Four bytes, for the single variable a.
a
main()
Here is the code for main(), with some blanks. The rules for the subroutine prolog are copied from above.
# main() # { # int a; # a = mysub( 6 ); # print( a ); # } .text .globl main main: # prolog sub $sp,$sp,4 # 1. Push return address sw $ra,($sp) sub $sp,$sp,4 # 2. Push caller's frame pointer sw $fp,($sp) # 3. No S registers to push sub , , # 4. $fp = $sp - space_for_variables $sp,$fp # 5. $sp = $fp # subroutine call . . . . # return from subroutine . . . . # epilog jr $ra # return to OS
Fill in the blanks as the comments suggest.