linux-kernel - Re: [Patch] uml: fix undeclared variables

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Message-ID: <20081121170711.GA23653@hack.voiplan.pt>
Date:	Fri, 21 Nov 2008 17:07:11 +0000
From:	Américo Wang <xiyou.wangcong@...il.com>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	LKML <linux-kernel@...r.kernel.org>, Andrew Morton <akpm@...l.org>,
	Jeff Dike <jdike@...toit.com>,
	user-mode-linux-devel@...ts.sourceforge.net
Subject: Re: [Patch] uml: fix undeclared variables

On Wed, Nov 19, 2008 at 07:06:36PM +0000, Al Viro wrote:
>On Wed, Nov 19, 2008 at 06:40:14PM +0000, Am??rico Wang wrote:
>> On Tue, Nov 18, 2008 at 07:26:26PM +0000, Al Viro wrote:
>> >On Tue, Nov 18, 2008 at 05:42:51PM +0000, Am??rico Wang wrote:
>> >> 
>> >> Fix three compile errors about undeclared variables in
>> >> arch/um/kernel/mem.c.
>> >
>> >And what, pray tell, would initialize it?
>> 
>> Sorry, I can't fully understand you. I got the following error:
>> 
>> arch/um/kernel/mem.c: In function ???init_highmem???:
>> arch/um/kernel/mem.c:177: error: ???pkmap_page_table??? undeclared (first
>> use in this function)
>> arch/um/kernel/mem.c:177: error: (Each undeclared identifier is
>> reported only once
>> arch/um/kernel/mem.c:177: error: for each function it appears in.)
>
>The error is there, all right.  However, proposed patch only hides the
>real problem.  Building uml/i386 with CONFIG_HIGHMEM will result in
>a badly broken kernel with that patch, with no visible hints at the
>cause of problems.
>
>You've got it to link, but that's not enough.  The problems you are seeing
>come from arch/x86/mm/highmem_32.c.  It uses several variables from
>arch/x86/mm/init_32.c and you have copied them to arch/um.  However, getting
>these variable defined is not going to make it work - the code that used
>to set it had been in init_32.c too and you've just left your copy initialized
>to NULL.  Which will *not* work.
>

Thanks for teaching this! I will look deep into this problem.


-- 
"Sometimes the only way to stay sane is to go a little crazy."

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