GDB Debugging Setup

This guide describes how to set up the environment to debug webOS Open Source Edition (OSE) with GDB.

Prerequisites

Before you begin setting up the environment for GDB debugging, you must:

• Build the webOS OSE image as webos-image-devel. For more information, see Building webOS OSE.
• Flash the built image to a microSD card and insert the microSD card in the target device. For more information, see Flashing webOS OSE.

Booting up the Target

First, boot up the target device and make sure that processes run normally.

Downloading and Decompressing dbg Package

Even if the image has been built as webos-image-devel, it does not contain symbol or source code of each module that will be used for debugging. You must download the dbg package (.ipk) and decompress the package.

In this guide, we will use a process called event-monitor as an example. The target device is Raspberry Pi 4.

1. Copy the dbg package containing debug symbol of event-monitor, located under BUILD directory, to the target device.

   $ cd ./BUILD/work/raspberrypi4-webos-linux-gnueabi/event-monitor/1.1.0-2-r2/deploy-ipks/raspberrypi4/
   $ ls
   event-monitor_1.1.0-2-r2_raspberrypi4.ipk
   event-monitor-dbg_1.1.0-2-r2_raspberrypi4.ipk
   ...
   $ scp event-monitor-dbg_1.1.0-2-r2_raspberrypi4.ipk root@[DEVICE_IP]:/sysroot/home/root/
   

2. On the target device, decompress the dbg package.

   root@raspberrypi4:/sysroot/home/root# ls
   event-monitor-dbg_1.1.0-2-r2_raspberrypi4.ipk
   root@raspberrypi4:/sysroot/home/root# opkg install event-monitor-dbg_1.1.0-2-r2_raspberrypi4.ipk --nodeps
   

3. After decompressing the dbg package, you can find the binary including debug symbols and the source code.

   root@raspberrypi4:/sysroot/home/root# cd /
   root@raspberrypi4:/# find usr
   ...
   usr/sbin/.debug/event-monitor
   ...
   usr/src/debug/event-monitor/1.1.0-2-r2/git/src/service/main.cpp
   

Running GDB

1. Run GDB by attaching to the running process.

   root@raspberrypi4:/# pidof event-monitor
   1404
   root@raspberrypi4:/# gdb /usr/sbin/.debug/event-monitor 1404
   GNU gdb (gdb) 8.2
   ...
   ---Type <return> to continue, or q <return> to quit---
   0x76c85c0c in poll () from /lib/libc.so.6
   

2. Once attached, you can look up the thread in use and print out the call stack.

   (gdb) info threads
   Id Target Id Frame
   * 1  Thread 0xb6f62ea0 (LWP 1404) "event-monitor" __libc_do_syscall () at libc-do-syscall.S:48
   

   (gdb) bt
   #0  __libc_do_syscall () at libc-do-syscall.S:48
   #1  0xb6c5933e in __GI___poll (fds=0x2203d88, nfds=5, timeout=-1)
   at ../sysdeps/unix/sysv/linux/poll.c:29
   #2  0xb6ea789c in ?? () from /usr/lib/libglib-2.0.so.0
   Backtrace stopped: previous frame identical to this frame (corrupt stack?)
   

3. By specifying the location of source code, you become fully prepared to debug webOS OSE with GDB.

   (gdb) dir /
   Source directories searched: /:$cdir:$cwd