Re: [PATCH 3/6] fixup! reftable: rest of library

[Han-Wen Nienhuys <hanwen@google.com>]

On Tue, Dec 1, 2020 at 11:26 AM Jeff King <peff@peff.net> wrote:
>
> On Sat, Nov 28, 2020 at 06:44:35AM +0000, Johannes Schindelin via GitGitGadget wrote:
>
> > From: Johannes Schindelin <johannes.schindelin@gmx.de>
> >
> > 0-sized arrays are actually not portable.
>
> Definitely.
>
> >  static void test_sizes_to_segments_empty(void)
> >  {
> > -     uint64_t sizes[0];
> > +     uint64_t sizes[1];
> >
> >       int seglen = 0;
> >       struct segment *segs =
> > -             sizes_to_segments(&seglen, sizes, ARRAY_SIZE(sizes));
> > +             sizes_to_segments(&seglen, sizes, 0);
> >       EXPECT(seglen == 0);
> >       reftable_free(segs);
>
> I think passing:
>
>   sizes_to_segments(&seglen, NULL, 0);
>
> may make the code more obvious. Unlike system functions like memcpy(),
> we can be assured of whether our functions avoid looking at a
> zero-length array (and size_to_segments does follow that rule).
>
>   This function, of course, is nonsense that real code would not do, and

This test was added because 'real' code did this. In particular, if
you initialize a stack of reftables, the stack has zero elements. The
test was for the following bugfix

https://github.com/google/reftable/commit/b2e42ecb54e413e494c1fcc13c21e24422645007

Changing the array size to 1 here also prevents Valgrind to mark a
regression as a OOB write.

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