On Wed, Feb 14, 2024 at 11:37:21AM +0100, Greg Kroah-Hartman wrote:

On Wed, Feb 14, 2024 at 09:46:33AM +0000, David Laight wrote:

quoted

From: Segher Boessenkool

quoted

Sent: 13 February 2024 19:13

On Tue, Feb 13, 2024 at 11:17:49AM +0100, Arnd Bergmann wrote:

quoted

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]

quoted

 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.

Yes, and I said so.  My point is that the warning message pretends the
cast is bad or dangerous.  It is not, similar casts are the only way in
C to do certain things (yes, you can always avoid it completely, by
writing completely different code, like the patch does, and that
sometimes is a better idea even).

But the warning message is misleading and does more damage than it helps
avoid.


Segher