Re: [BUG] (firsttupleslot)==NULL is redundant or is possible nulldereference? - Mailing list pgsql-hackers

On Fri, Nov 22, 2019 at 10:57:13PM +0000, Ranier Vilela wrote:
>Hi,
>Sorry, you are right.
>Had not seen this line:
>firsttupleslot = node->ss.ss_ScanTupleSlot;
>

OK, no problem. When writing future messages to this list, please

* Make sure you explain why you think a given code is broken. Ideally,
   bug reports come with a reproducer (instructions how to hit it) but
   that may be difficult in some cases.

* Don't top post, but respond in-line. Top posting makes it much harder
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We're OK with answering querstions and helping people learn the code
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regards

>Best regards.
>Ranier Vilela
>________________________________________
>De: Tomas Vondra <tomas.vondra@2ndquadrant.com>
>Enviado: sexta-feira, 22 de novembro de 2019 22:54
>Para: Ranier Vilela
>Cc: pgsql-hackers@postgresql.org
>Assunto: Re: [BUG] (firsttupleslot)==NULL is redundant or is possible null dereference?
>
>On Fri, Nov 22, 2019 at 10:32:11PM +0000, Ranier Vilela wrote:
>>Hi,
>>This is real bug? firsttupleslot == NULL.
>>
>
>Ranier, I don't want to be rude, but I personally am getting a bit
>annoyed by this torrent of bug reports that are essentially just a bunch
>of copy-pasted chunks of code, without any specification of bench,
>position in the file, etc.
>
>And more importantly, without any clear explanation why you think it is
>a bug (or even a demonstration of an issue), and "Is this a bug?"
>
>>\backend\executor\nodeGroup.c
>>       if (TupIsNull(firsttupleslot))
>>       {
>>               outerslot = ExecProcNode(outerPlanState(node));
>>               if (TupIsNull(outerslot))
>>               {
>>                       /* empty input, so return nothing */
>>                       node->grp_done = true;
>>                       return NULL;
>>               }
>>               /* Copy tuple into firsttupleslot */
>>               ExecCopySlot(firsttupleslot, outerslot);
>>
>>include\executor\tuptable.h:
>>#define TupIsNull(slot) \
>>       ((slot) == NULL || TTS_EMPTY(slot))
>>
>>static inline TupleTableSlot *
>>ExecCopySlot(TupleTableSlot *dstslot, TupleTableSlot *srcslot)
>>{
>>       Assert(!TTS_EMPTY(srcslot));
>>
>>       dstslot->tts_ops->copyslot(dstslot, srcslot);
>>
>>       return dstslot;
>>}
>>
>
>And why do you think this is a bug? Immediately before the part of code
>you copied we have this:
>
>     /*
>      * The ScanTupleSlot holds the (copied) first tuple of each group.
>      */
>     firsttupleslot = node->ss.ss_ScanTupleSlot;
>
>And node->ss.ss_ScanTupleSlot is expected to be non-NULL. So the initial
>assumption that firsttupleslot is NULL is incorrect.
>
>regards
>
>--
>Tomas Vondra                  http://www.2ndQuadrant.com
>PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
>
>

-- 
Tomas Vondra                  http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services