x86_64: further cleanup of 32-bit compat syscall mechanisms

AMD only supports "syscall" from 32-bit compat usermode.
Intel and Centaur(?) only support "sysenter" from 32-bit compat usermode.

Set the X86 feature bits accordingly, and set up the vdso in
accordance with those bits.  On the offchance we run on in a 64-bit
environment which supports neither syscall nor sysenter from 32-bit
mode, then fall back to the int $0x80 vdso.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

1 files changed, 7 insertions, 3 deletions

diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
index 3e11779755c3..e3648e64a637 100644
--- a/arch/x86/xen/setup.c
+++ b/arch/x86/xen/setup.c
@@ -83,12 +83,16 @@ static void xen_idle(void)
 
 /*
  * Set the bit indicating "nosegneg" library variants should be used.
+ * We only need to bother in pure 32-bit mode; compat 32-bit processes
+ * can have un-truncated segments, so wrapping around is allowed.
  */
 static void __init fiddle_vdso(void)
 {
-#if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION)
-        extern const char vdso32_default_start;
-        u32 *mask = VDSO32_SYMBOL(&vdso32_default_start, NOTE_MASK);
+#ifdef CONFIG_X86_32
+        u32 *mask;
+        mask = VDSO32_SYMBOL(&vdso32_int80_start, NOTE_MASK);
+        *mask |= 1 << VDSO_NOTE_NONEGSEG_BIT;
+        mask = VDSO32_SYMBOL(&vdso32_sysenter_start, NOTE_MASK);
         *mask |= 1 << VDSO_NOTE_NONEGSEG_BIT;
 #endif
 }