x86: Add 32 bit vDSO time function support

[Stefani Seibold <stefani at seibold dot net>]

Hi,

in the near future the linux will support vDSO time functions for the
x86 32 bit kernels. This will be also supported the ia32 emulation mode.

The VDSO time functions __vdso_time(), __vdso_gettimeofday() and
__vdso_clock_getttime() are fast and a reliable way to get the exact
time without the overhead of a kernel system call.

This result in a  performance increase between 4 and 13 for this
functions, depending on the CPU and the function.

I will attach the patch against glibc-2.19, which is not very intrusive,
since it only make changes in the  sysdeps/unix/sysv/linux/i386 path.

How is the procedure to get this patch into the glibc mainline?

- Stefani

diff -u -N -r -p glibc-2.18.orig/sysdeps/unix/sysv/linux/i386/bits/libc-vdso.h glibc-2.18/sysdeps/unix/sysv/linux/i386/bits/libc-vdso.h
--- glibc-2.18.orig/sysdeps/unix/sysv/linux/i386/bits/libc-vdso.h	1970-01-01 01:00:00.000000000 +0100
+++ glibc-2.18/sysdeps/unix/sysv/linux/i386/bits/libc-vdso.h	2014-03-03 11:29:26.799650036 +0100
@@ -0,0 +1,31 @@
+/* Resolve function pointers to VDSO functions.
+   Copyright (C) 2005-2013 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
+
+#include <time.h>
+#include <sys/time.h>
+
+#ifdef SHARED
+
+extern long int (*__vdso_clock_gettime) (clockid_t, struct timespec *);
+
+#endif
+
+#endif /* _LIBC_VDSO_H */
diff -u -N -r -p glibc-2.18.orig/sysdeps/unix/sysv/linux/i386/clock_gettime.c glibc-2.18/sysdeps/unix/sysv/linux/i386/clock_gettime.c
--- glibc-2.18.orig/sysdeps/unix/sysv/linux/i386/clock_gettime.c	1970-01-01 01:00:00.000000000 +0100
+++ glibc-2.18/sysdeps/unix/sysv/linux/i386/clock_gettime.c	2014-03-03 11:44:54.873047522 +0100
@@ -0,0 +1,20 @@
+#include "bits/libc-vdso.h"
+
+#ifdef SHARED
+# define SYSCALL_GETTIME(id, tp) \
+  ({ long int (*f) (clockid_t, struct timespec *) = __vdso_clock_gettime; \
+  long int v_ret;							  \
+  PTR_DEMANGLE (f);							  \
+  v_ret = f (id, tp);							  \
+  if (INTERNAL_SYSCALL_ERROR_P (v_ret, )) {				  \
+    __set_errno (INTERNAL_SYSCALL_ERRNO (v_ret, ));			  \
+    v_ret = -1;								  \
+  }									  \
+  v_ret; })
+# define INTERNAL_GETTIME(id, tp) \
+  ({ long int (*f) (clockid_t, struct timespec *) = __vdso_clock_gettime; \
+  PTR_DEMANGLE (f);							  \
+  f (id, tp); })
+#endif
+
+#include "../clock_gettime.c"
diff -u -N -r -p glibc-2.18.orig/sysdeps/unix/sysv/linux/i386/gettimeofday.c glibc-2.18/sysdeps/unix/sysv/linux/i386/gettimeofday.c
--- glibc-2.18.orig/sysdeps/unix/sysv/linux/i386/gettimeofday.c	1970-01-01 01:00:00.000000000 +0100
+++ glibc-2.18/sysdeps/unix/sysv/linux/i386/gettimeofday.c	2014-03-03 17:08:02.021699309 +0100
@@ -0,0 +1,65 @@
+/* Copyright (C) 2002-2013 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/>.  */
+
+#include <sys/time.h>
+
+#ifdef SHARED
+
+# include <dl-vdso.h>
+# include <sysdep.h>
+# include <errno.h>
+
+static int
+fallback_gettimeofday (struct timeval *tv, struct timezone *tz)
+{
+  return INLINE_SYSCALL (gettimeofday, 2, tv, tz);
+}
+
+void *gettimeofday_ifunc (void) __asm__ ("__gettimeofday");
+
+void *
+gettimeofday_ifunc (void)
+{
+  PREPARE_VERSION (linux25, "LINUX_2.5", 61765109);
+
+  /* If the vDSO is not available we fall back on the old syscall.  */
+  return (_dl_vdso_vsym ("__vdso_gettimeofday", &linux25)
+	  ?: (void *) fallback_gettimeofday);
+}
+asm (".type __gettimeofday, %gnu_indirect_function");
+
+/* This is doing "libc_hidden_def (__gettimeofday)" but the compiler won't
+   let us do it in C because it doesn't know we're defining __gettimeofday
+   here in this file.  */
+asm (".globl __GI___gettimeofday\n"
+     "__GI___gettimeofday = __gettimeofday");
+
+#else
+
+# include <sysdep.h>
+# include <errno.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)
diff -u -N -r -p glibc-2.18.orig/sysdeps/unix/sysv/linux/i386/init-first.c glibc-2.18/sysdeps/unix/sysv/linux/i386/init-first.c
--- glibc-2.18.orig/sysdeps/unix/sysv/linux/i386/init-first.c	1970-01-01 01:00:00.000000000 +0100
+++ glibc-2.18/sysdeps/unix/sysv/linux/i386/init-first.c	2014-03-03 16:16:37.766257808 +0100
@@ -0,0 +1,52 @@
+/* Initialization code run first thing by the ELF startup code.  Linux/i386.
+   Copyright (C) 2007-2013 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 <time.h>
+# include <sysdep.h>
+# include <dl-vdso.h>
+# include <bits/libc-vdso.h>
+
+long int (*__vdso_clock_gettime) (clockid_t, struct timespec *)
+  __attribute__ ((nocommon));
+strong_alias (__vdso_clock_gettime, __GI___vdso_clock_gettime attribute_hidden)
+
+
+long int fallback_clock_gettime(clockid_t id, struct timespec *tp)
+{
+  INTERNAL_SYSCALL_DECL (err);
+  return INTERNAL_SYSCALL (clock_gettime, err, 2, id, tp);
+}
+
+
+static inline void
+_libc_vdso_platform_setup (void)
+{
+  PREPARE_VERSION (linux25, "LINUX_2.5", 61765109);
+
+  void *p = _dl_vdso_vsym ("__vdso_clock_gettime", &linux25);
+  if (p == NULL)
+    p = fallback_clock_gettime;
+  PTR_MANGLE (p);
+  __GI___vdso_clock_gettime = p;
+}
+
+# define VDSO_SETUP _libc_vdso_platform_setup
+#endif
+
+#include <csu/init-first.c>
diff -u -N -r -p glibc-2.18.orig/sysdeps/unix/sysv/linux/i386/Makefile glibc-2.18/sysdeps/unix/sysv/linux/i386/Makefile
--- glibc-2.18.orig/sysdeps/unix/sysv/linux/i386/Makefile	2013-08-11 00:52:55.000000000 +0200
+++ glibc-2.18/sysdeps/unix/sysv/linux/i386/Makefile	2014-03-03 11:34:21.922960487 +0100
@@ -21,3 +21,7 @@ endif
 ifeq ($(subdir),stdlib)
 gen-as-const-headers += ucontext_i.sym
 endif
+
+ifeq ($(subdir),elf)
+sysdep_routines += dl-vdso
+endif
diff -u -N -r -p glibc-2.18.orig/sysdeps/unix/sysv/linux/i386/time.c glibc-2.18/sysdeps/unix/sysv/linux/i386/time.c
--- glibc-2.18.orig/sysdeps/unix/sysv/linux/i386/time.c	1970-01-01 01:00:00.000000000 +0100
+++ glibc-2.18/sysdeps/unix/sysv/linux/i386/time.c	2014-03-03 16:19:09.428361771 +0100
@@ -0,0 +1,67 @@
+/* Copyright (C) 2001-2013 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
+/* Redefine time so that the compiler won't complain about the type
+   mismatch with the IFUNC selector in strong_alias, below.  */
+#undef time
+#define time __redirect_time
+#include <time.h>
+#include <sysdep.h>
+
+static time_t
+fallback_time (time_t *t)
+{
+  INTERNAL_SYSCALL_DECL (err);
+  return INTERNAL_SYSCALL (time, err, 1, t);
+}
+
+
+#include <dl-vdso.h>
+
+/* Avoid DWARF definition DIE on ifunc symbol so that GDB can handle
+   ifunc symbol properly.  */
+extern __typeof (__redirect_time) __libc_time;
+void *time_ifunc (void) __asm__ ("__libc_time");
+
+void *
+time_ifunc (void)
+{
+  PREPARE_VERSION (linux25, "LINUX_2.5", 61765109);
+
+  /* If the vDSO is not available we fall back on the old syscall.  */
+  return _dl_vdso_vsym ("__vdso_time", &linux25) ?: (void *) fallback_time;
+}
+__asm (".type __libc_time, %gnu_indirect_function");
+
+#undef time
+strong_alias (__libc_time, time)
+libc_hidden_ver (__libc_time, time)
+
+#else
+
+# include <time.h>
+# include <sysdep.h>
+
+time_t
+time (time_t *t)
+{
+  INTERNAL_SYSCALL_DECL (err);
+  return INTERNAL_SYSCALL (time, err, 1, t);
+}
+
+#endif
diff -u -N -r -p glibc-2.18.orig/sysdeps/unix/sysv/linux/i386/timespec_get.c glibc-2.18/sysdeps/unix/sysv/linux/i386/timespec_get.c
--- glibc-2.18.orig/sysdeps/unix/sysv/linux/i386/timespec_get.c	1970-01-01 01:00:00.000000000 +0100
+++ glibc-2.18/sysdeps/unix/sysv/linux/i386/timespec_get.c	2014-03-03 11:22:34.829800368 +0100
@@ -0,0 +1,10 @@
+#include "bits/libc-vdso.h"
+
+#ifdef SHARED
+# define INTERNAL_GETTIME(id, tp) \
+  ({ long int (*f) (clockid_t, struct timespec *) = __vdso_clock_gettime; \
+  PTR_DEMANGLE (f);							  \
+  f (id, tp); })
+#endif
+
+#include "../timespec_get.c"