Comment by rramadass

Couldn't find UDW in the intel docs - https://intel.github.io/SDM/sdm.html

But found it in wikipedia which is well structured and has detailed notes/comments on all instructions - https://en.wikipedia.org/wiki/List_of_x86_instructions

There is also UD2A and UD2B which just seem to be synonyms for UD2 and UD1 respectively? Google tells me that they are legacy tool specific mnemonics used in older GNU GCC/Binutils.