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