Q1

shieldMe:
  oldEbp = 0
  retAddr = oldEbp + 4
  pShielded = retAddr + 4
  n = pShielded + 4
  op = n + 4
  
  // PROBLEM:
  shield = oldEbp - 256
  
  pushl %ebp
  movl %esp,%ebp
  
  // PROBLEM:
  addl  $shield,%esp
  
  pushl %eax
  pushl %ebx
  pushl %ecx
  pushl %edx
  
  movl n(%ebp),%ecx  // ecx is n
  cmpl $256,%ecx     // compare n with 256
  jb L1              // jmp iff n < 256
  movl $256,%ecx     // else n <- 256
  // end if
L1:                  // ecx is n
  movl $0,%eax       // eax is i, i <- 0
L2:
  cmpl $0,%ecx       //
  jz L3              // iff n == 0 jmp L3
  // PROBLEM PROBLEM PROBLEM!!!!!
  // movb pShielded(%ebp,%eax),%bl 
  movl pShielded(%ebp),%edx
  movb (%edx,%eax),%bl
  // END PROBLEM
  movb %bl,shield(%ebp,%eax)
  addl $1,%eax
  // PROBLEM:
  subl $1,%ecx
  jmp L2             // end of for
L3:
  pushl %ebp
  // PROBLEM
  // addl shield,(%esp)
  addl $shield,(%esp)
  // END PROBLEM
  call *op(%ebp)
  addl $4,%esp
  
  popl %edx
  popl %ecx
  popl %ebx
  popl %eax
  
  // NOT A PROBLEM:
  subl $shield, %esp
  
  movl %ebp,%esp
  popl %ebp
  ret
  
Q2:

strcat:
  oldEbp = 0
  retAddr = oldEbp + 4
  dest = retAddr + 4
  src = dest + 4
  
  pushl %ebp
  movl %esp,%ebp
  pushl %eax
  pushl %ebx
  pushl %ecx
  
  movl dest(%ebp),%eax  // eax is dest
L1:
  cmp (%eax),$0         // cmp should be cmpb
                        // reverse the operands
  jz L2
  addl $1,%eax
  jmp L1
  // end while
L2: 
  movl src(%ebp),%ebx   // ebx is src
L3: // begin while
  movb (%ebx),(%eax)    // this is not allowed
                           movb (%ebx),%cl
                           movb %cl,(%eax)
  cmpb %cl,$0           // reverse the operands
  jnz L4                // jnz should be jz
  addl $1,%ebx
  addl $1,%eax
  jmp L2  // end while  // PROBLEM L3, not L2
L4:
  
  popl %ecx
  popl %ebx
  popl %eax
  
  movl dest(%ebp),%eax
  
  movl %ebp,%esp
  popl %ebp
  ret
  
modX:
  oldEbp = 0
  retAddr = oldEbp + 4
  pX = retAddr + 4
  
  pushl %ebp
  movl %esp,%ebp
  
  pushl %eax
  pushl %ebx
  pushl %ecx
  pushl %edx
  
  movl pX(%esp),%eax      // eax is pX
  movl X_myValue(%eax),%ebx // ebx is pX->myValue
  movl (%ebx),%ebx  // PROBLEM ebx is *(pX->myValue)
                    // remove it
  addl X_peers,%eax // eax is &pX->peers
                    // eax is the base address of
                    // the peers array of the
                    // struct X pointed to by
                    // pX
                    // the address of the first
                    // element (says Willow)
  movl %eax,%edx    // edx is &pX->peers
  addl $X_size*NPEERS,%edx // PROBLEM: X_size
                           // should be 4
                    // edx points to the byte
                    // immediately following
                    // the peers array
  
L1:
  cmpl %eax,%edx    // compare eax with the
                    // end address of the array
  jz L2
  movl X_myValue(%eax),%ecx // PROBLEM
  // new code:
  movl (%eax),%ecx // this is the fix
  movl %ebx,X_myValue(%ecx)
  addl $4,%eax
  jmp L1
L2:
  
  popl %edx
  popl %ecx
  popl %ebx
  popl %eax
  
  movl %ebp,%esp
  popl %ebp
  ret