From b65d3e5f0f452e86f81d21d59b065feeb31357be Mon Sep 17 00:00:00 2001 From: Nathan Lynch Date: Thu, 4 Jun 2015 21:10:43 +0000 Subject: ARM: VDSO support Beginning with the upcoming 4.1 release, Linux on a subset of 32-bit ARM hardware will provide fast user-space implementations of the following system calls: - gettimeofday - clock_gettime The kernel implementation depends on the ARMv7 Generic Timers Extension to accelerate these system calls. So CPUs such as Cortex-A15 and -A7 benefit, while Cortex-A9, -A8, and pre-v7 CPUs do not. On systems where the VDSO does not provide any speedup, the kernel prevents the relevant symbol lookups from succeeding. On OMAP5 (Cortex-A15) gettimeofday latency decreases from ~350ns to ~120ns. On BeagleBone Black (Cortex-A8) it goes from ~650ns to ~660ns, which to my mind is an acceptable cost. Verified that no new test failures are introduced on kernels with and without the VDSO. * sysdeps/unix/sysv/linux/arm/Makefile: (sysdep_routines): Include dl-vdso. * sysdeps/unix/sysv/linux/arm/init-first.c: New file: Use VDSO routines for gettimeofday, clock_gettime if available. * sysdeps/unix/sysv/linux/arm/libc-vdso.h: New file: Declare VDSO symbols. * sysdeps/unix/sysv/linux/arm/sysdep.h: [HAVE_GETTIMEOFDAY_VSYSCALL]: Define. [HAVE_CLOCK_GETTIME_VSYSCALL]: Define. * sysdeps/unix/sysv/linux/arm/Versions: Add __vdso_clock_gettime. --- sysdeps/unix/sysv/linux/arm/init-first.c | 44 ++++++++++++++++++++++++++++++++ 1 file changed, 44 insertions(+) create mode 100644 sysdeps/unix/sysv/linux/arm/init-first.c (limited to 'sysdeps/unix/sysv/linux/arm/init-first.c') diff --git a/sysdeps/unix/sysv/linux/arm/init-first.c b/sysdeps/unix/sysv/linux/arm/init-first.c new file mode 100644 index 0000000000..2fa4fb75a7 --- /dev/null +++ b/sysdeps/unix/sysv/linux/arm/init-first.c @@ -0,0 +1,44 @@ +/* Initialization code run first thing by the ELF startup code. Linux/ARM. + Copyright (C) 2015 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 + . */ + +#ifdef SHARED +# include +# include + +int (*VDSO_SYMBOL(gettimeofday)) (struct timeval *, void *) attribute_hidden; +int (*VDSO_SYMBOL(clock_gettime)) (clockid_t, struct timespec *); + +static inline void +_libc_vdso_platform_setup (void) +{ + PREPARE_VERSION_KNOWN (linux26, LINUX_2_6); + + void *p = _dl_vdso_vsym ("__vdso_gettimeofday", &linux26); + PTR_MANGLE (p); + VDSO_SYMBOL (gettimeofday) = p; + + p = _dl_vdso_vsym ("__vdso_clock_gettime", &linux26); + PTR_MANGLE (p); + VDSO_SYMBOL (clock_gettime) = p; +} + +# define VDSO_SETUP _libc_vdso_platform_setup +#endif + +#include -- cgit v1.2.3-70-g09d2