linux-kernel - Re: [x86 patch] Fix UML signal.h build errors

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Date:	Sat, 27 Oct 2007 11:35:10 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Al Viro <viro@....linux.org.uk>
CC:	Jeff Dike <jdike@...toit.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [x86 patch] Fix UML signal.h build errors

Al Viro wrote:
> On Thu, Oct 25, 2007 at 09:01:52PM +0530, Balbir Singh wrote:
> 
>> Thats nice, I wonder why I missed them searching on lkml in my gmail box
>> :(
>>
>> Is __arch_um__ the right thing to do or BITS_PER_LONG == 32? I prefer
>> BITS_PER_LONG == 32 over #if defined(__i386__) || defined(__arch__um__).
>> I guess its a matter of personal preference.
> 
> Huh?
> 
> a) we really shouldn't mess with compiler defines (i.e. we should not
> undef __i386__ or __x86_64__)
> 

I agree

> b) I'd rather have __arch_um__ mentioned explicitly in 3 places where
> we do care about difference between i386 and uml/i386 than have certain
> to be forgotten rules for places like include/asm-x86
> 
> c) if you look at those places, you'll see
> 	* drivers/char/mem.c::uncached_access().  Really per-architecture
> and I wonder if it might be include/asm-* fodder...
> 	* kernel/signal.c debugging printks.  Should die or be sanitized, IMO.
> 	* raid6 algorithms.  Hell knows - immediate reason why we don't do
> those on uml is the lack of kernel_fpu_begin()/kernel_fpu_end() (and
> boot_cpu_has(), but that's easier to add).  Do we care to implement that
> stuff?
> 

I suspect that list might grow and anybody writing i386 or x86_64 code
will need to double check if the code will work under __arch_um__.
Probably worth documenting somewhere.

> That's _all_.  Nothing else has to care.
> 

:-)

-- 
	Warm Regards,
	Balbir Singh
	Linux Technology Center
	IBM, ISTL
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