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

[Adhemerval Zanella <adhemerval dot zanella at linaro dot org>]

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>

[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.
>