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+.. _gdb_examples:
+
+.. toctree::
+
+GDB Examples
+===============
+
+In this section we have a few useful gdb commands.
+
+Starting GDB
+----------------------------
+
+Once at the gdb prompt VPP can be started with the following:
+
+.. code-block:: console
+
+ (gdb) run -c /etc/vpp/startup.conf
+ Starting program: /scratch/vpp-master/build-root/install-vpp_debug-native/vpp/bin/vpp -c /etc/vpp/startup.conf
+ [Thread debugging using libthread_db enabled]
+ Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
+ vlib_plugin_early_init:361: plugin path /scratch/vpp-master/build-root/install-vpp_debug-native/vpp/lib/vpp_plugins:/scratch/vpp-master/build-root/install-vpp_debug-native/vpp/lib64/vpp_plugins
+ ....
+
+Backtrace
+----------------------------
+
+If you encounter issues when running VPP, such as VPP terminating due to a segfault
+or abort signal, you can run the VPP debug binary and then execute **backtrace** or **bt**.
+
+.. code-block:: console
+
+ (gdb) bt
+ #0 ip4_icmp_input (vm=0x7ffff7b89a40 <vlib_global_main>, node=0x7fffb6bb6900, frame=0x7fffb6725ac0) at /scratch/vpp-master/build-data/../src/vnet/ip/icmp4.c:187
+ #1 0x00007ffff78da4be in dispatch_node (vm=0x7ffff7b89a40 <vlib_global_main>, node=0x7fffb6bb 6900, type=VLIB_NODE_TYPE_INTERNAL, dispatch_state=VLIB_NODE_STATE_POLLING, frame=0x7fffb6725ac0, last_time_stamp=10581236529 65565) at /scratch/vpp-master/build-data/../src/vlib/main.c:988
+ #2 0x00007ffff78daa77 in dispatch_pending_node (vm=0x7ffff7b89a40 <vlib_global_main>, pending_f rame_index=6, last_time_stamp=1058123652965565) at /scratch/vpp-master/build-data/../src/vlib/main.c:1138
+ ....
+
+Get to the GDB prompt
+---------------------------------------
+
+When running VPP is running get to the command prompt with CTRL-c.
+
+Breakpoints
+---------------------------------------
+
+When at the GDB prompt set a breakpoint like so:
+
+.. code-block:: console
+
+ (gdb) break ip4_icmp_input
+ Breakpoint 4 at 0x7ffff6b9c00b: file /scratch/vpp-master/build-data/../src/vnet/ip/icmp4.c, line 142.
+
+List the breakpoints already set:
+
+.. code-block:: console
+
+ (gdb) i b
+ Num Type Disp Enb Address What
+ 1 breakpoint keep y 0x00007ffff6b9c00b in ip4_icmp_input at /scratch/vpp-master/build-data/../src/vnet/ip/icmp4.c:142
+ breakpoint already hit 3 times
+ 2 breakpoint keep y 0x00007ffff6b9c00b in ip4_icmp_input at /scratch/vpp-master/build-data/../src/vnet/ip/icmp4.c:142
+ 3 breakpoint keep y 0x00007ffff640f646 in tw_timer_expire_timers_internal_1t_3w_1024sl_ov
+ at /scratch/vpp-master/build-data/../src/vppinfra/tw_timer_template.c:775
+
+Delete a breakpoint:
+
+.. code-block:: console
+
+ (gdb) del 2
+ (gdb) i b
+ Num Type Disp Enb Address What
+ 1 breakpoint keep y 0x00007ffff6b9c00b in ip4_icmp_input at /scratch/vpp-master/build-data/../src/vnet/ip/icmp4.c:142
+ breakpoint already hit 3 times
+ 3 breakpoint keep y 0x00007ffff640f646 in tw_timer_expire_timers_internal_1t_3w_1024sl_ov
+ at /scratch/vpp-master/build-data/../src/vppinfra/tw_timer_template.c:775
+
+Step/Next/List
+---------------------------------------
+
+Step through the code using (s)tep into, (n)ext, and list some lines before and after where you are with list.
+
+.. code-block:: console
+
+ Thread 1 "vpp_main" hit Breakpoint 1, ip4_icmp_input (vm=0x7ffff7b89a40 <vlib_global_main>, node=0x7fffb6bb6900, frame=0x7fffb6709480)
+ at /scratch/jdenisco/vpp-master/build-data/../src/vnet/ip/icmp4.c:142
+ 142 {
+ (gdb) n
+ 143 icmp4_main_t *im = &icmp4_main;
+ (
+ (gdb) list
+ 202 vlib_put_next_frame (vm, node, next, n_left_to_next);
+ 203 }
+ 204
+ 205 return frame->n_vectors;
+ 206 }
+ 207
+ 208 /* *INDENT-OFF* */
+ 209 VLIB_REGISTER_NODE (ip4_icmp_input_node,static) = {
+ 210 .function = ip4_icmp_input,
+ 211 .name = "ip4-icmp-input",
+
+Examining Data and packets
+-----------------------------------------------
+
+To look at data and packets use e(x)amine or (p)rint.
+
+
+For example in this code look at the ip packet:
+
+.. code-block:: console
+
+ (gdb) p/x *ip0
+ $3 = {{ip_version_and_header_length = 0x45, tos = 0x0, length = 0x5400,
+ fragment_id = 0x7049, flags_and_fragment_offset = 0x40, ttl = 0x40, protocol = 0x1,
+ checksum = 0x2ddd, {{src_address = {data = {0xa, 0x0, 0x0, 0x2},
+ data_u32 = 0x200000a, as_u8 = {0xa, 0x0, 0x0, 0x2}, as_u16 = {0xa, 0x200},
+ as_u32 = 0x200000a}, dst_address = {data = {0xa, 0x0, 0x0, 0xa}, data_u32 = 0xa00000a,
+ as_u8 = {0xa, 0x0, 0x0, 0xa}, as_u16 = {0xa, 0xa00}, as_u32 = 0xa00000a}},
+ address_pair = {src = {data = {0xa, 0x0, 0x0, 0x2}, data_u32 = 0x200000a,
+ as_u8 = {0xa, 0x0, 0x0, 0x2}, as_u16 = {0xa, 0x200}, as_u32 = 0x200000a},
+ dst = {data = {0xa, 0x0, 0x0, 0xa}, data_u32 = 0xa00000a, as_u8 = {0xa, 0x0, 0x0, 0xa},
+ as_u16 = {0xa, 0xa00}, as_u32 = 0xa00000a}}}}, {checksum_data_64 =
+ {0x40704954000045, 0x200000a2ddd0140}, checksum_data_64_32 = {0xa00000a}},
+ {checksum_data_32 = {0x54000045, 0x407049, 0x2ddd0140, 0x200000a, 0xa00000a}}}
+
+Then the icmp header
+
+.. code-block:: console
+
+ (gdb) p/x *icmp0
+ $4 = {type = 0x8, code = 0x0, checksum = 0xf148}
+
+Then look at the actual bytes:
+
+.. code-block:: console
+
+ (gdb) x/50w ip0
+ 0x7fde9953510e: 0x54000045 0x00407049 0x2ddd0140 0x0200000a
+ 0x7fde9953511e: 0x0a00000a 0xf1480008 0x03000554 0x5b6b2e8a
+ 0x7fde9953512e: 0x00000000 0x000ca99a 0x00000000 0x13121110
+ 0x7fde9953513e: 0x17161514 0x1b1a1918 0x1f1e1d1c 0x23222120