Machine Code in x86 | Search for a title, author or keyword | ||||||||
Machine Code in x86 CS301: Assembly Language Programming Lecture, Dr. Lawlor, UNIVERSITY OF ALASKA FAIRBANKS, Department of Computer Science. The basic idea with machine code is to use binary bytes to represent a computation. Different machines use different bytes, but Intel x86 machines use "0xc3" to represent the "ret" instruction, and "0xb8" to represent the "load a 32-bit constant into eax" instruction. "mov" is an instruction, encoded with the operation code or "opcode" 0xb8. Since mov takes an argument, the next 4 bytes are the constant to move into eax: 0: b8 05 00 00 00 0: 0: mov eax,0x5 The opcode 0xb9 moves a constant into ecx. 0xba moves a constant into edx: 0: b9 05 00 00 00 0: mov ecx,0x5 5: ba 05 00 00 00 5: mov edx,0x5
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