RFA [PPC kernel] Avoid upcoming PPC kernel build failure

[H.J. Lu]

On Fri, Mar 27, 2020 at 7:54 AM Yu-cheng Yu <yu-cheng.yu at intel.com> wrote:
>
> On Thu, 2020-02-06 at 04:55 -0800, H.J. Lu wrote:
> > On Wed, Feb 5, 2020 at 7:26 PM Michael Ellerman <mpe at ellerman.id.au> wrote:
> > > "H.J. Lu" <hjl.tools at gmail.com> writes:
> > > > On Tue, Feb 4, 2020 at 3:37 PM kbuild test robot <lkp at intel.com> wrote:
> > > > > tree:   https://github.com/yyu168/linux_cet.git cet
> > > > > head:   bba707cc4715c1036b6561ab38b16747f9c49cfa
> > > > > commit: 71bb971dd76eeacd351690f28864ad5c5bec3691 [55/58] Discard .note.gnu.property sections in generic NOTES
> > > > > config: powerpc-rhel-kconfig (attached as .config)
> > > > > compiler: powerpc64le-linux-gcc (GCC) 7.5.0
> > > > > reproduce:
> > > > >         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
> > > > >         chmod +x ~/bin/make.cross
> > > > >         git checkout 71bb971dd76eeacd351690f28864ad5c5bec3691
> > > > >         # save the attached .config to linux build tree
> > > > >         GCC_VERSION=7.5.0 make.cross ARCH=powerpc
> > > > >
> > > > > If you fix the issue, kindly add following tag
> > > > > Reported-by: kbuild test robot <lkp at intel.com>
> > > > >
> > > > > All warnings (new ones prefixed by >>):
> > > > >
> > > > >    powerpc64le-linux-ld: warning: discarding dynamic section .rela___ksymtab_gpl+__wait_rcu_gp
> > > >
> > > > arch/powerpc/kernel/vmlinux.lds.S has
> > > >
> > > >  .rela.dyn : AT(ADDR(.rela.dyn) - (0xc000000000000000 -0x00000000))
> > > >  {
> > > >   __rela_dyn_start = .;
> > > >   *(.rela*) <<<<<<<< Keep .rela* sections
> > > >  }
> > >
> > > The above is inside #ifdef CONFIG_RELOCATABLE
> > >
> > > > ...
> > > >  /DISCARD/ : {
> > > >   *(*.EMB.apuinfo)
> > > >   *(.glink .iplt .plt .rela* .comment)
> > > >                            ^^^^ Discard  .rela* sections.  But it is ignored.
> > > >   *(.gnu.version*)
> > > >   *(.gnu.attributes)
> > > >   *(.eh_frame)
> > > >  }
> > >
> > > But that is not #ifdef'ed at all.
> > >
> > > > With my
> > > >
> > > > ommit 71bb971dd76eeacd351690f28864ad5c5bec3691
> > > > Author: H.J. Lu <hjl.tools at gmail.com>
> > > > Date:   Thu Jan 30 12:39:09 2020 -0800
> > > >
> > > >     Discard .note.gnu.property sections in generic NOTES
> > > >
> > > >     With the command-line option, -mx86-used-note=yes, the x86 assembler
> > > >     in binutils 2.32 and above generates a program property note in a note
> > > >     section, .note.gnu.property, to encode used x86 ISAs and features.  But
> > > >     kernel linker script only contains a single NOTE segment:
> > > >
> > > > /DISCARD/ : { *(.note.gnu.property) }
> > > >
> > > > is placed before
> > > >
> > > > .rela.dyn : AT(ADDR(.rela.dyn) - (0xc000000000000000 -0x00000000))
> > > >  {
> > > >   __rela_dyn_start = .;
> > > >   *(.rela*) <<<<<<<< Keep .rela* sections
> > > >  }
> > > >
> > > > Then .rela* in
> > > >
> > > >  /DISCARD/ : {
> > > >   *(*.EMB.apuinfo)
> > > >   *(.glink .iplt .plt .rela* .comment)
> > > >   *(.gnu.version*)
> > > >   *(.gnu.attributes)
> > > >   *(.eh_frame)
> > > >  }
> > > >
> > > > is honored.  Can someone from POWERPC comment on it?
> > >
> > > Hmm OK. I'm not really a toolchain person.
> > >
> > > The comment on DISCARDS says:
> > >
> > >    * Some archs want to discard exit text/data at runtime rather than
> > >    * link time due to cross-section references such as alt instructions,
> > >    * bug table, eh_frame, etc.  DISCARDS must be the last of output
> > >    * section definitions so that such archs put those in earlier section
> > >    * definitions.
> > >    */
> > >
> > > But I guess you're changing those semantics in your series.
> > >
> > > This seems to fix the warning for me?
> > >
> > > diff --git a/arch/powerpc/kernel/vmlinux.lds.S b/arch/powerpc/kernel/vmlinux.lds.S
> > > index b4c89a1acebb..076b3e8a849d 100644
> > > --- a/arch/powerpc/kernel/vmlinux.lds.S
> > > +++ b/arch/powerpc/kernel/vmlinux.lds.S
> > > @@ -365,9 +365,12 @@ SECTIONS
> > >         DISCARDS
> > >         /DISCARD/ : {
> > >                 *(*.EMB.apuinfo)
> > > -               *(.glink .iplt .plt .rela* .comment)
> > > +               *(.glink .iplt .plt .comment)
> > >                 *(.gnu.version*)
> > >                 *(.gnu.attributes)
> > >                 *(.eh_frame)
> > > +#ifndef CONFIG_RELOCATABLE
> > > +               *(.rela*)
> > > +#endif
> > >         }
> > >  }
> > >
> > >
> > > cheers
> >
> > This looks correct me.
> >
> > Reviewed-by: H.J. Lu <hjl.tools at gmail.com>
> >
> > Thanks.
> >
>
> Has this been merged into any branch yet?  I just checked the tip tree and did
> not see it.
>

FYI, my patches have been queued on x86/build branch.   Could someone
from PPC community add this patch to PPC kernel to avoid upcoming PPC
kernel build failure?

Thanks.

-- 
H.J.