Temp workspace. Callee can overwrite without warning!

$RAX$

$RCX$

$RDX$

$RSI$

$RDI$

$R8$

$R9$

$R10$

$R11$

Protected workspace. Callee must restore before returning!

$RBX$

$RSP$

$RBP$

$R12$

$R13$

$R14$

$R15$