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

[Lukasz Majewski <lukma at denx dot de>]

Hi Alistair,

> 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.

Thank you for preparing and applying this patch.


Just informative note (for the record). For ARM 32 bit systems - after
checking with [1] it has been apparent that those systems doesn't yet
support __vdso_clock_gettime64 [2].

If anybody would need to build glibc with headers from Linux 5.1+ (with
clock_gettime64 support), he/she shall apply attached patch.


This is not a problem for now, as we still have some time until
__ASSUME_TIME64_SYSCALLS is enabled by default in glibc. 
Moreover, I do guess that __vdso_clock_gettime64 for ARM 32 bits will
be available by then :-).


Links:

[1] - https://github.com/lmajewski/meta-y2038
[2] -
https://elixir.bootlin.com/linux/latest/ident/__vdso_clock_gettime64

> 
> 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.
> > >  




Best regards,

Lukasz Majewski

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From d48860f4f8a8d75e689ee7f91214698598fbbcb8 Mon Sep 17 00:00:00 2001
From: Lukasz Majewski <lukma@denx.de>
Date: Thu, 5 Dec 2019 11:12:48 +0100
Subject: [PATCH] Y2038: clock_gettime: Use non vDSO syscall for
 clock_gettime64 on 32 bit ARM

Up till Linux v5.4 [*], there is no 64 bit version of __vdso_clock_gettime64()
available for 32 bit ARM.

For that reason one shall use non VDSO syscall for this purpose.

Link:
[*] - https://elixir.bootlin.com/linux/latest/ident/__vdso_clock_gettime64
---
 sysdeps/unix/sysv/linux/clock_gettime.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/sysdeps/unix/sysv/linux/clock_gettime.c b/sysdeps/unix/sysv/linux/clock_gettime.c
index 875c4fe905..a717d8d88a 100644
--- a/sysdeps/unix/sysv/linux/clock_gettime.c
+++ b/sysdeps/unix/sysv/linux/clock_gettime.c
@@ -38,7 +38,11 @@ __clock_gettime64 (clockid_t clock_id, struct __timespec64 *tp)
 #  define __NR_clock_gettime64   __NR_clock_gettime
 #  define __vdso_clock_gettime64 __vdso_clock_gettime
 # endif
+# ifdef HAVE_CLOCK_GETTIME64_VSYSCALL
    return INLINE_VSYSCALL (clock_gettime64, 2, clock_id, tp);
+# else
+   return INLINE_SYSCALL (clock_gettime64, 2, clock_id, tp);
+# endif
 #else
 # if defined HAVE_CLOCK_GETTIME64_VSYSCALL
   int ret64 = INLINE_VSYSCALL (clock_gettime64, 2, clock_id, tp);
-- 
2.20.1

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