Re: [PATCH -rcu/kcsan 04/23] kcsan: Add core support for a subset of weak memory modeling

Marco Elver
2021-10-05T13:13:39Z

On Tue, 5 Oct 2021 at 14:53, Peter Zijlstra <peterz@infradead.org> wrote:
> On Tue, Oct 05, 2021 at 12:58:46PM +0200, Marco Elver wrote:
> > +#if !defined(CONFIG_ARCH_WANTS_NO_INSTR) || defined(CONFIG_STACK_VALIDATION)
> > +/*
> > + * Arch does not rely on noinstr, or objtool will remove memory barrier
> > + * instrumentation, and no instrumentation of noinstr code is expected.
> > + */
> > +#define kcsan_noinstr
>
> I think this still wants to be at the very least:
>
> #define kcsan_noinstr noinline notrace
>
> without noinline it is possible LTO (or similarly daft things) will end
> up inlining the calls, and since we rely on objtool to NOP out CALLs
> this must not happen.

Good point about noinline, will add.

> And since you want to mark these functions as uaccess_safe, there must
> not be any tracing on, hence notrace.

In the Makefile we've relied on:

CFLAGS_REMOVE_core.o = $(CC_FLAGS_FTRACE)

just to disable it for all code here. That should be enough, right?