Description

1. The assignment specification doesn’t fully explain the assignment. What can I do?
2. What is gitlab.cse.unsw.edu.au? How do I want use it for assignment 2?
3. Discuss strategies for decoding instructions for the assignment.
Assembler C Bit Pattern
add $d, $s, $t d = s + t 000000ssssstttttddddd00000100000
sub $d, $s, $t d = s – t 000000ssssstttttddddd00000100010
and $d, $s, $t d = s & t 000000ssssstttttddddd00000100100
or $d, $s, $t d = s | t 000000ssssstttttddddd00000100101
slt $d, $s, $t d = 1 if s < t else 0 000000ssssstttttddddd00000101010
mul $d, $s, $t d = s * t 011100ssssstttttddddd00000000010
beq $s, $t, I if (s == t) PC += I 000100ssssstttttIIIIIIIIIIIIIIII
bne $s, $t, I if (s != t) PC += I 000101ssssstttttIIIIIIIIIIIIIIII
addi $t, $s, I t = s + I 001000ssssstttttIIIIIIIIIIIIIIII
slti $t, $s, I t = (s < I) 001010ssssstttttIIIIIIIIIIIIIIII
andi $t, $s, I t = s & I 001100ssssstttttIIIIIIIIIIIIIIII
ori $t, $s, I t = s | I 001101ssssstttttIIIIIIIIIIIIIIII
lui $t, I t = I << 16 00111100000tttttIIIIIIIIIIIIIIII
syscall syscall
What should my smips.c do for this example: 00000000000000000000000000001100
$ cat test.s
136bfffa
$ ./smips test.s
4.
Decode it this instruction mean?
What should happen when t is executed by smips.c
How can check my answer?
5. We say that the Unix filesystem is tree-structured, with the directory called / as the root of the tree, e.g.,

Answer the following based on the above diagram:
a. What is the full pathname of COMP1521’s web directory?
b. Which directory is ~jas/../..?
c. Links to the children of a given directory are stored as entries in the directory structure. Where is the link to the parent directory stored?
d. What kind of filesystem object is cat?
e. What kind of filesystem object is home?
f. What kind of filesystem object is tty0?
g. What kind of filesystem object is a symbolic link? What value does it contain?
h. Symbolic links change the filesystem from a tree structure to a graph structure. How do they do this?
6. The stat() and lstat() functions both take an argument which is a pointer to a struct stat object, and fill it with the meta-data for a named file.
On Linux, a struct stat contains the following fields (among others, which have omitted for simplicity):

Explain what each of the fields represents (in more detail than given in the comment!) and give a typical value for a regular file which appears as follows:
$ ls -ls stat.c
8 -rw-r–r– 1 jas cs1521 1855 Sep 9 14:24 stat.c
Assume that jas has user id 516, and the cs1521 group has group id 36820.
7. Consider the following (edited) output from the command ls -l ~cs1521:
drwxr-x— 11 cs1521 cs1521 4096 Aug 27 11:59 17s2.work drwxr-xr-x 2 cs1521 cs1521 4096 Aug 20 13:20 bin -rw-r—– 1 cs1521 cs1521 38 Jul 20 14:28 give.spec drwxr-xr-x 3 cs1521 cs1521 4096 Aug 20 13:20 lib drwxr-x–x 3 cs1521 cs1521 4096 Jul 20 10:58 public_html drwxr-xr-x 12 cs1521 cs1521 4096 Aug 13 17:31 spim drwxr-x— 2 cs1521 cs1521 4096 Sep 4 15:18 tmp
lrwxrwxrwx 1 cs1521 cs1521 11 Jul 16 18:33 web -> public_html
a. Who can access the 17s2.work directory?
b. What operations can a typical user perform on the public_html directory? c. What is the file web?
d. What is the difference between stat(“web”, &info) and lstat(“web”, &info)?
(where info is an object of type (struct stat))
8. Write a C program, chmod_if_public_write.c, which is given 1+ command-line arguments which are the pathnames of files or directories
If the file or directory is publically-writeable, it should change it to be not publically-writeable, leaving other permissions unchanged.
It also should print a line to stdout as in the example below
$ dcc chmod_if_public_write.c -o chmod_if_public_write
$ ls -ld file_modes.c file_modes file_sizes.c file_sizes
-rwxr-xrwx 1 z5555555 z5555555 116744 Nov 2 13:00 file_sizes
-rw-r–r– 1 z5555555 z5555555 604 Nov 2 12:58 file_sizes.c -rwxr-xr-x 1 z5555555 z5555555 222672 Nov 2 13:00 file_modes
-rw-r–rw- 1 z5555555 z5555555 2934 Nov 2 12:59 file_modes.c $ ./file_modes file_modes file_modes.c file_sizes file_sizes.c removing public write from file_sizes file_sizes.c is not publically writable file_modes is not publically writable removing public write from file_modes.c
$ ls -ld file_modes.c file_modes file_sizes.c file_sizes
-rwxr-xr-x 1 z5555555 z5555555 116744 Nov 2 13:00 file_sizes
-rw-r–r– 1 z5555555 z5555555 604 Nov 2 12:58 file_sizes.c -rwxr-xr-x 1 z5555555 z5555555 222672 Nov 2 13:00 file_modes
-rw-r–r– 1 z5555555 z5555555 2934 Nov 2 12:59 file_modes.c
Make sure you handle errors.
9. Write a C program, fgrep.c, which is given 1+ command-line arguments which is a string to search for.
9. Write a C program, fgrep.c, which is given 1+ command line arguments which is a string to search for.
If there is only 1 command-line argument it should read lines from stdin and print them to stdout iff they contain the string specified as the first command line argumenbt.
If there are 2 or more command line arguments, it should treat arguments after the first as fiilenames and print any lines they contain which contain the string specified as the first command line arguments.
When printing lines your program should prefix them with a line number.
It should print suitable error messages if given an incorrect number of arguments or if there is an error opening a file.
For all enquiries, please email the class account at cs1521@cse.unsw.edu.au
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