Re: [PATCH] static_call: fix function type mismatch

[Peter Zijlstra]

On Mon, Mar 22, 2021 at 05:29:21PM -0400, Steven Rostedt wrote:
> On Mon, 22 Mar 2021 22:18:17 +0100
> Arnd Bergmann <arnd@xxxxxxxxxx> wrote:
> 
> > I think the code works correctly on all architectures we support because
> > both 'int' and 'long' are returned in a register with any unused bits cleared.
> > It is however undefined behavior in C because 'int' and 'long' are not
> > compatible types, and the calling conventions don't have to allow this.
> 
> Static calls (and so do tracepoints) currently rely on these kind of
> "undefined behavior" in C. This isn't the only UB that it relies on.

Right, most of the kernel lives in UB. That's what we have -fwrapv
-fno-strict-aliassing and lots of other bits for, to 'fix' the stupid C
standard.

This is one more of them, so just ignore the warning and make it go
away:

 -Wno-cast-function-type

seems to be the magic knob.