Solving section mismatches

[Sam Ravnborg]

On Sun, Sep 27, 2009 at 07:39:04PM +0100, Russell King - ARM Linux wrote:
> On Sun, Sep 27, 2009 at 08:27:07PM +0200, Sam Ravnborg wrote:
> > On Sun, Sep 27, 2009 at 05:41:16PM +0100, Russell King - ARM Linux wrote:
> > > Sam,
> > > 
> > > Any idea how to solve this:
> > > 
> > > WARNING: arch/arm/kernel/built-in.o(.text+0x1ebc): Section mismatch in reference from the function cpu_idle() to the function .cpuexit.text:cpu_die()
> > > The function cpu_idle() references a function in an exit section.
> > > Often the function cpu_die() has valid usage outside the exit section
> > > and the fix is to remove the __cpuexit annotation of cpu_die.
> > > 
> > > WARNING: arch/arm/kernel/built-in.o(.cpuexit.text+0x3c): Section mismatch in reference from the function cpu_die() to the function .cpuinit.text:secondary_start_kernel()
> > > The function __cpuexit cpu_die() references
> > > a function __cpuinit secondary_start_kernel().
> > > This is often seen when error handling in the exit function
> > > uses functionality in the init path.
> > > The fix is often to remove the __cpuinit annotation of
> > > secondary_start_kernel() so it may be used outside an init section.
> > > 
> > > Logically, the annotations are correct - in the first case, cpu_die()
> > > will only ever be called if hotplug CPU is enabled, since you can't
> > > offline a CPU without hotplug CPU enabled.  In that case, the __cpuexit.*
> > > sections are not discarded.
> > 
> > The annotation of cpu_die() is wrong.
> > To be annotated __cpuexit the function shall:
> > - be used in exit context and only in exit context with HOTPLUG_CPU=n
> > - be used outside exit context with HOTPLUG_CPU=y
> > 
> > cpu_die() fails on the first condition because it is only used
> > if HOTPLUG_CPU=y.
> > The annotation is wrongly used as a replacement for an ifdef.
> > As cpu_die() is already inside ifdef CONFIG_HOTPLUG_CPU is should
> > be enough to just remove the annotation.
> > 
> > Like this (copy'n'paste so it does not apply)
> > 
> > diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
> > index e0d3277..de4ef1c 100644
> > --- a/arch/arm/kernel/smp.c
> > +++ b/arch/arm/kernel/smp.c
> > @@ -214,7 +214,7 @@ void __cpuexit __cpu_die(unsigned int cpu)
> >   * of the other hotplug-cpu capable cores, so presumably coming
> >   * out of idle fixes this.
> >   */
> > -void __cpuexit cpu_die(void)
> > +void cpu_die(void)
> >  {
> >         unsigned int cpu = smp_processor_id();
> 
> This is wrong.  cpu_die() does not need to exist if hotplug CPU is
> disabled.  In that case, it should be discarded and this is precisely
> what __cpuexit does.  The annotation is, therefore, correct.