CS140 Final Exam Page 1 of 13 Initials _____ Points ______ CS140 Operating Systems and Systems Programming Final Exam. Summer 2006. By Adam L Beberg. Given August 19th, 2006. Total time = 3 hours, Total Points = 335 Name: (please print)_____________________________________________________ In recognition of and in the spirit of the Stanford University Honor Code, I certify that I will neither give nor receive unpermitted aid on this exam. Signature:_____________________________________________________________ • This exam is closed notes and closed book. • No collaboration of any kind is permitted. • You have 3 hours to complete the exam. • There are 24 questions totaling 335 points. Some questions have multiple parts. Read all parts before answering! • Please check that you have all 13 pages. • Before starting, write your initials on each page, in case they become separated during grading. • Please print or write legibly. • Answers may not require all the space provided. Complete but concise answers are encouraged. • SCPD students: If you wish to have the exam returned to you at your company, please check the box. Page 2 /10 Page 3 /30 Page 4 /30 Page 5 /25 Page 6 /25 Page 7 /35 Page 8 /40 Page 9 /35 Page 10 /40 Page 11 /30 Page 12 /35 TOTAL /335 SCPD?CS140 Final Exam Page 2 of 13 Initials _____ Points ______ INSTRUCTIONS Near the beginning of the course, if not the first lecture, I said that even the "Hello World" application involved millions of lines of code to make run. Now that the course is over, and with your experience with Pintos, you should understand what all of those lines of code are doing. This is your chance to demonstrate that you understand operating systems. If you watched the lectures, did the assignment, and read the materials, all of these questions should be easy. This exam is 1/3 of your grade, so show us you know the material. You should have much more time then you need to do a great job. All questions will refer to the source code on the LAST page of this exam as "the code". Feel free to rip that page off and refer to it, and use it as scratch paper, you do not need to turn that page in (we have a copy). READ ALL THE QUESTIONS FIRST! Unlike most tests, this is not just a suggestion. In general you're asked what happens when things go smoothly, then about when things go a different way, each questions follows from the one before. If you're not about to be asked about an edge case, or an important issue, go ahead and mention it however. BEGIN CS 140 FINAL EXAM 1. [10] You take the code and run `gcc -c final.c -o final.o` to compile the code. What stuff is in the final.o file? Exact names/number are not needed, you did that in the midterm.CS140 Final Exam Page 3 of 13 Initials _____ Points ______ 2. [10] (a) Next you link final.o along with the standard C library. What does the linker spit out if the C library is a static library - libc.a? [5] (b) What unused code will end up in the program, and why? 3. [10] Same as question #2, but with a dynamic stared library - libc.so, how is this program different? 4. [5] List 3 things in the ELF header(s) of the program.CS140 Final Exam Page 4 of 13 Initials _____ Points ______ 5. [20] (a) Now you run `final`. What does the operating system do up to the point where you add it to the ready list? Assume lazy loading like in the project. (completely ignore the details of the file system for now, we'll get to that) [5] (b) And if we weren't so lazy? 6. [5] When you run final, all physical memory is already in use. What happens?CS140 Final Exam Page 5 of 13 Initials _____ Points ______ 7. [5] List 2 situations where the OS will not let the program run for you at that moment, but would let you if the situation was not happening. 8. [5] (a) Finally everything is going according to plan, you're ready. When do you get to run? [5] (b) Why could this be a while? [10] (c) If this was a typical type of program on the machines you administered, what scheduling algorithm would you want to use? Justify your choice.CS140 Final Exam Page 6 of 13 Initials _____ Points ______ 9. [5] (a) Which lines of code always generate a systems call? List #'s. [5] (b) Which lines of code might generate a system call? List #'s. 10. [10] (a) Assume timeslices end right after every line of code by using the Pyschic Timeslice Algorithm™. If we're using an exponential feedback algorithm, what's happening to our priority as we go through the program. Use lower to mean low priority in your description, not a low queue number, and higher to mean higher priority. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 [5] (b) What if we're billing all time spent in the system call time to the process, would this change your answers? Which ones?CS140 Final Exam Page 7 of 13 Initials _____ Points ______ 11. [20] (a) Now back to that file system were ignoring. If we're running on the Elaine machines and using an ACL based access control system, what happens when the open() in line 5 is run? Describe all the structures and OS ideas involved. (now you can ignore the syscall details) [10] (b) What if we were in a Capabilities based system? Also, What happened at login to make this possible? [5] (c) What if the file isn’t openable, what's different between how ACL and Capabilities handle it?CS140 Final Exam Page 8 of 13 Initials _____ Points ______ 12. [10] Now we're in a typical UNIX file system with inodes. What's going to be happening as far as figuring out where the blocks are as we read (many) blocks due to line 7. [5] (b) … and with an extent based file system? 13. [10] How would this be different if before line 7 there was a call to mmap(). 14. [10] (a) By now we know what disk blocks we need and have a long list, and so do other processes (maybe they have short lists). What do we tell the disk to do so everyone is happy? [5] (b) What does SCSI do that IDE doesn’t that's makes this a non-issue.CS140 Final Exam Page 9 of 13 Initials _____ Points ______ 15. [10] After we start this program, the system comes to a standstill, and becomes unbearably slow. In what ways could
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