https://docs.microsoft.com/en-us/cpp/build/x64-calling-convention?view=vs-2019 https://docs.microsoft.com/en-us/cpp/build/x64-calling-conve... After you read t

https://docs.microsoft.com/en-us/cpp/build/x64-calling-convention?view=vs-2019 https://docs.microsoft.com/en-us/cpp/build/x64-calling-conve... After you read that, you might want to look at the LLVM source https://github.com/llvm-mirror/llvm/blob/master/lib/Target/X86/X86CallingConv.td https://github.com/llvm-mirror/llvm/blob/master/lib/Target/X... /// The C convention as implemented on Windows/x86-64 and /// AArch64. This convention differs from the more common /// \c X86_64_SysV convention in a number of ways, most notably in /// that XMM registers used to pass arguments are shadowed by GPRs, /// and vice versa. /// On AArch64, this is identical to the normal C (AAPCS) calling /// convention for normal functions, but floats are passed in integer /// registers to variadic functions.