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

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

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AMD64 Technology 24594 Rev. 3.10 February 2005450 Appendix B: General-Purpose Instructions in 64-Bit Mode

24594 Rev. 3.10 February 2005 AMD64 TechnologyAppendix CDifferences Between Long Mode and LegacyModeTable C-1 summarizes the major differences between 64-bitmode and legacy protected mode. The third column indicatesdifferences between 64-bit mode and legacy mode. The fourthcolumn indicates whether that difference also applies tocompatibility mode.Table C-1.Differences Between Long Mode and Legacy ModeType Subject 64-Bit Mode DifferenceApplies ToCompatibilityMode?ApplicationProgrammingAddressingData and AddressSizesInstructionDifferencesRIP-relative addressing availableDefault data size is 32 bitsREX Prefix toggles data size to 64 bitsDefault address size is 64 bitsAddress size prefix toggles address size to 32 bitsVarious opcodes are invalid or changed in 64-bit mode(see Table B-2 on page 445 and Table B-3 on page 446)Various opcodes are invalid in long mode (see Table B-4on page 446)MOV reg,imm32 becomes MOV reg,imm64 (with REXoperand size prefix)REX is always enabledDirect-offset forms of MOV to or from accumulatorbecome 64-bit offsetsMOVD extended to MOV 64 bits between MMX registersand long GPRs (with REX operand-size prefix)noyesnoAppendix C: Differences Between Long Mode and Legacy Mode 451

AMD64 Technology 24594 Rev. 3.10 February 2005450 Appendix B: <strong>General</strong>-<strong>Purpose</strong> <strong>Instructions</strong> in 64-Bit Mode

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