linux-kernel - Re: [PATCH] Fix section type conflict in arch/ia64/xen/xen_pv

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Message-ID: <20081106214848.GA3579@uranus.ravnborg.org>
Date:	Thu, 6 Nov 2008 22:48:48 +0100
From:	Sam Ravnborg <sam@...nborg.org>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Takashi Iwai <tiwai@...e.de>, Tony Luck <tony.luck@...el.com>,
	Isaku Yamahata <yamahata@...inux.co.jp>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Fix section type conflict in arch/ia64/xen/xen_pv_ops.c

On Thu, Nov 06, 2008 at 10:57:21AM -0800, Jeremy Fitzhardinge wrote:
> Takashi Iwai wrote:
> >__initdata and const cannot be always a happy pair, as gcc-4.3.3 gives
> >the compile errors like:
> >
> >  arch/ia64/xen/xen_pv_ops.c:156: error: xen_init_ops causes a section 
> >  type conflict
> >  arch/ia64/xen/xen_pv_ops.c:340: error: xen_iosapic_ops causes a section 
> >  type conflict
> >
> >This patch simply removes const from data with __initdata.
> >  
> 
> Yeah, I've seen these sort of messages before, but I don't see why 
> there's an inherent problem with having const __initdata.
> 
> Sam?

The root problem here is that in some cases gcc will stuff this into
a section marked CONST and in other cases not.
So when we manually specify the section we better not mix const and
non-const stuff in the same section.
The problem is that it is very gcc dependent. I have with powerpc
seen that the same code was not put in CONST with a 32 bit build,
but with the 64 bit build it was.
The only cure was to remove the const and use initdata.
You can try to play with initconst - and it may work.
But you need to have pretty good build coverage to be sure.

	Sam
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