Re: Style question: Should one check for NULL pointers?

[H. Peter Anvin]

Followup to:  <[e-mail]>
By author:    Eli Carter <[e-mail]>
In newsgroup: linux.dev.kernel
> > 
> > Not really needed, since a segfault will produce almost as much 
> > information as a BUG_ON().  Certainly it will produce enough to let a 
> > developer know that the pointer was NULL.
> 
> Your first message said, "I see no reason for pure paranoia, 
> particularly if it's not commented as such."  A BUG_ON() call makes it 
> clear that the condition should never happen.  Dereferencing a NULL 
> leaves the question of whether NULL is an unhandled case or invalid 
> input.  BUG_ON() is an explicit paranoia check, and with a bit of 
> preprocessing magic, you could compile out all of those checks.
> 
> So it documents invalid input conditions, allows you to eliminate the 
> checks in the name of speed or your personal preference, or use them to 
> help with debugging/testing.
> 

... but it also bloats the code, in this case, in many ways
needlessly.  You don't want to compile out all BUG_ON()'s, just the
ones that wouldn't be checked for anyway.

In fact, have a macro that explicitly tests for nullness by
dereferencing a pointer might be a good idea; on most architectures it
will be a lot cheaper than BUG_ON() (which usually requires an
explicit test), and the compiler at least has a prayer at optimizing
it out.

	-hpa
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