linux-kernel - Re: [IDE] Fix build bug

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Date:	Thu, 1 Nov 2007 18:43:16 +0000
From:	Denys Vlasenko <vda.linux@...glemail.com>
To:	Ralf Baechle <ralf@...ux-mips.org>
Cc:	Bartlomiej Zolnierkiewicz <bzolnier@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-ide@...r.kernel.org,
	linux-mips@...ux-mips.org,
	Martijn Uffing <mp3project@...ijopen.student.utwente.nl>
Subject: Re: [IDE] Fix build bug

On Tuesday 30 October 2007 12:41, Ralf Baechle wrote:
> On Tue, Oct 30, 2007 at 11:34:29AM +0000, Denys Vlasenko wrote:
> 
> > On Thursday 25 October 2007 22:41, Bartlomiej Zolnierkiewicz wrote:
> > > > -static const struct ide_port_info generic_chipsets[] __devinitdata = {
> > > > +static struct ide_port_info generic_chipsets[] __devinitdata = {
> > > >  	/*  0 */ DECLARE_GENERIC_PCI_DEV("Unknown",	0),
> > > >  
> > > >  	{	/* 1 */
> > > 
> > > I would prefer to not remove const from generic_chipsets[] so:
> > > 
> > > [PATCH] drivers/ide/pci/generic: fix build for CONFIG_HOTPLUG=n
> > > 
> > > It turns out that const and __{dev}initdata cannot be mixed currently
> > > and that generic IDE PCI host driver is also affected by the same issue:
> > > 
> > > On Thursday 25 October 2007, Ralf Baechle wrote:
> > > >   CC      drivers/ide/pci/generic.o
> > > > drivers/ide/pci/generic.c:52: error: __setup_str_ide_generic_all_on causes a
> > > > +section type conflict
> > > 
> > > [ Also reported by Martijn Uffing <mp3project@...ijopen.student.utwente.nl>. ]
> > > 
> > > This patch workarounds the problem in a bit hackish way but without
> > > removing const from generic_chipsets[] (it adds const to __setup() so
> > > __setup_str_ide_generic_all becomes const).
> > 
> > You wouldn't believe how much const data is not marked as const because
> > we don't have __constinitdata etc. Literally megabytes.
> 
> The gain from marking it const is very little and once any non-const
> __initdata object is added to a compilation unit all other const declarations
> will have to be removed.  Bad tradeoff.

We can intrduce new, ro sections or teach gcc that combining const objects into
non-ro sections is not a crime. I wonder why it currently disallows that.
(And it does it only _somethimes_, const pointers happily go into rw sections!)
--
vda
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