Exactly. My understanding of the conventions and macros in those source files is that you declare what registers you will be trashing, and then the registers ar

Exactly. My understanding of the conventions and macros in those source files is that you declare what registers you will be trashing, and then the registers are saved/restored as required by that platform. On Linux it would be a NOP, and on Windows it saves and restores XMM6 and XMM7 (XMM0-XMM5 are volatile).