R: Re: libstc++ (?) problem on CURRENT?

[Barbara]

>On Sat, Nov 6, 2010 at 11:31 AM, Barbara <barbara.xxx1975 at libero.it> wrote:
>>
>>
>>>On Sat, Nov 6, 2010 at 10:57 AM, Barbara <barbara.xxx1975 at libero.it> wrote:
>>>>
>>>> I had a problem running the IcedTea java plugin on CURRENT i386, while it
>>>> works on 8_STABLE.
>>>> But maybe it's not a problem related to the port.
>>>> Just to be clear, I'm not looking for a solution about the port here, I'm
>> just
>>>> wondering why the same c++ code is working on 8_STABLE and it's 
segfaulting
>> on
>>>> CURRENT, considering also that AFAIK the gcc version in both the base
>> systems
>>>> is the same.
>>>>
>>>> In the part of the code causing the crash, a std::map is read with an
>> iterator
>>>> in a for loop, and if a condition is met, an entry is erased.
>>>> The following is the bt I'm getting:
>>>> #0  0x29e36247 in kill () from /lib/libc.so.7
>>>> #1  0x29e361a6 in raise () from /lib/libc.so.7
>>>> #2  0x282424f6 in XRE_LockProfileDirectory () from
>>>>        /usr/local/lib/firefox3/libxul.so
>>>> #3  <signal handler called>
>>>> #4  0x29c8f1b2 in std::_Rb_tree_increment () from
>>>>        /usr/lib/libstdc++.so.6 #5  0x2ef92402 in
>>>>        IcedTeaPluginUtilities::invalidateInstance () from
>>>>        /usr/local/openjdk6/jre/lib/IcedTeaPlugin.so
>>>> ...
>>>>
>>>> I wrote a "patch" for the IcedTea plugin, replacing the for loop with a
>> while
>>>> and increasing the iterator before erasing from the map, and it seems
>> working.
>>>> Then I wrote a simple program that do something similar to IcedTea, so
>> there
>>>> is no need to build the whole java/openjdk6 port to do some testing.
>>>> Running it on 8_STABLE it works, on CURRENT it crashes.
>>>> You can find more details in this discussion on the freebsd-java ml:
>>>> http://lists.freebsd.org/pipermail/freebsd-java/2010-November/008978.html
>>>>
>>>> You can find the patch and the sample code in the discussion above, 
anyway
>> I'm
>>>> reporting them here too:
>>>> icedtea patch:
>>>> http://pastebin.com/b2KKFNSG
>>>> test case:
>>>> http://pastebin.com/Amk4UJ0g
>>>
>>>You appear to invalidate the iterator inside the loop and then
>>>increment it. Do the following:
>>>
>>>-- cut here --
>>>for (iter = cars.begin(); iter != cars.end(); ) {
>>> if ((*iter).second == modelName)
>>>  cars.erase(iter++);
>>> else
>>>  ++iter;
>>>}
>>>-- and here --
>>>
>>>In this example, you first increment the iterator and then erase its
>>>previous value.
>>>
>>
>> So there is a bug in my source code! Well, I'm not surprised.
>>
>> I'm trying to report the code in icedtea here, extracting it from the patch 
so
>> I hope it's accurate enough:
>>
>>    std::map<void*,NPP>::iterator iterator;
>>    for (iterator = instance_map->begin(); iterator != instance_map->end();
>> iterator++)
>>    {
>>      if ((*iterator).second == instance)
>>        {
>>           instance_map->erase((*iterator).first);
>>        }
>>     }
>>
>> So, do you think, like Ed Schouten said, that there is a bug in the source
>> code but it's just exposed on CURRENT?
>> Is that code bad too?
>>
>> Thanks
>> Barbara
>>
>>
>
>Yes, I believe CURRENT's malloc zeroes out the memory upon deletion,
>whereas STABLE doesn't. So in STABLE you get an old copy of the
>invalidated iterator, hence it works.
>

Very nice explanation.

Thanks