%% LyX 1.1 created this file. For more info, see http://www.lyx.org/. %% Do not edit unless you really know what you are doing. \documentclass[11pt]{article} \usepackage[T1]{fontenc} \setlength\parskip{\medskipamount} \setlength\parindent{0pt} \makeatletter %%%%%%%%%%%%%%%%%%%%%%%%%%%%%% LyX specific LaTeX commands. \providecommand{\LyX}{L\kern-.1667em\lower.25em\hbox{Y}\kern-.125emX\@} %%%%%%%%%%%%%%%%%%%%%%%%%%%%%% User specified LaTeX commands. \usepackage[T1]{fontenc} \setlength\parskip{\medskipamount} \setlength\parindent{0pt} \makeatletter \usepackage[T1]{fontenc} \setlength\parskip{\medskipamount} \setlength\parindent{0pt} \makeatletter \usepackage[T1]{fontenc} \setlength\parskip{\medskipamount} \setlength\parindent{0pt} \makeatletter \usepackage[T1]{fontenc} \setlength\parskip{\medskipamount} \setlength\parindent{0pt} \makeatletter \setlength{\oddsidemargin}{-0.5in} \setlength{\evensidemargin}{-0.5in} \setlength{\topmargin}{0.0in} \setlength{\headheight}{0in} \setlength{\headsep}{0in} \setlength{\textwidth}{7.0in} \setlength{\textheight}{9.5in} \setlength{\parindent}{0in} \setlength{\parskip}{0.1in} \setlength{\columnseprule}{0.4pt} \makeatother \makeatother \makeatother \makeatother \makeatother \begin{document} Name: \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ \textbf{Directions: Work only on this sheet (on both sides, if needed); do not turn in any supplementary sheets of paper. There is actually plenty of room for your answers, as long as you organize yourself BEFORE starting writing. In order to get full credit, SHOW YOUR WORK. In fill-in questions, the number of blanks shown has no relation to the number of characters in the answer. Note that earlier questions tend to be easier.} \textbf{1.} (5) Look at the instruction JNS NXT on p.83 of Neveln. What would the machine code 0F8904000000 change to if the instruction were changed to JS GCD? (Note that both the operation and operand are changed.) \textbf{3.} (5) The --gstabs option of \textbf{as} is similar to what option of \textbf{gcc}? \textbf{4.} (10) Fill in the blank: One aspect of the Intel hardware which we mentioned in class could be accessed via assembly language but not via C is \_\_\_\_\_\_\_\_\_. \textbf{5.} (10) Choose the correct statement: If in Prog. 6.2 we were to use JC (or JNC) instead of ADC, the code would be (i) faster and larger, (ii) faster and smaller, (iii) slower and smaller, (iv) slower and larger, \textbf{6.} (10) State the two reasons discussed in class as to why jump instructions typically specify the location of the place to be jumped to in terms of a distance rather than an absolute address. \textbf{7.} (10) An example of an instruction discussed in class as being present in the Intel CPUs but ironically not in the more modern SPARC is \_\_\_\_\_\_\_\_\_\_. \textbf{8.} (10) When multiplying two 16-bit quantities, MUL places the product in DX:AX. It would have been more natural to have the product go into EAX or some other 32-bit register. Why was this not done? \textbf{9.} (10) Write assembly code, using AT\&T syntax (this is required), which will replace the current contents of EAX by its absolute value. For instance, if EAX currently contains -12, that value will be changed to +12. (Note: Ideally, your code should not be longer than, say, 5 or 6 lines; feel free to copy the contents of EAX to other registers, say EBX, but don't use memory; I am just asking for a program fragment here, not a whole source code with lines line .text etc.) \textbf{10.} Below is the output obtained when \textbf{as} was applied with the -a option to a certain source file. Assume that the .data and .text segments are loaded into memory at the locations indicated above. Assume there is no instruction prefetching. \begin{itemize} \item (a) (5) In line 20, if the 23 in the source code had been 28, what would the machine code BA17000000 change to? \item (b) (10) Consider the third iteration of the loop. At the very end of the execution of the instruction in line 23, state which values will be in the PC, MAR and MDR. \item (c) 10) Answer (b) for line 22. \end{itemize} \begin{verbatim} 1 2 # calculate the first 25 Fibonacci numbers 3 4 .data 5 6 .globl fib 7 0000 01000000 fib: .long 1 8 0004 01000000 .long 1 9 .rept 23 10 .long 0 11 .endr 12 0008 00000000 12 00000000 12 00000000 12 00000000 12 00000000 13 .text 14 15 .globl _start 16 _start: 17 0000 BB010000 movl $1, %ebx # EBX will be fib_i-2 17 00 18 0005 B9010000 movl $1, %ecx # ECX will be fib_i-1 18 00 19 000a B8080000 movl $fib+8, %eax # EAX will point to fib_i 19 00 20 000f BA170000 movl $23, %edx # loop counter 20 00 21 0014 89CE top: movl %ecx, %esi # make a copy of old fib_i-1 22 0016 01D9 addl %ebx, %ecx # calculate fib_i 23 0018 8908 movl %ecx, (%eax) # store fib_i 24 001a 89F3 movl %esi, %ebx # old fib_i-1 is new fib_i-2 25 001c 83C004 addl $4, %eax 26 001f 4A decl %edx # decrement loop counter 27 0020 75F2 jnz top 28 0022 BE000000 done: movl $0, %esi # dummy for breakpoint 28 00 \end{verbatim} \textbf{Solutions:} \textbf{1.} 0F880B000000 \textbf{3.} -g 4. The flags. \textbf{5.} (iv) \textbf{6.} Shorter instructions, position-independent code. \textbf{7.} MUL \textbf{8.} Backwards compatibility. Back when Intel chips were 16-bit, there was no EAX. So even when they went to 32 bits and had an EAX, they still needed MUL to operate as before. \textbf{9.} \begin{verbatim} movl $0,%ebx subl %eax,%ebx jns eaxneg jmp done movl %ebx,%eax eaxneg: movl %ebx, %eax done: \end{verbatim} Many other solutions are possible. \textbf{10.a.} BA1C000000 \textbf{10.b.} PC: 1A, MAR: 10, MDR: 5 \textbf{10.c.} PC:18, MAR: 16 (or 17), MDR: 1D9 (or D9) \end{document}