Q1:

do_begin:            # do {
  movl i,%eax        #   if (i < j)
  cmpl j,%eax
  jnl  else
  addl $1,i          #     ++i
  jmp  endif
else:                #   else
  subl $1,j          #     --j
endif:
  movl i,%eax        # } while (i + k < j);
  addl k,%eax
  cmpl j,%eax
  jl   dO_begin

Q2:
oldEbp = 0
retAddr = oldEbp + 4
x = retAddr + 4
p = x + 4
myX = oldEbp - X_size # myX versus y is not important, but
y = myX - 4           # the amount of space allocated together is


Q3:
movl p(%ebp),%eax     # eax points to whatever p points to
movl X_i(%eax),%eax   # copy field i of that to eax
addl x(%ebp),%eax     # add x to that
pushl %eax            # save it for later
movl $X_size,%eax     # compute offset to element
movl x(%ebp),%ebx
mull %ebx             # eax is now the offset to element
popl myX+X_i(%ebp,%eax) # myX+%ebp is the base of the array
                        # myX+%ebp+%eax is the base of the
                        # element
                        # myX+%ebp+%eax+X_i is the address
                        # of field i of the element

Q4:
X_f1 = 0
X_f2 = X_f1 + 4
X_f3 = X_f2 + 16
X_size = X_f3 + 4 # f3 is a pointer, not a struct X!

Y_buffer = 0
Y_f2 = X_size * 4 # this is the tricky part
Y_size = X_f2 + 4

Q5:
movl i(%ebp),%eax   # eax is i
movl $X_size,%ebx   
mull %ebx           # eax is offset to element from array base
addl $Y_buffer,%eax # eax is offset to element from
                    # the base of a struct Y
addl py(%ebp),%eax  # py is the base of a struct Y, so now
                    # eax is the address of element i of the
                    # field "buffer" of whatever py points to
pushl %eax          # push it as parameter
call  sub1          # call
addl  $4,%esp       # clean up the stack (popl %eax is fine)
movl py(%ebp),%eax  # eax points to a struct Y
addl $1,Y_f2(%eax)  # add one to field "f2" of whatever py points to

Q6:
pushl pSecond(%ebp)     # save the pointer value, not what it points to
movl pFirst(%ebp),%eax  # eax points to a struct X
popl X_f3(%eax)         # update field "f3" of whatever pFirst points
                        # to using whatever we saved on the stack