Still playing with Native Boost assembler. This code instantly crashes Pharo 1.4 with NB installed: TestAssem swapDoubFirst: 1.0 withSecond: 2.0. TestAssem>>swapDoubFirst: r1 withSecond: r2 <primitive: #primitiveNativeCall module: #NativeBoostPlugin> ^ NBFFICallout cdecl: #( double ( double r1, double r2 )) emitCall: [:gen | | asm proxy smpfr scnt| asm := gen asm. proxy := gen proxy. asm pop: asm ECX. asm fld: asm ESP ptr64 . asm fld: asm ESP ptr64 + 8 . asm fxch: asm ST0. ] -- Squeak from the very start (introduction to Squeak and Pharo Smalltalk for the (almost) complete and compleate beginner). https://www.youtube.com/playlist?list=PL6601A198DF14788D&feature=view_all