Re: violating function pointer signature

Segher Boessenkool
2020-11-18T19:20:35Z

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