linux-kernel - Re: [PATCH] recordmcount: Support empty section from recent binutils

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Date:   Mon, 28 Mar 2022 22:31:40 +0000
From:   Joel Stanley <joel@....id.au>
To:     Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Segher Boessenkool <segher@...nel.crashing.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH] recordmcount: Support empty section from recent binutils

On Mon, 29 Nov 2021 at 22:43, Christophe Leroy
<christophe.leroy@...roup.eu> wrote:
>
>
>
> Le 29/11/2021 à 18:43, Steven Rostedt a écrit :
> > On Fri, 26 Nov 2021 08:43:23 +0000
> > LEROY Christophe <christophe.leroy@...roup.eu> wrote:
> >
> >> Le 24/11/2021 à 15:43, Christophe Leroy a écrit :
> >>> Looks like recent binutils (2.36 and over ?) may empty some section,
> >>> leading to failure like:
> >>>
> >>>     Cannot find symbol for section 11: .text.unlikely.
> >>>     kernel/kexec_file.o: failed
> >>>     make[1]: *** [scripts/Makefile.build:287: kernel/kexec_file.o] Error 1
> >>>
> >>> In order to avoid that, ensure that the section has a content before
> >>> returning it's name in has_rel_mcount().
> >>
> >> This patch doesn't work, on PPC32 I get the following message with this
> >> patch applied:
> >>
> >> [    0.000000] ftrace: No functions to be traced?
> >>
> >> Without the patch I get:
> >>
> >> [    0.000000] ftrace: allocating 22381 entries in 66 pages
> >> [    0.000000] ftrace: allocated 66 pages with 2 groups
> >
> > Because of this report, I have not applied this patch (even though I was
> > about to push it to Linus).
> >
> > I'm pulling it from my queue until this gets resolved.
> >
>
> I have no idea on how to fix that for the moment.
>
> With GCC 10 (binutils 2.36) an objdump -x on kernel/kexec_file.o gives:
>
> 0000000000000000 l    d  .text.unlikely 0000000000000000 .text.unlikely
> 0000000000000000  w    F .text.unlikely 0000000000000038
> .arch_kexec_apply_relocations_add
> 0000000000000038  w    F .text.unlikely 0000000000000038
> .arch_kexec_apply_relocations
>
>
> With GCC 11 (binutils 2.37) the same gives:
>
> 0000000000000000  w    F .text.unlikely 0000000000000038
> .arch_kexec_apply_relocations_add
> 0000000000000038  w    F .text.unlikely 0000000000000038
> .arch_kexec_apply_relocations
>
>
> The problem is that recordmcount drops weak symbols, and it doesn't find
> any non-weak symbol in .text.unlikely
>
> Explication given at
> https://elixir.bootlin.com/linux/v5.16-rc2/source/scripts/recordmcount.h#L506
>
> I have no idea on what to do.

Did you end up finding a solution for this issue?

Cheers,

Joel