where is the main source file to build the echo test in Linux userspace?

[jg-spitfire]

Hi, I am trying to run the openamp echo test from Linux userspace, my apps are running in the RPU(cortex r5 - baremetal) and APU(cortex A53 - Linux) in a Xilinx Ultrascale MPSoC, I already have the sources for the RPU but I need the sources for the APU, it seems that in this repo https://github.com/OpenAMP/open-amp/tree/main/apps/machine/zynqmp are some of the sources for the Linux side of the app (APU), but there is not a file which contains the main function for the app, where is located?

Xilinx provides a pre-built example for this test but I need the sources in order to modify it and fix some issues, thanks.