Thank you @Werner for your time. But this method does not produce the desired result.
The `customize-image.sh` script is called from an environment with no development tools. I tried running `gcc` and got
The link you provided says "You can run additional commands to customize the created image." and it works successfully, but nothing more. That is, I can copy, delete files from the image, I can call `apt-get` to install packages, but I can't find the development tools to build packages there.
I assumed that I could compile and build the SWUpdate package from the environment where the Linux kernel and U-Boot are built. Is this how to do it?