xen/enlighten: Fix compile warnings and set cx to known value.

We get:
linux/arch/x86/xen/enlighten.c: In function ‘xen_start_kernel’:
linux/arch/x86/xen/enlighten.c:226: warning: ‘cx’ may be used uninitialized in this function
linux/arch/x86/xen/enlighten.c:240: note: ‘cx’ was declared here

and the cx is really not set but passed in the xen_cpuid instruction
which masks the value with returned masked_ecx from cpuid. This
can potentially lead to invalid data being stored in cx.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 2d69617950f7c94a8e14c7e5fe7ad8730aa26eeb..da8afd576a6b7d161e3e81f2997912a73fec3d31 100644 (file)
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -251,6 +251,7 @@ static void __init xen_init_cpuid_mask(void)
                        ~((1 << X86_FEATURE_APIC) |  /* disable local APIC */
                          (1 << X86_FEATURE_ACPI));  /* disable ACPI */
        ax = 1;
+       cx = 0;
        xen_cpuid(&ax, &bx, &cx, &dx);
 
        xsave_mask =