RAX Volatile Return value register.
RCX Volatile First integer argument.
RDX Volatile Second integer argument.
R8 Volatile Third integer argument.
R9 Volatile Fourth integer argument.
R10:R11 Volatile Must be preserved as required by caller; used in syscall/sysret instructions.
R12:R15 Nonvolatile Must be preserved by called function.
RDI Nonvolatile Must be preserved by called function.
RSI Nonvolatile Must be preserved by called function.
RBX Nonvolatile Must be preserved by called function.
RBP Nonvolatile Can be used as a frame pointer. Must be preserved by called function.
RSP Nonvolatile Stack Pointer.
XMM0 Volatile First FP argument.
XMM1 Volatile Second FP argument.
XMM2 Volatile Third FP argument.
XMM3 Volatile Fourth FP argument.
XMM4:XMM5 Volatile Must be preserved as required by caller.
XMM6:XMM15 Nonvolatile Must be preserved as required by called function.
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