The article explains the origin of the x86 undefined instruction mnemonic “UD2”. It traces the naming back to Intel’s early documentation where the opcode was listed as “Undefined 2”, and discusses why the trailing “2” was kept even after the instruction became a formal way to raise an invalid‑opcode exception.
Background
UD2 is the canonical way for software on x86 to deliberately cause an invalid‑opcode exception, often used for debugging or to mark unreachable code.
- Source
- Hacker News (RSS)
- Published
- Sep 13, 2026 at 08:30 PM
- Score
- 5.0 / 10