linux-kernel - Re: [PATCH] elfnote: mark all .note sections SHF

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Message-ID: <CAKwvOdm8tQaa6BW7EQAz4TxFZETnJCS3z9isY4HvcU7UYqWZUA@mail.gmail.com>
Date:   Fri, 3 Apr 2020 15:13:34 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     clang-built-linux <clang-built-linux@...glegroups.com>,
        Ilie Halip <ilie.halip@...il.com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] elfnote: mark all .note sections SHF_ALLOC

dropping Jeremy; I got bounceback from the email address. Ping for review?

On Wed, Mar 25, 2020 at 4:13 PM Nick Desaulniers
<ndesaulniers@...gle.com> wrote:
>
> ELFNOTE_START allows callers to specify flags for .pushsection assembler
> directives.  All callsites but ELF_NOTE use "a" for SHF_ALLOC. For
> vdso's that explicitly use ELF_NOTE_START and BUILD_SALT, the same
> section is specified twice after preprocessing, once with "a" flag, once
> without. Example:
>
> .pushsection .note.Linux, "a", @note ;
> .pushsection .note.Linux, "", @note ;
>
> While GNU as allows this ordering, it warns for the opposite ordering,
> making these directives position dependent. We'd prefer not to precisely
> match this behavior in Clang's integrated assembler.  Instead, the non
> __ASSEMBLY__ definition of ELF_NOTE uses
> __attribute__((section(".note.Linux"))) which is created with SHF_ALLOC,
> so let's make the __ASSEMBLY__ definition of ELF_NOTE consistent with C
> and just always use "a" flag.
>
> This allows Clang to assemble a working mainline (5.6) kernel via:
> $ make CC=clang AS=clang
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/913
> Cc: Jeremy Fitzhardinge <jeremy@...source.com>
> Debugged-by: Ilie Halip <ilie.halip@...il.com>
> Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
> ---
> Ilie has further treewide cleanups:
> https://github.com/ihalip/linux/commits/elfnote
> This patch is the simplest to move us forwards.
>
>  include/linux/elfnote.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/linux/elfnote.h b/include/linux/elfnote.h
> index 594d4e78654f..69b136e4dd2b 100644
> --- a/include/linux/elfnote.h
> +++ b/include/linux/elfnote.h
> @@ -54,7 +54,7 @@
>  .popsection                            ;
>
>  #define ELFNOTE(name, type, desc)              \
> -       ELFNOTE_START(name, type, "")           \
> +       ELFNOTE_START(name, type, "a")          \
>                 desc                    ;       \
>         ELFNOTE_END
>
> --
> 2.26.0.rc2.310.g2932bb562d-goog
>


-- 
Thanks,
~Nick Desaulniers