RE: Re: Re: Why does this dump core?

[Jim Melton]

For the sake of the archives, the issue was virtual inheritance. See https://www.cprogramming.com/tutorial/virtual_inheritance.html

 

One thing to be aware of is that if either transmitter or receiver attempted to invoke the storable constructor in their initialization lists, that call will be completely skipped when constructing a radio object! Be careful, as this could cause a subtle bug!

 

Because the interface class virtually inherited from gr::block, then the impl must explicitly invoke the gr::block ctor with the desired arguments. Because it didn’t, the default gr::block ctor was invoked. That ctor demonstrably instantiates an object where message_port_register_out dumps core. Whether that is desired behavior or not is another matter. In my case, it was failure to properly initialize a virtual base class.

---

Jim Melton

 

From: Jim Melton
Sent: Wednesday, September 15, 2021 16:38
To: 'Jeff Long' <willcode4@gmail.com>; GNURadio Discussion List <discuss-gnuradio@gnu.org>
Subject: RE: [EXTERNAL] Re: Re: Why does this dump core?

 

I can’t explain it, but I found what’s wrong. My failing Test class that derives from gr::block called the default ctor. That’s bad. If instead, Test calls the “real” ctor, with io_signature and everything, it works. Note that the example that derives from gr::sync_block does call the “real” ctor; if I use the default gr::sync_block ctor, it still fails.

 

I didn’t think I was calling the default ctor, but apparently I was.

 

The interface class:

class CYBERRADIO_API vita_udp_rx : virtual public gr::block

{

…

protected:

    using gr::block::block; // "inherit" base class ctor

};

 

Since this interface doesn’t really do anything, I thought I could just pass-through to the gr::block constructor(s).

 

 

The impl class:

class vita_udp_rx_impl : public vita_udp_rx

{

    using Base = vita_udp_rx;

…

};

 

 

The impl ctor:

vita_udp_rx_impl::vita_udp_rx_impl(Cfg const& cfg)

    : Base("vita_udp_rx",

           gr::io_signature::make(0, 0, 0),

           gr::io_signature::make(1, 1, sizeof(gr_complex))),

…

{

…

}

 

What this should do is pass through to the gr::block constructor. But it doesn’t appear to do so. If instead, I write

vita_udp_rx_impl::vita_udp_rx_impl(Cfg const& cfg)

    : gr::block("vita_udp_rx",

           gr::io_signature::make(0, 0, 0),

           gr::io_signature::make(1, 1, sizeof(gr_complex))),

…

{

…

}

 

Then it works.

 

---

Jim Melton

 

From: Discuss-gnuradio <discuss-gnuradio-bounces+jim.melton=sncorp.com@gnu.org> On Behalf Of Jeff Long
Sent: Wednesday, September 15, 2021 16:23
To: GNURadio Discussion List <discuss-gnuradio@gnu.org>
Subject: [EXTERNAL] Re: Re: Why does this dump core?

 

The Message Strobe block:

 

  gr-blocks/include/gnuradio/blocks/message_strobe.h

  gr-blocks/lib/message_strobe_impl.h

  gr-blocks/lib/message_strobe_impl.cc

 

looks like the simplest builtin block that has a message out port. It subclasses gr::block, so that should work.

 

Instantiating gr::block directly, and on the stack, is not something I've tried. Your longer bit of code shows you're using sptrs.

 

 

On Wed, Sep 15, 2021 at 5:57 PM Jim Melton <jim.melton@sncorp.com> wrote:

If I derived from a different block, it doesn’t crash:

 

class Test : public gr::sync_block

{

public:

Test();

int work(int, gr_vector_const_void_star&, gr_vector_void_star&) override { return 0;};

};

 

Test::Test() : gr::sync_block("test",

           gr::io_signature::make(0, 0, 0),

           gr::io_signature::make(1, 1, sizeof(gr_complex)))

{

}

 

---

Jim Melton

 

From: Jim Melton
Sent: Wednesday, September 15, 2021 14:57
To: 'Jeff Long' <willcode4@gmail.com>
Cc: GNURadio Discussion List <discuss-gnuradio@gnu.org>
Subject: RE: [EXTERNAL] Re: Why does this dump core?

 

Simpler example. This still dumps core. Please explain what is wrong with the argument:

 

class Test : public gr::block

{

public:

Test();

};

 

Test::Test() : gr::block() {

message_port_register_out(pmt::mp("test"));

}

 

int main(int argc, char** argv)

{

Test test; // dumps core

Return 0;

}

 ---

Jim Melton

 

From: Jeff Long <willcode4@gmail.com>
Sent: Tuesday, September 14, 2021 14:10
To: Jim Melton <jim.melton@sncorp.com>
Cc: GNURadio Discussion List <discuss-gnuradio@gnu.org>
Subject: [EXTERNAL] Re: Why does this dump core?

 

gr::CyberRadio::vita_udp_rx_impl::vita_udp_rx_impl() is calling gr::basic_block::message_port_register_out() with a bad argument most likely.

 

On Tue, Sep 14, 2021 at 2:40 PM Jim Melton <jim.melton@sncorp.com> wrote:

As briefly discussed on IRC last night,  I am trying to modify someone else’s block to be more robust (detect or eliminate packet drops). In the ctor, I call message_port_register_out() and it dumps core. The offending call is here: https://github.com/jwmelto/gr-cyberradio/blob/7b048a14f76b140f5cd3edd7d8dfa533e1f892a7/gr-CyberRadio/lib/vita_udp_rx_impl.cc#L427

 

The stack trace from the core is

#0  0x00007ffff4b04973 in pmt::is_pair(boost::shared_ptr<pmt::pmt_base> const&) () from /usr/local/lib64/libgnuradio-pmt.so.3.8.2

#1  0x00007ffff4b07328 in pmt::assv(boost::shared_ptr<pmt::pmt_base>, boost::shared_ptr<pmt::pmt_base>) () from /usr/local/lib64/libgnuradio-pmt.so.3.8.2

#2  0x00007ffff4b075fd in pmt::dict_has_key(boost::shared_ptr<pmt::pmt_base> const&, boost::shared_ptr<pmt::pmt_base> const&) () from /usr/local/lib64/libgnuradio-pmt.so.3.8.2

#3  0x00007ffff73b72e2 in gr::basic_block::message_port_register_out(boost::shared_ptr<pmt::pmt_base>) () from /usr/local/lib64/libgnuradio-runtime.so.3.8.2

#4  0x00007ffff7b58d73 in gr::CyberRadio::vita_udp_rx_impl::vita_udp_rx_impl (this=0x622800, cfg=..., __in_chrg=<optimized out>, __vtt_parm=<optimized out>)

    at /tmp/gr-cyberradio/gr-CyberRadio/lib/vita_udp_rx_impl.cc:427

#5  0x00007ffff7b56cb3 in gr::CyberRadio::vita_udp_rx::make (cfg=...) at /tmp/gr-cyberradio/gr-CyberRadio/lib/vita_udp_rx_impl.cc:111

#6  0x000000000040c51d in main (argc=1, argv=0x7fffffffdf18) at /usr/src/project/main.cc:23

 

My minimal test program is here:

#include <CyberRadio/vita_udp_rx.h>

#include <gnuradio/top_block.h>

#include <gnuradio/blocks/file_sink.h>

 

int main(int argc, char** argv)

{

gr::CyberRadio::vita_udp_rx::Cfg cfg;

 

cfg.src_ip = "192.168.110.10";

cfg.port = 8010;

cfg.header_byte_offset = 48;

cfg.samples_per_packet = 1024;

cfg.bytes_per_packet = 4152;

cfg.swap_bytes = true;

cfg.swap_iq = false;

cfg.tag_packets = true;

cfg.uses_v49_1 = false;

 

cfg.debug = true;

 

auto v49 = gr::CyberRadio::vita_udp_rx::make(cfg); // core dump

auto sink = gr::blocks::file_sink::make(sizeof(gr_complex), "test.dat");

 

auto top = gr::make_top_block("Test");

top->connect(v49, 0, sink, 0);

 

return 0;

}

 

According to all that I know, this should work. It clearly does not. I would appreciate any pointers on how to get past this roadblock.

---

Jim Melton

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