linux-kernel - Re: fs/exec.c: use BUILD_BUG_ON for VM_STACK_FLAGS & VM_STACK_INCOMPLETE

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Date:	Thu, 16 Jun 2011 11:36:32 +0200
From:	Richard Weinberger <richard@....at>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Randy Dunlap <randy.dunlap@...cle.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Michal Hocko <mhocko@...e.cz>
Subject: Re: fs/exec.c: use BUILD_BUG_ON for VM_STACK_FLAGS &
 VM_STACK_INCOMPLETE_SETUP

On Wed, 15 Jun 2011 21:52:07 -0700, Andrew Morton
<akpm@...ux-foundation.org> wrote:
> On Wed, 15 Jun 2011 21:45:00 -0700 Linus Torvalds
> <torvalds@...ux-foundation.org> wrote:
> 
>> On Wed, Jun 15, 2011 at 9:35 PM, Randy Dunlap <randy.dunlap@...cle.com> wrote:
>> >
>> > fwiw, I just reported that this causes a build error in UML on x86_64
>> > in mmotm-2011-06-15:
>>
>> Gaah. That sounds really familiar. Have we done this same mistake once
>> before already, or is it just deja-vu for some other reason.
>>
>> On x86-64 UML, we have
>>
>>   #define VM_STACK_DEFAULT_FLAGS vm_stack_flags
>>
>> so VM_STACK_FLAGS ends up not being a constant, even though it really
>> looks like one.
>>
>> UML is _really_ confused in this area, btw. It seems to re-define that
>> thing if TIF_IA32 is defined. That's some crazy stuff. Doesn't the
>> compiler warn about it?
>>
>> I guess I should just revert that commit, though. Even if it does seem
>> to be the case that UML is just being crazy. Andrew?
>>
> 
> Sure, it was just a tiny optimization.
> 
> We can bring it back if Richard feels like decrazyifying UML ;)
> 

I'll look at this.
BTW: 64bit UML is really crazy. :P

Thanks,
//richard
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