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

[René Scharfe]

Am 10.03.2017 um 21:13 schrieb Junio C Hamano:
René Scharfe <l....@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).

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?).

There are redundancies. This semantic patch here:

        @@
        type T;
        T dst;
        T *src;
        @@
        - memcpy(&dst, src, sizeof(dst));
        + dst = *src;

would match e.g. this (from convert.c):

        memcpy(&new_stats, &stats, sizeof(new_stats));

and transform it to:

        new_stats = *&stats;

We'd need just one more rule to remove the "*&" part and could then get 
rid of two of the "T src" variants, to arrive at something like this:

        @@
        type T;
        T dst, src;
        @@
        - memcpy(&dst, &src, sizeof(src));
        + dst = src;

        @ r @
        type T;
        T dst;
        T *src;
        @@
        (
        - memcpy(&dst, src, sizeof(dst));
        + dst = *src;
        |
        - memcpy(&dst, src, sizeof(*src));
        + dst = *src;
        |
        - memcpy(&dst, src, sizeof(T));
        + dst = *src;
        )

        @ depends on r @
        expression E;
        @@
        - *&
          E

René