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

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Message-ID: <efc0e15e-fc93-fb59-068d-602f96ec7431@csgroup.eu>
Date:   Fri, 26 Nov 2021 08:43:23 +0000
From:   LEROY Christophe <christophe.leroy@...roup.eu>
To:     Peter Zijlstra <peterz@...radead.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH] recordmcount: Support empty section from recent binutils



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

Christophe

> 
> Suggested-by: Steven Rostedt <rostedt@...dmis.org>
> Link: https://github.com/linuxppc/issues/issues/388
> Link: https://lore.kernel.org/all/20210215162209.5e2a475b@gandalf.local.home/
> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
> ---
>   scripts/recordmcount.h | 2 ++
>   1 file changed, 2 insertions(+)
> 
> diff --git a/scripts/recordmcount.h b/scripts/recordmcount.h
> index 1e9baa5c4fc6..cc6600b729ae 100644
> --- a/scripts/recordmcount.h
> +++ b/scripts/recordmcount.h
> @@ -575,6 +575,8 @@ static char const *has_rel_mcount(Elf_Shdr const *const relhdr,
>   				  char const *const shstrtab,
>   				  char const *const fname)
>   {
> +	if (!shdr0->sh_size)
> +		return NULL;
>   	if (w(relhdr->sh_type) != SHT_REL && w(relhdr->sh_type) != SHT_RELA)
>   		return NULL;
>   	return __has_rel_mcount(relhdr, shdr0, shstrtab, fname);
>