x86/xen: Support objtool vmlinux.o validation in xen-head.S

The Xen hypercall page is filled with zeros, causing objtool to fall
through all the empty hypercall functions until it reaches a real
function, resulting in a stack state mismatch.

The build-time contents of the hypercall page don't matter because the
page gets rewritten by the hypervisor.  Make it more palatable to
objtool by making each hypervisor function a true empty function, with
nops and a return.

Cc: Juergen Gross <jgross@suse.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/0883bde1d7a1fb3b6a4c952bc0200e873752f609.1611263462.git.jpoimboe@redhat.com

diff --git a/arch/x86/xen/xen-head.S b/arch/x86/xen/xen-head.S
index 2d7c8f3..cb6538a 100644 (file)
--- a/arch/x86/xen/xen-head.S
+++ b/arch/x86/xen/xen-head.S
@@ -68,8 +68,9 @@ SYM_CODE_END(asm_cpu_bringup_and_idle)
        .balign PAGE_SIZE
 SYM_CODE_START(hypercall_page)
        .rept (PAGE_SIZE / 32)
-               UNWIND_HINT_EMPTY
-               .skip 32
+               UNWIND_HINT_FUNC
+               .skip 31, 0x90
+               ret
        .endr
 
 #define HYPERCALL(n) \