OpenVMS

This document details the calling standard for OpenVMS on VAX, Alpha, and Itanium (I64) architectures. It covers register usage, stack structure, parameter passing mechanisms (immediate value, reference, and descriptor), function return conventions, and condition handling. It also provides specific conventions for each architecture, including stack unwinding and exception handling on I64 systems, and signature information for interoperability between native and translated images. The standard is intended for compiler and debugger writers and provides the foundational architecture for procedure calls in OpenVMS environments.