Ah, this is the talk behind the sandsifter tool that was making its round a few weeks back. Nice to get the deeper picture.

github: https://github.com/xoreaxeaxeax/sandsifter white paper: https://github.com/xoreaxeaxeax/sandsifter/blob/master/refer...

Sandsifter: find undocumented instructions and bugs on x86 CPU | https://news.ycombinator.com/item?id=14872418 (91 comments, July 2017)