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Reverse Engineering

Glossary

Operand

The argument(s) to an assembly instruction — the registers, memory addresses, or immediate values it acts upon.

An operand is an argument supplied to an assembly instruction that specifies what data the instruction acts on. An instruction can have zero, one, or two operands. Operands come in three flavours: a register (e.g. EAX), an immediate (a literal number embedded in the instruction), or a memory reference (e.g. [EBP-4]).

asm
MOV  EAX, 1        ; destination operand: EAX, source operand: 1 (immediate)
ADD  [EBP-4], EAX  ; memory operand + register operand

Understanding operand encoding is crucial when reading raw opcodes or writing shellcode.