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The main rule for data access is max(CPL, RPL) ≤ DPL. For code transfers, the rules get considerably more complex -- conforming segments, call gates, and interrupt gates each have different privilege and state validation logic. If all these checks were done in microcode, each segment load would need a cascade of conditional branches: is it a code or data segment? Is the segment present? Is it conforming? Is the RPL valid? Is the DPL valid? This would greatly bloat the microcode ROM and add cycles to every protected-mode operation.
，这一点在爱思助手下载最新版本中也有详细论述
Without Seccomp:
There are about 33 distinct test constants, covering every protection scenario on the 386. Each activates a different subset of the 148 product terms, encoding the specific privilege rules for that scenario. To give a feel for what the PLA does concretely, here are the possible outcomes for two tests:
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