Re: [PATCH v5 00/18] Rework READ_ONCE() to improve codegen

[Martin LiÅka]

On 6/3/20 9:23 PM, Marco Elver wrote:
> On Wed, 03 Jun 2020, Borislav Petkov wrote:
>
> > On Thu, May 14, 2020 at 12:05:38PM +0100, Will Deacon wrote:
> > > Talking off-list, Clang >= 7 is pretty reasonable wrt inlining decisions
> > > and the behaviour for __always_inline is:
> > >
> > >    * An __always_inline function inlined into a __no_sanitize function is
> > >      not instrumented
> > >    * An __always_inline function inlined into an instrumented function is
> > >      instrumented
> > >    * You can't mark a function as both __always_inline __no_sanitize, because
> > >      __no_sanitize functions are never inlined
> > >
> > > GCC, on the other hand, may still inline __no_sanitize functions and then
> > > subsequently instrument them.
> >
> > Yeah, about that: I've been looking for a way to trigger this so that
> > I can show preprocessed source to gcc people. So do you guys have a
> > .config or somesuch I can try?
>
> For example take this:
>
> 	int x;
>
> 	static inline __attribute__((no_sanitize_thread)) void do_not_sanitize(void) {
> 	  x++;
> 	}
>
> 	void sanitize_this(void) {
> 	  do_not_sanitize();
> 	}
>
> Then
>
> 	gcc-10 -O3 -fsanitize=thread -o example.o -c example.c
> 	objdump -D example.o

Hello.

Thank you for the example. It seems to me that Clang does not inline a no_sanitize_* function
into one which is instrumented. Is it a documented behavior ([1] doesn't mention that)?
If so, we can do the same in GCC.

Thanks,
Martin

[1] https://clang.llvm.org/docs/AttributeReference.html#no-sanitize

> will show that do_not_sanitize() was inlined into sanitize_this() and is
> instrumented. (With Clang this doesn't happen.)
>
> Hope this is enough.
>
> Thanks,
> -- Marco