Syntax Notation

In the descriptions of assembly language syntax in this chapter:

• Brackets ([ ]) enclose optional items.
• Asterisks (*) indicate items to be repeated zero or more times.
• Braces ({ }) enclose alternate item choices, which are separated from each other by vertical bars (|).
• Wherever blanks are allowed, arbitrary numbers of blanks and horizontal tabs may be used. Newline characters are not allowed in place of blanks.

Assembler File Syntax

The syntax of assembly language files is:

[line]*

Lines Syntax

The syntax of assembly language lines is:

[statement [ ; statement]*] [!comment]

Statement Syntax

The syntax of an assembly language statement is:

[label:] [instruction]

where:

label

   is a symbol name.

instruction

is an encoded pseudo-op, synthetic instruction, or instruction.

Lexical Features

This section describes the lexical features of the assembler syntax.

Case Distinction

Uppercase and lowercase letters are distinct everywhere except in the names of special symbols. Special symbol names have no case distinction.

Comments

A comment is preceded by an exclamation mark character (!); the exclamation mark character and all following characters up to the end of the line are ignored. C language-style comments (''/*...*/'') are also permitted and may span multiple lines.

Labels

A label is either a symbol or a single decimal digit n (0...9). A label is immediately followed by a colon ( : ).

Numeric labels may be defined repeatedly in an assembly file; normal symbolic labels may be defined only once.

A numeric label n is referenced after its definition (backward reference) as nb, and before its definition (forward reference) as nf.

Numbers

Decimal, hexadecimal, and octal numeric constants are recognized and are written as in the C language. However, integer suffixes (such as L) are not recognized.

For floating-point pseudo-operations, floating-point constants are written with 0r or 0R (where r or R means REAL) followed by a string acceptable to atof(3); that is, an optional sign followed by a non-empty string of digits with optional decimal point and optional exponent.

The special names 0rnan and 0rinf represent the special floating-point values Not-A-Number (NaN) and INFinity. Negative Not-A-Number and Negative INFinity are specified as 0r-nan and 0r-inf.

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Note - The names of these floating-point constants begin with the digit zero, not the letter "O."

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Strings

A string is a sequence of characters quoted with either double-quote mark (") or single-quote mark (') characters. The sequence must not include a newline character. When used in an expression, the numeric value of a string is the numeric value of the ASCII representation of its first character.

The suggested style is to use single quote mark characters for the ASCII value of a single character, and double quote mark characters for quoted-string operands such as used by pseudo-ops. An example of assembly code in the suggested style is:

add %g1,'a'-'A',%g1 ! g1 + ('a' - 'A') --> g1

The escape codes described in Table 2-1, derived from ANSI C, are recognized in strings.

Table 2-1

Escape Code	Description
\a	Alert
\b	Backspace
\f	Form feed
\n	Newline (line feed)
\r	Carriage return
\t	Horizontal tab
\v	Vertical tab
\nnn	Octal value nnn
\xnn...	Hexadecimal value nn...

Symbol Names

The syntax for a symbol name is:

{ letter | _ | $ | . } { letter | _ | $ | . | digit }*

In the above syntax:

• Uppercase and lowercase letters are distinct; the underscore ( _ ), dollar sign ($), and dot ( . ) are treated as alphabetic characters.
• Symbol names that begin with a dot ( . ) are assumed to be local symbols. To simplify debugging, avoid using this type of symbol name in hand-coded assembly language routines.
• The symbol dot ( . ) is predefined and always refers to the address of the beginning of the current assembly language statement.
• External variable names beginning with the underscore character are reserved by the ANSI C Standard. Do not begin these names with the underscore; otherwise, the program will not conform to ANSI C and unpredictable behavior may result.

Special Symbols - Registers

Special symbol names begin with a percentage sign (%) to avoid conflict with user symbols. Table 2-2 lists these special symbol names.

Table 2-2

Symbol Object	Name	Comment
General-purpose registers General-purpose global registers General-purpose out registers General-purpose local registers General-purpose in registers	%r0 ... %r31 %g0 ... %g7 %o0 ... %o7 %l0 ... %l7 %i0 ... %i7	Same as %r0 ... %r7 Same as %r8 ... %r15 Same as %r16 ... %r23 Same as %r24 ... %r31
Stack-pointer register Frame-pointer register	%sp %fp	(%sp = %o6 = %r14) (%fp = %i6 = %r30)
Floating-point registers Floating-point status register Front of floating-point queue Coprocessor registers Coprocessor status register Coprocessor queue	%f0 ... %f31 %fsr %fq %c0 ... %c31 %csr %cq
Program status register Trap vector base address register Window invalid mask Y register	%psr %tbr %wim %y

Table 2-2 (Continued)

Symbol Object	Name	Comment
Unary operators	%lo	Extracts least significant
	%hi	10 bits Extracts most significant
	%r_disp32	22 bits Used only in Sun
	%r_plt32	compiler-generated code. Used only in Sun compiler-generated code.
Ancillary state registers	%asr1 ... %asr31

There is no case distinction in special symbols; for example,

%PSR

is equivalent to

%psr

The suggested style is to use lowercase letters.

The lack of case distinction allows for the use of non-recursive preprocessor substitutions, for example:

#define psr %PSR

The special symbols %hi and %lo are true unary operators which can be used in any expression and, as other unary operators, have higher precedence than binary operations. For example:

%hi a+b = (%hi a)+b %lo a+b = (%lo a)+b

To avoid ambiguity, enclose operands of the %hi or %lo operators in parentheses. For example:

%hi(a) + b

Operators and Expressions

The operators described in Table 2-3 are recognized in constant expressions. Table 2-3

Operators Recognized in Constant Expressions

Binary	Operators	Unary	Operators
+	Integer addition	+	(No effect)
-	Integer subtraction	-	2's Complement
*	Integer multiplication	~	1's Complement
/	Integer division	%lo	Extract least significant 10 bits
%	Modulo	%hi	Extract most significant 22 bits
^	Exclusive OR	%r_disp32	Used in Sun compiler-generated code only to instruct the assembler to generate specific relocation information for the given expression.
<<	Left shift	%r_plt32	Used in Sun compiler-generated code only to instruct the assembler to generate specific relocation information for the given expression.
>>	Right shift

Table 2-3 (Continued)

Binary	Operators	Unary	Operators
&	Bitwise AND
|	Bitwise OR

Since these operators have the same precedence as in the C language, put expressions in parentheses to avoid ambiguity.

To avoid confusion with register names or with the %hi,%lo, %r_disp32, or %r_plt32 operators, the modulo operator % must not be immediately followed by a letter or digit. The modulo operator is typically followed by a space or left parenthesis character.

Assembler Error Messages

Messages generated by the assembler are generally self-explanatory and give sufficient information to allow correction of a problem.

Certain conditions will cause the assembler to issue warnings associated with delay slots following Control Transfer Instructions (CTI). These warnings are:

• Set synthetic instructions in delay slots
• Labels in delay slots
• Segments that end in control transfer instructions

These warnings point to places where a problem could exist. If you have intentionally written code this way, you can insert an .empty pseudo-operation immediately after the control transfer instruction.

The .empty pseudo-operation in a delay slot tells the assembler that the delay slot can be empty or can contain whatever follows because you have verified that either the code is correct or the content of the delay slot does not matter.