xen: disable vdso "nosegneg" on native boot

One of the nice ideas behind paravirt is that CONFIG_XEN=y can be included
in a standard configuration and be no worse for native booting than as a
Xen guest.  The glibc feature that supports the vDSO "nosegneg" note is
designed specifically to make this easy.  You just have to flip one bit at
boot time.  This patch makes Xen flip the bit, so a CONFIG_XEN=y kernel on
bare hardware does not make glibc use the less-optimized library builds.

Signed-off-by: Roland McGrath <roland@redhat.com>
Acked-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 15 insertions, 0 deletions

diff --git a/arch/i386/xen/setup.c b/arch/i386/xen/setup.c
index 2fe6eac510f0..f84e77226646 100644
--- a/arch/i386/xen/setup.c
+++ b/arch/i386/xen/setup.c
@@ -19,6 +19,7 @@
 #include <xen/features.h>
 
 #include "xen-ops.h"
+#include "vdso.h"
 
 /* These are code, but not functions.  Defined in entry.S */
 extern const char xen_hypervisor_callback[];
@@ -55,6 +56,18 @@ static void xen_idle(void)
         }
 }
 
+/*
+ * Set the bit indicating "nosegneg" library variants should be used.
+ */
+static void fiddle_vdso(void)
+{
+        extern u32 VDSO_NOTE_MASK; /* See ../kernel/vsyscall-note.S.  */
+        extern char vsyscall_int80_start;
+        u32 *mask = (u32 *) ((unsigned long) &VDSO_NOTE_MASK - VDSO_PRELINK +
+                             &vsyscall_int80_start);
+        *mask |= 1 << VDSO_NOTE_NONEGSEG_BIT;
+}
+
 void __init xen_arch_setup(void)
 {
         struct physdev_set_iopl set_iopl;
@@ -93,4 +106,6 @@ void __init xen_arch_setup(void)
 #endif
 
         paravirt_disable_iospace();
+
+        fiddle_vdso();
 }