Breaking the x86 Instruction Set

Caption notes

Christopher Domas uses SandSifter to probe which instructions x86 processors actually accept, then compares observed behavior with disassemblers. He first develops ways to observe decoding length and exceptions, then presents undocumented instructions, analysis-tool errors and several hardware anomalies. A crucial turn is that the disassembler used as a proxy for documentation can itself be wrong, and multiple tools can share an interpretation error. These are findings on the systems tested at the time. Undocumented behavior does not automatically establish a malicious backdoor, and a severe anomaly on one processor does not generalize to all modern processors.