Messages in this thread |  | | | Date | Sun, 27 Sep 2009 20:46:45 +0200 | | From | Sam Ravnborg <> | | Subject | Re: Solving section mismatches |
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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.
From arch/arm/kernel/smp.c
#ifdef CONFIG_HOTPLUG_CPU
... void __cpuexit cpu_die(void) { unsigned int cpu = smp_processor_id(); local_irq_disable(); idle_task_exit();
/* * actual CPU shutdown procedure is at least platform (if not * CPU) specific */ platform_cpu_die(cpu); /* * Do not return to the idle loop - jump back to the secondary * cpu initialisation. There's some initialisation which needs * to be repeated to undo the effects of taking the CPU offline. */ __asm__("mov sp, %0\n" " b secondary_start_kernel" : : "r" (task_stack_page(current) + THREAD_SIZE - 8)); } #endif /* CONFIG_HOTPLUG_CPU */
Please look at the above and realise that cpu_die() is only ever defined in case that HOTPLUG_CPU is defined. So there is nothing to discard if HOTPLUG_CPU equals to n.
And just to repeat myself.... The only correct use of __cpu* annotation is for function/data that is used with or without HOTPLUG_CPU equals to y. Which is NOT the case for cpu_die(). The __cpu* annotation is not a replacement for ifdeffed out code that is not relevant for the non-HOTPLUG_CPU case.
Sam
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