Source code for Pilot-discovery Binary

Hi Team
I want to build https://github.com/istio/istio/blob/a4d901c1670e1cd79650fe58d43d2b93ac3474a0/pilot/docker/Dockerfile.pilot Pilot image
On-Line 18 https://github.com/istio/istio/blob/a4d901c1670e1cd79650fe58d43d2b93ac3474a0/pilot/docker/Dockerfile.pilot#L18 you are copying amd64/pilot-discovery binary to the image
Where is the source code for this binary pilot-discovery and how can we build this binary ?