objtool,efi: Update __efi64_thunk annotation

The current annotation relies on not running objtool on the file; this
won't work when running objtool on vmlinux.o. Instead explicitly mark
__efi64_thunk() to be ignored.

This preserves the status quo, which is somewhat unfortunate. Luckily
this code is hardly ever used.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20220308154317.402118218@infradead.org

arch/x86/platform/efi/Makefile

 # SPDX-License-Identifier: GPL-2.0
-OBJECT_FILES_NON_STANDARD_efi_thunk_$(BITS).o := y
 KASAN_SANITIZE := n
 GCOV_PROFILE := n
 

arch/x86/platform/efi/efi_thunk_64.S

@@ -20,12 +20,14 @@
  */
 
 #include <linux/linkage.h>
+#include <linux/objtool.h>
 #include <asm/page_types.h>
 #include <asm/segment.h>
 
 	.text
 	.code64
-SYM_CODE_START(__efi64_thunk)
+SYM_FUNC_START(__efi64_thunk)
+STACK_FRAME_NON_STANDARD __efi64_thunk
 	push	%rbp
 	push	%rbx
 
@@ -79,7 +81,7 @@ SYM_CODE_START(__efi64_thunk)
 2:	pushl	$__KERNEL_CS
 	pushl	%ebp
 	lret
-SYM_CODE_END(__efi64_thunk)
+SYM_FUNC_END(__efi64_thunk)
 
 	.bss
 	.balign 8