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x86 Assembly Language Reference Manual

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Updated: March 2018

2.1 Assembly Language Lexical Conventions

This section discusses the lexical conventions of the Oracle Solaris x86 assembly language.

2.1.1 Assembly Language Statements

An x86 assembly language program consists of one or more files containing statements. A statement consists of tokens separated by whitespace and terminated by either a newline character (ASCII 0x0A) or a semicolon (;) (ASCII 0x3B). Whitespace consists of spaces (ASCII 0x20), tabs (ASCII 0x09), and form feeds (ASCII 0x0B) that are not contained in a string or comment. More than one statement can be placed on a single input line provided that each statement is terminated by a semicolon. A statement can consist of a comment. Empty statements, consisting only of whitespace, are allowed. Assembly Language Comments

A comment can be appended to a statement. The comment consists of the slash character (/) (ASCII 0x2F) followed by the text of the comment. The comment is terminated by the newline that terminates the statement. Assembly Language Labels

A label can be placed at the beginning of a statement. During assembly, the label is assigned the current value of the active location counter and serves as an instruction operand. There are two types of labels: symbolic and numeric.

Assembly Language Symbolic Labels

A symbolic label consists of an identifier (or symbol) followed by a colon (:) (ASCII 0x3A). Symbolic labels must be defined only once. Symbolic labels have global scope and appear in the object file's symbol table.

Symbolic labels with identifiers beginning with a period (.) (ASCII 0x2E) are considered to have local scope and are not included in the object file's symbol table.

Assembly Language Numeric Labels

A numeric label consists of a unsigned decimal int32 value followed by a colon (:). Numeric labels are used only for local reference and are not included in the object file's symbol table. Numeric labels have limited scope and can be redefined repeatedly.

When a numeric label is used as a reference (as an instruction operand, for example), the suffixes b ("backward") or f ("forward") should be added to the numeric label. For numeric label N, the reference Nb refers to the nearest label N defined before the reference, and the reference Nf refers to the nearest label N defined after the reference. The following example illustrates the use of numeric labels:

1:          / define numeric label "1"
one:        / define symbolic label "one"

/ ... assembler code ...

jmp   1f    / jump to first numeric label "1" defined
            / after this instruction
            / (this reference is equivalent to label "two")

jmp   1b    / jump to last numeric label "1" defined
            / before this instruction
            / (this reference is equivalent to label "one")

1:          / redefine label "1"
two:        / define symbolic label "two"

jmp   1b    / jump to last numeric label "1" defined
            / before this instruction
            / (this reference is equivalent to label "two")

2.1.2 Assembly Language Tokens

    There are five classes of tokens:

  • Identifiers (symbols)

  • Keywords

  • Numerical constants

  • String Constants

  • Operators Assembly Language Identifiers

An identifier is an arbitrarily-long sequence of letters and digits. The first character must be a letter; the underscore (_) (ASCII 0x5F) and the period (.) (ASCII 0x2E) are considered to be letters. Case is significant: uppercase and lowercase letters are different. Assembly Language Keywords

Keywords such as x86 instruction mnemonics ("opcodes") and assembler directives are reserved for the assembler and should not be used as identifiers. See Instruction Set Mapping for a list of the Oracle Solaris x86 mnemonics. See Assembler Directives for the list of as assembler directives. Numerical Constants

Numbers in the x86 architecture can be integers or floating point. Integers can be signed or unsigned, with signed integers represented in two's complement representation. Floating-point numbers can be: single-precision floating-point; double-precision floating-point; and double-extended precision floating-point.

Integer Constants

    Integers can be expressed in several bases:

  • Decimal. Decimal integers begin with a non-zero digit followed by zero or more decimal digits (0-9).

  • Binary. Binary integers begin with "0b" or "S0B" followed by zero or more binary digits (0, 1).

  • Octal. Octal integers begin with zero (0) followed by zero or more octal digits (0-7).

  • Hexadecimal. Hexadecimal integers begin with "0x" or "0X" followed by one or more hexadecimal digits (0-9, A–F). Hexadecimal digits can be either uppercase or lowercase.

Assembly Language Floating Point Constants

    Floating point constants have the following format:

  • Sign (optional) – Either plus (+) or minus (–)

  • Integer (optional) – Zero or more decimal digits (0–9)

  • Fraction (optional) – Decimal point (.) followed by zero or more decimal digits

  • Exponent (optional) – The letter "e" or "E", followed by an optional sign (plus or minus), followed by one or more decimal digits (0-9)

A valid floating point constant must have either an integer part or a fractional part. Assembly Language String Constants

A string constant consists of a sequence of characters enclosed in double quotes ( ") (ASCII 0x22). To include a double-quote character ("), single-quote character ('), or backslash character (\) within a string, precede the character with a backslash (\) (ASCII 0x5C). A character can be expressed in a string as its ASCII value in octal preceded by a backslash (for example, the letter "J" could be expressed as "\112"). The assembler accepts the following escape sequences in strings:

Escape Sequence
Character Name
ASCII Value (hex)
carriage return
horizontal tab
form feed
vertical tab
0B Assembly Language Operators

The assembler supports the following operators for use in expressions. Operators have no assigned precedence. Expressions can be grouped in square brackets ([]) to establish precedence.










Bitwise logical AND


Bitwise logical OR


Shift right


Shift left




Bitwise logical AND NOT


Bitwise logical XOR

Note - The asterisk (*), slash (/), and percent sign (%) characters are overloaded. When used as operators in an expression, these characters must be preceded by the backslash character (\).