About This Guide
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## About This Guide

This publication describes the assembly language supported by the IRIX operating system, its syntax rules, and how to write assembly programs. For information about assembling and linking an assembly language program, see the MIPSpro N32/64 Compiling and Performance Tuning Guide.

This book assumes that you are an experienced assembly language programmer. The assembler produces object modules from the assembly instructions that the C and Fortran compilers generate. It therefore lacks many of the functions normally present in an assembler. You should use the assembler only when you must:

- Maximize the efficiency of a routine, which might not be possible in C, Fortran, or another high-level language (for example, to write low-level I/O drivers).

- Access machine functions unavailable in high-level languages or satisfy special constraints such as restricted register usage.

- Change the operating system.

- Change the compiler system.

The assembler converts assembly language statements into machine code. In most assembly languages, each instruction corresponds to a single machine instruction; however, some assembly language instructions can generate several machine instructions. This feature results in assembly programs that can run without modification on future machines, which might have different machine instructions.

In this release, the assembler supports compilations in `-o32`, `-n32`, and `-64` mode. Some of the implications of these different data sizes are explained in this book. For more information, see the MIPSpro 64-Bit Porting and Transition Guide.

Many assembly language instructions have direct equivalents to machine instructions. For more information about the operations of a specific architecture, see the book that is appropriate for your hardware type.

## Related Publications

This manual is one of a set of manuals that describes the compiler. The complete set of manuals is as follows:

- MIPSpro 64-Bit Porting and Transition Guide

- MIPSpro N32/64 Compiling and Performance Tuning Guide

- MIPSpro N32 ABI Handbook

## Obtaining Publications

To obtain SGI documentation, go to the SGI Technical Publications Library at:

    http://docs.sgi.com.

## Conventions

The following conventions are used throughout this document:

Convention |  | Meaning
`command` |  | This fixed-space font denotes literal items such as commands, files, routines, path names, signals, messages, and programming language structures.
variable |  | Italic typeface denotes variable entries and words or concepts being defined.
`user input` |  | This bold, fixed-space font denotes literal items that the user enters in interactive sessions. (Output is shown in nonbold, fixed-space font.)
[ ] |  | Brackets enclose optional portions of a command or directive line.

## Reader Comments

If you have comments about the technical accuracy, content, or organization of this publication, contact SGI. Be sure to include the title and document number of the publication with your comments. (Online, the document number is located in the front matter of the publication. In printed publications, the document number is located at the bottom of each page.)

You can contact SGI in any of the following ways:

- Send e-mail to the following address:

  techpubs@sgi.com

- Use the Feedback option on the Technical Publications Library Web page:

  http://docs.sgi.com

- Contact your customer service representative and ask that an incident be filed in the SGI incident tracking system.

- Send mail to the following address:

  Technical Publications
  SGI
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- Send a fax to the attention of “Technical Publications” at +1 650 932 0801.

SGI values your comments and will respond to them promptly.

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New Features in This Manual |  | Chapter 1. Registers