OpenVMS Calling Standard

This document defines the OpenVMS Calling Standard, outlining the requirements, mechanisms, and conventions for procedure-to-procedure calls within the OpenVMS interface. It applies to both Alpha and VAX environments, enabling 32-bit or 64-bit native user-mode procedures to operate correctly in multilanguage and multithreaded settings.

Key aspects covered include:

• Run-time data structures, constants, algorithms, conventions, methods, and functional interfaces.
• Specific conventions for OpenVMS VAX systems, detailing register and stack usage, calling sequences, argument list formats, and processor synchronization.
• Fundamental concepts and conventions for OpenVMS Alpha systems, including register usage, address representation, procedure types (stack, register, null frame), procedure call chains, transfer of control, and data passing mechanisms.
• Common specifications for both Alpha and VAX, such as argument-passing data types and argument descriptors.
• Condition and exception handling requirements, including condition values, handler options, and operations involving condition handlers.

The standard is primarily intended for implementers of compilers, debuggers, run-time tools, libraries, and base operating systems, but the information is relevant for all programmers dealing with procedure calls. It emphasizes performance, portability, efficiency, and consistency in intermodule interfaces.