x86/kexec: Use RIP relative addressing

Normally identity_mapped is not visible to objtool, due to:

  arch/x86/kernel/Makefile:OBJECT_FILES_NON_STANDARD_relocate_kernel_$(BITS).o := y

However, when we want to run objtool on vmlinux.o there is no hiding
it:

  vmlinux.o: warning: objtool: .text+0x4c0f1: unsupported intra-function call

Replace the (i386 inspired) pattern:

	call 1f
  1:	popq %r8
	subq $(1b - relocate_kernel), %r8

With a x86_64 RIP-relative LEA:

	leaq relocate_kernel(%rip), %r8

Suggested-by: Brian Gerst <brgerst@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lkml.kernel.org/r/20200324160924.143334345@infradead.org

diff --git a/arch/x86/kernel/relocate_kernel_64.S b/arch/x86/kernel/relocate_kernel_64.S
index ef3ba99..cc5c8b9 100644 (file)
--- a/arch/x86/kernel/relocate_kernel_64.S
+++ b/arch/x86/kernel/relocate_kernel_64.S
@@ -196,10 +196,7 @@ SYM_CODE_START_LOCAL_NOALIGN(identity_mapped)
 
        /* get the re-entry point of the peer system */
        movq    0(%rsp), %rbp
-       call    1f
-1:
-       popq    %r8
-       subq    $(1b - relocate_kernel), %r8
+       leaq    relocate_kernel(%rip), %r8
        movq    CP_PA_SWAP_PAGE(%r8), %r10
        movq    CP_PA_BACKUP_PAGES_MAP(%r8), %rdi
        movq    CP_PA_TABLE_PAGE(%r8), %rax