x86 Architecture 1-Byte Opcode Reference and Technical Documentation
By
eklitzke
Pulled from the oven just right. Trustworthy, fact-dense, deeply satisfying.
Summary
This technical article documents x86 architecture 1-byte opcodes, presenting a detailed reference table of hexadecimal opcode mappings to assembly instructions. It covers opcodes from 0x0h to 0x4xh, including operations like ADD, ADC, AND, XOR with various addressing modes and prefixes like LOCKable. The content appears to be a technical reference or documentation for low-level x86 assembly programming, with mentions of specific architectural details like REX2 prefix and historical context about opcode allocation decisions from 2001.
Key quotes
· 6 pulledx86 architecture1 byte opcodes
LOCKableADDEb,Gb
LOCKableADDEv,Gv
ADDGb,Eb
ADDGv,Ev
I did spot that zeroing the upper 32 bits of RAX leads to undesired non-NOP behavior, but failed to convince our team in 2001 to use one of the freed up 1-byte opcodes (a la UDB)
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