[Error]I build my code successfully but get segmentation fault(SIGSEGV) after that.

[Kohei MORIYAMA]

Hi all.

I've built my code successfully but the simulations stopped with segmentation fault(SIGSEGV). 

That fault came up after I changed the interference range from "all other nodes" to "within 2 hops away" (see the Flow Image below).

When the range is "all node", my code always succeed in simulation.

I think it is because more nodes try to send packets when the range is "within 2 hops away" than when the range is "all node".

But I don't know which code to fix...

---Flow Image---

　　　　　　n7 ●

　　　　　　　　↓

　　　　　　n8 ●

　　　　　　　　↓

　　　　　　n9 ●

                　↓     

　●→●→●→●←●←●←●

　n1  n2　n3 ↑    n4  n5  n6

　　　　　　　　●n10

　　　　　　　　↑

　　　　　　　　●n11

　　　　　　　　↑

　　             ●n12

Source      : n1~n12　　　　　　　　

Destination: the cross point node(n0)

Baud rate   : 54Mbps

Packet Size:1000 byte [OnOffApplication]

DataRate     :0.1~5 Mbps [OnOffApplication]

MaxQueue   :400

-----------------

Even if the range is "within 2 hops away", simulations work fine when DataRate[OnOffApplication] is from 0.1 to 1 Mbps.

When I increase DataRate[OnOffApplication] from 1.1666667 to 5 Mbps, simulations stop with segmentation fault(SIGSEGV).

Here are stacks when the error comes up.

void

SwMacCsma::ChannelAccessGranted ()

{

  NS_LOG_FUNCTION ("");

  if (m_pktQueue.size () == 0) { return; }

  

  m_backoffStart = Seconds (0);

  m_backoffRemain = Seconds (0);

  m_state = WAIT_TX;

  

  m_pktData = m_pktQueue.front();

  m_pktQueue.pop_front ();

  

  if (m_pktData == 0)

    NS_ASSERT ("Queue has null packet");

  

  SwMacHeader header;

  m_pktData->PeekHeader (header);//m_pktData is Ptr<Packet> and indicates the data packet a node is going to send.

 ↓

[packet.cc]

uint32_t

Packet::PeekHeader (Header &header) const

{

  uint32_t deserialized = header.Deserialize (m_buffer.Begin ());

 ↓

[buffer]

Buffer::Iterator 

Buffer::Begin (void) const

{

  NS_ASSERT (CheckInternalState ());

  return Buffer::Iterator (this); →"this" cannot access to memory at address 0x0 here.

　↓

Buffer::Iterator::Iterator (Buffer const*buffer)

{

  Construct (buffer); →buffer cannnot access memory at address 0x4.　　

  m_current = m_dataStart;

}

　↓

void

Buffer::Iterator::Construct (const Buffer *buffer)

{

  m_zeroStart = buffer->m_zeroAreaStart; →buffer cannnot access memory at address 0x4.

  m_zeroEnd = buffer->m_zeroAreaEnd;

  m_dataStart = buffer->m_start;

  m_dataEnd = buffer->m_end;

  m_data = buffer->m_data->m_data;

}

------

I've try to solve this problem but all that I tried can't solve it... Please help.

What I've tried to solve this problem are...

 

1. Increasing Stack Size  

    ulimit -s unlimited

2. Implementing Cleanup() method [If a packet stays longer than m_maxDelay in the queue, it is dropped.]

    

    .AddAttribute ("MaxDelay", "If a packet stays longer than this delay in the queue, it is dropped.",

                   TimeValue (Seconds (10.0)),

                   MakeTimeAccessor (&SwMacCsma::m_maxDelay),

                   MakeTimeChecker ())

    .

    .

    .         

void

SwMacCsma::Cleanup (void)

{

  NS_LOG_FUNCTION_NOARGS ();

  if (m_pktQueue.size () == 0)

    {

      return;

    }

  Time now = Simulator::Now ();

  std::list<Ptr<Packet> >::iterator it = m_pktQueue.begin();

while( it != m_pktQueue.end() )  

       {

SwMacHeader header;

Ptr<Packet> packet = *it;

packet->PeekHeader (header);

Time tstamp = header.GetTstamp(); //tstamp is the time a packet is enqueued.

if ( tstamp + m_maxDelay > now)

                {

                  m_pktQueue.remove(*it);

                  ++it;

                   }

                 else

                 {

  ++it; 

                  }

}

}

I'm new to ns3 and C++ programming, so any advice and suggestion to work on this problem are welcome.

Thanks.

---Additional Info.----

In fact, I removed Cleanup() method, because SIGIOT occurs when I use this method at the beginning of Enqueue (Ptr<Packet> packet, Mac48Address dest).

---SIGIOT Error---

Waf: Leaving directory `/home/kmoriyama/tarballs/ns-allinone-3.15/ns-3.15/build'

'build' finished successfully (6.765s)

assert failed. cond="m_current >= m_dataStart && m_current <= m_dataEnd", msg="You have attempted to read beyond the bounds of the available buffer space. This usually indicates that a Header::Deserialize or Trailer::Deserialize method is trying to read data which was not written by a Header::Serialize or Trailer::Serialize method. In short: check the code of your Serialize and Deserialize methods.", file=./ns3/buffer.h, line=823

terminate called without an active exception

Command ['/home/kmoriyama/tarballs/ns-allinone-3.15/ns-3.15/build/scratch/csmaca-cross-stat', '--rate=0.833333333Mbps'] terminated with signal SIGIOT. Run it under a debugger to get more information (./waf --run <program> --command-template="gdb --args %s <args>").

---

After I removed this method, no SIGIOT occurs after building successfully.

But, Header::Deserialize this message mentions is the same class where SIGSEGV occurs. Is this a clue?  

This error says Check the code of your Serialize and Deserialize methods, but I don't know what my Serialize and Deserialize methods and where they are...

Here is Enqueue method I use.

bool

SwMacCsma::Enqueue (Ptr<Packet> packet, Mac48Address dest)

{

  NS_LOG_FUNCTION ("dest" << dest << "#queue" << m_pktQueue.size () << 

                  "state" << m_state << "pktSize" << packet->GetSize ());

  Cleanup ();

  if (m_pktQueue.size () >= m_queueLimit)

    {

      return false;

    }

  m_traceEnqueue (m_device->GetNode ()->GetId (), m_device->GetIfIndex ());

  

  packet->AddHeader (SwMacHeader (m_address, dest, SW_PKT_TYPE_DATA, Simulator::Now ()));

  m_pktQueue.push_back (packet);

  

  if (m_state == IDLE)

    { 

      CcaForDifs ();

    }

  

  return false;

}

---

Kohei Moriyama

Undergraduate Student

University of Tsukuba, Japan

[Kohei MORIYAMA]

When is it possible the address of a Ptr<Packet> become 0x0(null)?

By debugging, I made sure a Ptr<Packet> has an address certainly when it is enqueued.

---Enqueue Function----

bool
SwMacCsma::Enqueue (Ptr<Packet> packet, Mac48Address dest)
{

  if (m_pktQueue.size () >= m_queueLimit) //m_pktQueue is std::list<Ptr<Packet> >
    {
      return false;
    }
 
  packet->AddHeader (SwMacHeader (m_address, dest, SW_PKT_TYPE_DATA));
  m_pktQueue.push_back (packet);
   
  return false;
}


But when a Ptr<Packet> that is returned by "m_pktQueue.front()" is 0x0, segmentation fault(SIGSEGV) occurs.

m_pktData = m_pktQueue.front(); //m_pktData is Ptr<Packet> and indicates the data packet a node is going to send.

  m_pktQueue.pop_front ();

  

  SwMacHeader header;

  m_pktData->PeekHeader (header); //SIGSEGV occurs.

It means a Ptr<Packet> that had its address become 0x0(null), but I don't know why... Please help...