Explain why multi-byte nop instructions are needed

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Reference no: EM132083472

The NOP (no-op) instruction is an instruction that does nothing. In x86, a 1byte opcode 0x90 is designated as NOP instruction.

In addition to this single-byte NOP instruction, x86 defines/recommends multi-byte NOP instructions as follows:

2 bytes: 0x66 0x90 /*0x66; NOP */

3 bytes: 0x0f 0x1f 0x00 /* NOP DWORD ptr [EAX] */

4 bytes: 0x0f 0x1f 0x40 0x00 /* NOP DWORD ptr [EAX + 00h]*/

5 bytes: 0x0f 0x1f 0x44 0x00 0x00 /* NOP DWORD ptr [EAX + EAX*1 + 00h]*/

6 bytes: 0x66 0x0f 0x1f 0x44 0x00 0x00 /*0x66; NOP DWORD ptr [EAX+EAX*1 + 00h]*/ and so on.

Explain why multi-byte NOP instructions are needed by pointing out the advantage of using the above multi-byte NOP instruction instead of just multiple single-byte NOPs.

Reference no: EM132083472

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