[R-pkg-devel] Valgrind warning: invalid size of 4, is it due to a simple overrun?

[Hugh Parsonage]

Hello,

I received a valgrind warning about my package, hutilscpp, from CRAN
(thank you).  I believe I've tracked down and fixed the problem, but I
wasn't able to reproduce the error on rhub (including with
--leak-check=full etc) so I'd like to know if I'm missing something.

The valgrind warning is "Invalid write of size 4" and refers to this
line https://github.com/HughParsonage/hutilscpp/blob/508f134b3f388653985eca372ed5f4f8b8eb3471/src/Cwhich_even.c#L43

the context for this line is:

const double * xp = REAL(xx);
for (R_xlen_t i = 0, j = 0; i < N; ++i) {
  int is_even = R_finite(xp[i]) && (fmod(xp[i], 2) == 0);
  ansp[j] = (int)(i + 1);        // # <-------- line 43
  j += is_even;
}

where ansp is a pointer to an integer vector whose length is the
number of "even" doubles in xx.  I can see that the problem arises
when the last even number occurs before the end of the vector xx, at
which point j == length(ansp), yet the loop continues.  I've amended
the i < N in the for loop to (i < N && j < n_even) which I believe is
sufficient, but obviously I thought it was ok before.

I'd rather not resubmit only to discover that I've overlooked something else.

As a supplementary question, does the valgrind check depend on the
runtime values in the test suite or does it perform fuzz testing?  In
other words, do I need to add tests to reproduce?

Best,


Hugh.