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

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Message-ID: <CAKwvOdkjJWDcN1bNJtcGjNJ0KStRH0Lk+Ge7wEU4gxXPDWQ_PQ@mail.gmail.com>
Date:   Fri, 10 Apr 2020 12:12:18 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Nathan Chancellor <natechancellor@...il.com>,
        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>,
        Fangrui Song <maskray@...gle.com>
Subject: Re: [PATCH] elfnote: mark all .note sections SHF_ALLOC

(bumping for review)

On Fri, Apr 3, 2020 at 5:40 PM Fangrui Song <maskray@...gle.com> wrote:
>
> On 2020-04-03, Nathan Chancellor wrote:
> >On Fri, Apr 03, 2020 at 03:13:34PM -0700, 'Nick Desaulniers' via Clang Built Linux wrote:
> >> 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>
> >
> >Reviewed-by: Nathan Chancellor <natechancellor@...il.com>
>
> I asked on binutils@...rceware.org whether GNU as is willing to change.
> https://sourceware.org/pipermail/binutils/2020-March/109997.html
> I'll also ping that thread.
>
>
> Reviewed-by: Fangrui Song <maskray@...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
> >> >
> >> > --

-- 
Thanks,
~Nick Desaulniers