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: > > 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. 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
