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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 ch

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?

KingLancelot 2y ago
Silicone is plastic, Silicon is the element.
- jghn 2y ago
  Not according to General Beringer of NORAD! :) [1] [1] https://youtu.be/iRsycWRQrc8?t=82 https://youtu.be/iRsycWRQrc8?t=82
wmf 2y ago
They always used microcode: https://www.righto.com/2022/11/how-8086-processors-microcode-engine.html 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.
- LukeShu 2y ago
  Microcode updates came the very next generation with the Pentium Pro.
Lammy 2y ago
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-of-the-v20s https://thechipletter.substack.com/p/intel-vs-nec-the-case-o... - https://www.upi.com/Archives/1994/03/10/Jury-backs-AMD-in-dispute-with-Intel/8611763275600/ 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 https://news.ycombinator.com/item?id=35934367
kens 2y ago
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.
- deleted 2y ago
  [deleted]
- peterfirefly 2y ago
  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!
  - Tuna-Fish 2y ago
    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 https://chipsandcheese.com/p/amd-disables-zen-4s-loop-buffer
userbinator 2y ago
Look at how long the public errata lists are, and use that as a lower bound. Related article: https://news.ycombinator.com/item?id=16058920 https://news.ycombinator.com/item?id=16058920

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?

KingLancelot 2y ago

Silicone is plastic, Silicon is the element.

jghn 2y ago
Not according to General Beringer of NORAD! :) [1] [1] https://youtu.be/iRsycWRQrc8?t=82 https://youtu.be/iRsycWRQrc8?t=82

wmf 2y ago

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

LukeShu 2y ago
Microcode updates came the very next generation with the Pentium Pro.

Lammy 2y ago

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-of-the-v20s https://thechipletter.substack.com/p/intel-vs-nec-the-case-o... - https://www.upi.com/Archives/1994/03/10/Jury-backs-AMD-in-dispute-with-Intel/8611763275600/ 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 https://news.ycombinator.com/item?id=35934367

kens 2y ago

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.

deleted 2y ago
[deleted]
peterfirefly 2y ago
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!
- Tuna-Fish 2y ago
  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 https://chipsandcheese.com/p/amd-disables-zen-4s-loop-buffer

userbinator 2y ago

Look at how long the public errata lists are, and use that as a lower bound. Related article: https://news.ycombinator.com/item?id=16058920 https://news.ycombinator.com/item?id=16058920