Re: Small patch for snapmgr.c

Hi Aleksander,

This has already been fixed with commit
4f9f495889d3d410195c9891b58228727b340189

Thanks

On Fri, Apr 8, 2016 at 6:02 PM, Aleksander Alekseev <
a(dot)alekseev(at)postgrespro(dot)ru> wrote:

> Hello
>
> Currently there is a following piece of code in snapmgr.c:
>
> ```
> /* Copy all required fields */
> snapshot = (Snapshot) MemoryContextAlloc(TopTransactionContext, size);
> snapshot->satisfies = HeapTupleSatisfiesMVCC;
> snapshot->xmin = serialized_snapshot->xmin;
> snapshot->xmax = serialized_snapshot->xmax;
> snapshot->xip = NULL;
> snapshot->xcnt = serialized_snapshot->xcnt;
> snapshot->subxip = NULL;
> /* ... */
>
> /* Copy XIDs, if present. */
> if (serialized_snapshot->xcnt > 0)
> {
> snapshot->xip = (TransactionId *) (snapshot + 1);
> memcpy(snapshot->xip, serialized_xids,
> serialized_snapshot->xcnt * sizeof(TransactionId));
> }
>
> /* Copy SubXIDs, if present. */
> if (serialized_snapshot->subxcnt > 0)
> {
> snapshot->subxip = snapshot->xip + serialized_snapshot->xcnt;
> memcpy(snapshot->subxip, ...
> ```
>
> It assumes that subxcnt > 0 iff xcnt > 0. As I understand this is true.
> At least I hope so, otherwise this code can call memcpy passing NULL as
> a first argument. But Clang Static Analyzer is not aware of all this:
>
> http://afiskon.ru/s/db/5c956077e9_snapmgr.png
>
> I propose a patch that makes static analyzers happy and makes intention
> of this code a little more obvious.
>
> --
> Best regards,
> Aleksander Alekseev
> http://eax.me/
>
>
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>

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