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Message-ID: <44D0E2EA.6030301@watson.ibm.com>
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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