Microcode, which is a no-go for modern designs

[Eric Smith]

On Wed, Jan 2, 2019 at 4:12 PM dwight via cctalk <cctalk at classiccmp.org>
wrote:

> I  thought I'd note that the divide problem couldn't have been patched
> with a micro code patch.


If you're talking about the Pentium FDIV bug, present on the early 80501
chips (60 and 66 MHz) and 80502 chips (75, 90, and 100 MHz), they weren't
able to fix that with a microcode patch. They actually issued a recall for
those chips.

However, Intel has successfully fixed other bugs using microcode patches,
including some but not all of the recent speculative execution side channel
problems (Meltdown and Spectre). They have also used microcode patches to
disable instructions that were broken and couldn't be fixed by microcode,
including the TSX-NI instructions of some Haswell, broadwell, and Skylake
CPUs.