LAB 1 SOLUTION

PART 1: SETTING UP THE XV6 DEVELOPMENT ENVIRONMENT.



We will use the Linux cluster provided by the CS Department.
1.
First, whenever the amount of AFS free space in your account is less than 500MB, you can

carry out the following process to increase. your disk quota (thanks to our Tech Support

Team!):


a. Log in to https://my.pitt.edu

b. Click on "Profile" at the top of the screen

c. Click on "Manage Your Account"

d. Click on "Manage Email Quota"
2.
e. Click on "Increase My UNIX Quota"

Log in to linux.cs.pitt.edu using your Pitt account. From a UNIX box, you can type:

use PuTTY.
assuming ksm73 is your Pitt ID. From Windows, you may
3.
h ksm73@linux.cs.pitt.edu


Under Linux, run the following command to download the Xv6 source code:
4.
cd xv6-public then type make qemu-nox to compile and run XV6. To exit, press CTRL+a

git clone git://github.com/mit-pdos/xv6-public.git
then x.



getcount
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PART 2: ADDING A SYSTEM CALL TO XV6
to xv6, which, when passed a valid

syscall.h


You'll then add a new system call named



system call number (listed in the file "


") as an argument, will return the number of
times the referenced system call was invoked by the calling process.

For instance, consider the following test program (getcount.c):



#include "types.h"
#include "user.h"
#include "syscall.h"
int main(int argc, char *argv[])
{
printf(1, "initial fork count %d\n", getcount(SYS_fork)); if (fork() == 0) {
printf(1, "child fork count %d\n", getcount(SYS_fork)); printf(1, "child write count %d\n", getcount(SYS_write));

} else { wait();

printf(1, "parent fork count %d\n", getcount(SYS_fork)); printf(1, "parent write count %d\n", getcount(SYS_write));

}
printf(1, "wait count %d\n", getcount(SYS_wait));
exit();
will} produce the following output (note that each character is output with a separate call to write/printf in xv6):

initial fork count 0

child fork count 0

child write count 19

wait count 0

parent fork count 1

parent write count 41

wait count 1


HintsYou will need to modify several files for this exercise, though the total number of lines of code you'll be adding is quite small. At a minimum, you'll need to alter

, and to implement your new system call. It may be helpfulsyscalltotrace.h, syscallhow.c, someuser.hother usyssystem.S call is implemented (e.g., uptime) for clues.

You will likely also need to update struct proc, located in proc.h, to add a syscall-count tracking data structure for each process. To re-initialize your data structure when a

    1 Adapted from http://moss.cs.iit.edu/cs450/assign01-xv6-syscall.html

    2 
process terminates, you may want to look into the functions in

Add the syscall
to
implementation into

Look at other syscall implementations inside


see how to pop the parameters from the stack.
proc.c.




sysproc.c.



sysproc.c


Chapter 3 of the xv6 book (in pdf) contains details on traps and system calls (though most of the low level details won't be necessary for you to complete this exercise).

TestingTotest your implementation, you'll run the executable (when booted into xv6), which is based on the program above. Becausegetcounttheprogram depends on your

getcount




implementation, it isn't compiled into xv6 by default. When you're ready to test, you
should add

getc unt example






to UPROGS declaration in the Makefile.


Note that while the



syscall.h




only prints out counts for three different system
calls, your implementation should support all the system calls listed in

. It is a
good exercise to add tests to the test program, located in getcount.c, for other system calls.


SUBMISSION INSTRUCTIONS



Submit to GradeScope the files that you have modified within the source code of xv6. You should modify the following files only:

    • syscall.h

    • syscall.c

    • user.h

    • usys.S

    • proc.h

    • proc.c

    • sysproc.c

    • Makefile
Your submission will be graded by compiling and running it and reviewing the source code.






















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