4 ms·

Nice quote there; I said "every single program using the instruction".

• mikeash 14y ago
  Sorry about that. Given that the code which uses the instruction is not a "program" per se but rather is found in OS kernels, I hope you can understand my confusion. How many x86-64 kernels existed and had to be changed at the time?
  • j_s 14y ago
    No worries! This whole issue is way lower-level than anything I deal with on a regular basis so the whole time I've been looking at it from the very general perspective, eg. 'a cpu instruction' rather than 'the specific cpu instruction used by operating systems to switch to user mode on 64-bit processors, originally implemented by AMD and later implemented by Intel in accordance to the spec but differing in implementation' as happened here.
    • mikeash 14y ago
      My understanding is that instructions which are only used by OS kernels tend to be a little less stable than those used by general-purpose user programs. However, this is not exactly my area of expertise.