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Comment by Cumpiler69 | Hacker News Reader

This is probably one of the reasons Intel went to a microcode architecture after.

I wonder how many yet to be discover silicone bugs are out there on modern chips?

Older Intel CPUs were already using microcode. Intel went after NEC with a copyright case over 8086 microcode, and after AMD with a copyright case over 287/386/486 microcode:

- https://thechipletter.substack.com/p/intel-vs-nec-the-case-o...

- https://www.upi.com/Archives/1994/03/10/Jury-backs-AMD-in-di...

I would totally believe the FDIV bug is why Intel went to a patchable microcode architecture however. See “Intel P6 Microcode Can Be Patched — Intel Discloses Details of Download Mechanism for Fixing CPU Bugs (1997)” https://news.ycombinator.com/item?id=35934367

Intel used microcode starting with the 8086. However, patchable microcode wasn't introduced until the Pentium Pro. The original purpose was for testing, being able to run special test microcode routines. But after the Pentium, Intel realized that being able to patch microcode was also good for fixing bugs in the field.

Being able to patch the microcode only solves part of the possible problems a CPU can have.

My guess -- and I hope you can confirm it at some point in the future -- is that more modern CPUs can patch other data structures as well. Perhaps the TLB walker state machine, perhaps some tables involved in computation (like the FDIV table), almost certainly some of the decoder machinery.

How does one make a patchable parallel multi-stage decoder is what I'd really like to know!

Mostly, you can turn off parts of the CPU (so called chicken bits). They are invaluable for validation, but they have also been frequently used for for fixing broken CPUs. Most recently AMD just recently turned off their loop buffer in Zen4: https://chipsandcheese.com/p/amd-disables-zen-4s-loop-buffer

They always used microcode: https://www.righto.com/2022/11/how-8086-processors-microcode...

I'm not sure when Intel started supporting microcode updates but I think it was much later.

Microcode updates came the very next generation with the Pentium Pro.

Look at how long the public errata lists are, and use that as a lower bound.

Silicone is plastic, Silicon is the element.

Not according to General Beringer of NORAD! :) [1]

[1] https://youtu.be/iRsycWRQrc8?t=82

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