# Error with running wifi\_loopback.grc from gr-ieee802-11

**URL:** <https://www.ruby-forum.com/t/error-with-running-wifi-loopback-grc-from-gr-ieee802-11/242983>\
**Category:** GNU Radio\
**Created:** [August 12, 2015, 7:24pm UTC](https://www.ruby-forum.com/t/error-with-running-wifi-loopback-grc-from-gr-ieee802-11/242983 "2015-08-12T19:24:28Z")\
**Posts on this page:** 10\
**Page:** 1

<div class="post-metadata">

**Author:** ![Rafa\_F](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/958977/32.png) [@Rafa\_F](https://www.ruby-forum.com/u/Rafa_F)\
**Post date:** [August 12, 2015, 7:24pm UTC](https://www.ruby-forum.com/t/error-with-running-wifi-loopback-grc-from-gr-ieee802-11/242983/1 "2015-08-12T19:24:28Z")

</div>

* * *

Discuss-gnuradio mailing list  
removed\_email\_address@domain.invalid  
[https://lists.gnu.org/mailman/listinfo/discuss-gnuradio](https://lists.gnu.org/mailman/listinfo/discuss-gnuradio)

---

<div class="post-metadata">

**Author:** ![Tian\_Alvin](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/7cd45c/32.png) [@Tian\_Alvin](https://www.ruby-forum.com/u/Tian_Alvin)\
**Post date:** [August 13, 2015, 3:11pm UTC](https://www.ruby-forum.com/t/error-with-running-wifi-loopback-grc-from-gr-ieee802-11/242983/2 "2015-08-13T15:11:32Z")

</div>

Tian,

Disable logging and debug in the GRC flowgraph. See if this solves the  
problem. For reference, see [1].

[1]  
[https://lists.gnu.org/archive/html/discuss-gnuradio/2015-07/msg00289.html](https://lists.gnu.org/archive/html/discuss-gnuradio/2015-07/msg00289.html)

---

<div class="post-metadata">

**Author:** ![Tian\_Alvin](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/7cd45c/32.png) [@Tian\_Alvin](https://www.ruby-forum.com/u/Tian_Alvin)\
**Post date:** [August 13, 2015, 4:38pm UTC](https://www.ruby-forum.com/t/error-with-running-wifi-loopback-grc-from-gr-ieee802-11/242983/3 "2015-08-13T16:38:00Z")

</div>

Make sure logging is disabled on ALL blocks. I haven’t seen that  
libstdcxx error before, but I do have the segfaults with the logging in  
Ubuntu 15.04 with pybombs install.

Paul G.

---

<div class="post-metadata">

**Author:** ![Tian\_Alvin](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/7cd45c/32.png) [@Tian\_Alvin](https://www.ruby-forum.com/u/Tian_Alvin)\
**Post date:** [August 13, 2015, 3:39pm UTC](https://www.ruby-forum.com/t/error-with-running-wifi-loopback-grc-from-gr-ieee802-11/242983/4 "2015-08-13T15:39:34Z")

</div>

* * *

Discuss-gnuradio mailing list  
removed\_email\_address@domain.invalid  
[https://lists.gnu.org/mailman/listinfo/discuss-gnuradio](https://lists.gnu.org/mailman/listinfo/discuss-gnuradio)

---

<div class="post-metadata">

**Author:** ![Tian\_Alvin](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/7cd45c/32.png) [@Tian\_Alvin](https://www.ruby-forum.com/u/Tian_Alvin)\
**Post date:** [August 13, 2015, 5:06pm UTC](https://www.ruby-forum.com/t/error-with-running-wifi-loopback-grc-from-gr-ieee802-11/242983/5 "2015-08-13T17:06:04Z")

</div>

Hi,

I just replied on github

> <https://github.com/bastibl/gr-ieee802-11/issues/18#issuecomment-130651522>
>
> when I run wifi\_loopback
> 
> Generating: "/home/sollo/gr-ieee802-11/examples/wifi\_l…oopback.py"
> 
> \> \> \> Warning: This flow graph may not have flow control: no audio or RF hardware blocks found. Add a Misc-\>Throttle block to your flow graph to avoid CPU congestion.
> 
> Executing: "/home/sollo/gr-ieee802-11/examples/wifi\_loopback.py"
> 
> linux; GNU C++ version 4.8.4; Boost\_105400; UHD\_003.009.git-217-g012381d9
> 
> Using Volk machine: avx\_32\_mmx\_orc
> OFDM MAPPER: encoding: 0
> set\_min\_output\_buffer on block 31 to 96000
> set\_min\_output\_buffer on block 33 to 96000
> set\_min\_output\_buffer on block 35 to 96000
> set\_min\_output\_buffer on block 36 to 96000
> set\_min\_output\_buffer on block 39 to 96000
> set\_min\_output\_buffer on block 50 to 96000
> 
> \> \> \> Done
> 
> this doesn\`t give me any figure graph.
> 
> I also use debug command and found that :
> 
> Program received signal SIGSEGV, Segmentation fault.
> \[Switching to Thread 0x82c5eb40 (LWP 4482)\]
> 0xb0796e30 in ofdm\_decode\_signal\_impl::print\_signal() ()
> from /usr/local/lib/libgnuradio-ieee802\_11.so
> (gdb) backtrace
> \#0 0xb0796e30 in ofdm\_decode\_signal\_impl::print\_signal() ()
> 
> from /usr/local/lib/libgnuradio-ieee802\_11.so
> \#1 0xb0797615 in ofdm\_decode\_signal\_impl::general\_work(int, std::vector\<int, std::allocator\<int\> \>&, std::vector\<void const\*, std::allocator\<void const\*\> \>&, std::vector\<void\*, std::allocator\<void\*\> \>&) ()
> 
> from /usr/local/lib/libgnuradio-ieee802\_11.so
> \#2 0xb6fd67f7 in gr::block\_executor::run\_one\_iteration (this=0x82c5e270)
> 
> \`\`\`
> at /home/sollo/gnuradio/gnuradio-runtime/lib/block\_executor.cc:438
> \`\`\`
> \#3 0xb7012a19 in gr::tpb\_thread\_body::tpb\_thread\_body (this=0x82c5e270,
> 
> \`\`\`
> block=..., max\_noutput\_items=10000000)
> at /home/sollo/gnuradio/gnuradio-runtime/lib/tpb\_thread\_body.cc:122
> \`\`\`
> \#4 0xb7008373 in operator() (this=0x927b9c8)
> 
> \`\`\`
> at /home/sollo/gnuradio/gnuradio-runtime/lib/scheduler\_tpb.cc:44
> \`\`\`
> \#5 operator() (this=0x927b9c8)
> 
> \`\`\`
> at /home/sollo/gnuradio/gnuradio-runtime/include/gnuradio/thread/thread\_body\_wrapper.h:51
> \`\`\`
> \#6 boost::detail::function::void\_function\_obj\_invoker0gr::thread::thread\_body\_wrapper\<gr::tpb\_container, void\>::invoke (function\_obj\_ptr=...)
> 
> \`\`\`
> at /usr/include/boost/function/function\_template.hpp:153
> \`\`\`
> \#7 0xb6fbe09d in operator() (this=0x92f263c)
> 
> \`\`\`
> at /usr/include/boost/function/function\_template.hpp:767
> \`\`\`
> \#8 boost::detail::thread\_databoost::function0\<void \>::run (this=0x92f2520)
> 
> that means Segmentation fault 
> 
> but how can I fix the problem? Could you please give me any tips since I am a beginner with gnuradio. Thanks a lot.

It would be great if you could try what I suggest there.

Best,  
Bastian

On 08/13/2015 02:32 PM, Garver, Paul W wrote:

> > Hi Paul,  
> > Thanks
> > 
> > > ```
> > > or, via email, send a message with subject or body 'help' to
> > > 
> > > ```
> > 
> > ```
> > _______________________________________________
> > 
> > ```
> 
> [Discuss-gnuradio Info Page](https://lists.gnu.org/mailman/listinfo/discuss-gnuradio)

–  
Dipl.-Inform. Bastian B.  
Distributed Embedded Systems  
University of Paderborn, Germany

> **[Home](https://www.bastibl.net/)**
>
> I'm Bastian Bloessl, a Research Group Leader at the Secure Mobile Networking Lab, TU Darmstadt. Checkout my blog, projects, publications, and resume; or connect on Github, Twitter, YouTube, or Facebook.

---

<div class="post-metadata">

**Author:** ![Tian\_Alvin](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/7cd45c/32.png) [@Tian\_Alvin](https://www.ruby-forum.com/u/Tian_Alvin)\
**Post date:** [August 13, 2015, 5:06pm UTC](https://www.ruby-forum.com/t/error-with-running-wifi-loopback-grc-from-gr-ieee802-11/242983/6 "2015-08-13T17:06:04Z")

</div>

* * *

Discuss-gnuradio mailing list  
removed\_email\_address@domain.invalid  
[https://lists.gnu.org/mailman/listinfo/discuss-gnuradio](https://lists.gnu.org/mailman/listinfo/discuss-gnuradio)

---

<div class="post-metadata">

**Author:** ![Tian\_Alvin](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/7cd45c/32.png) [@Tian\_Alvin](https://www.ruby-forum.com/u/Tian_Alvin)\
**Post date:** [August 13, 2015, 5:09pm UTC](https://www.ruby-forum.com/t/error-with-running-wifi-loopback-grc-from-gr-ieee802-11/242983/7 "2015-08-13T17:09:35Z")

</div>

Hi,

yes, this is how it is supposed to look. But please read the posts at  
the bottom of the thread. Actually, it should work without modifications  
now.

Best,  
Bastian

On 08/13/2015 04:03 PM, Tian Alvin wrote:

> Paul----Thank you very much for your suggestion and sharing!  
> [wifi\_loopback problem · Issue #18 · bastibl/gr-ieee802-11 · GitHub](https://github.com/bastibl/gr-ieee802-11/issues/18#issuecomment-130651522)  
> logging in  
> Hi Paul,
> 
> ```
> this
> <mailto:removed_email_address@domain.invalid>> wrote:
> or, via email, send a message with subject or body
> <mailto:removed_email_address@domain.invalid>>
> (Tian Alvin)
> 
> http://www.ccs-labs.org/~bloessl/
> 
> ```

–  
Dipl.-Inform. Bastian B.  
Distributed Embedded Systems  
University of Paderborn, Germany

> **[Home](https://www.bastibl.net/)**
>
> I'm Bastian Bloessl, a Research Group Leader at the Secure Mobile Networking Lab, TU Darmstadt. Checkout my blog, projects, publications, and resume; or connect on Github, Twitter, YouTube, or Facebook.

---

<div class="post-metadata">

**Author:** ![Tian\_Alvin](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/7cd45c/32.png) [@Tian\_Alvin](https://www.ruby-forum.com/u/Tian_Alvin)\
**Post date:** [August 13, 2015, 5:22pm UTC](https://www.ruby-forum.com/t/error-with-running-wifi-loopback-grc-from-gr-ieee802-11/242983/8 "2015-08-13T17:22:26Z")

</div>

Hi Bastian,

Thanks!

The file ( ofdm\_decode\_signal.cc) I have downloaded is still written as  
(Yes–no mylog(temp) now):

“mylog(boost::format(“encoding: %1% - length: %2% - symbols: %3%”)  
% d\_encoding % d\_len % d\_copy\_symbols);”

To make it work, I still need change it to  
"std::string temp = (boost::format(“encoding: %1% - length: %2% -  
symbols: %3%”)  
% d\_encoding % d\_len % d\_copy\_symbols).str();

Actually, I don’t really understand the difference between these two.  
What  
does this change mean? Does the problem relate to log4cpp?

On Thu, Aug 13, 2015 at 3:07 PM, Bastian B. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)

---

<div class="post-metadata">

**Author:** ![Tian\_Alvin](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/7cd45c/32.png) [@Tian\_Alvin](https://www.ruby-forum.com/u/Tian_Alvin)\
**Post date:** [August 13, 2015, 5:38pm UTC](https://www.ruby-forum.com/t/error-with-running-wifi-loopback-grc-from-gr-ieee802-11/242983/9 "2015-08-13T17:38:13Z")

</div>

Okay. I see. Thank you very much for your help!

On Thu, Aug 13, 2015 at 3:34 PM, Bastian B. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)

---

<div class="post-metadata">

**Author:** ![Tian\_Alvin](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/7cd45c/32.png) [@Tian\_Alvin](https://www.ruby-forum.com/u/Tian_Alvin)\
**Post date:** [August 13, 2015, 5:36pm UTC](https://www.ruby-forum.com/t/error-with-running-wifi-loopback-grc-from-gr-ieee802-11/242983/10 "2015-08-13T17:36:27Z")

</div>

Hi,

On 08/13/2015 04:20 PM, Tian Alvin wrote:

> “mylog(boost::format(“encoding: %1% - length: %2% - symbols: %3%”)  
> % d\_encoding % d\_len % d\_copy\_symbols);”
> 
> To make it work, I still need change it to  
> "std::string temp = (boost::format(“encoding: %1% - length: %2% -  
> symbols: %3%”)  
> % d\_encoding % d\_len % d\_copy\_symbols).str();
> 
> Actually, I don’t really understand the difference between these two.  
> What does this change mean? Does the problem relate to log4cpp?

This was suggested to debug the problem, not as a fix.

The problem is described in the issue you referenced (scroll down) and  
hopefully fixed by this commit

> <https://github.com/bastibl/gr-ieee802-11/commit/77548c73a95b0460250ef477e309190f20bf8d95>

Please update the module with git.

Best,  
Bastian

> ```
> yes, this is how it is supposed to look. But please read the posts
> I followed the suggestion on github:
> % d_encoding % d_len % d_copy_symbols);"
> 
> It would be great if you could try what I suggest there.
> logging in
> <mailto:removed_email_address@domain.invalid> <mailto:removed_email_address@domain.invalid
> Did you also see the below error in your case when
> <removed_email_address@domain.invalid <mailto:removed_email_address@domain.invalid>
> solves the problem. For reference, see [1].
> <mailto:removed_email_address@domain.invalid
> <mailto:removed_email_address@domain.invalid>
> removed_email_address@domain.invalid
> <mailto:removed_email_address@domain.invalid>
> than "Re: Contents of Discuss-gnuradio
> 
> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
> <mailto:removed_email_address@domain.invalid>>>
> 
> Dipl.-Inform. Bastian B.
> Distributed Embedded Systems
> University of Paderborn, Germany
> http://www.ccs-labs.org/~bloessl/
> 
> ```

–  
Dipl.-Inform. Bastian B.  
Distributed Embedded Systems  
University of Paderborn, Germany

> **[Home](https://www.bastibl.net/)**
>
> I'm Bastian Bloessl, a Research Group Leader at the Secure Mobile Networking Lab, TU Darmstadt. Checkout my blog, projects, publications, and resume; or connect on Github, Twitter, YouTube, or Facebook.