Re: [PATCH v2] fix integer overflow of tm_year in __secs_to_tm

[Rich Felker <dalias@libc.org>]

On Mon, Nov 07, 2016 at 10:40:52PM -0500, Daniel Sabogal wrote:
> On Mon, Nov 7, 2016 at 12:09 PM, Rich Felker <dalias@libc.org> wrote:
> > On Wed, Nov 02, 2016 at 10:29:36PM -0400, Daniel Sabogal wrote:
> >> From: Daniel Sabogal <dsabogal@ufl.edu>
> >>
> >> the overflow check for years+100 did not account for the extra
> >> year computed from the remaining months. instead, perform this
> >> check after obtaining the final number of years.
> >> ---
> >> v2: Subtract 12 from months, not 10.
> >
> > Thanks. I almost accepted the old patch with the error. Maybe in the
> > future consider including a test case with the patch.
> 
> I provided a sample program within the patch.
> Did you have something else in mind for test cases?

Admittedly I missed it somehow, but I guess to call it a test case I'd
want to see expected results and a justification for them. In this
case diff of old vs new output for various inputs would have caught
the bug in v1.

It might be nice to have a test in libc-test that just runs a bunch of
time_t-tm-time_t and tm-time_t-tm round trips for random inputs and
checks that they round-trip successfully...

> > I don't want to make testcases a prerequisite for bug fixes because
> > that leads to bugs going unfixed for a long time, but perhaps for
> > obscure issues like this unlikely to be hit in real-world use, it
> > would be good to strongly encourage submission of test cases with
> > patches.
> 
> I agree.

...but the above ideas are getting well beyond what I'd want to impose
on bug reporters/minor patch authors. So it's more just brainstorming
about the tests that would be helpful for someone with the time to
help with testing to implement.

Rich