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aarch64: Use an ifunc/VDSO to implement gettimeofday in shared glibc.

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This patch uses an ifunc to implement gettimeofday in the shared libc.
This is faster compared to the vsyscall mechanism that has to check a
global pointer, demangle it and call it indirectly when the VDSO is
present. Resolving the gettimeofday symbol directly to the VDSO code
is safe because there are no failures that the libc has to handle by
setting errno like in a generic vsyscall (the only failure when the
VDSO code falls back to a syscall is EFAULT, but passing an invalid
pointer is undefined behaviour so returning -EFAULT is fine).

If the kernel supports the VDSO interface we use it for extern calls,
otherwise the old vsyscall method is used which falls back to a syscall.
The static version of gettimeofday continues to use a syscall, libc.so
internal calls use the old vsyscall method.

	* sysdeps/unix/sysv/linux/aarch64/gettimeofday.c: New file.
This commit is contained in:
Steve Ellcey 2018-06-14 08:18:42 +01:00 committed by Szabolcs Nagy
parent c59ee916a6
commit 3c7b9f1fc3
2 changed files with 76 additions and 0 deletions
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@ -1,3 +1,8 @@
2018-06-14 Steve Ellcey <sellcey@caviumnetworks.com>
Szabolcs Nagy <szabolcs.nagy@arm.com>
* sysdeps/unix/sysv/linux/aarch64/gettimeofday.c: New file.
2018-06-14 Florian Weimer <fweimer@redhat.com> 2018-06-14 Florian Weimer <fweimer@redhat.com>
* scripts/update-abilist.sh: Accept empty list of files to patch. * scripts/update-abilist.sh: Accept empty list of files to patch.

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sysdeps/unix/sysv/linux/aarch64/gettimeofday.c Normal file
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/* Copyright (C) 2018 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
<http://www.gnu.org/licenses/>. */
/* Get the current time of day and timezone information,
putting it into *tv and *tz. If tz is null, *tz is not filled.
Returns 0 on success, -1 on errors. */
#ifdef SHARED
# define __gettimeofday __redirect___gettimeofday
# include <sys/time.h>
# undef __gettimeofday
# define HAVE_VSYSCALL
# include <dl-vdso.h>
# include <sysdep-vdso.h>
/* Used as a fallback in the ifunc resolver if VDSO is not available
and for libc.so internal __gettimeofday calls. */
static int
__gettimeofday_vsyscall (struct timeval *tv, struct timezone *tz)
{
return INLINE_VSYSCALL (gettimeofday, 2, tv, tz);
}
/* PREPARE_VERSION will need an __LP64__ ifdef when ILP32 support
goes in. See _libc_vdso_platform_setup in
sysdeps/unix/sysv/linux/aarch64/init-first.c. */
# undef INIT_ARCH
# define INIT_ARCH() \
PREPARE_VERSION (linux_version, "LINUX_2.6.39", 123718537); \
void *vdso_gettimeofday = \
_dl_vdso_vsym ("__kernel_gettimeofday", &linux_version);
libc_ifunc_hidden (__redirect___gettimeofday, __gettimeofday,
vdso_gettimeofday ?: (void *) __gettimeofday_vsyscall)
__hidden_ver1 (__gettimeofday_vsyscall, __GI___gettimeofday,
__gettimeofday_vsyscall);
#else
# include <sys/time.h>
# include <sysdep.h>
int
__gettimeofday (struct timeval *tv, struct timezone *tz)
{
return INLINE_SYSCALL (gettimeofday, 2, tv, tz);
}
libc_hidden_def (__gettimeofday)
#endif
weak_alias (__gettimeofday, gettimeofday)
libc_hidden_weak (gettimeofday)