Re: [PATCH v2 01/16] docs: deprecated.rst: Add uninitialized_var()

From: Nick Desaulniers <ndesaulniers@google.com>
To: Kees Cook <keescook@chromium.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>,
	Alexander Potapenko <glider@google.com>,
	Joe Perches <joe@perches.com>, Andy Whitcroft <apw@canonical.com>,
	"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
	<x86@kernel.org>,
	drbd-dev@lists.linbit.com, linux-block@vger.kernel.org,
	b43-dev@lists.infradead.org,
	Network Development <netdev@vger.kernel.org>,
	Linux Doc Mailing List <linux-doc@vger.kernel.org>,
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	linux-ide@vger.kernel.org, linux-clk@vger.kernel.org,
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	Linux Memory Management List <linux-mm@kvack.org>,
	clang-built-linux <clang-built-linux@googlegroups.com>
Subject: Re: [PATCH v2 01/16] docs: deprecated.rst: Add uninitialized_var()
Date: Mon, 22 Jun 2020 09:59:54 -0700	[thread overview]
Message-ID: <CAKwvOd=a+aSb5Scg=jD-jDfvnKJjOCVQ8CidgEo-39g2b2z-3A@mail.gmail.com> (raw)
In-Reply-To: <20200620033007.1444705-2-keescook@chromium.org>

On Fri, Jun 19, 2020 at 8:30 PM Kees Cook <keescook@chromium.org> wrote:
>
> Nothing should be using this macro, and the entire idea of tricking the
> compiler into silencing such warnings is a mistake.
>
> Signed-off-by: Kees Cook <keescook@chromium.org>

Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

> ---
>  Documentation/process/deprecated.rst | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
>
> diff --git a/Documentation/process/deprecated.rst b/Documentation/process/deprecated.rst
> index 652e2aa02a66..943a926ecbbb 100644
> --- a/Documentation/process/deprecated.rst
> +++ b/Documentation/process/deprecated.rst
> @@ -51,6 +51,24 @@ to make sure their systems do not continue running in the face of
>  "unreachable" conditions. (For example, see commits like `this one
>  <https://git.kernel.org/linus/d4689846881d160a4d12a514e991a740bcb5d65a>`_.)
>
> +uninitialized_var()
> +-------------------
> +For any compiler warnings about uninitialized variables, just add
> +an initializer. Using the uninitialized_var() macro (or similar
> +warning-silencing tricks) is dangerous as it papers over `real bugs
> +<https://lore.kernel.org/lkml/20200603174714.192027-1-glider@google.com/>`_
> +(or can in the future), and suppresses unrelated compiler warnings
> +(e.g. "unused variable"). If the compiler thinks it is uninitialized,
> +either simply initialize the variable or make compiler changes. Keep in
> +mind that in most cases, if an initialization is obviously redundant,
> +the compiler's dead-store elimination pass will make sure there are no
> +needless variable writes.
> +
> +As Linus has said, this macro
> +`must <https://lore.kernel.org/lkml/CA+55aFw+Vbj0i=1TGqCR5vQkCzWJ0QxK6CernOU6eedsudAixw@mail.gmail.com/>`_
> +`be <https://lore.kernel.org/lkml/CA+55aFwgbgqhbp1fkxvRKEpzyR5J8n1vKT1VZdz9knmPuXhOeg@mail.gmail.com/>`_
> +`removed <https://lore.kernel.org/lkml/CA+55aFz2500WfbKXAx8s67wrm9=yVJu65TpLgN_ybYNv0VEOKA@mail.gmail.com/>`_.
> +
>  open-coded arithmetic in allocator arguments
>  --------------------------------------------
>  Dynamic size calculations (especially multiplication) should not be
> --
> 2.25.1
>
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-- 
Thanks,
~Nick Desaulniers