linux-kernel - Re: [PATCH 4/4] x86/boot: Check that there are no runtime relocations

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Date:   Mon, 25 May 2020 15:22:21 -0400
From:   Arvind Sankar <nivedita@...m.mit.edu>
To:     Fangrui Song <maskray@...gle.com>
Cc:     Ard Biesheuvel <ardb@...nel.org>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, X86 ML <x86@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Dmitry Golovin <dima@...ovin.in>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Daniel Kiper <daniel.kiper@...cle.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/4] x86/boot: Check that there are no runtime relocations

On Mon, May 25, 2020 at 09:26:26AM -0700, Fangrui Song wrote:
> On 2020-05-25, Ard Biesheuvel wrote:
> >
> >Do we really need the macro here? Could we just do
> 
> The output section name does not matter: it will be discarded by the linker.
> 
> >.rel.dyn : { *(.rel.* .rela.*) }
> 
> If for some reasons there is at least one SHT_REL and at least one
> SHT_RELA, LLD will error "section type mismatch for .rel.dyn", while the
> intended diagnostic is the assert below.
> 
> >(or even
> >
> >.rel.dyn  : { *(.rel.* }
> >.rela.dyn : { *(.rela.*) }
> >
> >if the output section name matters, and always assert that both are empty)?
> 
>    .rel.dyn  : { *(.rel.* }
>    .rela.dyn : { *(.rela.*) }
> 
> looks good to me.
> 
> 
> FWIW I intend to add -z rel and -z rela to LLD: https://reviews.llvm.org/D80496#inline-738804
> (binutils thread https://sourceware.org/pipermail/binutils/2020-May/111244.html)
> 
> In case someone builds the x86-64 kernel with -z rel, your suggested
> input section description will work out of the box...
> 

Ok with me.