[RFA] [PATCH] Add a warning for invalid function casts

[Eric Gallager]

On Tue, Oct 3, 2017 at 3:33 PM, Bernd Edlinger
<bernd.edlinger@hotmail.de> wrote:
> Hi!
>
> I have implemented a warning -Wcast-function-type that analyzes
> type casts which change the function signatures.
>
> I would consider function pointers with different result type
> invalid, also if both function types have a non-null TYPE_ARG_TYPES
> I would say this deserves a warning.  As an exception I have
> used for instance in recog.h, the warning allows casting
> a function with the type typedef rtx (*stored_funcptr) (...);
> to any function with the same result type.
>
> I would think a warning like that should be enabled with -Wextra.
>
> Attached is a first version of the patch and as you can see
> the warning found already lots of suspicious type casts.  The worst
> is the splay-tree which always calls functions with uintptr_t
> instead of the correct parameter type.  I was unable to find
> a solution for this, and just silenced the warning with a
> second type-cast.
>
> Note that I also changed one line in libgo, but that is only
> a quick hack which I only did to make the boot-strap with
> all languages succeed.
>
> I'm not sure if this warning may be a bit too strict, but I think
> so far it just triggered on rather questionable code.
>
> Thoughts?
>
>
> Bernd.

Sorry if this is a stupid question, but could you explain how this
warning is different from -Wbad-function-cast? Something about direct
calls to functions vs. passing them as function pointers?