Assembly - (Pseudo|Synthetic) Instruction

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1 - About

Pseudo-instructions are not real machine instructions. They are extended mnemonics that are not available in the original instruction set and are implemented by the assembler


3 - Example

Many CPU's do not have an explicit NOP instruction, but do have instructions that can be used for the purpose.

In 8086:

  • the nop the instruction is encoded as xchg ax,ax
  • and disassemblers should decode xchg ax,ax as nop.

4 - List

In nasm(doc), the pseudo-instructions are DB, DW, DD, DQ, DT, DO, DY and DZ; their uninitialized counterparts RESB, RESW, RESD, RESQ, REST, RESO, RESY and RESZ; the INCBIN command, the EQU command, and the TIMES prefix.