Assembly - (Pseudo|Synthetic) Instruction


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


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.


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.

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