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

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24594 Rev. 3.10 February 2005 AMD64 TechnologyTable A-13.ModRM Memory References, 16-Bit Addressing (continued)AL/AX/EAX/MMX0/XMM0Effective Address 1ModRMmodField(binary)ModRM reg Field 2/0 /1 /2 /3 /4 /5 /6 /7Complete ModRM Byte (hex)C0 C8 D0 D8 E0 E8 F0 F8 000CL/CX/ECX/MMX1/XMM1 C1 C9 D1 D9 E1 E9 F1 F9 001DL/DX/EDX/MMX2/XMM2 C2 CA D2 DA E2 EA F2 FA 010BL/BX/EBX/MMX3/XMM3 C3 CB D3 DB E3 EB F3 FB 01111AH/SP/ESP/MMX4/XMM4 C4 CC D4 DC E4 EC F4 FC 100CH/BP/EBP/MMX5/XMM5 C5 CD D5 DD E5 ED F5 FD 101DH/SI/ESI/MMX6/XMM6 C6 CE D6 DE E6 EE F6 FE 110BH/DI/EDI/MMX7/XMM7 C7 CF D7 DF E7 EF F7 FF 111Note:1. In these combinations, “disp8” <strong>and</strong> “disp16” indicate an 8-bit or 16-bit signed displacement.2. See Table A-12 for complete specification of ModRM “reg” field.ModRMr/mField(binary)Register <strong>and</strong> Memory References for 32-Bit <strong>and</strong> 64-Bit Addressing.Table A-14 on page 406 shows the encoding for 32-bit <strong>and</strong> 64-bitregister references using the ModRM reg field. The first ninerows of Table A-14 show references when the REX.R bit iscleared to 0, <strong>and</strong> the last nine rows show references when theREX.R bit is set to 1. In this table, Mnemonic Notation meansthe syntax notation shown in “Mnemonic Syntax” on page 43for a register, <strong>and</strong> ModRM Notation (/r) means the opcodesyntaxnotation shown in “Opcode Syntax” on page 46 for theregister.Table A-15 on page 407 shows the encoding for 32-bit <strong>and</strong> 64-bitmemory references using the ModRM byte. This table describes32-bit <strong>and</strong> 64-bit addressing, with the REX.B bit set or cleared.The Effective Address is shown in the two left-most columns,followed by the binary encoding of the ModRM-byte mod field,followed by the eight possible hex values of the completeModRM byte (one value for each binary encoding of theModRM-byte reg field), followed by the binary encoding of theModRM r/m field.The /0 through /7 notation for the ModRM reg field (bits 5–3)means that the three-bit field contains a value from zero (binary000) to 7 (binary 111).Appendix A: Opcode <strong>and</strong> Oper<strong>and</strong> Encodings 405

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