Chapter 4.

Syntax

This chapter describes the machine independent syntax allowed in a source file.

as

syntax is similar

to what many other assemblers use; it is inspired by the BSD 4.2 assembler, except that

as

does not

assemble Vax bit fields.

4.1. Preprocessing

The

as

internal preprocessor:

adjusts and removes extra whitespace. It leaves one space or tab before the keywords on a line, and

turns any other whitespace on the line into a single space.

removes all comments, replacing them with a single space, or an appropriate number of newlines.

converts character constants into the appropriate numeric values.

It does not do macro processing, include file handling, or anything else you may get from your C

compiler's preprocessor. You can do include file processing with the

.include

directive (Section 8.47

.include "file"

). You can use the gnu C compiler driver to get other "CPP" style preprocessing

by giving the input file a

.S

suffix. .

Excess whitespace, comments, and character constants cannot be used in the portions of the input text

that are not preprocessed.

If the first line of an input file is

#NO_APP

or if you use the

 f

option, whitespace and comments are

not removed from the input file. Within an input file, you can ask for whitespace and comment removal

in specific portions of the by putting a line that says

#APP

before the text that may contain whitespace

or comments, and putting a line that says

#NO_APP

after this text. This feature is mainly intend to

support

asm

statements in compilers whose output is otherwise free of comments and whitespace.

4.2. Whitespace

Whitespace is one or more blanks or tabs, in any order. Whitespace is used to separate symbols, and to

make programs neater for people to read. Unless within character constants (Section 4.6.1 Character

Constants), any whitespace means the same as exactly one space.

4.3. Comments

There are two ways of rendering comments to

as

. In both cases the comment is equivalent to one

space.

Anything from

/*

through the next

*/

is a comment. This means you may not nest these comments.

/*

The only way to include a newline ('\n') in a comment

is to use this sort of comment.

*/

/* This sort of comment does not nest. */