On Tue, Dec 01, 2020 at 12:10:14PM +0100, Han-Wen Nienhuys wrote:

quoted

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.

Sorry to be unclear. I meant that real code would not allocate a static
zero-length array (though it might do so on the heap). I agree that
making sure the function behaves in the 0-segment case is quite
reasonable.

Passing NULL actually makes the test more rigorous IMHO (because it is a
strict superset of failure modes, and is something an actual caller
might do if it were dynamically growing an array that started at NULL).

-Peff