Description

1. How is the assignment going?
Does anyone have hints or advice for other students?
Has anyone discovered interesting cases that have to be handled?
2. Write a C program, print_diary.c, which prints the contents of the file $HOME/.diary to stdout
The lecture example getenv.c shows how to get the value of an environment variable.
snprintf is a convenient fucntion for constructing the pathname of the diary file.
3. Write a C program, print_file_bits.c, which given as a command line arguments the name of a file contain 32-bit hexadecimal numbers, one per line, prints the low (least significant) bytes of each number as a signed decimal number (-128..127).
4. Assume we have 6 virtual memory pages and 4 physical memory pages and are using a least-recently-used (LRU) replacement strategy.
What will happen if these virtualmemory pages were accessed?
5 3 5 3 0 1 2 2 3 5
5. Discuss code supplied for the lru lab exercise.

6. Each new process in a computer system will have a new address space. Which parts of the address space contain initial values at the point when the process starts running? Code? Data? Heap? Stack? Which parts of the address space can be modified as the process executes?
7. One possible (and quite old) approach to loading programs into memory is to load the entire program address space into a single contiguous chunk of RAM, but not necessarily at location 0. For example:

Doing this requires all of the addresses in the program to be rewritten relative to the new base address.
Consider the following piece of MIPS code, where loop1 is located at 0x1000, end_loop1 is located at 0x1028, and array is located at 0x2000. If the program containing this code is loaded starting at address A = 0x8000, which instructions need to be rewritten, and what addresses are in the relocated code?

8. What is the difference between a virtual address and a physical address?
9. Consider a process whose address space is partitioned into 4KB pages and the pages are distributed across the memory as shown in the diagram below:

The low byte address in the process is 0 (in Code1) and the top byte address in the process is 28671 (max address in page containing Stack2).
For each of the following process addresses (in decimal notation), determine what physical address it maps to. a. jal func, where the label func is at 5096
b. lw $s0,($sp), where $sp contains 28668
c. la $t0, msg, where the label msg is at 10192
10. The working set of a process could be defined as the set of pages being referenced by the process over a small window of time. This would naturally include the pages containing the code being executed, and the pages holding the data being accessed by this code.
Consider the following code, which computes the sum of all values in a very large array:

Answer the questions below under the assumptions that pages are 4 KiB (4096 bytes), all of the above code fits in a single page, the sum and i variables are implemented in registers, and there is just one process running in the system. a. How large is the working set of this piece of code?
g g p
b. Assuming that the code is already loaded in memory, but that none of bigArray is loaded, and that only the working set is held in memory, how many page faults are likely to be generated during the execution of this code?
11. Consider a (very small) virtual memory system with the following properties:
a process with 5 pages a memory with 4 frames
page table entries containing (Status, MemoryFrameNo, LastAccessTime)
pages status is one of NotLoaded, Loaded, Modified (where Modified implies Loaded)
Page table:

If all of the memory frames are initially empty, and the page table entries are flagged as NotLoaded, show how the page table for this process changes as the following operations occur:
read page0, read page4, read page0, write page4, read page1, read page3, read page2, write page2, read page1, read page0,
Assume that a LRU page replacement policy is used, and unmodified pages are considered for replacement before modified pages. Assume also that access times are clock ticks, and each of the above operations takes one clock tick.
12. Some commands on Unix allow you to name the files that they operate on, e.g.,
$ cat file
Commands that read from their standard input allow you to specify which file they read their input from by redirecting their standard input, e.g.,
$ cat < file
Describe how each of these cases might be implemented. Assume that once the file is made accessible, it is scanned and copied to the standard output (file descriptor 1, or the #define’d constant STDOUT_FILENO) as follows:

Revision questions
19. Write a C program, compile.c, which is given 1+ command-line arguments which are the pathname of single file C programs.
It should compile each program with dcc.
It also should print the compile command to stdout.
$ dcc compile.c -o compile
$ ./compile file_sizes.c file_modes.c
/usr/local/bin/dcc file_modes.c -o file_modes
/usr/local/bin/dcc file_sizes.c -o file_sizes
Make sure you handle errors, for example, you should stop if any compile fails.
20. Consider the following edited output from the ps(1) command running on one of the CSE servers:
PID VSZ RSS TTY STAT START TIME COMMAND
1 3316 1848 ? Ss Jul08 1:36 init
321 6580 3256 pts/52 Ss+ Aug26 0:00 -bash
334 41668 11384 pts/44 Sl+ Aug02 0:00 vim timing_result.txt
835 6584 3252 pts/124 Ss+ Aug27 0:00 -bash
857 41120 10740 pts/7 Sl+ Aug22 0:00 vi echon.pl
924 6524 3188 pts/184 Ss 15:52 0:00 -bash
938 3664 96 pts/184 S 15:52 0:00 /usr/local/bin/checkmail
1199 6400 3004 pts/142 Ss Oct05 0:00 -bash
1381 41504 11436 pts/142 Sl+ Oct05 0:00 vim PageTable.h
2558 3664 96 pts/120 S 13:47 0:00 /usr/local/bin/checkmail
2912 41512 11260 pts/46 Sl+ Aug02 0:00 vim IntList.c
3483 14880 5168 pts/149 S+ Sep20 0:00 gnuplot Window.plot
3693 41208 11240 pts/120 Tl 13:50 0:00 vim trace4
3742 6580 3320 pts/116 Ss+ Sep07 0:00 -bash
5531 6092 2068 pts/158 R+ 16:04 0:00 ps au
5532 4624 684 pts/158 S+ 16:04 0:00 cut -c10-15,26-
5538 3664 92 pts/137 S 15:05 0:00 /usr/local/bin/checkmail
6620 5696 3028 pts/89 S+ Aug13 0:00 nano PingClient.java
7132 41516 11196 pts/132 Sl+ Sep08 0:00 vim board1.s
12256 335316 10436 ? Sl Aug14 15:01 java PingServer 3331
12272 4260 2816 ? Ss Aug02 10:34 tmux 12323 10276 4564 ? S Sep09 0:02 /usr/lib/i386-linux-gnu/gconf/gconfd-2
12461 4260 2808 ? Ss Sep02 5:42 tmux
13051 43448 13320 pts/110 Sl+ Sep05 0:02 vim frequency.pl
13200 47772 21928 ? Ssl 15:19 0:02 gvim browser.cgi
13203 41756 11560 pts/26 Sl+ Aug12 0:02 vim DLList.h
13936 11872 6856 ? S Sep19 0:06 /usr/lib/gvfs/gvfs-gdu-volume-monitor
30383 7624 3828 pts/77 S+ Aug23 336:28 top
a. Where might you look to find out the answers to the following questions?
b. What does each of the columns represent?
c. What do the first characters in the STAT column mean?
d. Which process has consumed the most CPU time?
e. Why do some processes have no TTY?
f. When was this machine last re-booted?
21. The Unix/Linux shell is a text-oriented program that runs other programs. It behaves more-or-less as follows:
print a prompt while (read another command line) {
break the command line into an array of words (args[])
// args[0] is the name of the command, a[1],… are the command-line args if (args[0] starts with ‘.’ or ‘/’) check whether args[0] is executable else
search the command PATH for an executable file called args[0] if (no executable called args[0]) print “Command not found” else
execute the command print a prompt
}
a. How can you find what directories are in the PATH?
b. Describe the “search the command PATH” process in more detail. What the kinds of system calls would be needed to determine whether there was an executable file in one of the path directories?
22. The kill(1) command (run from the shell command-line) and the kill() system call can be used to send any of the defined signals to a specified process. For each of the following signals, explain the circumstances under which it might be generated (apart from kill(1)), and what is the default effect on the process receiving the signal: a. SIGHUP
b. SIGINT
c. SIGQUIT
d. SIGABRT
e. SIGFPE f SIGSEGV
f. SIGSEGV
g. SIGPIPE
h. SIGTSTP
i. SIGCONT
23. The sigaction(2) function for defining signal handlers takes three arguments:
int signum … the signal whose handler is being defined struct sigaction *act … pointer to a record describing how to handle the signal
struct sigaction *oldact … pointer to a record describing how the signal was handled (set by sigaction(3) if not NULL)
The struct sigaction record includes a field of type void (*sa_handler)(int).
Describe precisely what this field is, and what its type signature means.
24. Consider the following program:

What does this program do if it receives
a. a SIGHUP signal?
b. a SIGINT signal?
c. a SIGTSTP signal?
d. a SIGKILL signal?
For all enquiries, please email the class account at cs1521@cse.unsw.edu.au
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