linux-hardening - Re: [PATCH] Kconfig.debug: Make DEBUG

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Date:   Fri, 10 Dec 2021 10:40:12 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Kees Cook <keescook@...omium.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Arnd Bergmann <arnd@...db.de>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        Peter Zijlstra <peterz@...radead.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH] Kconfig.debug: Make DEBUG_INFO selectable from a choice

On Fri, Dec 10, 2021 at 1:09 AM Kees Cook <keescook@...omium.org> wrote:
>
> Currently it's not possible to enable DEBUG_INFO for an all*config
> build, since it is marked as "depends on !COMPILE_TEST". This generally
> makes sense because a debug build of an all*config target ends up taking
> much longer and the output is much larger. Having this be "default off"
> makes sense. However, there are cases where enabling DEBUG_INFO for such
> builds is useful for doing treewide A/B comparisons of build options,
> etc.
>
> Make DEBUG_INFO selectable from any of the DWARF version choice options,
> with DEBUG_INFO_NONE being the default for COMPILE_TEST. The mutually
> exclusive relationship between DWARF5 and BTF must be inverted, but the
> result remains the same. Additionally moves DEBUG_KERNEL and DEBUG_MISC
> up to the top of the menu because was enabling features _above_ it,
> making it weird to navigate menuconfig.
>
> Suggested-by: Arnd Bergmann <arnd@...db.de>
> Signed-off-by: Kees Cook <keescook@...omium.org>

Looks good to me,

Reviewed-by: Arnd Bergmann <arnd@...db.de>

One detail:

> +choice
> +       prompt "Debug information"
> +       depends on DEBUG_KERNEL
> +       default DEBUG_INFO_NONE if COMPILE_TEST
> +       default DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT if DEBUG_KERNEL

I think this line should be simplified to

          default DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT

since DEBUG_KERNEL is always enabled at this point. You can also consider
turning the 'menu' into 'menuconfig DEBUG_KERNEL' and dropping the 'depends
on DEBUG_KERNEL' in favor of the implied dependency.

       Arnd