Sun Studio 12: C User's Guide


Functions return results in the following registers:

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


Type Returned  



long long

%edx and %eax

float, double, and long double


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.