F.3.1.1 64-Bit SPARC

All integral arguments are passed as eight-byte values.

Floating-point arguments are passed in floating-point registers when possible.

(x86)

Functions return results in the following registers:

Table F–21 Registers Used by x86 Functions to Return Types

Register	Type Returned
int	%eax
long long	%edx and %eax
float, double, and long double	%st(0)
float _Complex	%eax for the real part and %edx for the imaginary part
double _Complex and long double _Complex	The same as a struct that contains two elements of the corresponding floating point type.

All arguments except structs, unions, long longs, doubles and long doubles are passed as four-byte values; a long long is passed as an eight-byte value, a double is passed as an eight-byte value, and a long double is passed as a 12-byte value.

structs and unions are copied onto the stack. The size is rounded up to a multiple of four bytes. Functions returning structs and unions are passed a hidden first argument, pointing to the location into which the returned struct or union is stored.

Upon return from a function, it is the responsibility of the caller to pop arguments from the stack, except for the extra argument for struct and union returns that is popped by the called function.