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>
diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
index 3e11779..e3648e6 100644
--- a/arch/x86/xen/setup.c
+++ b/arch/x86/xen/setup.c
@@ -83,12 +83,16 @@
/*
* 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
}