assembly - Encoding the multi-byte no-operation instruction (x86/x64) -


this instruction on page 1018 of intel x64 reference manual. here's looks like:

opcode    instruction description 90        nop         1 byte no-operation instruction. 0f 1f /0  nop r/m16   multi-byte no-operation instruction. 0f 1f /0  nop r/m32   multi-byte no-operation instruction.

i read somewhere max no-op length 9 bytes. no-op length in 16/32 bit register or memory address or encode bunch of zeroes myself , if how r/m16 or r/m32 apply?

from xed:

xed64 -64 -e nop mem4:eax,eax,1,00000000 operand order: mem0  encodable! 670f18a40000000000 .byte 0x67,0x0f,0x18,0xa4,0x00,0x00,0x00,0x00,0x00

the advantage of using 9 byte nop reduce strain decoder, can decode 4 instructions per cycle. , nop technically instruction.


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