> +
> +  if ((r == 0 || errno != ENOSYS) && rem)
> +    *rem = valid_timespec_to_timespec64 (tr32);
> +#endif /* __ASSUME_TIME64_SYSCALLS */
> +
>    return (INTERNAL_SYSCALL_ERROR_P (r, err)
> -	  ? INTERNAL_SYSCALL_ERRNO (r, err) : 0);
> +          ? INTERNAL_SYSCALL_ERRNO (r, err) : 0);
>  }
> +
> +#if __TIMESIZE != 64
> +int
> +__clock_nanosleep (clockid_t clock_id, int flags, const struct
> timespec *req,
> +                   struct timespec *rem)
> +{
> +  int r;
> +  struct __timespec64 treq64, trem64;
> +

^^^^^^^^^^^^ - [*]

> +  treq64 = valid_timespec_to_timespec64 (*req);

The above line would cause regression. Please find below explanation:

The check on *rqtp (in Linux kernel's clock_nanosleep syscall handling):
https://elixir.bootlin.com/linux/v5.4-rc5/source/kernel/time/posix-timers.c#L1220

When compiling test program with clock_nanosleep() passing *request [1]
as NULL [3] - the clock_nanosleep returns 14, which corresponds to 
#define EFAULT 14 [2] (which matches [1]).

Hence we should have following code in [*]:

if (req == NULL)
  {
    __set_errno(EFAULT)
    returm 1;
  }


Otherwise we will break in glibc before we enter the clock_nanosleep
syscall (which would then return with proper error code).


Links:
[1] - http://man7.org/linux/man-pages/man2/clock_nanosleep.2.html
[2] - cpp -dM /usr/include/errno.h | grep 'define E' | sort -n -k 3
[3] - test program:

int main(int argc, char **argv)
{
  int result;

  result = clock_nanosleep(CLOCK_REALTIME, 0 /* relative */,
    NULL, NULL);

  if (result)
    printf("clock_nanosleep: %d\n", result);

  return 0;
}

> +  r = __clock_nanosleep_time64 (clock_id, flags, &treq64, &trem64);
> +
> +  if (r == 0 || errno != ENOSYS)
> +    {
> +      if (rem)
> +        *rem = valid_timespec64_to_timespec (trem64);
> +    }
> +
> +  return r;
> +}
> +#endif
>  libc_hidden_def (__clock_nanosleep)
>  versioned_symbol (libc, __clock_nanosleep, clock_nanosleep,
> GLIBC_2_17); /* clock_nanosleep moved to libc in version 2.17;




Best regards,

Lukasz Majewski

--

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