linux-kernel - Re: [PATCH] tty: hvc-iucv: fix function pointer casts

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Date: Tue, 13 Feb 2024 13:12:54 -0600
From: Segher Boessenkool <segher@...nel.crashing.org>
To: Arnd Bergmann <arnd@...nel.org>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>, Arnd Bergmann <arnd@...db.de>,
        llvm@...ts.linux.dev, Nick Desaulniers <ndesaulniers@...gle.com>,
        linux-kernel@...r.kernel.org, Nathan Chancellor <nathan@...nel.org>,
        Bill Wendling <morbo@...gle.com>, linux-serial@...r.kernel.org,
        Justin Stitt <justinstitt@...gle.com>, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH] tty: hvc-iucv: fix function pointer casts

On Tue, Feb 13, 2024 at 11:17:49AM +0100, Arnd Bergmann wrote:
> clang warns about explicitly casting between incompatible function
> pointers:
> 
> drivers/tty/hvc/hvc_iucv.c:1100:23: error: cast from 'void (*)(const void *)' to 'void (*)(struct device *)' converts to incompatible function type [-Werror,-Wcast-function-type-strict]
>  1100 |         priv->dev->release = (void (*)(struct device *)) kfree;
>       |                              ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Such a cast of course is explicitly allowed by 6.3.2.3/8, only calling a
function using a non-compatible type is UB.  This warning message is
quite misleading.  Doubly so because of the -Werror, as always.

Your proposed new code of course is nice and simple (albeit a bit bigger
than it was before, both source and binary).  Such is life ;-)


Segher