linux-kernel - Re: [PATCH] x86,nmi: Fix section mismatch warnings on 32-bit

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Message-ID: <20120605172208.GA29862@merkur.ravnborg.org>
Date:	Tue, 5 Jun 2012 19:22:08 +0200
From:	Sam Ravnborg <sam@...nborg.org>
To:	Jan Beulich <JBeulich@...e.com>
Cc:	x86@...nel.org, Don Zickus <dzickus@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86,nmi: Fix section mismatch warnings on 32-bit

On Tue, Jun 05, 2012 at 05:18:40PM +0100, Jan Beulich wrote:
> >>> On 05.06.12 at 18:13, Sam Ravnborg <sam@...nborg.org> wrote:
> > On Tue, Jun 05, 2012 at 10:47:34AM -0400, Don Zickus wrote:
> >> On Tue, Jun 05, 2012 at 09:12:13AM +0100, Jan Beulich wrote:
> >> > >>> On 04.06.12 at 21:56, Don Zickus <dzickus@...hat.com> wrote:
> >> > > It was reported that compiling for 32-bit caused a bunch of section
> >> > > mismatch warnings:
> >> > > 
> >> > >  VDSOSYM arch/x86/vdso/vdso32-syms.lds
> >> > >   LD      arch/x86/vdso/built-in.o
> >> > >   LD      arch/x86/built-in.o
> >> > > WARNING: arch/x86/built-in.o(.data+0x5af0): Section mismatch in reference 
> >> > > from the variable
> >> > > test_nmi_ipi_callback_na.10451 to the function 
> >> > 
> >> > Did you check what this (compiler introduced) variable actually
> >> > represents? The problem clearly is that the compiler has no way
> >> > of knowing that data it generates referencing an __init function
> >> > would actually need to go into .init.data or alike.
> >> 
> >> I do not know enough about behind the scene compiler magic to track this
> >> down correctly.  So any insight/help is greatly appreciated. :-)
> > 
> > We register a function annotated __init. And the normal use of this 
> > register()
> > is for functions that survive the init phase.
> > So drop the __init annotation on the function we register and the mismatch 
> > is fixed.
> 
> But in the case here the function really is being used at init time
> only.
This is only for testing. Ando nly if CONFIG_DEBUG_NMI_SELFTEST is set.

> Plus it still escapes me why there would be differences in
> behavior depending on bit-ness or compiler version.
It is often different inline decisions that has influence.

	Sam
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