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<h1 id="cmpt-295--fall-2021">CMPT 295 – Fall 2021</h1>
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<p>Assignment 5</p>
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<h2 id="objectives">Objectives:</h2>
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<ul>
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<li>x86-64 function calls and stack</li>
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<li>Investigating the size of some x86-64 assembly instructions</li>
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</ul>
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<hr />
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<h2 id="submission">Submission:</h2>
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<ul>
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<li>Submit your document called Assignment_5.pdf om CourSys.
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<ul>
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<li>Add your full name and student number at the top of the first page of your document.</li>
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</ul>
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</li>
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<li><strong>If you write your answers by hand (as opposed to using a computer application to
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write them)</strong>, when putting your assignment document together, do not take photos of
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your assignment sheets! Scan them instead! Better quality -> easier to read -> easier to
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mark!</li>
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</ul>
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<hr />
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<h2 id="due">Due:</h2>
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<ul>
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<li>Friday Oct. 29 at 4pm on CourSys</li>
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<li>Late assignments will receive a grade of 0, but they will be marked (if they are submitted
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before the solutions are posted on Monday) in order to provide feedback to the
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student.</li>
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</ul>
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<hr />
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<h2 id="marking-scheme">Marking scheme:</h2>
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<ul>
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<li>All questions of this assignment will be marked for correctness.</li>
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<li>The amount of marks for each question is indicated as part of the question.</li>
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<li>solution will be posted on Monday after the due date.</li>
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</ul>
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<hr />
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<h3 id="1-10-marks-x86-64-function-calls-and-stack">1) [10 marks] x86-64 function calls and stack</h3>
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<p>a. Hand trace the code from our Lab 4 (main.c , main.s, p1.c, p1.s, p2.c and p2.s) using the test case, i.e., x = 6, y = 9, buf[40].</p>
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<ul>
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<li>As you do so, draw the corresponding Stack Diagram for the entire program, i.e.,
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until you reach (but have not yet executed) the ret instruction of the main
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function. To do so, you can either print the “Stack Diagram” sheet at the end of
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this assignment and do the drawing by hand, then scan the result and include it
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into this assignment document OR do the drawing by electronically annotating the
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“Stack Diagram” sheet at the end of this assignment then include the result into
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this assignment document.</li>
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<li>The use of the Register Table is optional: use it only if you find it useful. You do
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not have to include it as part of your assignment document.</li>
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<li>Indicate the movement of %rsp by crossing its old location and rewriting “%rsp”
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to indicate its new location (as we have done in our lectures and Lab 4).</li>
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<li>Cross the content of the stack that has been popped.</li>
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<li>When the value of a stack location is changed, cross its old value and write the
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new value in the same stack location.</li>
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<li>Make sure you include the content of buf in your Stack Diagram.</li>
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<li>When drawing your stack diagram, you do not have to show the effect on the stack
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of the 5 call instructions at lines 33, 43, 45 and 57 in main.s and at line 47 in
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p1.s. These are calls to printf(…), puts(…) and sprintf(…). In other
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words, you do not have to add the return addresses associated to these 5 calls
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onto the stack.</li>
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<li>Hint: The solution to Participation Activity 6 (which will be posted after its
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deadeline on Monday) will give us a great head start!</li>
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</ul>
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<p>b. Modify main.c by reducing the size of buf[] from 40 to 24.</p>
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<ul>
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<li>Remake the code and hand trace it using the following test case, i.e., x = 6, y =
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9, buf[24].</li>
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<li>Repeat the instructions found in the section a. above and create a second drawing
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of the stack using the Stack Diagram sheet found at the end of this assignment.</li>
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<li>Make sure you include the content of buf in your Stack Diagram drawing.</li>
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<li>On the same sheet as your Stack Diagram, asnwer the question:What happens to
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the “canary value” in this situation?</li>
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</ul>
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<hr />
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<h3 id="2-10-marks-investigating-the-size-of-some-x86-64-assembly-instructions">2. [10 marks] Investigating the size of some x86-64 assembly instructions</h3>
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<p>Complete the following three tables:</p>
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<p>Table 1:</p>
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<table>
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<thead>
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<tr>
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<th>X86-64 Instructions</th>
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<th>Their size (in bytes)</th>
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</tr>
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</thead>
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<tbody>
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<tr>
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<td>xorq %rax, %rax</td>
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<td> </td>
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</tr>
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<tr>
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<td>xorl %eax, %eax</td>
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<td> </td>
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</tr>
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<tr>
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<td>movq $0, %rax</td>
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<td> </td>
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</tr>
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<tr>
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<td>movl $0, %eax</td>
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<td> </td>
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</tr>
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</tbody>
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</table>
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<p>Table 2:</p>
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<table>
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<thead>
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<tr>
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<th>X86-64 Instructions</th>
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<th>Their size (in bytes)</th>
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</tr>
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</thead>
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<tbody>
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<tr>
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<td>addl $1, %eax</td>
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<td> </td>
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</tr>
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<tr>
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<td>leal 1(%eax), %eax</td>
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<td> </td>
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</tr>
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<tr>
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<td>incl %eax</td>
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<td> </td>
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</tr>
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</tbody>
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</table>
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<p>Table 3:</p>
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<table>
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<thead>
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<tr>
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<th>X86-64 Instructions</th>
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<th>Their size (in bytes)</th>
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</tr>
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</thead>
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<tbody>
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<tr>
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<td>addl $8, %eax</td>
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<td> </td>
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</tr>
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<tr>
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<td>leal 8(%eax), %eax</td>
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<td> </td>
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</tr>
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</tbody>
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</table>
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<p>To complete the above tables, you must:</p>
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<ul>
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<li>Write an assembly program and include all the above x86-64 instructions in it. Of
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course, this program is going to be rather nonsensical. Not a problem!</li>
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<li>Compile your program.</li>
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<li>Use the objdump tool on the resulting object file you obtained from the
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compilation process.</li>
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<li>Looking at the result will lead you to the answer, i.e., the size of each of these x8664 instructions in bytes.</li>
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<li>In each table, bold the instruction that is the most space efficient.</li>
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<li>Copy the content of your program (*.s) into this assignment (into this
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Assignment_5.pdf document). <!--*--></li>
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<li>Copy the result you obtained from the objdump tool into this assignment (into this
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Assignment_5.pdf document).</li>
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</ul>
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<hr />
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<table>
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<thead>
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<tr>
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<th>Base + Displacement</th>
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<th>Stack</th>
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<th>Purpose</th>
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</tr>
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</thead>
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<tbody>
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</table>
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<p>Register Table:</p>
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<table>
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<thead>
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<tr>
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<th>Register</th>
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<th>Value</th>
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</tr>
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</thead>
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</table>
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<footer>
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</footer>
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</div>
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</main>
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</body>
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</html>
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