Document revision date: 30 March 2001
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OpenVMS Calling Standard

OpenVMS Calling Standard

Order Number: AA--QSBBD--TE


April 2001

This standard defines the requirements, mechanisms, and conventions used in the OpenVMS interface that supports procedure-to-procedure calls for Alpha and VAX environments. The standard defines the run-time data structures, constants, algorithms, conventions, methods, and functional interfaces that enable a 32-bit or 64-bit native user-mode procedure to operate correctly in a multilanguage and multithreaded environment on Alpha and VAX processors.

Revision/Update Information: This manual supersedes the OpenVMS Calling Standard for OpenVMS Alpha Version 7.1 and OpenVMS VAX Version 7.1.

Software Version: OpenVMS Alpha Version 7.3 OpenVMS VAX Version 7.3



Compaq Computer Corporation Houston, Texas


© 2001 Compaq Computer Corporation

Compaq, VAX, VMS, and the Compaq logo Registered in U.S. Patent and Trademark Office.

OpenVMS is a trademark of Compaq Information Technologies Group, L.P. in the United States and other countries.

All other product names mentioned herein may be trademarks of their respective companies.

Confidential computer software. Valid license from Compaq required for possession, use, or copying. Consistent with FAR 12.211 and 12.212, Commercial Computer Software, Computer Software Documentation, and Technical Data for Commercial Items are licensed to the U.S. Government under vendor's standard commercial license.

Compaq shall not be liable for technical or editorial errors or omissions contained herein. The information in this document is provided "as is" without warranty of any kind and is subject to change without notice. The warranties for Compaq products are set forth in the express limited warranty statements accompanying such products. Nothing herein should be construed as constituting an additional warranty.

ZK5973

The Compaq OpenVMS documentation set is available on CD-ROM.

Contents Index


Preface

The OpenVMS Calling Standard defines the requirements, mechanisms, and conventions used in the OpenVMS interface that supports procedure-to-procedure calls for both Alpha and VAX environments. The standard defines the run-time data structures, constants, algorithms, conventions, methods, and functional interfaces that enable a native user-mode procedure to operate correctly in a multilanguage environment on Alpha and VAX systems. Properties of the run-time environment that must apply at various points during program execution are also defined.

The 32-bit user mode of the OpenVMS Alpha standard provides a high degree of compatibility with current programs written for the OpenVMS VAX environment.

The 64-bit user mode of the OpenVMS Alpha standard is a compatible superset of the OpenVMS Alpha 32-bit environment.

The interfaces, methods, and conventions specified in this manual are primarily intended for use by implementers of compilers, debuggers, and other run-time tools, run-time libraries, and base operating systems. These specifications may or may not be appropriate for use by higher level system software and applications.

This standard is under engineering change order (ECO) control. This manual includes all ECOs through ECO #48. ECOs are approved by Compaq's Calling Standard committee.

Intended Audience

This manual primarily defines requirements for compiler and debugger writers, but the information can apply to procedure calling for all programmers in various levels of programming.

Document Structure

This manual contains six chapters. Some chapters are restricted to either an Alpha or a VAX environment.

Chapter 1 provides an overview of the standard, defines goals, and defines terms used in the text.

Chapter 2 describes the primary conventions in calling a procedure in an OpenVMS VAX environment. It defines the VAX register usage and argument-passing list as well as vector and scalar processor synchronization.

Chapter 3 describes the fundamental concepts and conventions in calling a procedure in an OpenVMS Alpha environment. The chapter identifies the Alpha register usage and addressing, and focuses on aspects of the calling standard that pertain to procedure-to-procedure flow of control.

Chapter 4 defines the argument-passing data types used in calling a procedure for both OpenVMS Alpha and OpenVMS VAX environments.

Chapter 5 defines the argument descriptors used in calling a procedure for both OpenVMS Alpha and OpenVMS VAX environments.

Chapter 6 describes the OpenVMS condition- and exception-handling requirements for both OpenVMS Alpha and OpenVMS VAX environments.

Related Documents

The following manuals contain related information:

For additional information about Compaq OpenVMS products and services, access the Compaq website at the following location:


http://www.openvms.compaq.com 

Reader's Comments

Compaq welcomes your comments on this manual. Please send comments to either of the following addresses:
Internet openvmsdoc@compaq.com
Mail Compaq Computer Corporation
OSSG Documentation Group, ZKO3-4/U08
110 Spit Brook Rd.
Nashua, NH 03062-2698

How To Order Additional Documentation

Use the following World Wide Web address to order additional documentation:


http://www.openvms.compaq.com 

If you need help deciding which documentation best meets your needs, call 800-282-6672.

Conventions

The following conventions are used in this manual:
Ctrl/ x A sequence such as Ctrl/ x indicates that you must hold down the key labeled Ctrl while you press another key or a pointing device button.
PF1 x A sequence such as PF1 x indicates that you must first press and release the key labeled PF1 and then press and release another key or a pointing device button.
[Return] In examples, a key name enclosed in a box indicates that you press a key on the keyboard. (In text, a key name is not enclosed in a box.)

In the HTML version of this document, this convention appears as brackets, rather than a box.

... A horizontal ellipsis points in examples indicate one of the following possibilities:
  • Additional optional arguments in a statement have been omitted.
  • The preceding item or items can be repeated one or more times.
  • Additional parameters, values, or other information can be entered.
.
.
.
A vertical ellipsis points indicate the omission of items from a code example or command format; the items are omitted because they are not important to the topic being discussed.
( ) In command format descriptions, parentheses indicate that you must enclose choices in parentheses if you specify more than one.
[ ] In command format descriptions, brackets indicate optional choices. You can choose one or more items or no items. Do not type the brackets on the command line. However, you must include the brackets in the syntax for OpenVMS directory specifications and for a substring specification in an assignment statement.
{ } In command format descriptions, braces indicate required choices; you must choose at least one of the items listed. Do not type the braces on the command line.
bold text This typeface represents the introduction of a new term or the name of an argument, an attribute, or a reason.
italic text Italic text indicates important information, complete titles of manuals, or variables. Variables include information that varies in system output (Internal error number), in command lines (/PRODUCER= name), and in command parameters in text (where dd represents the predefined code for the device type).
UPPERCASE TEXT Uppercase text indicates a command, the name of a routine, the name of a file, or the abbreviation for a system privilege.
Monospace text Monospace type indicates code examples and interactive screen displays.

In the C programming language, monospace type in text identifies the following elements: keywords, the names of independently compiled external functions and files, syntax summaries, and references to variables or identifiers introduced in an example.

- A hyphen at the end of a command format description, command line, or code line indicates that the command or statement continues on the following line.
numbers All numbers in text are assumed to be decimal unless otherwise noted. Nondecimal radixes---binary, octal, or hexadecimal---are explicitly indicated.


Chapter 1
Introduction

This standard defines properties such as the run-time data structures, constants, algorithms, conventions, methods, and functional interfaces that enable a native user-mode procedure to operate correctly in a multilanguage and multithreaded environment on OpenVMS Alpha and OpenVMS VAX systems. These properties include the contents of key registers, format and contents of certain data structures, and actions that procedures must perform under certain circumstances.

This standard also defines properties of the run-time environment that must apply at various points during program execution. These properties vary in scope and applicability. Some properties apply at all points throughout the execution of standard-conforming user-mode code and must, therefore, be held constant at all times. Examples of such properties include those defined for the stack pointer and various properties of the call-chain navigation mechanism. Other properties apply only at certain points, such as call conventions that apply only at the point of transfer of control to another procedure.

Furthermore, some properties are optional depending on circumstances. For example, compilers are not obligated to follow the argument list conventions when a procedure and all of its callers are in the same module, have been analyzed by an interprocedural analyzer, or have private interfaces (such as language-support routines).

Note

In many cases, significant performance gains can be realized by selective use of nonstandard calls when the safety of such calls is known. Compiler or tools writers are encouraged to make full use of such optimizations.

The OpenVMS Alpha portion of this calling standard is intended to provide a calling standard that contains a high degree of compatibility with the OpenVMS VAX environment. Conventions that differ are, for the most part, those that are dictated by differences between the Alpha and VAX hardware architectures.

The procedure call mechanism depends on agreement between the calling and called procedures to interpret the argument list. The argument list does not fully describe itself. This standard requires language extensions to permit a calling program to generate some of the argument-passing mechanisms expected by called procedures.

This standard specifies the following attributes of the interfaces between modules:

1.1 Applicability

This standard defines the rules and conventions that govern the native user-mode run-time environment on Alpha and VAX processors. It is applicable to all products of Compaq Computer Corporation that execute in native user mode.

Uses of this standard include:

1.2 Architectural Level

This standard defines an implementation-level run-time software architecture for OpenVMS operating systems.

The interfaces, methods, and conventions specified in this document are primarily intended for use by implementers of compilers, debuggers, and other run-time tools, run-time libraries, and base operating systems. These specifications may or may not be appropriate for use by higher-level system software and applications.

Compilers and run-time libraries may provide additional support of these capabilities via interfaces that are more suited for compiler and application use. This specification neither prohibits nor requires such additional interfaces.

1.3 Goals

Generally, this calling standard promotes the highest degree of performance, portability, efficiency, and consistency in the interface between called procedures of a common OpenVMS environment. Specifically, the calling standard:

The OpenVMS Alpha portion of this standard:

The OpenVMS procedure calling mechanisms of this standard do not provide:

Note

1 The Compaq POSIX Threads Library was formerly known as DECthreads

1.4 Definitions

The following terms are used in this standard:


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