On Wed, Mar 24, 2021 at 3:53 PM Rasmus Villemoes <li...@rasmusvillemoes.dk> wrote: > > On 24/03/2021 23.34, Sami Tolvanen wrote: > > On Wed, Mar 24, 2021 at 2:51 PM Rasmus Villemoes > > <li...@rasmusvillemoes.dk> wrote: > >> > >> On 24/03/2021 18.33, Peter Zijlstra wrote: > >>> On Wed, Mar 24, 2021 at 05:45:52PM +0100, Rasmus Villemoes wrote: > >>>> Sorry, I think I misread the code. The static calls are indeed > >>>> initialized with a function with the right prototype. Try adding > >>>> "preempt=full" on the command line so that we exercise these lines > >>>> > >>>> static_call_update(cond_resched, > >>>> (typeof(&__cond_resched)) __static_call_return0); > >>>> static_call_update(might_resched, > >>>> (typeof(&__cond_resched)) __static_call_return0); > >>>> > >>>> I would expect that to blow up, since we end up calling a long (*)(void) > >>>> function using a function pointer of type int (*)(void). > >>> > >>> Note that on x86 there won't actually be any calling of function > >>> pointers. See what arch/x86/kernel/static_call.c does :-) > >> > >> I know, but so far x86 is the only one with HAVE_STATIC_CALL, so for > >> arm64 which is where CFI seems to be targeted initially, static_calls > >> are function pointers. And unless CFI ignores the return type, I'd > >> really expect the above to fail. > > > > I think you're correct, this would trip CFI without HAVE_STATIC_CALL. > > However, arm64 also doesn't support PREEMPT_DYNAMIC at the moment, so > > this isn't currently a problem there. > > Well, there's PREEMPT_DYNAMIC and HAVE_PREEMPT_DYNAMIC. The former > doesn't depend on the latter (and the latter does depend on > HAVE_STATIC_CALL, so effectively not for anything but x86). You should > be able to select both PREEMPT_DYNAMIC and CFI_CLANG, and test if > booting with preempt=full does give the fireworks one expects.
Actually, it looks like I can't select PREEMPT_DYNAMIC, and tweaking Kconfig to force enable it on arm64 results in a build error ("implicit declaration of function 'static_call_mod'"). Sami