NOP Variant

Daily AlpacaHackTopic: x86Released: Jul 21, 2026

65 solves

by

tan90909090

Tags

I heard that the x86 NOP instruction can be represented in multiple ways.

Beginner Hint: Approach to Solving the Challenge

Intel® 64 and IA-32 Architectures Software Developer's Manual Combined Volumes 2A, 2B, 2C, and 2D: Instruction Set Reference, A- Z, mentioned in a comment in chal.py, is an excellent resource.
To understand the structure of machine code in x86, see Figure 2-1. Intel 64 and IA-32 Architectures Instruction Format in the resource.
To understand the structure of the machine code for known_nop in chal.py, see the NOP—No Operation instruction and Table 4-12. Recommended Multi-Byte Sequence of NOP Instruction in the resource.
Finally, to consider how to satisfy the requirements in chal.py, see Table 2-2. 32-Bit Addressing Forms with the ModR/M Byte and Table 2-3. 32-Bit Addressing Forms with the SIB Byte in the resource.