linux-kernel - Re: [PATCH v9 1/3] vmlinux.lds.h: add DWARF v5 sections

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Date:   Sat, 06 Feb 2021 16:02:09 +0100
From:   Mark Wielaard <mark@...mp.org>
To:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Masahiro Yamada <masahiroy@...nel.org>
Cc:     Nathan Chancellor <natechancellor@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Sedat Dilek <sedat.dilek@...il.com>,
        linux-kernel@...r.kernel.org, clang-built-linux@...glegroups.com,
        linux-kbuild@...r.kernel.org, linux-arch@...r.kernel.org,
        Jakub Jelinek <jakub@...hat.com>,
        Fangrui Song <maskray@...gle.com>,
        Caroline Tice <cmtice@...gle.com>,
        Nick Clifton <nickc@...hat.com>, Yonghong Song <yhs@...com>,
        Jiri Olsa <jolsa@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        Chris Murphy <bugzilla@...orremedies.com>,
        stable@...r.kernel.org, Chris Murphy <lists@...orremedies.com>,
        Nathan Chancellor <nathan@...nel.org>
Subject: Re: [PATCH v9 1/3] vmlinux.lds.h: add DWARF v5 sections

Hi Nick,

On Fri, 2021-02-05 at 12:22 -0800, Nick Desaulniers wrote:
> We expect toolchains to produce these new debug info sections as part of
> DWARF v5. Add explicit placements to prevent the linker warnings from
> --orphan-section=warn.
> 
> Compilers may produce such sections with explicit -gdwarf-5, or based on
> the implicit default version of DWARF when -g is used via DEBUG_INFO.
> This implicit default changes over time, and has changed to DWARF v5
> with GCC 11.
> 
> .debug_sup was mentioned in review, but without compilers producing it
> today, let's wait to add it until it becomes necessary.

I don't think that will be necessary. .debug_sup is for Dwarf
Supplemental file producers like dwz. Those would run after the linker.

> Cc: stable@...r.kernel.org
> Link: https://bugzilla.redhat.com/show_bug.cgi?id=1922707
> Reported-by: Chris Murphy <lists@...orremedies.com>
> Suggested-by: Fangrui Song <maskray@...gle.com>
> Reviewed-by: Nathan Chancellor <nathan@...nel.org>
> Tested-by: Sedat Dilek <sedat.dilek@...il.com>
> Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
> ---
>  include/asm-generic/vmlinux.lds.h | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
> index 34b7e0d2346c..1e7cde4bd3f9 100644
> --- a/include/asm-generic/vmlinux.lds.h
> +++ b/include/asm-generic/vmlinux.lds.h
> @@ -842,8 +842,13 @@
>  		/* DWARF 4 */						\
>  		.debug_types	0 : { *(.debug_types) }			\
>  		/* DWARF 5 */						\
> +		.debug_addr	0 : { *(.debug_addr) }			\
> +		.debug_line_str	0 : { *(.debug_line_str) }		\
> +		.debug_loclists	0 : { *(.debug_loclists) }		\
>  		.debug_macro	0 : { *(.debug_macro) }			\
> -		.debug_addr	0 : { *(.debug_addr) }
> +		.debug_names	0 : { *(.debug_names) }			\
> +		.debug_rnglists	0 : { *(.debug_rnglists) }		\
> +		.debug_str_offsets	0 : { *(.debug_str_offsets) }
>  
>  /* Stabs debugging sections. */
>  #define STABS_DEBUG							\

Looks good to me.

Cheers,

Mark