Re: [Discuss-gnuradio] constellation soft decoder

[Philip Balister]

On 12/16/2013 08:16 AM, Miklos Maroti wrote:
> Hi Marcus,
> 
> Ok, that makes sense. It does not crash with QPSK, but it does with
> BPSK and 8PSK, and BPSK and 8PSK do not set the pre_diff_code. This
> explains why there is crash in one case and not the other. Although
> neither sets the apply_pre_diff_code, so even QPSK should not set
> pre_diff_code.

I took a quick look in Coverity for issues in gr-digital. It flags a
bunch of uninitialized variables. I'll try and take a look at these this
week.

There is an intermittent QA failure in some QA code and this might be an
explanation.

Philip

> 
> I think the real problem is in constellation::calc_soft_dec. I does
> not check whether d_apply_pre_diff_code is set or not.
> 
> (By the way, I do not understand the usefulness of pre_diff_code. Can
> you just permute the constellation points and get the same effect?)
> 
> Miklos
> 
> On Mon, Dec 16, 2013 at 1:34 PM, Marcus Müller <address@hidden> wrote:
> Well, after having a debug build and then adding a lot of "volatile"s
> into the code at the crashing function, it looks as if the
> d_pre_diff_code of the constellation has size 0; and thus, you can't
> access the 0. (read: first) element. How this could happen with a QPSK
> object is currently subject to my confusion. Stay tuned for more
> confusing facts as the code unfolds :).
> 
> Greetings,
> Marcus
> 
> On 16.12.2013 08:30, Miklos Maroti wrote:
>>>> Hi Marcus,
>>>>
>>>> I do not think it is a compiler bug, but something uninitialized.
>>>> Constellation_qpsk and constellation_calcdist does not crash (I
>>>> did not verify if they work). However, if I generate the LUT for
>>>> constellation_qpsk, then it crashes.
>>>>
>>>> # uname -a Linux maroti-t410 3.11.0-14-generic #21-Ubuntu SMP Tue
>>>> Nov 12 17:04:55 UTC 2013 x86_64 x86_64 x86_64 GNU/Linux
>>>>
>>>> # gcc --version gcc (Ubuntu/Linaro 4.8.1-10ubuntu9) 4.8.1
>>>>
>>>> Using latest master branch of gnuradio, hash 117058bac41c91, both
>>>> CMAKE_BUILD_TYPE=Debug and Release produces the same behavior
>>>>
>>>> # gdb `which python` core Reading symbols from
>>>> /usr/bin/python2.7...(no debugging symbols found)...done.
>>>>
>>>> warning: core file may not match specified executable file. [New
>>>> LWP 2249] [New LWP 2251] [New LWP 2240] [New LWP 2248] [New LWP
>>>> 2247] [New LWP 2239] [New LWP 2250]
>>>>
>>>> warning: Can't read pathname for load map: Input/output error.
>>>> [Thread debugging using libthread_db enabled] Using host
>>>> libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
>>>> Core was generated by `python ./constellation_simulation.py'.
>>>> Program terminated with signal 11, Segmentation fault. #0
>>>> 0x00007f98dbbe01a7 in gr::digital::constellation::calc_soft_dec (
>>>> this=0x48321c0, sample=..., npwr=<optimized out>) at
>>>> /home/mmaroti/workspace/gnuradio/gr-digital/lib/constellation.cc:286
>>>>
>>>>
> 286        for(int j = 0; j < k; j++) {
>>>>
>>>> i stack #0  0x00007f98dbbe01a7 in
>>>> gr::digital::constellation::calc_soft_dec ( this=0x48321c0,
>>>> sample=..., npwr=<optimized out>) at
>>>> /home/mmaroti/workspace/gnuradio/gr-digital/lib/constellation.cc:286
>>>>
>>>>
> #1  0x00007f98dbbe0f7e in gr::digital::constellation::soft_decision_maker (
>>>> this=0x48321c0, sample=...) at
>>>> /home/mmaroti/workspace/gnuradio/gr-digital/lib/constellation.cc:355
>>>>
>>>>
> #2  0x00007f98dbbe94dc in
>>>> gr::digital::constellation_soft_decoder_cf_impl::work
>>>> (this=0x4fb11a0, noutput_items=8190, input_items=...,
>>>> output_items=...) at
>>>> /home/mmaroti/workspace/gnuradio/gr-digital/lib/constellation_soft_decoder_cf_impl.cc:68
>>>>
>>>>
> #3  0x00007f98e1c5dd38 in gr::sync_interpolator::general_work (
>>>> this=0x4fb11c0, noutput_items=<optimized out>, ninput_items=...,
>>>> input_items=..., output_items=...) at
>>>> /home/mmaroti/workspace/gnuradio/gnuradio-runtime/lib/sync_interpolator.cc:67
>>>>
>>>>  You should be able to reproduce the problem quite easily, but if
>>>> needed I can provided a test program.
>>>>
>>>> Best, Miklos
>>>>
>>>> On Mon, Dec 16, 2013 at 7:59 AM, Marcus Müller <address@hidden>
>>>> wrote:
>>>>> Could you post the whole backtrace (as a github gist, pastebin
>>>>> etc)? That would be very helpful, along with information such
>>>>> as: Compiler (Gcc (version), VC++, clang ...), Platform (Linux,
>>>>> win, mac,...), architecture (x86(64), ARMv9, IBM S7390,...) and
>>>>> GNU Radio source version.
>>>>>
>>>>> Thanks and happy hacking, Marcus
>>>>>
>>>>> On 12/16/2013 01:05 AM, Miklos Maroti wrote:
>>>>>>
>>>>>> Hi Guys,
>>>>>>
>>>>>> Constellation soft decoder crashes for constellation_bpsk()
>>>>>> and constellation_8psk(). I could not find the cause of this
>>>>>> problem, the back trace on my machine points to
>>>>>>
>>>>>> gnuradio/gr-digital/lib/constellation.cc:286 for(int j = 0; j <
>>>>>> k; j++) {
>>>>>>
>>>>>> which does not make any sense. Any idea what could go wrong?
>>>>>>
>>>>>> Miklos
>>>>>>
>>>>>> _______________________________________________
>>>>>> Discuss-gnuradio mailing list address@hidden
>>>>>> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
>>>>>
>>>>>
>>>>>
>>>>> _______________________________________________ Discuss-gnuradio
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