On Wed, Mar 1, 2017 at 5:55 PM, Andres Freund <andres@anarazel.de> wrote:
> The issue was that on 32bit platforms the Datum returned by some
> functions (int2int4_sum in this case) isn't actually a separately
> allocated Datum, but rather just something embedded in a larger
> struct. That, combined with the following code:
> if (!peraggstate->resulttypeByVal && !*isnull &&
> !MemoryContextContains(CurrentMemoryContext,
> DatumGetPointer(*result)))
> seems somewhat problematic to me. MemoryContextContains() can give
> false positives when used on memory that's not a distinctly allocated
> chunk, and if so, we violate memory lifetime rules. It's quite
> unlikely, given the required bit patterns, but nonetheless it's making
> me somewhat uncomfortable.
>
> Do others think this isn't an issue and we can just live with it?
I think it's 100% broken to call MemoryContextContains() on something
that's not guaranteed to be a palloc'd chunk.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
