Re: [PATCH] printf: mark errptr() noinline

Tamir Duberstein
2026-04-07T13:35:34Z

On Tue, Apr 7, 2026 at 7:27 AM Petr Mladek <pmladek@suse.com> wrote:
>
> On Mon 2026-04-06 12:32:32, Steven Rostedt wrote:
> > On Mon, 6 Apr 2026 11:21:39 -0400
> > Tamir Duberstein <tamird@kernel.org> wrote:
> >
> > > Thanks Steve. IMO that is a very big hammer and not warranted in this
> > > case. There's been talk of encouraging distros to enable CONFIG_KUNIT
> > > by default [0], which would probably interact poorly with the change
> > > you propose.
> > >
> >
> > Branch profiling is really just a niche that is enabled specifically for
> > seeing all branches taken in the kernel. It hooks to all "if" statements!
> > As you can imagine, it causes a rather large overhead in performance.
> >
> > This option is only used by developers doing special analysis of their code
> > (namely me ;-).
> >
> > The only real concern I would have is if the kunit test developers would
> > want to use the branch profiling on their code, in which case my suggestion
> > would prevent that.
>
> I wonder if it might be possible to disable the branch profiling just
> for the printf_kunit.c as a compromise.
>
> Would "#undef if" in printf_kunit.c help?
>
> Or I see that DISABLE_BRANCH_PROFILING is an official
> way to disable the feature.
>
> I wonder if the following change would solve the problem.
> I am sorry, I could not test it easily.

Yes, we can disable it for the whole file. I decided against that
because narrow workarounds are better than broad ones IMO, but it is
ultimately up to your preference.

FWIW I did test that this patch fixes the problem in GCC 8.5.0.