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See: Wikipedia on cdecl, stdcall and other calling conventions].
Also highly informative: The history of calling conventions, part 1 and further parts.
An extract from “libcgo/386.S” about the 8c/8a/8g calling convention:
* Calling into the 8c tool chain, where all registers are caller save.
Otherwise (regarding the stack), the convention in [“cc” 8c]/[“asm” 8a]/8g seems to be cdecl-like (callee does not pop the arguments from the stack).