On Fri, Mar 10, 2017 at 12:13:11PM -0800, Junio C Hamano wrote:
> René Scharfe <l.s.r@xxxxxx> writes:
>
> >> I think this misses the other two cases: (*dst, src) and (*dst, *src).
> >
> > ... and that's why I left them out. You can't get dst vs. *dst wrong
> > with structs (at least not without the compiler complaining); only
> > safe transformations are included in this round.
>
> I haven't followed this discussion to the end, but the omission of 2
> out of obvious 4 did pique my curiosity when I saw it, too, and made
> me wonder if the omission was deliberate. If so, it would be nice
> to state why in the log message (or in copy.cocci file itself as a
> comment).
Yeah, it definitely would be worth mentioning. I'm still undecided on
whether we want to be endorsing struct assignment more fully.
> It also made me wonder if we would be helped with a further
> combinatorial explosion from "T **dstp, **srcp" and somesuch (in
> other words, I am wondering why a rule for 'T *src' that uses '*src'
> need to be spelled out separately when there already is a good rule
> for 'T src' that uses 'src'---is that an inherent restriction of the
> tool?).
I had that thought, too, but I think the 4-way rules are necessary,
because the transformations aren't the same in each case. E.g., for the
four cases, the resulting assignments are:
(dst, src): dst = src;
(dst, *src): dst = *src;
(*dst, src): *dst = src;
(*dst, *src): *dst = *src;
For pointer-to-pointer, I assumed the tool would handle that
automatically by matching "T" as "T*". Though if that is the case, I
think "(dst, src)" and "(*dst, *src)" would be equivalent (though of
course our rule matches are different, as you do not memcpy the raw
structs).
-Peff