linux-kernel - Re: [PATCH] ppdev: Distribute switch variables for initialization

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Date:   Mon, 24 Feb 2020 12:34:12 +0000
From:   Sudip Mukherjee <sudipm.mukherjee@...il.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Alexander Potapenko <glider@...gle.com>,
        linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH] ppdev: Distribute switch variables for initialization

On Wed, Feb 19, 2020 at 10:23:11PM -0800, Kees Cook wrote:
> Variables declared in a switch statement before any case statements
> cannot be automatically initialized with compiler instrumentation (as
> they are not part of any execution flow). With GCC's proposed automatic
> stack variable initialization feature, this triggers a warning (and they
> don't get initialized). Clang's automatic stack variable initialization
> (via CONFIG_INIT_STACK_ALL=y) doesn't throw a warning, but it also
> doesn't initialize such variables[1]. Note that these warnings (or silent
> skipping) happen before the dead-store elimination optimization phase,
> so even when the automatic initializations are later elided in favor of
> direct initializations, the warnings remain.
> 
> To avoid these problems, move such variables into the "case" where
> they're used or lift them up into the main function body.
> 
> drivers/char/ppdev.c: In function ‘pp_do_ioctl’:
> drivers/char/ppdev.c:516:25: warning: statement will never be executed [-Wswitch-unreachable]
>   516 |   struct ieee1284_info *info;
>       |                         ^~~~
> 
> [1] https://bugs.llvm.org/show_bug.cgi?id=44916
> 
> Signed-off-by: Kees Cook <keescook@...omium.org>

Acked-by: Sudip Mukherjee <sudipm.mukherjee@...il.com>

Greg, Can you please take it in your tree...

--
Regards
Sudip