linux-kernel - [PATCH v2 01/16] docs: deprecated.rst: Add uninitialized

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Date:   Fri, 19 Jun 2020 20:29:52 -0700
From:   Kees Cook <keescook@...omium.org>
To:     linux-kernel@...r.kernel.org
Cc:     Kees Cook <keescook@...omium.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        Alexander Potapenko <glider@...gle.com>,
        Joe Perches <joe@...ches.com>,
        Andy Whitcroft <apw@...onical.com>, x86@...nel.org,
        drbd-dev@...ts.linbit.com, linux-block@...r.kernel.org,
        b43-dev@...ts.infradead.org, netdev@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-wireless@...r.kernel.org,
        linux-ide@...r.kernel.org, linux-clk@...r.kernel.org,
        linux-spi@...r.kernel.org, linux-mm@...ck.org,
        clang-built-linux@...glegroups.com
Subject: [PATCH v2 01/16] docs: deprecated.rst: Add uninitialized_var()

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@...omium.org>
---
 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