svn commit: r337535 - head/sbin/init

[Conrad Meyer]

On Thu, Aug 9, 2018 at 5:52 AM, Benjamin Kaduk <bjkfbsd at gmail.com> wrote:
> On Thu, Aug 9, 2018 at 7:17 AM, Edward Tomasz Napierala <trasz at freebsd.org>
> wrote:
>>   Use NULLs instead of casted zeroes, for consistency.
>
> It's probably helpful to note explicitly that these are not in arguments to
> varargs functions,

I don't think it's helpful.

> in which case the explicit cast is needed in order to produce a program that
> will have
> correct behavior on all compliant compilers/systems.

Here "compliant" means "minimally compliant to the C standard."  Use
of NULL in varargs is functionally correct on all FreeBSD systems.

>  (We do define NULL to
> be a zero-with-cast,
> but programs

(Ones that care about portability to weird systems.)  I don't think
BSD's 500 line init — hyper local to FreeBSD — is a strong candidate
for portability.

> should not assume that NULL will be of pointer type -- "An
> integer constant
> expression with the value 0, or such an expression cast to type void *, is
> called a null pointer constant".)

Right.  The problem only arises when both conditions are met:

1. The system's varargs representation is smaller than the pointer
representation, and
2. The runtime headers do not defined NULL as a pointer-typed value.
(3. The function being invoked is actually varargs?)

Neither is true on FreeBSD and v7-style init is not a useful place to
call for portability.

All the best,
Conrad