linux-kernel - Re: [PATCH v2] usb: gadget: net2280: Distribute switch variables for initialization

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Date:   Fri, 21 Feb 2020 09:54:02 -0500 (EST)
From:   Alan Stern <stern@...land.harvard.edu>
To:     Kees Cook <keescook@...omium.org>
cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Felipe Balbi <balbi@...nel.org>,
        Alexander Potapenko <glider@...gle.com>,
        <linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] usb: gadget: net2280: Distribute switch variables
 for initialization

On Thu, 20 Feb 2020, 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/usb/gadget/udc/net2280.c: In function ‘handle_stat0_irqs_superspeed’:
> drivers/usb/gadget/udc/net2280.c:2871:22: warning: statement will never be executed [-Wswitch-unreachable]
>  2871 |   struct net2280_ep *e;
>       |                      ^
> 
> [1] https://bugs.llvm.org/show_bug.cgi?id=44916
> 
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
> v2: put everything in function body (Alan Stern)
> v1: https://lore.kernel.org/lkml/20200220062315.69253-1-keescook@chromium.org

You might want to remove part of the last sentence in the patch
description.  Aside from that,

Acked-by: Alan Stern <stern@...land.harvard.edu>

Alan Stern