The Spectre and Meltdown attacks are as unanticipated as the incompleteness theorem and failure of naive set theory. Though the issue is easy to see now, simply none of the world’s smartest chip designers had anticipated that system integrity could fail in this way.
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This had been studied rigorously as early as 1964 (https://en.wikipedia.org/wiki/Out-of-order_execution …), so I don't think it was ever one of those "I guess this should work" hacks that programmers are wont to attempt.
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One note--the first designs still lacked precise exceptions. It wasn't until HPS & Result Buffer (simultaneous with the development of the Reorder Buffer) that OoO developed in the modern sense; cf. "HPS Papers: A Retrospective". http://www.zytek.com/~melvin/HPSPapersARetrospective_IEEEMicro_201608.pdf …, it's pretty fascinating!
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Caches are supposed to be invisible. The state of the caches doesn’t affect the program correctness in any way, so you don’t need to rollback the cache state. The only problem is that you can measure the cache state by timing, leaking you info about speculative execution.
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The law of leaky abstractions in action https://www.joelonsoftware.com/2002/11/11/the-law-of-leaky-abstractions/ …
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