Re: [PATCH] elfnote: mark all .note sections SHF_ALLOC

[Fangrui Song]

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@xxxxxxxxxx> 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@xxxxxxxxxxxxx>
> > > Debugged-by: Ilie Halip <ilie.halip@xxxxxxxxx>
> > > Signed-off-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
>
> Reviewed-by: Nathan Chancellor <natechancellor@xxxxxxxxx>

I asked on binutils@xxxxxxxxxxxxxx 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@xxxxxxxxxx>

> > > ---
> > > 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
>
>
> --
> You received this message because you are subscribed to the Google Groups "Clang Built Linux" group.
> To unsubscribe from this group and stop receiving emails from it, send an email to clang-built-linux+unsubscribe@xxxxxxxxxxxxxxxxx
> To view this discussion on the web visit https://groups.google.com/d/msgid/clang-built-linux/20200403222458.GA49554%40ubuntu-m2-xlarge-x86.