xen/x86: Zero out .bss for PV guests

ELF spec is unclear about whether .bss must me cleared by the loader.
Currently the domain builder does it when loading the guest but because
it is not (or rather may not be) guaranteed we should zero it out
explicitly.

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/arch/x86/xen/xen-head.S b/arch/x86/xen/xen-head.S
index b65f59a358a2..5c63d2d955bb 100644
--- a/arch/x86/xen/xen-head.S
+++ b/arch/x86/xen/xen-head.S
@@ -38,6 +38,15 @@
         __INIT
 ENTRY(startup_xen)
         cld
+
+        /* Clear .bss */
+        xor %eax,%eax
+        mov $__bss_start, %_ASM_DI
+        mov $__bss_stop, %_ASM_CX
+        sub %_ASM_DI, %_ASM_CX
+        shr $__ASM_SEL(2, 3), %_ASM_CX
+        rep __ASM_SIZE(stos)
+
 #ifdef CONFIG_X86_32
         mov %esi,xen_start_info
         mov $init_thread_union+THREAD_SIZE,%esp