HOWTO debug smart pointer

Suppose I have an ns-3 smart pointer such as:

 Ptr<Packet> p = ...

To access the underlying raw pointer via gdb (e.g. to inspect the contents), you want to access the p->m_ptr member:

 (gdb) p *p
 $22 = (
   ns3::Packet &) @0x80b0ea0: {<ns3::SimpleRefCount<ns3::Packet, ns3::empty, ns3::DefaultDeleter<ns3::Packet> >> 
 = {<ns3::empty> = {<No data fields>}, 
   m_count = 1}, m_buffer = {m_data = 0x80b0f28, m_maxZeroAreaStart = 7, 
   static g_recommendedStart = 7, m_zeroAreaStart = 7, m_zeroAreaEnd = 27, 
   m_start = 0, m_end = 29}, m_byteTagList = {m_used = 0, m_data = 0x0}, 
 m_packetTagList = {static g_free = <optimized out>, 
   static g_nfree = <optimized out>, m_next = 0x0}, m_metadata = {
   static m_freeList = {<std::vector<ns3::PacketMetadata::Data*, std::allocator<ns3::PacketMetadata::Data*> >> = 
 {<std::_Vector_base<ns3::PacketMetadata::Data*, std::allocator<ns3::PacketMetadata::Data*> >> = {
         _M_impl = {<std::allocator<ns3::PacketMetadata::Data*>> = 
 {<__gnu_cxx::new_allocator<ns3::PacketMetadata::Data*>> = {<No data fields>}, <No data fields>}, _M_start = 0x0, 
 _M_finish = 0x0, 
           _M_end_of_storage = 0x0}}, <No data fields>}, <No data fields>}, 
   static m_enable = true, static m_enableChecking = false, 
   static m_metadataSkipped = false, static m_maxSize = 26, 
   static m_chunkUid = 4, m_data = 0x80b0f48, m_head = 8, m_tail = 17, 
   m_used = 26, m_packetUid = 0}, m_nixVector = {m_ptr = 0x0}, 
 static m_globalUid = 2}

This will not work:

 (gdb) p p->m_buffer
 There is no member or method named m_buffer.

Instead, do this:

 (gdb) p (p->m_ptr)->m_buffer
 $24 = {m_data = 0x80b0f28, m_maxZeroAreaStart = 7, 
 static g_recommendedStart = 7, m_zeroAreaStart = 7, m_zeroAreaEnd = 27, 
 m_start = 0, m_end = 29}

Going further, suppose you want to look at the raw bytes of the packet buffer. This is stored in the m_data field of the buffer, (0x80b0f28 above). To inspect the memory contents of that address, use the "x" command of gdb; e.g. this will print out three bytes starting at the referenced address:

 (gdb) x/3 0x80b0f28
 0x80b0f28:	0x00000001	0x00000009	0x00000000

Keep in mind that data contents in a packet buffer are in network byte order and may be endian swapped with respect to your (x86) host operating system.