Andrew login ID Full Name Section 15 213 18 243 Spring 2011 Final Exam Tuesday May 3 2011 Page 1 of 33 Instructions Make sure that your exam is not missing any sheets then write your Andrew login ID full name and section on the front This exam is closed book and closed notes A notes sheet is attached to the back Write your answers in the space provided below the problem If you make a mess clearly indicate your final answer The exam has a maximum score of 200 points The problems are of varying difficulty The point value of each problem is indicated Good luck 1 24 2 14 3 20 4 14 5 14 6 10 7 14 8 25 9 15 10 14 11 14 12 14 13 8 TOTAL 200 Page 2 of 33 Problem 1 24 points Multiple choice Write the correct answer for each question in the following table 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 1 Which of the following is a legitimate difference between IA 32 and x86 64 a Buffer overflow exploits are impossible under x86 64 b IA 32 has caller and callee saved register conventions while x86 64 does not c Under x86 64 any instructions that take 32 bit operands are illegal d None of the above 2 Which of the following is the best justification for using the middle bits of an address as the set index into a cache rather than the most significant bits a Indexing with the most significant bits would necessitate a smaller cache than is possible with middle bit indexing resulting in generally worse cache performance b It is impossible to design a system that uses the most significant bits of an address as the set index c The process of determining whether a cache access will result in a hit or a miss is faster using middle bit indexing d A program with good spatial locality is likely to make more efficient use of the cache with middle bit indexing than with high bit indexing 3 Which of the following is not true about POSIX style signals a Certain signals cannot be blocked b A process can send a signal to itself c A signal handler executing as the result of a received signal can never be interrupted by another incoming signal d Signals can only be delivered when returning from system mode Page 3 of 33 4 Which of the following is not a benefit of virtual memory a It allows the virtual address space to be larger than the physical address space b No process can accidentally access the memory of another process c The TLB is more effective since without it dereferencing a virtual address now requires two or more memory accesses d Different processes can have overlapping virtual address spaces without conflict 5 Which of the following is a difference between blocking and ignoring a signal a Once a blocked signal is unblocked it will be handled by the process A signal that comes while it is being ignored will never be handled b SIGSTOP and SIGINT can be ignored but not blocked c Ignoring a signal only causes it to have no effect while blocking a signal returns the signal to its sender d None of the above 6 Where is the first argument to a function located in 32 bit assembly code immediately after the call instruction is executed a ebp 0x4 b ebp 0x4 c esp 0x4 d exp 0x4 Page 4 of 33 7 Consider the following piece of code where out txt s contents are abc int main int argc char argv int fd open out txt O RDWR char str xyz char c write fd1 str 1 read fd1 c 1 write fd1 c 1 return 0 What is the contents of out txt after the code is run Assume all system calls succeed a xbb b xba c xac d boat 8 Which of the following is the best reason to choose FastCGI over CGI a Superior support by web servers like Apache b Lower process creation costs c Lower process communication costs d Better process locality all tasks can be executed locally 9 Which of the following system calls can fail due to a network failure a socket b listen c bind d gethostbyname 10 Which of the following are copied on fork and preserved on exec a Global variables b File descriptor tables c Open file entry structs d None of the above Page 5 of 33 11 Why would the kernel designer opt for a 2 level page table when a full 2 level page table takes up more memory than a full 1 level page table a 2 level tables can translate virtual addresses faster b 2 level tables can reference more memory than 1 level tables c Most of the time a 2 level page table will take up less memory than a 1 level page table d They wouldn t Adding more tables offers no advantages 12 What section of memory holds the assembly for printf a Stack b Kernel memory c Shared libraries d Heap 13 Every thread has its own a Heap b Global values c Stack d Text data 14 Why is gethostbyname not thread safe a Only one thread at a time can do a DNS lookup b It doesn t have a mutex around it c It returns a pointer to global shared memory d It shares instructions with other threads 15 If a page table on a 32 bit system is 2KB in size how many entries does it contain a 2048 b 1024 c 512 d 256 Page 6 of 33 16 What is the function of the TLB a Caches data b Caches instructions c Caches translation of virtual addresses d Translates physical addresses to virtual addresses 17 What is distinctive about superscalar processors a Can run at frequencies over 3 5GHz b Can address over 4GB of memory c Can perform more than one instruction per cycle d Can have more than 2 levels of cache e Have more than one core per processor 18 True False When requested to send 20 bytes over a network socket execution will block until all 20 bytes have been sent a True b False 19 True False When printf returns the programmer cannot be guaranteed that the data has appeared on the user s terminal a True b False 20 Which of the following tools would you first use to debug an application which is exiting with the error Segmentation fault a gdb b strace c strings d objdump Page 7 of 33 21 Which of the following tools would you first use to debug a network application that never appears to accept any connections a gdb b strace c objdump d valgrind 22 Which of the following tools would you first use to debug an application which is exiting with a glibc error double free detected a gdb b strace c wireshark d valgrind 23 A 256 byte 4 …
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