linux-kernel - Re: linux-next: build warnings from the build of Linus' tree

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Message-Id: <20180911231012.fdc45840f3d91860daa2e180@kernel.org>
Date:   Tue, 11 Sep 2018 23:10:12 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Peter Oberparleiter <oberpar@...ux.ibm.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        "Steven Rostedt (VMware)" <rostedt@...dmis.org>,
        Linux-Next Mailing List <linux-next@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        arnd@...db.de
Subject: Re: linux-next: build warnings from the build of Linus' tree

On Tue, 11 Sep 2018 20:49:25 +0900
Masami Hiramatsu <mhiramat@...nel.org> wrote:

> On Mon, 10 Sep 2018 15:27:20 +0200
> Peter Oberparleiter <oberpar@...ux.ibm.com> wrote:
> 
> > On 08.09.2018 05:57, Masami Hiramatsu wrote:
> > > On Fri, 7 Sep 2018 14:50:59 +0200
> > > Peter Oberparleiter <oberpar@...ux.ibm.com> wrote:
> > > 
> > >> On 06.09.2018 18:42, Masami Hiramatsu wrote:
> > >>> Peter Oberparleiter <oberpar@...ux.ibm.com> wrote:
> > >>>> I've attached a quick fix that should address both problems. I'd
> > >>>> appreciate if this patch could get some testing before I post proper fix
> > >>>> patches.
> > >>>
> > >>> Hmm, I'm still not able to reproduce it on powerpc cross build even with
> > >>> CONFIG_LD_DEAD_CODE_DATA_ELIMINATION=y ... So, sorry I couldn't test this patch.
> > >>
> > >> Maybe this is related to the compiler/binutils versions used. I'm using
> > >> Fedora 28's gcc-powerpc64 and binutils-powerpc64 packages:
> > >>
> > >> powerpc64-linux-gnu-gcc (GCC) 7.1.1 20170622 (Red Hat Cross 7.1.1-3)
> > >> GNU ld version 2.29.1-4.fc28
> > >>
> > >> For reference I'm also attaching the config that I used to reproduce the
> > >> problem on kernel v4.18.
> > >>
> > >>>> diff --git a/arch/arm/kernel/vmlinux.lds.h b/arch/arm/kernel/vmlinux.lds.h
> > >>>> index ae5fdff18406..2ca33277a28b 100644
> > >>>> --- a/arch/arm/kernel/vmlinux.lds.h
> > >>>> +++ b/arch/arm/kernel/vmlinux.lds.h
> > >>>> @@ -48,6 +48,7 @@
> > >>>>
> > >>>>  #define ARM_DISCARD							\
> > >>>>  		*(.ARM.exidx.exit.text)					\
> > >>>> +		*(.ARM.exidx.text.exit)					\
> > >>>
> > >>> BTW, why would we need this?
> > >>
> > >> That's necessary to fix one of the two ARM linker failures reported via
> > >> https://lkml.org/lkml/2018/8/24/345
> > >>
> > >>>>> `.text.exit' referenced in section `.ARM.exidx.text.exit' of
> > >>>>> kernel/trace/trace_clock.o: defined in discarded section `.text.exit'
> > >>>>> of kernel/trace/trace_clock.o
> > >>
> > >> Section ".ARM.exidx.text.exit" refers to ".text.exit" which was
> > >> discarded. With the change above, the extraneous section
> > >> ".ARM.exidx.text.exit" is also discarded, resolving the linker failure.
> > > 
> > > OK, so your patch fixes following issue too?
> > > 
> > > https://patchwork.kernel.org/patch/10584685/
> > 
> > Yes it does, by discarding the text.exit section unconditionally. I
> > don't think we need to keep any exit-related section introduced by GCOV
> > profiling. It is my understanding that the code contained in such a
> > section is only relevant for user-space profiling, to process profiling
> > data when a program ends.
> > 
> > Also discarding .ARM.exidx.text.exit seems to be more consistent to how
> > .ARM.exidx.exit.text is handled.
> > 
> > > In that case, we should drop above patch.
> > 
> > Yes, I agree.
> 
> Hm, with your patch (on linus tree), I still have this error on arm cross build.
> 
>   CC      init/version.o
>   AR      init/built-in.a
>   AR      built-in.a
>   LD      vmlinux.o
>   MODPOST vmlinux.o
> `.exit.text' referenced in section `.alt.smp.init' of net/dns_resolver/dns_key.o: defined in discarded section `.exit.text' of net/dns_resolver/dns_key.o

Ah, sorry, this is not from GCOV, but alternatives for SMP.
This should be a different issue.

> 
> I attached my config.
> 
> Since this comes from section discarding, with my patch (which prevent discarding) this error didn't happen.

So, this is just a side effect. your patch is good when CONFIG_DNS_RESOLVER=n

Thank you,


-- 
Masami Hiramatsu <mhiramat@...nel.org>