linux-kernel - Re: [PATCH v2] cpufreq: qcom-kryo: Fix section mismatch warning

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Date:   Thu, 20 Sep 2018 00:45:55 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     ndesaulniers@...gle.com, natechancellor@...il.com,
        ilia.lin@...il.com, "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] cpufreq: qcom-kryo: Fix section mismatch warning

On Wed, Sep 19, 2018 at 11:54 PM Viresh Kumar <viresh.kumar@...aro.org> wrote:
>
> On 19-09-18, 14:50, Viresh Kumar wrote:
> > On 19-09-18, 14:45, Nick Desaulniers wrote:
> > > On Wed, Sep 19, 2018 at 11:22 AM Nathan Chancellor
> > > <natechancellor@...il.com> wrote:
> > > >
> > > > WARNING: vmlinux.o(.text+0x8aa424): Section mismatch in reference from
> > > > the function qcom_cpufreq_kryo_probe() to the function
> > > > .init.text:qcom_cpufreq_kryo_get_msm_id()
> > > > The function qcom_cpufreq_kryo_probe() references
> > > > the function __init qcom_cpufreq_kryo_get_msm_id().
> > > > This is often because qcom_cpufreq_kryo_probe lacks a __init
> > > > annotation or the annotation of qcom_cpufreq_kryo_get_msm_id is wrong.
> > > >
> > > > Add the '__init' annotation to qcom_cpufreq_kryo_probe so that there is
> > > > no more mismatch warning.
> > >
> > > I wonder why this driver has an exit function marked __init rather
> > > than __exit?
> >
> > I think it was just a mistake.
> >
> > > Does that mean it gets cleaned up after kernel init, and
> > > so on unloading of the driver, the kernel jumps to unmapped memory?
> >
> > The __init/exit sections are only useful when the driver is builtin
> > and so there is no unloading. Yeah, if you would have tried to call
> > shutdown for the kernel, it may have crashed or something. I don't
> > know.
> >
> > > Does this patch now produce a warning for `qcom_cpufreq_kryo_driver`
> > > referencing `qcom_cpufreq_kryo_probe`?
> >
> > Why should it ? It doesn't though.
>
> I thought you replied to my commit where I marked the exit routine
> with __exit and realised just now that it wasn't the case. I haven't
> build-tested this thing, but the question still stands. Why should it
> ?

Because __init things go away at one point and calling them from the
other sections is a bad idea.  OTOH, __exit things are simply not
needed in built-in drivers and they are never there if the driver is
built-in, so calling them from the other sections is a bad idea too.

Can you guys, please, prepare *one* patch fixing all of the
__init/__exit annotations in this driver and post it?

Thanks,
Rafael