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[PATCH v2] ARM: VDSO support
- From: Nathan Lynch <nathan_lynch at codesourcery dot com>
- To: <libc-alpha at sourceware dot org>
- Date: Fri, 29 May 2015 15:58:27 -0500
- Subject: [PATCH v2] ARM: VDSO support
- Authentication-results: sourceware.org; auth=none
Beginning with 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.
2015-05-29 Nathan Lynch <nathan_lynch@codesourcery.com>
* 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 and __vdso_gettimeofday.
---
This version has been reworked on top of Adhemerval's recent VDSO
refactoring.
sysdeps/unix/sysv/linux/arm/Makefile | 1 +
sysdeps/unix/sysv/linux/arm/Versions | 2 ++
sysdeps/unix/sysv/linux/arm/init-first.c | 43 ++++++++++++++++++++++++++++++++
sysdeps/unix/sysv/linux/arm/libc-vdso.h | 32 ++++++++++++++++++++++++
sysdeps/unix/sysv/linux/arm/sysdep.h | 4 +++
5 files changed, 82 insertions(+)
create mode 100644 sysdeps/unix/sysv/linux/arm/init-first.c
create mode 100644 sysdeps/unix/sysv/linux/arm/libc-vdso.h
diff --git a/sysdeps/unix/sysv/linux/arm/Makefile b/sysdeps/unix/sysv/linux/arm/Makefile
index 50410b67b5fc..270cb73f70e5 100644
--- a/sysdeps/unix/sysv/linux/arm/Makefile
+++ b/sysdeps/unix/sysv/linux/arm/Makefile
@@ -1,4 +1,5 @@
ifeq ($(subdir),elf)
+sysdep_routines += dl-vdso
sysdep-rtld-routines += aeabi_read_tp libc-do-syscall
endif
diff --git a/sysdeps/unix/sysv/linux/arm/Versions b/sysdeps/unix/sysv/linux/arm/Versions
index a251b0fd7d87..7bc5936372bb 100644
--- a/sysdeps/unix/sysv/linux/arm/Versions
+++ b/sysdeps/unix/sysv/linux/arm/Versions
@@ -10,5 +10,7 @@ libc {
GLIBC_PRIVATE {
# A copy of sigaction lives in libpthread, and needs these.
__default_sa_restorer; __default_rt_sa_restorer;
+ __vdso_clock_gettime;
+ __vdso_gettimeofday;
}
}
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 000000000000..f4868b834cf1
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/arm/init-first.c
@@ -0,0 +1,43 @@
+/* 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
+ <http://www.gnu.org/licenses/>. */
+
+#ifdef SHARED
+# include <dl-vdso.h>
+# include <libc-vdso.h>
+
+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 <csu/init-first.c>
diff --git a/sysdeps/unix/sysv/linux/arm/libc-vdso.h b/sysdeps/unix/sysv/linux/arm/libc-vdso.h
new file mode 100644
index 000000000000..2ebcc62cd284
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/arm/libc-vdso.h
@@ -0,0 +1,32 @@
+/* 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
+ <http://www.gnu.org/licenses/>. */
+
+#ifndef _LIBC_VDSO_H
+#define _LIBC_VDSO_H
+
+#ifdef SHARED
+
+# include <sysdep-vdso.h>
+
+extern int (*VDSO_SYMBOL(gettimeofday)) (struct timeval *, void *)
+ attribute_hidden;
+extern int (*VDSO_SYMBOL(clock_gettime)) (clockid_t, struct timespec *);
+
+#endif
+
+#endif /* _LIBC_VDSO_H */
diff --git a/sysdeps/unix/sysv/linux/arm/sysdep.h b/sysdeps/unix/sysv/linux/arm/sysdep.h
index 37eac192b1e2..200f77a62ef1 100644
--- a/sysdeps/unix/sysv/linux/arm/sysdep.h
+++ b/sysdeps/unix/sysv/linux/arm/sysdep.h
@@ -387,6 +387,10 @@ __local_syscall_error: \
#undef INTERNAL_SYSCALL_ERRNO
#define INTERNAL_SYSCALL_ERRNO(val, err) (-(val))
+/* List of system calls which are supported as vsyscalls. */
+#define HAVE_CLOCK_GETTIME_VSYSCALL 1
+#define HAVE_GETTIMEOFDAY_VSYSCALL 1
+
#define LOAD_ARGS_0()
#define ASM_ARGS_0
#define LOAD_ARGS_1(a1) \
--
2.1.0