x86 Assembly Language Reference Manual

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Updated: December 2014

2.2.1 Instructions

An instruction is a statement that is executed at runtime. An x86 instruction statement can consist of four parts:

  • Label (optional)

  • Instruction (required)

  • Operands (instruction specific)

  • Comment (optional)

See Statements for the description of labels and comments.

The terms instruction and mnemonic are used interchangeably in this document to refer to the names of x86 instructions. Although the term opcode is sometimes used as a synonym for instruction, this document reserves the term opcode for the hexadecimal representation of the instruction value.

For most instructions, the Oracle Solaris x86 assembler mnemonics are the same as the Intel or AMD mnemonics. However, the Oracle Solaris x86 mnemonics might appear to be different because the Oracle Solaris mnemonics are suffixed with a one-character modifier that specifies the size of the instruction operands. That is, the Oracle Solaris assembler derives its operand type information from the instruction name and the suffix. If a mnemonic is specified with no type suffix, the operand type defaults to long. Possible operand types and their instruction suffixes are:


Byte (8–bit)


Word (16–bit)


Long (32–bit) (default)


Quadword (64–bit)

The assembler recognizes the following suffixes for x87 floating-point instructions:

[no suffix]

Instruction operands are registers only

l (“long”)

Instruction operands are 64–bit

s (“short”)

Instruction operands are 32–bit

See Chapter 3, Instruction Set Mapping for a mapping between Oracle Solaris x86 assembly language mnemonics and the equivalent Intel or AMD mnemonics.