This topic provides details on using the open-source GDB tool on a host PC to debug a sandboxed app on a target device. This type of remote debugging is useful where resources are limited like embedded apps. The sample code in this topic has an app named hw with one executable hw_exe and a few processes created in the same executable (hw_proc1, hw_proc2, etc.).

These are the high-level steps to use GDB with a sandboxed app.

On the target device:

Run the sandboxed app without the process that's being debugged.
Make gdbserver available in the sanboxed app.
Run the sandboxed app with gdbserver with the process being debugged.
Remove gdb from the sandboxed app after you're finished debugging.

On the host PC:

Launch gdbserver on the host PC.
Remote connect to the target and run regular gdb commands.

See Configure IP Address if you need to setup your host/target communications.

Sample Code

The following simple app sample code is used in this topic's 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.

Run without Process

To use GDB, you 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

Make GDB Available

On the target, make gdbserver available in the sandboxed /bin directory:

gdbCfg hw

Run with Process

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

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

It will return this:
Process /bin/hw_exe created; pid = 9783
Listening on port 2000

Launch GDB on Host

You need to complete these steps on the host PC:

Launch gdb on the host PC.
Remote connect to the target and run regular gdb commands.

You need to run the commands from the directory where the hw app was made.

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 the host PC to determine your toolchain path. 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.

~/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 192.168.2.2:2000

Remote debugging from host 192.168.2.3 will display on the target.

Note: 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:

gdbCfg hw --reset

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