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Date: Fri, 10 Apr 2009 21:45:24 +0400
From: Cyrill Gorcunov <gorcunov@gmail.com>
To: Sam Ravnborg <sam@ravnborg.org>
Cc: Jaswinder Singh Rajput <jaswinder@kernel.org>, Ingo Molnar <mingo@elte.hu>,
       x86 maintainers <x86@kernel.org>, LKML <linux-kernel@vger.kernel.org>,
       Andrew Morton <akpm@linux-foundation.org>,
       Andi Kleen <andi@firstfloor.org>
Subject: Re: [git-pull -tip] x86: declaration patches
Message-ID: <20090410174524.GC8204@lenovo>
References: <1239381184.23116.5.camel@ht.satnam> <20090410172925.GA24446@uranus.ravnborg.org>
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[Sam Ravnborg - Fri, Apr 10, 2009 at 07:29:25PM +0200]
| Hi Jaswinder.
| 
| > diff --git a/arch/x86/include/asm/hw_irq.h b/arch/x86/include/asm/hw_irq.h
| > index 7309c0a..2f35e81 100644
| > --- a/arch/x86/include/asm/hw_irq.h
| > +++ b/arch/x86/include/asm/hw_irq.h
| > @@ -81,6 +81,11 @@ extern void eisa_set_level_irq(unsigned int irq);
| >  /* SMP */
| >  extern void smp_apic_timer_interrupt(struct pt_regs *);
| >  extern void smp_spurious_interrupt(struct pt_regs *);
| > +#ifdef CONFIG_X86_32
| > +extern void smp_generic_interrupt(struct pt_regs *);
| > +#else
| > +extern asmlinkage void smp_generic_interrupt(struct pt_regs *);
| > +#endif
| >  extern void smp_error_interrupt(struct pt_regs *);
| >  #ifdef CONFIG_SMP
| >  extern void smp_reschedule_interrupt(struct pt_regs *);
| > @@ -93,6 +98,15 @@ extern asmlinkage void smp_invalidate_interrupt(struct pt_regs *);
| >  #endif
| >  #endif
| >  
| > +#ifdef CONFIG_X86_IO_APIC
| > +#ifdef CONFIG_X86_32
| > +extern void smp_irq_move_cleanup_interrupt(void);
| > +#else
| > +extern asmlinkage void smp_irq_move_cleanup_interrupt(void);
| > +#endif
| > +#endif
| 
| The above is a lot ifdefs just to:
| 1) use asmlinkage only on 64 bit
| 2) hide the prototype if do not implement the function
| 
| Is there any relevant cost associated with asmlinkage or could we just make it
| always asmlinkage?

Hi,

as far as I see asmlinkage is just (on X86-64 after
all substitution) nothing, ie:

#define asmlinkage

(until we pass __cplusplus, do we ever?)

Which means we could safely pass asmlinkage on X86-64
in case if X86-32 requires it.

Like

| > +#ifdef CONFIG_X86_32
| > +extern void smp_generic_interrupt(struct pt_regs *);
| > +#else
| > +extern asmlinkage void smp_generic_interrupt(struct pt_regs *);
| > +#endif

could be just written as
	extern void smp_generic_interrupt(struct pt_regs *);
for both.

        Cyrill