netdev - Re: [PATCH 01/10] x86/mm/numa: Remove uninitialized

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Message-ID: <CANiq72mHhzfPMGbBn=NZfqLeejPG+t=GN++NJ-L0hg-2x4UPag@mail.gmail.com>
Date:   Thu, 4 Jun 2020 17:22:15 +0200
From:   Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Alexander Potapenko <glider@...gle.com>,
        Joe Perches <joe@...ches.com>,
        Andy Whitcroft <apw@...onical.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        drbd-dev@...ts.linbit.com, linux-block@...r.kernel.org,
        b43-dev@...ts.infradead.org,
        Network Development <netdev@...r.kernel.org>,
        linux-wireless <linux-wireless@...r.kernel.org>,
        linux-ide@...r.kernel.org, linux-clk@...r.kernel.org,
        linux-spi@...r.kernel.org, Linux-MM <linux-mm@...ck.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Masahiro Yamada <masahiroy@...nel.org>
Subject: Re: [PATCH 01/10] x86/mm/numa: Remove uninitialized_var() usage

On Thu, Jun 4, 2020 at 4:56 PM Kees Cook <keescook@...omium.org> wrote:
>
> Er? That's not what it looked like to me:
>
> #define IS_BUILTIN(option) __is_defined(option)
> #define IS_ENABLED(option) __or(IS_BUILTIN(option), IS_MODULE(option))
>
> But just to be sure, I just tested in with a real build:
>
> [    3.242160] IS_ENABLED(TEST_UNDEF) false
> [    3.242691] __is_defined(TEST_UNDEF) false
> [    3.243240] IS_ENABLED(TEST_VALUE_EMPTY) false
> [    3.243794] __is_defined(TEST_VALUE_EMPTY) false
> [    3.244353] IS_ENABLED(TEST_VALUE_1) true
> [    3.244848] __is_defined(TEST_VALUE_1) true
>
> and nope, it only works with a defined value present.

You are right, it follows the Kconfig logic, returning false for
defined-but-to-0 too.

We should probably add an `IS_DEFINED()` macro kernel-wide for this
(and add it to the `coding-guidelines.rst` since `IS_ENABLED()` is
mentioned there, with a warning not to mix it with `__is_defined()`
which looks it was only intended as an implementation detail for
`include/linux/kconfig.h`).

CC'ing Masahiro by the way.

Cheers,
Miguel