linux-kernel - Re: [patch 1/3] add basic accounting fields to taskstats

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Date:	Wed, 02 Aug 2006 13:37:46 -0400
From:	Shailabh Nagar <nagar@...son.ibm.com>
To:	balbir@...ibm.com
CC:	Jay Lan <jlan@....com>, Andrew Morton <akpm@...l.org>,
	lkml <linux-kernel@...r.kernel.org>, Jes Sorensen <jes@....com>,
	Chris Sturtivant <csturtiv@....com>, Tony Ernst <tee@....com>
Subject: Re: [patch 1/3] add basic accounting fields to taskstats

Balbir Singh wrote:

> 
> I am not sure if there is a version of BUG_ON() for compile time
> asserts. Basically, if we have an infrastructure of the form
> 
> /*
>  * From C/C++ users journal November 2004
>  */
> #define STATIC_BUG_ON(e)     \
>     switch (0) {        \
>     case  0:        \
>     case (e):        \
>         ;        \
>     }
> 
> Then the STATIC_BUG_ON() can catch as shown below.
> 
> #define TASK_COMM_LEN     16
> #define T_COMM_LEN    20
> 
> int
> main(void)
> {
>     STATIC_BUG_ON(TASK_COMM_LEN == T_COMM_LEN);
> }
> 
> STATIC_BUG_ON gives the following warning
> 
> bug_on_c.c: In function `main':
> bug_on_c.c:19: duplicate case value
> bug_on_c.c:19: previously used here
> 
> but with T_COMM_LEN set to 16
> 
> It compiles without any errors, the code generated also
> looks like it has no overhead
> 
> int
> main(void)
> {
>  8048310:       55                      push   %ebp
>  8048311:       89 e5                   mov    %esp,%ebp
>  8048313:       83 ec 08                sub    $0x8,%esp
>  8048316:       83 e4 f0                and    $0xfffffff0,%esp
>         STATIC_BUG_ON(TASK_COMM_LEN == T_COMM_LEN);
> }
>  8048319:       c9                      leave
>  804831a:       c3                      ret
>  804831b:       90                      nop
> 
> 
> Assuming such infrastructure is available, you could then
> do
> 
> #ifdef __KERNEL__
> #include <linux/sched.h>
> #define TS_COMM_LEN    16
> STATIC_BUG_ON (TS_COMM_LEN == TASK_COMM_LEN);
> #endif
> 
> Comments?
> 

Neat trick !
Perhaps STATIC_WARNING is a more appropriate name but
something like this for general use may be good.


--Shailabh
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