On Mon, Aug 29, 2022 at 10:06:55AM +0900, Kyotaro Horiguchi wrote: > At Fri, 26 Aug 2022 10:28:50 -0300, Ranier Vilela <ranier...@gmail.com> wrote > in > > At function has_matching_range, if variable ranges->nranges == 0, > > we exit quickly with a result equal to false. > > > > This means that nranges can be zero. > > It occurs then that it is possible then to occur an array out of bonds, in > > the initialization of the variable maxvalue. > > So if nranges is equal to zero, there is no need to initialize minvalue and > > maxvalue. > > > > The patch tries to fix it, avoiding possible errors by using maxvalue. > > However it seems that nranges will never be zero, still the fix looks > good to me since it is generally allowed to be zero. I don't find a > similar mistake related to Range.nranges.
Actually, the nranges==0 branch is hit during regression tests: https://coverage.postgresql.org/src/backend/access/brin/brin_minmax_multi.c.gcov.html I'm not sure, but I *suspect* that compilers usually check ranges->nranges==0 before reading ranges->values[2 * ranges->nranges - 1]; Especially since it's a static function. Even if they didn't (say, under -O0), values[-1] would probably point to a palloc header, which would be enough to "not crash" before returning one line later. But +1 to fix this and other issues even if they would never crash. -- Justin
