Re: [PATCH 4/8] ppc: Use libc_ifunc macro for time, gettimeofday.

[Stefan Liebler <stli at linux dot vnet dot ibm dot com>]

On 08/02/2016 05:45 PM, Paul E. Murphy wrote:
> Ok, pending approval of the first patch.
This is an updated version due to changes in the first patch with 
libc_ifunc fallback if gcc does not support gcc attribute ifunc.
>From 223b642762d639bca416cc3e99af98d21074fcd7 Mon Sep 17 00:00:00 2001
From: Stefan Liebler <stli@linux.vnet.ibm.com>
Date: Thu, 4 Aug 2016 18:46:23 +0200
Subject: [PATCH 4/8] ppc: Use libc_ifunc macro for time, gettimeofday.

This patch uses the libc_ifunc_hidden macro to create already existing ifunc functions
time and gettimeofday on power. This way, the libc_hidden_def macro can be used
instead of inline assemblies.
On ppc32, the __GI_* symbols do not target the ifunc symbol and thus the
redirection construct has to be applied here.

ChangeLog:

	* sysdeps/unix/sysv/linux/powerpc/gettimeofday.c (__gettimeofday):
	Use libc_ifunc_hidden and libc_hidden_def macro. Redirect ifunced function
	in header for using it as type for ifunc function because __GI_* symbols
	for ppc32 do not target the ifunc symbols.
	* sysdeps/unix/sysv/linux/powerpc/time.c (time): Likewise.
---
 sysdeps/unix/sysv/linux/powerpc/gettimeofday.c | 60 ++++++++++++-----------
 sysdeps/unix/sysv/linux/powerpc/time.c         | 67 +++++++++++++-------------
 2 files changed, 65 insertions(+), 62 deletions(-)

diff --git a/sysdeps/unix/sysv/linux/powerpc/gettimeofday.c b/sysdeps/unix/sysv/linux/powerpc/gettimeofday.c
index 25a4e7c..16c00d7 100644
--- a/sysdeps/unix/sysv/linux/powerpc/gettimeofday.c
+++ b/sysdeps/unix/sysv/linux/powerpc/gettimeofday.c
@@ -15,6 +15,11 @@
    License along with the GNU C Library; if not, see
    <http://www.gnu.org/licenses/>.  */
 
+#if defined SHARED && !defined __powerpc64__
+# define __gettimeofday __redirect___gettimeofday
+#else
+# define __redirect___gettimeofday __gettimeofday
+#endif
 
 #include <sys/time.h>
 
@@ -24,30 +29,14 @@
 # include <libc-vdso.h>
 # include <dl-machine.h>
 
-void *gettimeofday_ifunc (void) __asm__ ("__gettimeofday");
-
-static int
-__gettimeofday_syscall (struct timeval *tv, struct timezone *tz)
-{
-  return INLINE_SYSCALL (gettimeofday, 2, tv, tz);
-}
+# ifndef __powerpc64__
+#  undef __gettimeofday
 
-void *
-gettimeofday_ifunc (void)
+int
+__gettimeofday_vsyscall (struct timeval *tv, struct timezone *tz)
 {
-  PREPARE_VERSION (linux2615, "LINUX_2.6.15", 123718565);
-
-  /* If the vDSO is not available we fall back syscall.  */
-  void *vdso_gettimeofday = _dl_vdso_vsym ("__kernel_gettimeofday", &linux2615);
-  return (vdso_gettimeofday ? VDSO_IFUNC_RET (vdso_gettimeofday)
-	  : (void*)__gettimeofday_syscall);
+  return INLINE_VSYSCALL (gettimeofday, 2, tv, tz);
 }
-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");
 
 /* __GI___gettimeofday is defined as hidden and for ppc32 it enables the
    compiler make a local call (symbol@local) for internal GLIBC usage. It
@@ -55,16 +44,29 @@ asm (".globl __GI___gettimeofday");
    For ppc64 a call to a function in another translation unit might use a
    different toc pointer thus disallowing direct branchess and making internal
    ifuncs calls safe.  */
-#ifdef __powerpc64__
-asm ("__GI___gettimeofday = __gettimeofday");
-#else
-int
-__gettimeofday_vsyscall (struct timeval *tv, struct timezone *tz)
+#  undef libc_hidden_def
+#  define libc_hidden_def(name)					\
+  __hidden_ver1 (__gettimeofday_vsyscall, __GI___gettimeofday,	\
+	       __gettimeofday_vsyscall);
+
+# endif /* !__powerpc64__  */
+
+static int
+__gettimeofday_syscall (struct timeval *tv, struct timezone *tz)
 {
-  return INLINE_VSYSCALL (gettimeofday, 2, tv, tz);
+  return INLINE_SYSCALL (gettimeofday, 2, tv, tz);
 }
-asm ("__GI___gettimeofday = __gettimeofday_vsyscall");
-#endif
+
+# define INIT_ARCH()							\
+  PREPARE_VERSION (linux2615, "LINUX_2.6.15", 123718565);		\
+  void *vdso_gettimeofday = _dl_vdso_vsym ("__kernel_gettimeofday", &linux2615);
+
+/* If the vDSO is not available we fall back syscall.  */
+libc_ifunc_hidden (__redirect___gettimeofday, __gettimeofday,
+		   vdso_gettimeofday
+		   ? VDSO_IFUNC_RET (vdso_gettimeofday)
+		   : (void *) __gettimeofday_syscall);
+libc_hidden_def (__gettimeofday)
 
 #else
 
diff --git a/sysdeps/unix/sysv/linux/powerpc/time.c b/sysdeps/unix/sysv/linux/powerpc/time.c
index 7973419..3da0b66 100644
--- a/sysdeps/unix/sysv/linux/powerpc/time.c
+++ b/sysdeps/unix/sysv/linux/powerpc/time.c
@@ -17,6 +17,11 @@
    <http://www.gnu.org/licenses/>.  */
 
 #ifdef SHARED
+# ifndef __powerpc64__
+#  define time __redirect_time
+# else
+#  define __redirect_time time
+# endif
 
 # include <time.h>
 # include <sysdep.h>
@@ -24,7 +29,26 @@
 # include <libc-vdso.h>
 # include <dl-machine.h>
 
-void *time_ifunc (void) asm ("time");
+# ifndef __powerpc64__
+#  undef time
+
+time_t
+__time_vsyscall (time_t *t)
+{
+  return INLINE_VSYSCALL (time, 1, t);
+}
+
+/* __GI_time is defined as hidden and for ppc32 it enables the
+   compiler make a local call (symbol@local) for internal GLIBC usage. It
+   means the PLT won't be used and the ifunc resolver will be called directly.
+   For ppc64 a call to a function in another translation unit might use a
+   different toc pointer thus disallowing direct branchess and making internal
+   ifuncs calls safe.  */
+#  undef libc_hidden_def
+#  define libc_hidden_def(name)					\
+  __hidden_ver1 (__time_vsyscall, __GI_time, __time_vsyscall);
+
+# endif /* !__powerpc64__  */
 
 static time_t
 time_syscall (time_t *t)
@@ -42,42 +66,19 @@ time_syscall (time_t *t)
   return result;
 }
 
-void *
-time_ifunc (void)
-{
-  PREPARE_VERSION (linux2615, "LINUX_2.6.15", 123718565);
-
-  /* If the vDSO is not available we fall back to the syscall.  */
+# define INIT_ARCH()							\
+  PREPARE_VERSION (linux2615, "LINUX_2.6.15", 123718565);		\
   void *vdso_time = _dl_vdso_vsym ("__kernel_time", &linux2615);
-  return (vdso_time ? VDSO_IFUNC_RET (vdso_time)
-	  : (void*)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");
-
-/* __GI_time is defined as hidden and for ppc32 it enables the
-   compiler make a local call (symbol@local) for internal GLIBC usage. It
-   means the PLT won't be used and the ifunc resolver will be called directly.
-   For ppc64 a call to a function in another translation unit might use a
-   different toc pointer thus disallowing direct branchess and making internal
-   ifuncs calls safe.  */
-#ifdef __powerpc64__
-asm ("__GI_time = time");
-#else
-time_t
-__time_vsyscall (time_t *t)
-{
-  return INLINE_VSYSCALL (time, 1, t);
-}
-asm ("__GI_time = __time_vsyscall");
-#endif
+/* If the vDSO is not available we fall back to the syscall.  */
+libc_ifunc_hidden (__redirect_time, time,
+		   vdso_time
+		   ? VDSO_IFUNC_RET (vdso_time)
+		   : (void *) time_syscall);
+libc_hidden_def (time)
 
 #else
 
 #include <sysdeps/posix/time.c>
 
-#endif
+#endif /* !SHARED */
-- 
2.3.0