Re: violating function pointer signature

[Segher Boessenkool]

On Wed, Nov 18, 2020 at 01:58:23PM -0500, Steven Rostedt wrote:
> I wonder if we should define on all architectures a void void_stub(void),
> in assembly, that just does a return, an not worry about gcc messing up the
> creation of the stub function.
> 
> On x86_64:
> 
> GLOBAL(void_stub)
> 	retq
> 
> 
> And so on.

I don't see how you imagine a compiler to mess this up?

void void_stub(void) { }

will do fine?

        .globl  void_stub
        .type   void_stub, @function
void_stub:
.LFB0:
        .cfi_startproc
        ret
        .cfi_endproc
.LFE0:
        .size   void_stub, .-void_stub


Calling this via a different declared function type is undefined
behaviour, but that is independent of how the function is *defined*.
Your program can make ducks appear from your nose even if that function
is never called, if you do that.  Just don't do UB, not even once!


Segher