linux-kernel - Re: [PATCH v3 04/26] x86/kexec: Use RIP relative addressing

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Date:   Wed, 25 Mar 2020 10:34:53 +0100 (CET)
From:   Miroslav Benes <mbenes@...e.cz>
To:     Peter Zijlstra <peterz@...radead.org>
cc:     tglx@...utronix.de, jpoimboe@...hat.com,
        linux-kernel@...r.kernel.org, x86@...nel.org, mhiramat@...nel.org,
        brgerst@...il.com
Subject: Re: [PATCH v3 04/26] x86/kexec: Use RIP relative addressing

On Tue, 24 Mar 2020, Peter Zijlstra wrote:

> 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@...il.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Acked-by: Josh Poimboeuf <jpoimboe@...hat.com>

Reviewed-by: Miroslav Benes <mbenes@...e.cz>

M