Re: [RFC] ftrace: Add support to keep some functions out of ftrace

Jiri Olsa
2022-08-16T08:52:00Z

On Mon, Aug 15, 2022 at 05:48:44PM +0200, Peter Zijlstra wrote:
> On Mon, Aug 15, 2022 at 08:35:53AM -0700, Alexei Starovoitov wrote:
> > On Mon, Aug 15, 2022 at 8:28 AM Peter Zijlstra <peterz@infradead.org> wrote:
> > >
> > > On Mon, Aug 15, 2022 at 08:17:42AM -0700, Alexei Starovoitov wrote:
> > > > It's hiding a fake function from ftrace, since it's not a function
> > > > and ftrace infra shouldn't show it tracing logs.
> > > > In other words it's a _notrace_ function with nop5.
> > >
> > > Then make it a notrace function with a nop5 in it. That isn't hard.
> >
> > That's exactly what we're trying to do.
>
> All the while claiming ftrace is broken while it is not.
>
> > Jiri's patch is one way to achieve that.
>
> Fairly horrible way.
>
> > What is your suggestion?
>
> Mailed it already.
>
> > Move it from C to asm ?
>
> Would be much better than proposed IMO.

nice, that would be independent of the compiler atributes
and config checking.. will check on this one ;-)

thanks,
jirka

>
> > Make it naked function with explicit inline asm?
>
> Can be made to work but is iffy because the compiler can do horrible
> things with placing the asm().