Re: [PATCH v2 4/4] x86/static_call: Add inline static call implementation for x86-64

Peter Zijlstra
2018-11-26T16:39:36Z

On Mon, Nov 26, 2018 at 05:11:05PM +0100, Ard Biesheuvel wrote:
> On Mon, 26 Nov 2018 at 17:08, Peter Zijlstra <peterz@infradead.org> wrote:
> >
> > On Mon, Nov 26, 2018 at 07:55:00AM -0600, Josh Poimboeuf wrote:
> > > +#ifdef CONFIG_HAVE_STATIC_CALL_INLINE
> > > +void arch_static_call_defuse_tramp(void *site, void *tramp)
> > > +{
> > > + unsigned short opcode = INSN_UD2;
> > > +
> > > + mutex_lock(&text_mutex);
> > > + text_poke((void *)tramp, &opcode, 2);
> > > + mutex_unlock(&text_mutex);
> > > +}
> > > +#endif
> >
> > I would rather think that makes the trampoline _more_ dangerous, rather
> > than less so.
> >
> > My dictionary sayeth:
> >
> > defuse: verb
> >
> > - remove the fuse from (an explosive device) in order to prevent it
> > from exploding.
> >
> > - make (a situation) less tense or dangerous
> >
> > patching in an UD2 seems to do the exact opposite.
>
> That is my fault.
>
> The original name was 'poison' iirc, but on arm64, we need to retain
> the trampoline for cases where the direct branch is out of range, and
> so poisoning is semantically inaccurate.
>
> But since you opened your dictionary anyway, any better suggestions? :-)

I was leaning towards: "prime", but I'm not entirely sure that works
with your case.