[lldb-dev] Assertion failure in DYLDRendezvous::UpdateSOEntries()

Fri Oct 10 10:41:08 PDT 2014

Ok great, if you're ok with it then I will update that assert to be:

assert(m_previous.state == eConsistent || (m_previous.state == eAdd &&
m_current.state == eDelete));

since it would still be invalid (as far as we can tell) to be in there on a
transition from eDelete to eAdd.

Let me know if that looks okay and I'll push the change.

On Fri, Oct 10, 2014 at 6:46 PM, Todd Fiala <tfiala at google.com> wrote:

> Ok that's starting to sound like something we probably wouldn't cover.
>
> So maybe it's like when (in your example) the loader starts processing
> libqmng.so, does the add, then immediately reverses it out as it hadn't
> officially "finished", and then reverses it out.
>
> So it's probably fair to change that assert to asserting it is either
> stable, or if the previous state was an add (for the delete case).  In any
> event, the assert as it stands seems not inclusive enough.
>
> I'd be okay with removing that one since we've found a case where it
> doesn't hold.
>
> On Fri, Oct 10, 2014 at 9:30 AM, Andrew MacPherson <andrew.macp at gmail.com>
> wrote:
>
>> I ran everything with LD_DEBUG=all to see what was being loaded around
>> the assertion and tracked it down to a dlopen() on a library that exists
>> but that has unmet dependencies of its own. Writing a trivial C program
>> causes the same assertion failure:
>>
>> #include <dlfcn.h>
>> int main()
>> {
>>   dlopen("./libqmng.so", RTLD_NOW);
>>   return 0;
>> }
>>
>> Where "ldd libqmng.so" gives:
>>
>>   linux-vdso.so.1 =>  (0x00007fffe61fe000)
>>   libmng.so.1 => not found
>>   ...
>>
>> So it looks like this may be a valid transition on a failed dlopen() call?
>>
>>
>> On Fri, Oct 10, 2014 at 5:12 PM, Todd Fiala <tfiala at google.com> wrote:
>>
>>> >  I'm not sure if this is a valid transition or not
>>>
>>> I'm not sure yet either - can you try another scenario and see if you're
>>> consistently hitting that?  (I mean without Maya --- are you trying to
>>> debug plugins?)  If you are doing some kind of plugin that gets dynamically
>>> loaded, can you write a bare-bones exe that loads a bare-bones shared
>>> library (.so) manually and see if you hit the same issue on that?  I'm just
>>> looking to help isolate the scenario.
>>>
>>> The other thing that would be interesting would be to know if maybe
>>> there is an exec (essentially executing another exe) happening in between?
>>> If that was the case, there might be an issue where a clean sweep call to
>>> reset state isn't doing the right thing.  You might see more info on exec
>>> behavior with 'log enable lldb process'.
>>>
>>> Let me know how that goes.
>>>
>>> On Fri, Oct 10, 2014 at 7:56 AM, Andrew MacPherson <
>>> andrew.macp at gmail.com> wrote:
>>>
>>>> I don't see anything very interesting in the dyld log but it looks like
>>>> we're hitting the breakpoint at
>>>> DynamicLoaderPOSIXDYLD::RendezvousBreakpointHit() where its rendezvous
>>>> state is first eAdd and then hitting it again and the state is eDelete
>>>> without transitioning to eConsistent between eAdd and eDelete. I've never
>>>> looked at this runtime linker stuff before so I'm not sure if this is a
>>>> valid transition or not, this is what's causing the assertion failure
>>>> though. Any idea?
>>>>
>>>> Cheers,
>>>> Andrew
>>>>
>>>> On Thu, Oct 9, 2014 at 5:06 PM, Todd Fiala <tfiala at google.com> wrote:
>>>>
>>>>> I just took a peek at the code around there.  It's not immediately
>>>>> clear whether the assert is entirely useful, but I think it is intending to
>>>>> guard against adding new dynamic library info when the previous state of
>>>>> the data structures are not settled.
>>>>>
>>>>> I think a good starting point for you would be to enable 'log enable
>>>>> lldb dyld' and see what kind of activity is showing up for the existing log
>>>>> lines.  Maybe post that here if that doesn't help.
>>>>>
>>>>> I probably wouldn't remove the assert until we understand the root
>>>>> issue since the assert seems reasonable.
>>>>>
>>>>> Worst case if this doesn't get you further, you can add some if code
>>>>> around the condition and stick a breakpoint in the unexpected case so you
>>>>> can break the debugger in action and inspect what's going on.
>>>>>
>>>>> I hope that gets you started!
>>>>>
>>>>> -Todd
>>>>>
>>>>> On Thu, Oct 9, 2014 at 7:49 AM, Andrew MacPherson <
>>>>> andrew.macp at gmail.com> wrote:
>>>>>
>>>>>> Hi Todd,
>>>>>>
>>>>>> I just backed out your change and the behaviour remained the same.
>>>>>> When I say it's been awhile since I rebuilt though the last build I have
>>>>>> around is from June and it doesn't assert there. Has the default assertion
>>>>>> behaviour changed to enabled by default? I'm building with "cmake -G Ninja
>>>>>> ..".
>>>>>>
>>>>>> In fact checking the June build I don't get an assertion failure (I
>>>>>> assume they're disabled) but the values do differ and I would get one if
>>>>>> they were enabled. So it looks like this issue may have been around for
>>>>>> awhile.
>>>>>>
>>>>>> I can investigate further if you have any pointers around what I
>>>>>> might want to look for.
>>>>>>
>>>>>> Cheers,
>>>>>> Andrew
>>>>>>
>>>>>>
>>>>>> On Thu, Oct 9, 2014 at 3:30 PM, Todd Fiala <tfiala at google.com> wrote:
>>>>>>
>>>>>>> I did a POSIX Dynamic Loader change yesterday.  It might be causing
>>>>>>> this (not obvious yet, but could be.)  r219371.  If you're in a position to
>>>>>>> do a test of your run with that one change reverted out, and if that fixes
>>>>>>> it, I can yank out that change.
>>>>>>>
>>>>>>> Ideally I'd love to isolate if that is the cause of the changed
>>>>>>> behavior.
>>>>>>>
>>>>>>> -Todd
>>>>>>>
>>>>>>> On Thu, Oct 9, 2014 at 4:24 AM, Andrew MacPherson <
>>>>>>> andrew.macp at gmail.com> wrote:
>>>>>>>
>>>>>>>> I just compiled the latest LLDB HEAD on Linux 64-bit and am seeing
>>>>>>>> an assertion failure on launch when debugging a specific application
>>>>>>>> (Autodesk maya):
>>>>>>>>
>>>>>>>> lldb:
>>>>>>>> ../tools/lldb/source/Plugins/DynamicLoader/POSIX-DYLD/DYLDRendezvous.cpp:206:
>>>>>>>> bool DYLDRendezvous::UpdateSOEntries(): Assertion `m_previous.state ==
>>>>>>>> eConsistent' failed.
>>>>>>>>
>>>>>>>> It's been awhile since I've rebuilt from HEAD so not sure when this
>>>>>>>> may have been introduced and simply commenting out the assertion appears to
>>>>>>>> run fine.
>>>>>>>>
>>>>>>>> Does anyone know if this assertion is still relevant and if so have
>>>>>>>> any tips on where I should look to figure out what's happening?
>>>>>>>>
>>>>>>>> Thanks,
>>>>>>>> Andrew
>>>>>>>>
>>>>>>>> _______________________________________________
>>>>>>>> lldb-dev mailing list
>>>>>>>> lldb-dev at cs.uiuc.edu
>>>>>>>> http://lists.cs.uiuc.edu/mailman/listinfo/lldb-dev
>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> --
>>>>>>> Todd Fiala | Software Engineer | tfiala at google.com
>>>>>>>
>>>>>>>
>>>>>>
>>>>>
>>>>>
>>>>> --
>>>>> Todd Fiala | Software Engineer | tfiala at google.com
>>>>>
>>>>>
>>>>
>>>
>>>
>>> --
>>> Todd Fiala | Software Engineer | tfiala at google.com
>>>
>>>
>>
>
>
> --
> Todd Fiala | Software Engineer | tfiala at google.com
>
>
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