Messages in this thread | | | Date | Wed, 23 Jun 2004 15:46:36 -0400 | From | Jeff Garzik <> | Subject | Re: [RFC] replace assorted ASSERT()s by something officially sanctioned |
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Dean Nelson wrote: > It doesn't appear that an officially 'sanctioned' version of ASSERT() or > an ASSERT()-like macro exists. > > And by the proliferation of its use in the linux 2.6 kernel (I saw over > 3000 references to it), it would seem that BUG_ON() does not satisfy all > of the requirements of the community. > > One problem with BUG_ON() is that it is always enabled. And even though > the compiler does a good job of minimizing the impact of the conditional > expression, there are times when the conditional check requires the > accessing of a cacheline that would not get accessed had the BUG_ON() not > been enabled. And if that cacheline were one that is hotly contended for, > one's performance can be adversely affected. > > For debugging purposes it would be nice to have a version of BUG_ON() that > was only enabled if DEBUG was set. This is what appears to be behind the use > of the ASSERT()-like macros. > > As an example of what I have in mind, I've included the following quilt > patch. > > Thanks, > Dean > > > Index: linux/include/asm-i386/bug.h > =================================================================== > --- linux.orig/include/asm-i386/bug.h > +++ linux/include/asm-i386/bug.h > @@ -21,6 +21,12 @@ > > #define BUG_ON(condition) do { if (unlikely((condition)!=0)) BUG(); } while(0) > > +#ifdef DEBUG > +#define DBUG_ON(condition) BUG_ON(condition) > +#else > +#define DBUG_ON(condition) > +#endif
This won't work as it often needs to be driver-granular. Also, WARN_ON() is often the closer implementation of assert(), than BUG_ON()
Jeff
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