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

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Message-ID: <2024021426-unleveled-unhearing-8021@gregkh>
Date: Wed, 14 Feb 2024 11:37:21 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: David Laight <David.Laight@...lab.com>
Cc: 'Segher Boessenkool' <segher@...nel.crashing.org>,
	Arnd Bergmann <arnd@...nel.org>,
	"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
	Arnd Bergmann <arnd@...db.de>,
	"llvm@...ts.linux.dev" <llvm@...ts.linux.dev>,
	Nick Desaulniers <ndesaulniers@...gle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Nathan Chancellor <nathan@...nel.org>,
	Bill Wendling <morbo@...gle.com>,
	"linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
	Justin Stitt <justinstitt@...gle.com>,
	Jiri Slaby <jirislaby@...nel.org>
Subject: Re: [PATCH] tty: hvc-iucv: fix function pointer casts

On Wed, Feb 14, 2024 at 09:46:33AM +0000, David Laight wrote:
> From: Segher Boessenkool
> > Sent: 13 February 2024 19:13
> > 
> > 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.
> 
> But it will get called using the wrong type.
> And (is it) fine-ibt will reject the incorrect call.

And rightfully so, this type of casting abuse is just that, abuse.

Almost no one should be just calling kfree() on a device pointer, I'll
look at the surrounding code as odds are something odd is going on.  But
for now, this patch is correct.

thanks,

greg k-h