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Volume 3: General-Purpose and System Instructions - Stanford ...

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24594 Rev. 3.10 February 2005 AMD64 TechnologyAppendix AOpcode <strong>and</strong> Oper<strong>and</strong> EncodingsA.1 Opcode-Syntax NotationThis section specifies the hexadecimal <strong>and</strong>/or binary encodingsfor the opcodes <strong>and</strong> the implicit oper<strong>and</strong> references used in theAMD64 instruction set. For an overview of the instructionformats to which these encodings apply, see Chapter 1,“Instruction Formats.”The following notation is used in this section to specify opcodes<strong>and</strong> their oper<strong>and</strong>s:ACDEFGIJMOPPRQFar pointer is encoded in the instruction.Control register specified by the ModRM reg field.Debug register specified by the ModRM reg field.<strong>General</strong> purpose register or memory oper<strong>and</strong> specified bythe ModRM byte. Memory addresses can be computedfrom a segment register, SIB byte, <strong>and</strong>/or displacement.rFLAGS register.<strong>General</strong> purpose register specified by the ModRM regfield.Immediate value.The instruction includes a relative offset that is added tothe rIP.A memory oper<strong>and</strong> specified by the ModRM byte.The offset of an oper<strong>and</strong> is encoded in the instruction.There is no ModRM byte in the instruction. Complexaddressing using the SIB byte cannot be done.64-bit MMX register specified by the ModRM reg field.64-bit MMX register specified by the ModRM r/m field.The ModRM mod field must be 11b.64-bit MMX-register or memory oper<strong>and</strong> specified by theModRM byte. Memory addresses can be computed from asegment register, SIB byte, <strong>and</strong>/or displacement.Appendix A: Opcode <strong>and</strong> Oper<strong>and</strong> Encodings 375

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