linux-kernel - Re: [patch 1/5] Introduce _

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Date:	Sun, 06 Jan 2008 17:09:44 +0100
From:	Richard Knutsson <ricknu-0@...dent.ltu.se>
To:	Arjan van de Ven <arjan@...radead.org>
CC:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	heiko.carstens@...ibm.com, olof@...om.net, mingo@...e.hu,
	mpm@...enic.com
Subject: Re: [patch 1/5] Introduce __WARN()

Arjan van de Ven wrote:
> On Sun, 06 Jan 2008 12:44:56 +0100
> Richard Knutsson <ricknu-0@...dent.ltu.se> wrote:
>
>   
>> Arjan van de Ven wrote:
>>     
>>> From: Olof Johansson <olof@...om.net>
>>>
>>> Introduce __WARN() in the generic case, so the generic WARN_ON()
>>> can use arch-specific code for when the condition is true.
>>>
>>> Signed-off-by: Olof Johansson <olof@...om.net>
>>> Cc: <linux-arch@...r.kernel.org>
>>> Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
>>> ---
>>>
>>>  include/asm-generic/bug.h |   17 +++++++++++------
>>>  1 file changed, 11 insertions(+), 6 deletions(-)
>>>
>>> Index: linux-2.6.24-rc6/include/asm-generic/bug.h
>>> ===================================================================
>>> --- linux-2.6.24-rc6.orig/include/asm-generic/bug.h
>>> +++ linux-2.6.24-rc6/include/asm-generic/bug.h
>>> @@ -31,14 +31,19 @@ struct bug_entry {
>>>  #define BUG_ON(condition) do { if (unlikely(condition)) BUG(); }
>>> while(0) #endif
>>>  
>>> -#ifndef HAVE_ARCH_WARN_ON
>>> +#ifndef __WARN
>>> +#define __WARN() do
>>> {							\
>>> +	printk("WARNING: at %s:%d %s()\n",
>>> __FILE__,			\
>>> +		__LINE__,
>>> __FUNCTION__);				\
>>> +
>>> dump_stack();
>>> \ +} while (0) +#endif
>>> +
>>> +#ifndef WARN_ON
>>>  #define WARN_ON(condition)
>>> ({						\ int
>>> __ret_warn_on = !!(condition);				\ 
>>>       
>
>   
>> What about using a boolean for __ret_warn_on, which then let us
>> remove the '!!'?
>>     
>
> is iffy.. like what happens if an u64 is cast to a boolean?
> No matter what the final assembly code will need to be the same
>   
Well, the main point were to use the boolean type instead of an integer...
What about u64? "true" is still "not zero", and is really the assembly 
the same for !!u8, !!u64 and !!pointer? Isn't that the reason to use a 
macro instead of a function?
(If you really mean "what happens?": any 'bool b = some_var;' will set 
'b' according to the C-idiom "if zero: 'false', otherwise 'true'".)
>   
>> (btw, wouldn't 'var != 0' actually be the proper semantic instead of 
>> playing with '!'s?)
>>     
>
> no because var could be a pointer for example...
>   
You mean because in that case it would be '!= NULL', do you? Sorry, do 
not see your point here.

regards,
Richard Knutsson

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