linux-kernel - Re: [RFC][PATCH 04/16] objtool: Annotate identity

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Message-ID: <CAMzpN2gkRGEYEzgO55rBhkTdQO3XhEEfHrq6+j1dy5kzn-C5AA@mail.gmail.com>
Date:   Fri, 13 Mar 2020 12:46:05 -0400
From:   Brian Gerst <brgerst@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "the arch/x86 maintainers" <x86@...nel.org>
Subject: Re: [RFC][PATCH 04/16] objtool: Annotate identity_mapped()

On Thu, Mar 12, 2020 at 9:53 AM Peter Zijlstra <peterz@...radead.org> 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. Without the annotation we'll get complaints about the:
>
         call 1f
1:      popq %r8
        subq $(1b - relocate_kernel), %r8

It looks to me that this code is simply trying to get the virtual
address of relocate_kernel using the old 32-bit method of PIC address
calculation.  On 64-bit can be done with leaq relocate_kernel(%rip),
%r8.

--
Brian Gerst