Hi John,
i've retestet it and now it works, thank you very much.
Best regards,
Bernd
> Hi, Bernd,
>
> Thanks for the report and detailed explanation of issue. I am
> adopting a minimalist change right now, to remove the comparison
> invovling aggr_[j]. This should fix the problem with invalid read
> accesses.
>
> Regarding the issue of not showing duplicate variables in the select
> clause, I would treat it as a silly crook of FastBit code for the moment.
>
> Thanks again.
>
> John
>
> PS: The updated code is checked into the SVN repository as revision
> 719 if you have the time to try it out.
>
>
> On 4/25/14, 2:59 AM, Bernd Jaenichen wrote:
>> Hi,
>>
>> i found a possible bug in selectClause.cpp of version 1.3.9 when using
>> a select-statement with
>> duplicate column names i.e. "v_1,v_1,v_2".
>>
>> I know this is not a valid use-case for a select clause but it may
>> lead to
>> a segfault so i dug into it.
>>
>> Explaining the problem is somewhat tricky so i attached a simple testcase
>> that shows the issue with verbosity set to 5:
>>
>> selectClause::fillNames -- select clause internal details:
>> low-level expressions (names_[2], aggr_[2], atms_[2]):
>> 0: v_1, v_1
>> 1: v_2, v_2
>> high-level expressions (xnames_[3], xtms_[3]):
>> 0: v_1, v_1
>> 1: v_1, v_1
>> 2: _2, v_2
>>
>>
>> As you can see the size of internal terms-vectors in selectClause.cpp
>> differs
>> between high- and low-level expressions.
>>
>> In method ibis::selectClause::fillNames() a loop iterates over xtms_
>> vector
>> and accesses aggr_ in line 197:
>>
>> // fill the external names
>> for (uint32_t j = 0; j < xtms_.size(); ++ j) {
>> if (xnames_[j].empty() && aggr_[j] == ibis::selectClause::NIL_AGGR &&
>>
>> The test against "aggr_[j] == ibis::selectClause::NIL_AGGR" will
>> result in an access out of range
>> in the last iteration of the for-loop due to different sizes of aggr_
>> and xtms_.
>>
>> On initial load out of range access at aggr_[j] will access
>> null-initialized heap and so the test will
>> result in true and bug will not appear but a segfault may be possible.
>>
>> If memory outside aggr_ allocation is dirty and contains -1 test will
>> result in false and leads to
>> renaming of the last column in select from "v_2" into "_2".
>>
>> If the result of that query is stored within in-memory table by
>> ibis::table::select() any subsequent
>> access to column "v_2" will fail (that's how i came accross the issue).
>>
>> To fix this i patched selectClause.cpp a bit to avoid duplicate
>> columns wihtin high-level expressions.
>> (patch is attached also)
>>
>> But i'm not sure whether that's the correct place to fix it nor if it
>> is conceptually correct
>> to remove duplicate columns from the select-clause.
>>
>> Could you verify the bug and if so fix it please?
>>
>>
>> Thanks alot,
>> Bernd
>>
>>
>>
>>
>>
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--
Kind regards
Bernd Jänichen
EFS System Analyst
QuestBack GmbH | Gustav-Heinemann-Ufer 72a | 50968 Cologne | Germany
Tel: +49 221 27169 795 | Fax: +49 221 27169 788
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