svn commit: r336835 - head/lib/libc/gen

[Conrad Meyer]

On Sat, Jul 28, 2018 at 1:06 PM, Konstantin Belousov
<kostikbel at gmail.com> wrote:
> On Sat, Jul 28, 2018 at 07:08:00PM +0000, Conrad Meyer wrote:
>>   For unclear reasons, POSIX' definition of these routines spells NULL as
>>   "(char *)0."  This is needlessly unclear.  One guess might be that POSIX
>>   targets more exotic computer architectures than FreeBSD does.  Fortunately,
>>   there is no such problem on any reasonable platform for FreeBSD to support.
>>   Spell NULL as NULL.
>
> The reasons are quite clear.

Unclear here refers to the lack of documentation, not the absense of a
possible explanation.

> Practically NULL has to be defined as '0'
> or '0L' at best, for C and esp. C++ rules of the pointers automatic
> casts to work. This means that NULL cannot be used in vararg lists where
> the pointer is expected.

This is not true on FreeBSD.  NULL is (void*)0 in all C code, and the
special nullptr value in C++.  Yes, this is a stronger definition than
the C standard guarantees.  This is because the C standard permits
much more exotic architectures than FreeBSD actually runs on.

> In other words, the (char *)0 part of the pre-commit text was correct,
> while after-commit use of NULL only works on machines where pointers
> have the same representation as ints or longs.

I believe this encompasses all architectures FreeBSD supports — even
ignoring our sys/_null.h definition of NULL as (void *)0 or nullptr.

Best,
Conrad