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Comment by seanmclo | Hacker News Reader

I've been working on verifying memory coherency units of modern out-of-order CPUs for a few years now. Nowadays, this would be a huge miss if it were to escape to silicon. You'd have a dead on arrival product.

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I think the specific application of the CPU here makes it more palettable. It was a nice idea, but it doesn't work out, so scan for it and don't publish games that have that opcode; if possible, issue a microcode update that makes it either a noop or an illegal operation.

Game console CPUs get away with all sorts of brokenness. The Wii U CPU also has broken coherency, and needs workaround flush instructions in the core mutex primitives. You can't run standard PowerPC Linux on it multicore for this reason.

I agree that console silicon can be rushed and bugs slip through. But then again, we may not even be aware of all the bugs in Intel or AMD products where they have been fixed post silicon via mechanisms such as microcode patches.

What does ‘escape to silicon’ mean?

If Intel ships a CPU with a bug in it then that is an expensive mistake. If they produce a bunch of CPUs with a bug (escape to silicon) that can also be an expensive mistake.

That said: 1) I deal with CPU bugs pretty regularly on Chrome. Some old CPUs behave unreliably with certain sequences of instructions and we get bursts of crashes on these CPUs with some Chrome versions. 2) Intel regularly "fixes" CPU bugs with microcode updates. 3) The Spectre family of vulnerabilities are arguably CPU bugs. 4) The Pentium fdiv bug was definitely a CPU bug.

So, CPU bugs escape to silicon all the time. Way more than I would have guessed just a few years ago. Our industry is built on a pile of wobbly sand.

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