x86: Remove vsyscall usage

This patch removes the vsyscall usage for x86_64 port.  As indicated
by kernel code comments [1], vsyscalls are a legacy ABI and its concept
is problematic:

- It interferes with ASLR.
- It's awkward to write code that lives in kernel addresses but is
  callable by userspace at fixed addresses.
- The whole concept is impossible for 32-bit compat userspace.
- UML cannot easily virtualize a vsyscall.

The VDSO is a better approach for such functionality.  Tested on i686,
x86_64, and x32.

	* sysdeps/unix/sysv/linux/i386/gettimeofday.c
	(__gettimeofday_syscall): Remove vsyscall fallback.
	* sysdeps/unix/sysv/linux/i386/time.c (__time_syscall): Likewise.
	* sysdeps/unix/sysv/linux/x86/gettimeofday.c (__gettimeofday_syscall):
	Add syscall fallback function.
	(gettimeofday_ifunc): Use __gettimeofday_syscall as fallback mechanism
	if vDSO is not present.
	* sysdeps/unix/sysv/linux/x86/time.c (__time_syscall): Add syscall
	fallback function.
	(time_ifunc): Use __time_syscall as fallback mechanism if vDSO is not
	present.
	* sysdeps/unix/sysv/linux/x86_64/gettimeofday.c: Remove file.
	* sysdeps/unix/sysv/linux/x86_64/time.c: Likewise.

[1] arch/x86/kernel/vsyscall_64.c

1 files changed, 9 insertions, 2 deletions

diff --git a/sysdeps/unix/sysv/linux/x86/gettimeofday.c b/sysdeps/unix/sysv/linux/x86/gettimeofday.c
index c820fd767b..440cb0243a 100644
--- a/sysdeps/unix/sysv/linux/x86/gettimeofday.c
+++ b/sysdeps/unix/sysv/linux/x86/gettimeofday.c
@@ -21,6 +21,13 @@
 #ifdef SHARED
 
 # include <dl-vdso.h>
+# include <errno.h>
+
+static int
+__gettimeofday_syscall (struct timeval *tv, struct timezone *tz)
+{
+  return INLINE_SYSCALL (gettimeofday, 2, tv, tz);
+}
 
 void *gettimeofday_ifunc (void) __asm__ ("__gettimeofday");
 
@@ -29,9 +36,9 @@ gettimeofday_ifunc (void)
 {
   PREPARE_VERSION_KNOWN (linux26, LINUX_2_6);
 
-  /* If the vDSO is not available we fall back on the old vsyscall.  */
+  /* If the vDSO is not available we fall back to syscall.  */
   return (_dl_vdso_vsym ("__vdso_gettimeofday", &linux26)
-	  ?: GETTIMEOFAY_FALLBACK);
+	  ?: (void*) (&__gettimeofday_syscall));
 }
 asm (".type __gettimeofday, %gnu_indirect_function");