linux-kernel - Re: [PATCH] Kconfig.debug: split debug-level and DWARF-version into separate choices

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Message-ID: <CAKwvOdnS8mGiNWPyn+jA7=MdZ3NsO0zrq2hAK8bvndf_4z1MJQ@mail.gmail.com>
Date:   Fri, 30 Sep 2022 11:13:23 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
        Kees Cook <keescook@...omium.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Miguel Ojeda <ojeda@...nel.org>,
        Dmitrii Bundin <dmitrii.bundin.a@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] Kconfig.debug: split debug-level and DWARF-version into
 separate choices

On Fri, Sep 30, 2022 at 1:55 AM Masahiro Yamada <masahiroy@...nel.org> wrote:
>
> Commit f9b3cd245784 ("Kconfig.debug: make DEBUG_INFO selectable from
> a choice") added CONFIG_DEBUG_INFO_NONE into the DWARF version choice,
> but it should rather belong to the debug level choice.
>
> This commit cosolidates CONFIG options into two choices:

s/cosolidates/consolidates/

>
>  - Debug info level (NONE / REDUCED / DEFAULT)
>
>  - DWARF format (DWARF_TOOLCHAIN_DEFAULT / DWARF4 / DWARF5)
>
> This is more consistent with compilers' policy because the -g0 compiler
> flag means "no debug info".
>
>   GCC manual:
>
>     -g<level>
>
>       Request debugging information and also use level to specify how
>       much information. The default level is 2.
>
>       Level 0 produces no debug information at all. Thus, -g0 negates -g.
>
>       Level 1 produces minimal information, enough for making backtraces
>       in parts of the program that you don’t plan to debug. This includes
>       descriptions of functions and external variables, and line number
>       tables, but no information about local variables.
>
>       Level 3 includes extra information, such as all the macro
>       definitions present in the program. Some debuggers support macro
>       expansion when you use -g3.
>
>   Rustc Codegen manual:
>
>     debuginfo
>
>       This flag controls the generation of debug information. It takes
>       one of the following values:
>
>       0: no debug info at all (the default).
>       1: line tables only.
>       2: full debug info.
>
> I moved CONFIG_DEBUG_INFO_REDUCED into the debug level choice.
>
> This change will make it easier to add another debug info level if
> necessary.
>
> Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>

SGTM; thanks for the patch!
Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>

> ---
>
>  lib/Kconfig.debug | 60 +++++++++++++++++++++++++++++------------------
>  1 file changed, 37 insertions(+), 23 deletions(-)
>
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index d3e5f36bb01e..03e75a54be6c 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -232,17 +232,11 @@ config DEBUG_INFO
>           information will be generated for build targets.
>
>  choice
> -       prompt "Debug information"
> +       prompt "Debug information level"
>         depends on DEBUG_KERNEL
>         help
>           Selecting something other than "None" results in a kernel image
>           that will include debugging info resulting in a larger kernel image.
> -         This adds debug symbols to the kernel and modules (gcc -g), and
> -         is needed if you intend to use kernel crashdump or binary object
> -         tools like crash, kgdb, LKCD, gdb, etc on the kernel.
> -
> -         Choose which version of DWARF debug info to emit. If unsure,
> -         select "Toolchain default".
>
>  config DEBUG_INFO_NONE
>         bool "Disable debug information"
> @@ -250,9 +244,41 @@ config DEBUG_INFO_NONE
>           Do not build the kernel with debugging information, which will
>           result in a faster and smaller build.
>
> +config DEBUG_INFO_REDUCED
> +       bool "Reduced debugging information"
> +       select DEBUG_INFO
> +       help
> +         If you say Y here compiler is instructed to generate less debugging
> +         information for structure types. This means that tools that
> +         need full debugging information (like kgdb or systemtap) won't
> +         be happy. But if you merely need debugging information to
> +         resolve line numbers there is no loss. Advantage is that
> +         build directory object sizes shrink dramatically over a full
> +         DEBUG_INFO build and compile times are reduced too.
> +         Only works with newer gcc versions.
> +
> +config DEBUG_INFO_DEFAULT
> +       bool "Default-level debugging information"
> +       select DEBUG_INFO
> +       help
> +         If you say Y here compiler is instructed to generate the default
> +         level of debugging information.
> +
> +         This adds debug symbols to the kernel and modules (gcc -g), and
> +         is needed if you intend to use kernel crashdump or binary object
> +         tools like crash, kgdb, LKCD, gdb, etc on the kernel.
> +
> +endchoice # "Debug information level"
> +
> +choice
> +       prompt "DWARF version"
> +       depends on DEBUG_INFO
> +       prompt "DWARF version"
> +       help
> +         Which version of DWARF debug info to emit.
> +
>  config DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT
>         bool "Rely on the toolchain's implicit default DWARF version"
> -       select DEBUG_INFO
>         help
>           The implicit default version of DWARF debug info produced by a
>           toolchain changes over time.
> @@ -261,9 +287,10 @@ config DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT
>           support newer revisions, and prevent testing newer versions, but
>           those should be less common scenarios.
>
> +         If unsure, say Y.
> +
>  config DEBUG_INFO_DWARF4
>         bool "Generate DWARF Version 4 debuginfo"
> -       select DEBUG_INFO
>         depends on !CC_IS_CLANG || (CC_IS_CLANG && (AS_IS_LLVM || (AS_IS_GNU && AS_VERSION >= 23502)))
>         help
>           Generate DWARF v4 debug info. This requires gcc 4.5+, binutils 2.35.2
> @@ -275,7 +302,6 @@ config DEBUG_INFO_DWARF4
>
>  config DEBUG_INFO_DWARF5
>         bool "Generate DWARF Version 5 debuginfo"
> -       select DEBUG_INFO
>         depends on !CC_IS_CLANG || (CC_IS_CLANG && (AS_IS_LLVM || (AS_IS_GNU && AS_VERSION >= 23502)))
>         help
>           Generate DWARF v5 debug info. Requires binutils 2.35.2, gcc 5.0+ (gcc
> @@ -290,22 +316,10 @@ config DEBUG_INFO_DWARF5
>           config if they rely on tooling that has not yet been updated to
>           support DWARF Version 5.
>
> -endchoice # "Debug information"
> +endchoice # "DWARF version"
>
>  if DEBUG_INFO
>
> -config DEBUG_INFO_REDUCED
> -       bool "Reduce debugging information"
> -       help
> -         If you say Y here gcc is instructed to generate less debugging
> -         information for structure types. This means that tools that
> -         need full debugging information (like kgdb or systemtap) won't
> -         be happy. But if you merely need debugging information to
> -         resolve line numbers there is no loss. Advantage is that
> -         build directory object sizes shrink dramatically over a full
> -         DEBUG_INFO build and compile times are reduced too.
> -         Only works with newer gcc versions.
> -
>  config DEBUG_INFO_COMPRESSED
>         bool "Compressed debugging information"
>         depends on $(cc-option,-gz=zlib)
> --
> 2.34.1
>


-- 
Thanks,
~Nick Desaulniers