This topic provides details on using the open-source GDB tool on a dev machine to debug sandboxed apps. This type of remote debugging is useful where resources are limited like in embedded apps.

The sample code uses an app named hw with one executable hw_exe and processes created in the same executable (hw_proc1, hw_proc2, etc.).

High-level steps to use GDB with a sandboxed app:

On the target device:

• Make sure the devMode app is installed and running
• Run the sandboxed app without the process you want to debug.
• Start gdbserver in the sanboxed app.
• Start the process in the sandboxed app with gdbserver.
• Remove gdb from the sandboxed app after you're finished debugging.

On your dev machine:

• Launch gdb from the apps make directory.
• Remote connect to the target and run gdb commands.

See basicTargetConfigIP if you need to setup your host/target communications.

Sample Code

The following simple app sample code is used in examples.

hw.adef

start: manual
 
executables:
{
    hw_exe = ( hw )
}
 
processes:
{
    run:
    {
        hw_proc1 = ( hw_exe )
        hw_proc2 = ( hw_exe )
        hw_proc3 = ( hw_exe )
        hw_proc4 = ( hw_exe )
    }
}

See Create Apps for more info.

.cdef

hw/Component.cdef

sources:
{
    hello.c
}
 
cflags:
{
    -g
}

See cflags for more info on cflags.

hello.c

hw/hello.c

#include "legato.h"
 
COMPONENT_INIT
{
    LE_INFO("HELLO WORLD.");
}

See Create Apps for more info.

Running GDB on your Target Device

Running the App without a Process

To use GDB, start the sandboxed app excluding the process being debugged:

On the target, run the app excluding the process being debugged, hw_proc3:

# app start hw --norun=hw_proc3

Start GDB on an App

On your dev machine, set up port forwarding from local host to the target. This bypasses the firewall on the target and allows GDB server to connect.

$ ssh -L 2000:localhost:2000 root@192.168.2.2

Warning

Do not end this session to the Target or the port forwarding will end. GDB won't be able to connect to the Target.

On the target, start gdbserver in the sandboxed /bin directory by running:

# gdbCfg <app name>

For Example:

# gdbCfg hw

Start the Process with GDB enabled

On the target, start gdbserver by starting the app with the arguments specified after -- (two dashes):

# app runProc <app name> --exe=/bin/gdbserver --localhost:2000 /bin/<app bin dir>

For Example:

# app runProc hw --exe=/bin/gdbserver -- localhost:2000 /bin/hw_exe

If started successfully, the following will be returned:

Process /bin/hw_exe created; pid = 9783
Listening on port 2000

Launch GDB on your Dev Machine

To start GDB on your Dev Machine:

• Launch gdb on the Dev Machine.
• Remote connect to the target and run regular gdb commands.

Launch gdb from Dev Machine

You need to run the commands from the directory where the hw app was made. The path _build_hw/wp85/app/hw/staging/read-only/bin/hw_exe is relative to the app directory; this build directory is generated when an app is made and the gdb commands must be run here.

In this example, we're running the gdb tool (arm-poky-linux-gnueabi-gdb) located in our target's toolchain path (/opt/swi/y17-ext/sysroots/x86_64-pokysdk-linux/usr/bin/arm-poky-linux-gnueabi for wp85). Use the findtoolchain command on your dev machine to determine the toolchain path.

Launch GDB from the toolchain using the following command (substitute your program and path for hw):

$ ~/LegatoApps/hw$ /opt/swi/y17-ext/sysroots/x86_64-pokysdk-linux/usr/bin/arm-poky-linux-gnueabi/arm-poky-linux-gnueabi-gdb _build_hw/wp85/app/hw/staging/read-only/bin/hw_exe

Remote Connect

After GDB is launched, use the target remote command to connect to the target:

$ (gdb) target remote localhost:2000

Note

If you get an error about connecting make sure you have a ssh -L (port forwarding) session open between the dev machine and target.

The target will display:

Remote debugging using localhost:2000

You can now run any of the standard gdb debugging commands on hw_exe.

Remove GDB from Sandbox

Once you've finished debugging, remove gdbserver from the sandbox /bin directory on the target:

# gdbCfg hw --reset

Refer to the many available open source resources if you need help using gdb.

Copyright (C) Sierra Wireless Inc.