Functions return integer results in register %o0, float results in register %f0, and double results in registers %f0 and %f1.
long long integers are passed in registers with the higher word order in %oN, and the lower order word in %o(N+1). In-register results are returned in %o0 and %o1, with similar ordering.
All arguments, except doubles and long doubles, are passed as four-byte values. A double is passed as an eight-byte value. The first six four-byte values (double counts as 8) are passed in registers %o0 through %o5. The rest are passed onto the stack. Structures are passed by making a copy of the structure and passing a pointer to the copy. A long double is passed in the same manner as a structure.
Registers described are as seen by the caller.