Em sex., 25 de set. de 2020 às 11:30, Christoph Berg <m...@debian.org>
escreveu:
> Re: Tom Lane
> > > Tom> It's hardly surprising that datumCopy would segfault when given a
> > > Tom> null "value" and told it is pass-by-reference. However, to get to
> > > Tom> the datumCopy call, we must have passed the MemoryContextContains
> > > Tom> check on that very same pointer value, and that would surely have
> > > Tom> segfaulted as well, one would think.
> >
> > > Nope, because MemoryContextContains just returns "false" if passed a
> > > NULL pointer.
> >
> > Ah, right. So you could imagine getting here if the finalfn had returned
> > PointerGetDatum(NULL) with isnull = false. We have some aggregate
> > transfns that are capable of doing that for internal-type transvalues,
> > I think, but the finalfn never should do it.
>
> So I had another stab at this. As expected, the 13.0 upload to
> Debian/unstable crashed again on the buildd, while a manual
> everything-should-be-the-same build succeeded. I don't know why I
> didn't try this before, but this time I took this manual build and
> started a PG instance from it. Pasting the gs_group_1 queries made it
> segfault instantly.
>
> So here we are:
>
> #0 datumCopy (value=0, typLen=-1, typByVal=false) at
> ./build/../src/backend/utils/adt/datum.c:142
> #1 0x000002aa3bf6322e in datumCopy (value=<optimized out>,
> typByVal=<optimized out>, typLen=<optimized out>)
> at ./build/../src/backend/utils/adt/datum.c:178
> #2 0x000002aa3bda6dd6 in finalize_aggregate
> (aggstate=aggstate@entry=0x2aa3defbfd0,
> peragg=peragg@entry=0x2aa3e0671f0,
> pergroupstate=pergroupstate@entry=0x2aa3e026b78,
> resultVal=resultVal@entry=0x2aa3e067108, resultIsNull=0x2aa3e06712a)
> at ./build/../src/backend/executor/nodeAgg.c:1153
>
> (gdb) p *resultVal
> $3 = 0
> (gdb) p *resultIsNull
> $6 = false
>
> (gdb) p *peragg
> $7 = {aggref = 0x2aa3deef218, transno = 2, finalfn_oid = 0, finalfn =
> {fn_addr = 0x0, fn_oid = 0, fn_nargs = 0, fn_strict = false,
> fn_retset = false, fn_stats = 0 '\000', fn_extra = 0x0, fn_mcxt = 0x0,
> fn_expr = 0x0}, numFinalArgs = 1, aggdirectargs = 0x0,
> resulttypeLen = -1, resulttypeByVal = false, shareable = true}
>
> Since finalfn_oid is 0, resultVal/resultIsNull were set by the `else`
> branch of the if (OidIsValid) in finalize_aggregate():
>
> else
> {
> /* Don't need MakeExpandedObjectReadOnly; datumCopy will copy it */
> *resultVal = pergroupstate->transValue;
> *resultIsNull = pergroupstate->transValueIsNull;
> }
>
> (gdb) p *pergroupstate
> $12 = {transValue = 0, transValueIsNull = false, noTransValue = false}
>
Here transValueIsNull shouldn't be "true"?
thus, DatumCopy would be protected, for this test: "!*resultIsNull"
regards,
Ranier Vilela
