On Wed, May 13, 2020 at 4:36 PM Borislav Petkov <bp@xxxxxxx> wrote:
>
>
> Looking at them, they do have an mb() too so how about this then
> instead?
>
> #define prevent_tail_call_optimization() mb()
Yeah, I think a full mb() is likely safe, because that's pretty much
always going to be a real instruction with real semantics, and no
amount of link-time optimizations can move it around a call
instruction.
I could imagine some completely UP in-order CPU that doesn't need to
serialize with anything at all, and even "mb()" might be empty. I
think you can compile old ARM kernels for that. But realistically I
think we can ignore them at least for now - I'm not sure the link-time
optimization will even do things like that tailcall conversion, and
I'm not convinced that old pre-ARMv7 systems will be relevant by the
time (if) it ever does.
Linus
