Cross Compile with Yocto SDK

Cross-compiling and remote debugging for Gumstix COMs right on your workstation is the desired method to do application development. This article describes how to obtain, install and use the cross development kit - Yocto SDK.

Get Yocto SDK with Gumstix sysroot

You can download the SDK from Gumstix website. It is built based on the gumstix-console-image. It contains the same tool-chains used to build the image.

We will create a directory called workspace where you will not only install the SDK, but also compile the example code in. Choose a convenient location for you.

$ mkdir workspace
$ cd workspace
$ wget http://gumstix-yocto.s3.amazonaws.com/sdk.sh

Pro Tip: You can run bitbake gumstix-console-image -c populate_sdk to create your own SDK.

Install the SDK

Within the workspace directory, let's install the SDK:

#Install it to `workspace/sdk`
$ ./sdk.sh

Enter target directory for SDK (default: /opt/poky/1.7.2): ~/home/workspace/sdk/

Setting up the environment

You will notice these files in the workspace/sdk directory:

* environment-setup-cortexa8hf-vfp-neon-poky-linux-gnueabi
* site-config-cortexa8hf-vfp-neon-poky-linux-gnueabi
* sysroots
* version-cortexa8hf-vfp-neon-poky-linux-gnueabi

The first file is the environment setup file which exports important paths and variables. And the sysroots directory contains the target and the host system root file systems.

Before we can use the SDK, you need to source the environment:

$ source sdk/environment-setup-cortexa8hf-vfp-neon-poky-linux-gnueabi

Compile Hello World

Let's create an empty file helloworld.c and paste the following in:

#include <stdio.h>
int main(void)
{
   printf ("Hello World!\n");
   return 0;
}

Now we can compile it:

$ make helloworld

The output of the above is:

arm-poky-linux-gnueabi-gcc  -march=armv7-a -mthumb-interwork -mfloat-abi=hard -mfpu=neon -mtune=cortex-a8
--sysroot=/opt/poky/1.7.2/sysroots/cortexa8hf-vfp-neon-poky-linux-gnueabi  -O2 -pipe -g -feliminate-unused
debug-types  -Wl,-O1 -Wl,--hash-style=gnu -Wl,--as-needed  helloworld.c   -o helloworld

The magical make expands to this command because it is using the SDK environment variables which you sourced earlier:

* CC="arm-poky-linux-gnueabi-gcc  -march=armv7-a -mthumb-interwork -mfloat-abi=hard -mfpu=neon -mtune=cortex-a8 
  --sysroot=$SDKTARGETSYSROOT"
* SDKTARGETSYSROOT=/home/workspace/sdk/sysroots/cortexa8hf-vfp-neon-poky-linux-gnueabi
* CFLAGS=" -O2 -pipe -g -feliminate-unused-debug-types"
* LDFLAGS="-Wl,-O1 -Wl,--hash-style=gnu -Wl,--as-needed"

You should notice the output binary.

$ ls
helloworld  helloworld.c

Start Remote Debug

We first need to install the GDB Server on the COM:

$ smart update
$ smart install packagegroup-core-tools-debug

Copy the binary over to your Gumstix COM:

$ scp helloworld [email protected]:/usr/bin/helloworld

Start the GDB server on your COM:

root@overo:~# gdbserver localhost:2345 /usr/bin/helloworld

Process /usr/bin/helloworld created; pid = 1896
Listening on port 2345

From your host machine (workstation), you can run cross-gdb:

$ arm-poky-linux-gnueabi-gdb helloworld

If arm-poky-linux-genuabi-gdb is not found, be sure to source the SDK environment file again.

Connect to the Remote GDB Server

Now you can connect GDB to the GDB Server running on the COM. Type the following command from GDB using your COM's IP address:

# Substitute the ip address '192.168.1.125' with your COM's address
(gdb) target remote 192.168.1.125:2345

Use the Remote Debugger

We can put a breakpoint at main():

(gdb) break main
Breakpoint 1 at 0x82f4: file helloworld.c, line 4.

It will then stop at main():

(gdb) continue
continue
Continuing.

Breakpoint 1, main () at helloworld.c:4
4          printf ("Hello World!\n");
(gdb) 

References

• Yocto Developer's Manual - Debugging With the GNU Project Debugger (GDB) Remotely