Re: write-only variables in src/sys/ - possible bugs

On Wed, Feb 04, 2009 at 03:54:41PM +0100, Christoph Mallon wrote:
[..]

Yes, function arguments are considered being read. The problem is
different here: mtod() should be a macro, but the macro declaration was
missing (*cough* hacked build process *cough*). So the parser tried to
parse this as function call. Then it hit the "void *", which confused it
- it got a type while parsing an expression. I improved the error
correction, resolved a few other problems, too, and generated a new list:

http://tron.homeunix.org/unread_variables.log
(The list has a date at the top, if it is missing, you see the old list
in your browser cache)

The false positives, which you mentioned, are gone now - thanks for
reporting this. The list now contains about 1.000 entries and about 60
concern variables named 'error'.

Also.. one other thing I noticed:

void
bpf_buffer_append_mbuf(struct bpf_d *d, caddr_t buf, u_int offset, void *src,
u_int len)
{
const struct mbuf *m;
u_char *dst;
u_int count;

m = (struct mbuf *)src;
dst = (u_char *)buf + offset;
while (len > 0) {
if (m == NULL)
panic("bpf_mcopy");
count = min(m->m_len, len);
bcopy(mtod(m, void *), dst, count);
m = m->m_next;
dst += count;
len -= count;
}
}

dst += count

In this expression, both dst and count are read since this is the
same thing as:

dst = dst + count;
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