struct_layout

tool to show the structure layout of types in your C/C++ program, highlighting padding.

It recreates the structure layout based on DWARF debug information from a binary or object file. This tool analyzes the output from dwarfdump which will need to be installed for struct_layout to work.

On Mac, debug symbols are not typically linked into the final executable, but this tool can still be used on individual object and .dSYM files.

It is typically a good idea to pipe the output from struct_layout to less. Since the default is to colorize the output:

./struct_layout.py <object-file>.o | less -r

usage

usage: ./struct_layout.py [options] exe-file [name-prefix-filter]

exe-file must have DWARF debug symbols in it. It
may be an object file, shared library or executable. On Mac
dsymutils will be invoked for files with no direct debug symbols
in them.

name-prefix-filter is an optional argument. When
specified, only types whose prefix matches this are
printed. Names are fully qualified and start with ::
to denote the global scope.

OPTIONS
-a           print all types, including standard library
             and implementation detail types
-c           disable color output
-p <file>    use the specified access_profile output file
             to display use counts for only instrumented types

the dwarfdump tool is a dependency and need to be
installed on your system. On Mac OS X you may need dsymutil
in order to link debug symbols together

Output is colorized by default, use -c to disable. Types belonging to the standard library and compiler specific libraries are not printed by default. To see those types as well, pass in -a.

The optional filter simply filters the prefix of types. This is primarily useful if you're only interested in types from a specific namespace. For instance, passing in ::boost:: will only print types defined in the boost namespace.

The -p option takes the profile output generated from access_profiler.

example output

struct ::libtorrent::i2p_connection [104 Bytes]
     : [shared_ptr<libtorrent::i2p_stream> : 16] m_sam_socket
    0:   [i2p_stream* : 8] px
     :   [shared_count : 8] pn
    8:     [sp_counted_base* : 8] pi_
     : [proxy_settings : 40] m_sam_router
     :   [basic_string<char> : 8] hostname
     :     [_Alloc_hider : 8] _M_dataplus
     :       [allocator<char> : 1] <base-class>
   16:         [new_allocator<char> : 1] <base-class>
   16:       [char* : 8] _M_p
   24:   [int : 4] port
   --- 4 Bytes padding ---
     :   [basic_string<char> : 8] username
     :     [_Alloc_hider : 8] _M_dataplus
     :       [allocator<char> : 1] <base-class>
   32:         [new_allocator<char> : 1] <base-class>
   32:       [char* : 8] _M_p
     :   [basic_string<char> : 8] password
     :     [_Alloc_hider : 8] _M_dataplus
     :       [allocator<char> : 1] <base-class>
   40:         [new_allocator<char> : 1] <base-class>
   40:       [char* : 8] _M_p
   48:   [enum proxy_type : 4] type
   52:   [bool : 1] proxy_hostnames
   53:   [bool : 1] proxy_peer_connections
   --- 2 Bytes padding ---
     : [basic_string<char> : 8] m_i2p_local_endpoint
     :   [_Alloc_hider : 8] _M_dataplus
     :     [allocator<char> : 1] <base-class>
   56:       [new_allocator<char> : 1] <base-class>
   56:     [char* : 8] _M_p
     : [basic_string<char> : 8] m_session_id
     :   [_Alloc_hider : 8] _M_dataplus
     :     [allocator<char> : 1] <base-class>
   64:       [new_allocator<char> : 1] <base-class>
   64:     [char* : 8] _M_p
     : ["list<std::pair<std::basic_string<char>, boost::function<void (const boost::system::error_code &, const char * : 16] m_name_lookup
     :   ["_List_base<std::pair<std::basic_string<char>, boost::function<void (const boost::system::error_code &, const char * : 16] <base-class>
     :     [_List_impl : 16] _M_impl
     :       ["allocator<std::_List_node<std::pair<std::basic_string<char>, boost::function<void (const boost::system::error_code &, const char * : 1] <base-class>
   72:         ["new_allocator<std::_List_node<std::pair<std::basic_string<char>, boost::function<void (const boost::system::error_code &, const char * : 1] <base-class>
     :       [_List_node_base : 16] _M_node
   72:         [_List_node_base* : 8] _M_next
   80:         [_List_node_base* : 8] _M_prev
   88: [enum state_t : 4] m_state
   --- 4 Bytes padding ---
   96: [io_service& : 8] m_io_service