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'{{lowercase}} '''<code>mov</code>''' is an x86 assembly instruction identified to be Turing-complete by [[Stephen Dolan]] in ''mov is Turing-complete''<ref>S. Dolan, 2013. ''mov'' is Turing-complete. Preprint. https://drwho.virtadpt.net/files/mov.pdf https://harrisonwl.github.io/assets/courses/malware/spring2017/papers/mov-is-turing-complete.pdf</ref> and developed further by xoreaxeaxeax in [https://github.com/xoreaxeaxeax/movfuscator Movfuscator]. It may also be considered the basis of a [[OISC|one instruction set computer]] architecture which (unlike [[Subleq]]) does not have to use self modifying code. == About the <code>mov</code> instruction == The <code>mov</code> instruction has a number of different forms. Let r1,r2 denote registers, then for example: * mov r1, 42 % store the number 42 in r1 * mov r1, r2 % fetch the value in r2 and store it in r1 * mov [r1], 42 % store the number 42 in the address the register r1 points to * mov r1, [r2] % fetch the value the address in register r2 points to and store it in r1 * mov [r1], r2 % store the value register r2 in the address the register r1 points to The expressions in brackets can also include +offsets or even adding two register together. All of these features are made use of in different encodings. == Equality Test == To test equality of 'x' and 'y': mov [x], 0 mov [y], 1 mov result, [x] This works by having a large array which is written into and read back out from. If x = y the readback will give 1 and it would be 0 otherwise. == Arithmetic and Logic == Arithmetic and logic gates can be encoded using lookup tables. For example to find the xor of x and y we have the following lookup tables xor_xy: dd xor_0y, xor_1y xor_0y: dd 0, 1 xor_1y: dd 1, 0 and the code is mov r1,[xor_xy+x] mov r2,[y] mov result,[r1+r2] == As a compilation target == The movfuscator repo contains an example compiler from [[brainfuck]] to <code>mov</code> instructions. The author also wrote an lcc (C compiler) backend for it. The result is extremely long linear code with no branches which can cause reverse engineering tools to crash. == References == <references /> [[Category:Esoteric subset]] [[Category:Computational models]] [[Category:Turing complete]] [[Category:Before 1993]] [[Category:2013]] [[Category:Implemented]] [[Category:OISC]] [[Category:Languages]]'