linux-kernel - Re: [PATCH] arch/powerpc: use BUILD_BUG() when detect unfit {cmp}xchg, size

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Date:	Tue, 23 Feb 2016 21:39:52 +1100
From:	Michael Ellerman <mpe@...erman.id.au>
To:	Boqun Feng <boqun.feng@...il.com>,
	Pan Xinhui <xinhui@...ux.vnet.ibm.com>
Cc:	linuxppc-dev@...ts.ozlabs.org,
	open list <linux-kernel@...r.kernel.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	"'Peter Zijlstra (Intel)\"" <peterz@...radead.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] arch/powerpc: use BUILD_BUG() when detect unfit
 {cmp}xchg, size

On Tue, 2016-02-23 at 17:15 +0800, Boqun Feng wrote:
> On Tue, Feb 23, 2016 at 04:45:16PM +0800, Pan Xinhui wrote:
> > From: pan xinhui <xinhui.pan@...ux.vnet.ibm.com>
> > 
> > diff --git a/arch/powerpc/include/asm/cmpxchg.h b/arch/powerpc/include/asm/cmpxchg.h
> > index d1a8d93..20c0a30 100644
> > --- a/arch/powerpc/include/asm/cmpxchg.h
> > +++ b/arch/powerpc/include/asm/cmpxchg.h
> > @@ -92,12 +93,6 @@ __xchg_u64_local(volatile void *p, unsigned long val)
> >  }
> >  #endif
> >  
> > -/*
> > - * This function doesn't exist, so you'll get a linker error
> > - * if something tries to do an invalid xchg().
> > - */
> > -extern void __xchg_called_with_bad_pointer(void);
> > -
> >  static __always_inline unsigned long
> >  __xchg(volatile void *ptr, unsigned long x, unsigned int size)
> >  {
> > @@ -109,7 +104,7 @@ __xchg(volatile void *ptr, unsigned long x, unsigned int size)
> >  		return __xchg_u64(ptr, x);
> >  #endif
> >  	}
> > -	__xchg_called_with_bad_pointer();
> > +	BUILD_BUG();
> 
> Maybe we can use BUILD_BUG_ON_MSG(1, "Unsupported size for xchg"), which
> could provide more information.

Yes I would prefer there was a message. Please send a v2.

cheers