Instruction added to x86 CPU after release [closed]

Question

Has there ever been a case of an instruction added to an x86 CPU after release? That is, an instruction that didn't exist/work out of the box CPU, but could work on the same CPU sample after a microcode update?

Jayejaylene

Comments are not for extended discussion; this conversation has been moved to chat. – Shipowner

Some instructions may be not public at time of release. There was project github.com/xoreaxeaxeax/sandsifter to find which byte sequences and instruction spaces are recognized by instruction decoder. Text: github.com/xoreaxeaxeax/sandsifter/blob/master/references/… Also, Koppe's papers on microcode for old AMD usenix.org/system/files/conference/usenixsecurity17/… will give you some hints how microcode ROM and updates (patches) were organized long time ago. – Gordan