PowerPC: Add time vDSO support

[Adhemerval Zanella <azanella at linux dot vnet dot ibm dot com>]

Hi all,

PowerPC kernel now provides a vDSO implementation for time syscall:

http://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git/commit/?id=fcb41a2030abe0eb716ef0798035ef9562097f42

This is the glibc patch to actually uses it on time call. I also change
the time PowerPC behavior to use sysdeps/posix/time.c (as SPARC64 does)
since gettimeofday is a vDSO call.

I noticed speedups of about 6x using sysdeps/posix/time.c and about 10x
using the vDSO call. Tested on PPC32 and PPC64.

Any tips, comments, advices?

---

2013-04-26  Adhemerval Zanella  <azanella@linux.vnet.ibm.com>

	* sysdeps/unix/sysv/linux/powerpc/Versions: Add __vdso_time symbol.
	* sysdeps/unix/sysv/linux/powerpc/bits/libc-vdso.h: Add __vdso_time 
	definition.
	(VDSO_IFUNC_RET): Fix compiler warning on cast.
	* sysdeps/unix/sysv/linux/powerpc/init-first.c
	(_libc_vdso_platform_setup): Add __vdso_time initialization.
	* sysdeps/unix/sysv/linux/powerpc/time.c: New file: time implementation
	for PowerPC using vDSO where is avaliable or gettimeofday as a fallback.

--

diff --git a/sysdeps/unix/sysv/linux/powerpc/Versions b/sysdeps/unix/sysv/linux/powerpc/Versions
index 396a423..289c4fe 100644
--- a/sysdeps/unix/sysv/linux/powerpc/Versions
+++ b/sysdeps/unix/sysv/linux/powerpc/Versions
@@ -4,5 +4,6 @@ libc {
     __vdso_clock_gettime;
     __vdso_clock_getres;
     __vdso_getcpu;
+    __vdso_time;
   }
 }
diff --git a/sysdeps/unix/sysv/linux/powerpc/bits/libc-vdso.h b/sysdeps/unix/sysv/linux/powerpc/bits/libc-vdso.h
index 5f5fc1e..a68ff3c 100644
--- a/sysdeps/unix/sysv/linux/powerpc/bits/libc-vdso.h
+++ b/sysdeps/unix/sysv/linux/powerpc/bits/libc-vdso.h
@@ -32,14 +32,16 @@ extern void *__vdso_get_tbfreq;
 
 extern void *__vdso_getcpu;
 
+extern void *__vdso_time;
+
 /* This macro is needed for PPC64 to return a skeleton OPD entry of a vDSO
    symbol.  This works because _dl_vdso_vsym always return the function
    address, and no vDSO symbols use the TOC or chain pointers from the OPD
    so we can allow them to be garbage.  */
 #if defined(__PPC64__) || defined(__powerpc64__)
-#define VDSO_IFUNC_RET(value)  &value
+#define VDSO_IFUNC_RET(value)  (void*)(&value)
 #else
-#define VDSO_IFUNC_RET(value)  value
+#define VDSO_IFUNC_RET(value)  (void*)(value)
 #endif
 
 #endif
diff --git a/sysdeps/unix/sysv/linux/powerpc/init-first.c b/sysdeps/unix/sysv/linux/powerpc/init-first.c
index 204c0c6..f6f05f0 100644
--- a/sysdeps/unix/sysv/linux/powerpc/init-first.c
+++ b/sysdeps/unix/sysv/linux/powerpc/init-first.c
@@ -28,7 +28,7 @@ void *__vdso_clock_gettime;
 void *__vdso_clock_getres;
 void *__vdso_get_tbfreq;
 void *__vdso_getcpu;
-
+void *__vdso_time;
 
 static inline void
 _libc_vdso_platform_setup (void)
@@ -44,6 +44,8 @@ _libc_vdso_platform_setup (void)
   __vdso_get_tbfreq = _dl_vdso_vsym ("__kernel_get_tbfreq", &linux2615);
 
   __vdso_getcpu = _dl_vdso_vsym ("__kernel_getcpu", &linux2615);
+
+  __vdso_time = _dl_vdso_vsym ("__kernel_time", &linux2615);
 }
 
 # define VDSO_SETUP _libc_vdso_platform_setup
diff --git a/sysdeps/unix/sysv/linux/powerpc/time.c b/sysdeps/unix/sysv/linux/powerpc/time.c
new file mode 100644
index 0000000..e0dcb1a
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/powerpc/time.c
@@ -0,0 +1,63 @@
+/* Copyright (C) 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 <bits/libc-vdso.h>
+
+void *time_ifunc (void) __asm__ ("time");
+
+static time_t
+__time_syscall (time_t *t)
+{
+  struct timeval tv;
+  time_t result;
+
+  if (INLINE_VSYSCALL (gettimeofday, 2, &tv, NULL))
+    result = (time_t) -1;
+  else
+    result = (time_t) tv.tv_sec;
+
+  if (t != NULL)
+    *t = result;
+  return result;
+}
+
+void *
+time_ifunc (void)
+{
+  /* If the vDSO is not available we fall back syscall.  */
+  return (__vdso_time ? VDSO_IFUNC_RET (__vdso_time)
+	  : __time_syscall);
+}
+asm (".type time, %gnu_indirect_function");
+
+/* This is doing "libc_hidden_def (time)" but the compiler won't
+ * let us do it in C because it doesn't know we're defining time
+ * here in this file.  */
+asm (".globl __GI_time\n"
+     "__GI_time = time");
+
+#else
+
+#include <sysdeps/posix/time.c>
+
+#endif
-- 
1.7.1