Re: (ITS#8819) LMDB seg fault with MDB_DUPSORT on -O3

[hyc@symas.com]

github@nicwatson.org wrote:
> Full_Name: Nic Watson
> Version: LMDB v 0.9.21
> OS: Ubuntu 17.04
> URL: ftp://ftp.openldap.org/incoming/
> Submission from: (NULL) (108.56.136.246)
> 
> 
> I'm getting a seg fault in using LMDB on a database opened with MDB_DUPSORT.
> 
> Here's a minimal set of operations that will cause the problem:

> It will *not* crash under debug.  In fact, -O3 -fvect-cost-model=cheap will
> *not* crash.  This makes some sense since it is crashing on an SSE instruction.
> 
> I tried gcc versions (Ubuntu 7.2.0-8ubuntu3.2) and (Ubuntu 6.4.0-8ubuntu1) with
> the same result.  I also tried with the mdb.master branch (0.9.70) with the same
> result.
> 
> I'm not convinced this a fault in your code.  It may be a gcc bug.

Interesting. I've got gcc 5.4.0 on Ubuntu 16.04 here, and no crash. Also 
rather puzzled that there's anything vectorizable in this code, that seems 
pretty unlikely.

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