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

[Petr Mladek]

On Tue 2026-04-07 09:34:57, Tamir Duberstein wrote:
> On Tue, Apr 7, 2026 at 7:27 AM Petr Mladek <pmladek@xxxxxxxx> wrote:
> >
> > On Mon 2026-04-06 12:32:32, Steven Rostedt wrote:
> > > On Mon, 6 Apr 2026 11:21:39 -0400
> > > Tamir Duberstein <tamird@xxxxxxxxxx> 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.

I might be wrong but I think that nobody would want to
profile/optimize this kunit test. So, this looks like the best
solution because it is straightforward. The variant adding
"noinline" looks too hacky to me.

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

Thanks for testing.

Would you like to prepare a proper patch or should I do so?

Best Regards,
Petr