It's probably worth clarifying that on 64-bit Windows, the first first four arguments are passed in registers regardless of type, and the remainder (if any) ar

It's probably worth clarifying that on 64-bit Windows, the first first four arguments are passed in registers regardless of type, and the remainder (if any) are pushed to the stack. But on 64-bit Linux/BSD/OSX, depending on the mix of types, you might have as many as 14 register arguments. You get 6 "integer" registers, plus 8 "vector" registers, where "vector" registers are also used for floating point. http://www.agner.org/optimize/calling_conventions.pdf http://www.agner.org/optimize/calling_conventions.pdf