Hello;
Just been discussing the same issue in private as well ...
On 2/20/2017 6:40 PM, Conrad Meyer wrote:
On Sun, Feb 19, 2017 at 7:43 PM, Pedro F. Giffuni <p...@freebsd.org> wrote:
Author: pfg
Date: Mon Feb 20 03:43:12 2017
New Revision: 313982
URL: https://svnweb.freebsd.org/changeset/base/313982
Log:
sys/dev: Replace zero with NULL for pointers.
Makes things easier to read, plus architectures may set NULL to something
different than zero.
Hi Pedro,
I like the change for style reasons.
The comment about architectures with non-zero NULL is a little
misleading, though. This change has no impact on non-zero bit pattern
NULL architectures. The zero pointer value in C is NULL and NULL is
the zero pointer value in C. It may have a bit pattern other than
zero (i.e., printf("%p", NULL) may be non-zero and memset(&p, 0,
sizeof(p)) is bogus in portable code) but assigning the logical zero
value is always legitimate.
Grrr ... yes the comment is/was misleading: I would undo it if I didn't
have to revert the commit with it. Other project have SVN configured to
permit changing the log message BTW.
After all, NULL is just a casted zero value:
#define NULL ((void *)0)
The compiler is pretty good at detecting when the value is a pointer though.
The change has few (if any) effect on real life but coming from the
days where most computer languages were somewhat stronger typed I really
like to be able to distinguish between a zero valued pointer and a zero
valued int.
Maybe this is moot. I don't believe any architecture FreeBSD actually
supports has non-zero bitpattern NULL, but something weird like CHERI
might.
Such "weird" platforms are starting to appear:
https://reviews.llvm.org/D26196
Regards,
Pedro.
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