[04/18] linux: Only use 64-bit syscall if required for ppoll

  For !__ASSUME_TIME64_SYSCALLS there is no need to issue a 64-bit syscall
if the provided timeout fits in a 32-bit one.  The 64-bit usage should
be rare since the timeout is a relative one.  This also avoids the need
to use supports_time64() (which breaks the usage case of live migration
like CRIU or similar).

Checked on i686-linux-gnu on a 4.15 kernel and on a 5.11 kernel
(with and without --enable-kernel=5.1) and on x86_64-linux-gnu.
---
 sysdeps/unix/sysv/linux/Makefile    |  9 +++++++
 sysdeps/unix/sysv/linux/ppoll.c     | 41 +++++++++++------------------
 sysdeps/unix/sysv/linux/tst-ppoll.c | 15 +++++++++++
 3 files changed, 40 insertions(+), 25 deletions(-)
  

On Thu, 17 Jun 2021 08:50:50 -0300
Adhemerval Zanella <adhemerval.zanella@linaro.org> wrote:

> For !__ASSUME_TIME64_SYSCALLS there is no need to issue a 64-bit
> syscall if the provided timeout fits in a 32-bit one.  The 64-bit
> usage should be rare since the timeout is a relative one.  This also
> avoids the need to use supports_time64() (which breaks the usage case
> of live migration like CRIU or similar).
> 
> Checked on i686-linux-gnu on a 4.15 kernel and on a 5.11 kernel
> (with and without --enable-kernel=5.1) and on x86_64-linux-gnu.
> ---
>  sysdeps/unix/sysv/linux/Makefile    |  9 +++++++
>  sysdeps/unix/sysv/linux/ppoll.c     | 41
> +++++++++++------------------ sysdeps/unix/sysv/linux/tst-ppoll.c |
> 15 +++++++++++ 3 files changed, 40 insertions(+), 25 deletions(-)
> 
> diff --git a/sysdeps/unix/sysv/linux/Makefile
> b/sysdeps/unix/sysv/linux/Makefile index 294c366e3b..c36ea0e494 100644
> --- a/sysdeps/unix/sysv/linux/Makefile
> +++ b/sysdeps/unix/sysv/linux/Makefile
> @@ -137,6 +137,15 @@ tests-time64 += \
>  
>  CFLAGS-tst-sigcontext-get_pc.c = -fasynchronous-unwind-tables
>  
> +ifeq (yes,$(build-shared))
> +librt = $(common-objpfx)rt/librt.so
> +else
> +librt = $(common-objpfx)rt/librt.a
> +endif
> +
> +$(objpfx)tst-ppoll: $(librt)
> +$(objpfx)tst-ppoll-time64: $(librt)
> +
>  # Generate the list of SYS_* macros for the system calls (__NR_*
>  # macros).  The file syscall-names.list contains all possible system
>  # call names, and the generated header file produces SYS_* macros for
> diff --git a/sysdeps/unix/sysv/linux/ppoll.c
> b/sysdeps/unix/sysv/linux/ppoll.c index 624f14f517..e1ad316e2e 100644
> --- a/sysdeps/unix/sysv/linux/ppoll.c
> +++ b/sysdeps/unix/sysv/linux/ppoll.c
> @@ -21,9 +21,6 @@
>  #include <time.h>
>  #include <sys/poll.h>
>  #include <sysdep-cancel.h>
> -#include <kernel-features.h>
> -#include <time64-support.h>
> -
>  
>  int
>  __ppoll64 (struct pollfd *fds, nfds_t nfds, const struct
> __timespec64 *timeout, @@ -38,40 +35,34 @@ __ppoll64 (struct pollfd
> *fds, nfds_t nfds, const struct __timespec64 *timeout, timeout =
> &tval; }
>  
> -  int ret;
> -
> -  if (supports_time64 ())
> -    {
>  #ifndef __NR_ppoll_time64
>  # define __NR_ppoll_time64 __NR_ppoll
>  #endif
> +
> +#ifdef __ASSUME_TIME64_SYSCALLS
> +  return SYSCALL_CANCEL (ppoll_time64, fds, nfds, timeout, sigmask,
> +			 __NSIG_BYTES);
> +#else
> +  bool is32bit = timeout != NULL
> +		 ? in_time_t_range (timeout->tv_sec) : true;
> +  int ret;
> +  if (!is32bit)
> +    {
>        ret = SYSCALL_CANCEL (ppoll_time64, fds, nfds, timeout,
> sigmask, __NSIG_BYTES);
> -
>        if (ret == 0 || errno != ENOSYS)
>  	return ret;
> -
> -      mark_time64_unsupported ();
> +      __set_errno (EOVERFLOW);
> +      return -1;
>      }
>  
> -#ifndef __ASSUME_TIME64_SYSCALLS
>    struct timespec ts32;
> -  if (timeout)
> -    {
> -      if (! in_time_t_range (timeout->tv_sec))
> -        {
> -          __set_errno (EOVERFLOW);
> -          return -1;
> -        }
> -
> -      ts32 = valid_timespec64_to_timespec (*timeout);
> -    }
> +  if (timeout != NULL)
> +    ts32 = valid_timespec64_to_timespec (*timeout);
>  
> -  ret = SYSCALL_CANCEL (ppoll, fds, nfds, timeout ? &ts32 : NULL,
> sigmask,
> -			__NSIG_BYTES);
> +  return SYSCALL_CANCEL (ppoll, fds, nfds, timeout ? &ts32 : NULL,
> sigmask,
> +			 __NSIG_BYTES);
>  #endif
> -
> -  return ret;
>  }
>  
>  #if __TIMESIZE != 64
> diff --git a/sysdeps/unix/sysv/linux/tst-ppoll.c
> b/sysdeps/unix/sysv/linux/tst-ppoll.c index 9fe6ad07ce..e21e2fcc72
> 100644 --- a/sysdeps/unix/sysv/linux/tst-ppoll.c
> +++ b/sysdeps/unix/sysv/linux/tst-ppoll.c
> @@ -19,9 +19,11 @@
>  #include <time.h>
>  #include <poll.h>
>  #include <errno.h>
> +#include <intprops.h>
>  #include <support/check.h>
>  #include <support/xtime.h>
>  #include <support/timespec.h>
> +#include <support/support.h>
>  #include <stdbool.h>
>  
>  static int test_ppoll_timeout (bool zero_tmo)
> @@ -41,6 +43,16 @@ static int test_ppoll_timeout (bool zero_tmo)
>    return 0;
>  }
>  
> +static void
> +test_ppoll_large_timeout (void)
> +{
> +  support_create_timer (0, 100000000, false, NULL);
> +  struct timespec ts = { TYPE_MAXIMUM (time_t), 0 };
> +  struct pollfd fds = { -1, 0, 0 };
> +  TEST_COMPARE (ppoll (&fds, 1, &ts, 0), -1);
> +  TEST_VERIFY (errno == EINTR || errno == EOVERFLOW);
> +}
> +
>  static int
>  do_test (void)
>  {
> @@ -50,6 +62,9 @@ do_test (void)
>    /* Check if ppoll exits after specified timeout.  */
>    test_ppoll_timeout (false);
>  
> +  /* Check if ppoll with large timeout.  */
> +  test_ppoll_large_timeout ();
> +
>    return 0;
>  }
>  

Reviewed-by: Lukasz Majewski <lukma@denx.de>


Best regards,

Lukasz Majewski

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