Re: [PATCH v1] Travis: also test on 32-bit Linux

From: Jeff King <peff@peff.net>
Date: Mar 10, 2017, 20:18 UTC
Message-ID: <20170310201840.fubshjp2bjg4bjxq@sigill.intra.peff.net>
In-Reply-To: <xmqqfuikyjoo.fsf@gitster.mtv.corp.google.com>

On Fri, Mar 10, 2017 at 12:13:11PM -0800, Junio C Hamano wrote:

Show 13 quoted lines

> René Scharfe <l.s.r@web.de> 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.

Show 6 quoted lines

> 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