Reference Guide

16 Chapter 1

Introduction to PA-RISC Assembly Language

Assembler Features

• Expressions. Arithmetic expressions can be formed from symbolic

addresses and constants, integer constants, and arithmetic operators.

Expressions involving only symbolic and integer constants, or the

difference between two relocatable symbols, deﬁned in the current

module, are called absolute expressions. They can be used wherever

an integer constant can be used. Expressions involving the sum or

difference of a symbolic address and an absolute expression are called

relocatable expressions or address expressions. The constant part of

an expression, the part that does not refer to relocatable expressions,

can use parenthesized subexpressions to alter operator precedence.

• Storage Allocation. In addition to encoding machine language

instructions symbolically, storage may be initialized to constant

values or simply reserved. Symbolic addresses and labels can be

associated with these memory locations.

• Symbol Scope. When two or more object ﬁles are to be combined by

the linker, certain symbolic addresses can be deﬁned in one module

and used in another. Such symbols must be exported from the deﬁning

module and imported into the using module. In the deﬁning module,

the symbol has universal scope, while in the using module, the symbol

is unsatisﬁed. Other symbols declared in the source program that are

not exported have local scope.

• Subspaces and Location Counters. You can organize code and

data into separate subspaces, and into separate location counters

within each subspace. The programmer can move among the

subspaces and location counters, while the Assembler changes the

code and data into the correct order. In 64-bit mode, however, the

Executable and Linking Format (ELF) uses segments and sections

rather than spaces and subspaces.

• Macro Processing. A macro is a user-deﬁned word, which is

replaced by a sequence of instructions. Including a macro in a source

program causes the sequence of instructions to be inserted into the

program wherever the macro appears.