[09/18] linux: Remove time64-support

  It breaks the usage case of live migration like CRIU or similar
and most usages can be optimized away by either building glibc with
a minimum 5.1 kernel or by using the 32-bit syscall for the common
case.

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         |  2 +-
 sysdeps/unix/sysv/linux/time64-support.c | 23 --------
 sysdeps/unix/sysv/linux/time64-support.h | 70 ------------------------
 3 files changed, 1 insertion(+), 94 deletions(-)
 delete mode 100644 sysdeps/unix/sysv/linux/time64-support.c
 delete mode 100644 sysdeps/unix/sysv/linux/time64-support.h
  

On Thu, 17 Jun 2021 08:50:55 -0300
Adhemerval Zanella <adhemerval.zanella@linaro.org> wrote:

> It breaks the usage case of live migration like CRIU or similar
> and most usages can be optimized away by either building glibc with
> a minimum 5.1 kernel or by using the 32-bit syscall for the common
> case.
> 
> 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         |  2 +-
>  sysdeps/unix/sysv/linux/time64-support.c | 23 --------
>  sysdeps/unix/sysv/linux/time64-support.h | 70
> ------------------------ 3 files changed, 1 insertion(+), 94
> deletions(-) delete mode 100644
> sysdeps/unix/sysv/linux/time64-support.c delete mode 100644
> sysdeps/unix/sysv/linux/time64-support.h
> 
> diff --git a/sysdeps/unix/sysv/linux/Makefile
> b/sysdeps/unix/sysv/linux/Makefile index 710169a454..982755f980 100644
> --- a/sysdeps/unix/sysv/linux/Makefile
> +++ b/sysdeps/unix/sysv/linux/Makefile
> @@ -61,7 +61,7 @@ sysdep_routines += adjtimex clone umount umount2
> readahead sysctl \ open_by_handle_at mlock2 pkey_mprotect pkey_set
> pkey_get \ timerfd_gettime timerfd_settime prctl \
>  		   process_vm_readv process_vm_writev clock_adjtime \
> -		   time64-support pselect32 select32 \
> +		   pselect32 select32 \
>  		   xstat fxstat lxstat xstat64 fxstat64 lxstat64 \
>  		   fxstatat fxstatat64 \
>  		   xmknod xmknodat convert_scm_timestamps
> diff --git a/sysdeps/unix/sysv/linux/time64-support.c
> b/sysdeps/unix/sysv/linux/time64-support.c deleted file mode 100644
> index 0718e7421b..0000000000
> --- a/sysdeps/unix/sysv/linux/time64-support.c
> +++ /dev/null
> @@ -1,23 +0,0 @@
> -/* Auxiliary definitions for 64-bit time_t support.
> -   Copyright (C) 2020-2021 Free Software Foundation, Inc.
> -   This file is part of the GNU C Library.
> -
> -   The GNU C Library is free software; you can redistribute it and/or
> -   modify it under the terms of the GNU Lesser General Public
> -   License as published by the Free Software Foundation; either
> -   version 2.1 of the License, or (at your option) any later version.
> -
> -   The GNU C Library is distributed in the hope that it will be
> useful,
> -   but WITHOUT ANY WARRANTY; without even the implied warranty of
> -   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> -   Lesser General Public License for more details.
> -
> -   You should have received a copy of the GNU Lesser General Public
> -   License along with the GNU C Library; if not, see
> -   <https://www.gnu.org/licenses/>.  */
> -
> -#include <time64-support.h>
> -
> -#ifndef __ASSUME_TIME64_SYSCALLS
> -int __time64_support = 1;
> -#endif
> diff --git a/sysdeps/unix/sysv/linux/time64-support.h
> b/sysdeps/unix/sysv/linux/time64-support.h deleted file mode 100644
> index 8466d37f8f..0000000000
> --- a/sysdeps/unix/sysv/linux/time64-support.h
> +++ /dev/null
> @@ -1,70 +0,0 @@
> -/* Auxiliary definitions for 64-bit time_t support.
> -   Copyright (C) 2020-2021 Free Software Foundation, Inc.
> -   This file is part of the GNU C Library.
> -
> -   The GNU C Library is free software; you can redistribute it and/or
> -   modify it under the terms of the GNU Lesser General Public
> -   License as published by the Free Software Foundation; either
> -   version 2.1 of the License, or (at your option) any later version.
> -
> -   The GNU C Library is distributed in the hope that it will be
> useful,
> -   but WITHOUT ANY WARRANTY; without even the implied warranty of
> -   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> -   Lesser General Public License for more details.
> -
> -   You should have received a copy of the GNU Lesser General Public
> -   License along with the GNU C Library; if not, see
> -   <https://www.gnu.org/licenses/>.  */
> -
> -#include <stdbool.h>
> -#include <atomic.h>
> -
> -/* These helper functions are used to optimize the 64-bit time_t
> support on
> -   configurations that requires support for 32-bit time_t fallback
> -   (!__ASSUME_TIME64_SYSCALLS).  The idea is once the kernel
> advertises that
> -   it does not have 64-bit time_t support, glibc will stop to try
> issue the
> -   64-bit time_t syscall altogether.
> -
> -   For instance:
> -
> -     #ifndef __NR_symbol_time64
> -     # define __NR_symbol_time64 __NR_symbol
> -     #endif
> -     int r;
> -     if (supports_time64 ())
> -       {
> -         r = INLINE_SYSCALL_CALL (symbol, ...);
> -         if (r == 0 || errno != ENOSYS)
> -	   return r;
> -
> -         mark_time64_unsupported ();
> -       }
> -     #ifndef __ASSUME_TIME64_SYSCALLS
> -     <32-bit fallback syscall>
> -     #endif
> -     return r;
> -
> -   On configuration with default 64-bit time_t this optimization
> should be
> -   optimized away by the compiler resulting in no overhead.  */
> -
> -#ifndef __ASSUME_TIME64_SYSCALLS
> -extern int __time64_support attribute_hidden;
> -#endif
> -
> -static inline bool
> -supports_time64 (void)
> -{
> -#ifdef __ASSUME_TIME64_SYSCALLS
> -  return true;
> -#else
> -  return atomic_load_relaxed (&__time64_support) != 0;
> -#endif
> -}
> -
> -static inline void
> -mark_time64_unsupported (void)
> -{
> -#ifndef __ASSUME_TIME64_SYSCALLS
> -  atomic_store_relaxed (&__time64_support, 0);
> -#endif
> -}

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


Best regards,

Lukasz Majewski

--

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