Lab 3: Create A System Call Solution

Add a New System Call to XV6




In Lab3, you will download and install onto your Linux system an instance of XV6, a very small but complete operating system written in C. You will then add a new system call getsyscallinfo(), which returns the value of a global kernel integer named callCount, which is incremented each time a system call is executed.




Learning Objectives




Install and configure git, QEMU and XV6



Run XV6 under QEMU and execute shell commands to verify your installation



Modify XV6 to add a new system call getsyscallinfo()and add a global integer to the kernel named callCount, initialized to zero and incremented each time a system call is made.



Run provided program peep that calls getsyscallinfo() a few times interspersed with other system calls, and prints out either Success or a diagnostic message to aid in debugging.



Assignment




Begin by installing the tools you will need for this assignment:




mkdir -p ~/cs3100/lab3




cd ~/cs3100/lab3




sudo apt-get update # refresh the apt-get database




sudo apt-get install git




sudo apt-get install qemu




git clone git://github.com/WeberState/xv6-public.git




scp
USER@icarus.cs.weber.edu:/var/classes/cs3100/lab3/Makefile .
make get
# retrieve
the files we will be editing (once)
make
# this will build xv6 and launch
it under qemu
cat
README.TED
# displays
a XV6 README.TED file


CTRL-A X
# press and release CTRL-A, then type X
which will terminate QEMU and XV6



The next step is to modify the source files needed to implement the new system call. These are the files:




syscall.c syscall.h sysproc.c trap.c user.h usys.S peep.c




You are to implement the following:




a new system call called getsyscallinfo() which retrieves the current number of times any system call has been issued since boot (hint: sysproc.c, usys.h and user.h).



a global kernel integer named callCount (int callCount = 0;) that is incremented each time any system call is issued (hint: trap.c)



a new entry at the end of the system call table representing getsyscallinfo() (hint: syscall.c and syscall.h)



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Your workflow is to retrieve these source files from xv6-public so you can edit them, then copy them back into xv6-public for compilation. The Makefile you retrieved from icarus has these commands that facilitate your workflow:




make (or make install): copies your copy of the source files from ~/cs3100/lab3, builds the XV6 kernel and launches qemu to load and run xv6. You will receive a $ prompt and you can enter a very limited numer of shell commands, including peep. Type CTRL-A X to terminate xv6 and qemu.




make get: copies the specific source files you will need from ~/cs3100/lab3/xv6 -public to ~/cs3100/lab3 so you can edit them outside of the xv6-public folder. This copy is non-destructive, meaning that no files will be overwritten if you have already executed this command before.




A note about file peep.c: this is a program written by your instructor to test the implementation of your new system call. However, as delivered, all of the important code is commented out. This was done so you wouldn't get compilation errors when building your xv6 kernel. When you have updated the other source files with the code needed for this lab, remove the /* */ from peep.c and make install. When xv6 displays the $ prompt, type peep 20 (or some other number greater than 1) and see what peep reports. If you see the word "Success", your new system call should be working properly. If it reports a failure, you will receive additional information. If you receive nothing at all, you forgot to remove the comments. We reserve the right to enhance peep.c throughout the semester, even for this assignment. If we do, instructions will be provided.




Example output




Here is an example of how your xv6 should behave when compiled and run:



























































































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I typed "make"




tcowan@tcowan-Ubuntu:~/cs3100/lab3$ make

cp syscall.c syscall.h sysproc.c trap.c user.h usys.S peep.c xv6-public/




cd xv6-public; make; make qemu-nox Another makefile is run make[1]: Entering directory `/home/tcowan/cs3100/lab3/xv6-public'




gcc -fno-pic -static -fno-builtin -fno-strict-aliasing -fvar-tracking - fvar-tracking-assignments -O0 -g -Wall -MD -gdwarf-2 -m32 -Werror -fno-

omit-frame-pointer -fno-stack-protector
-c -o syscall.o syscall.c
.
A bunch of compilation
.
.
steps take place
.





dd if=/dev/zero of=xv6.img count=10000




10000+0 records in The xv6 file system image is created

10000+0 records out




5120000 bytes (5.1 MB) copied, 0.053437 s, 95.8 MB/s




if=bootblock of=xv6.img conv=notrunc 1+0 records in



1+0 records out




512 bytes (512 B) copied, 0.000103275 s, 5.0 MB/s dd if=kernel of=xv6.img seek=1 conv=notrunc 353+1 records in




353+1 records out




180820 bytes (181 kB) copied, 0.00047917 s, 377 MB/s




make[1]: Leaving directory `/home/tcowan/cs3100/lab3/xv6-public'




make[1]: Entering directory `/home/tcowan/cs3100/lab3/xv6-public' qemu-system-i386 -nographic -hdb fs.img xv6.img -smp 2 -m 512 xv6...




cpu1:
starting
qemu loads and runs xv6
cpu0:
starting


sb: size 1000 nblocks 941 ninodes 200 nlog 30 logstart 2 inodestart 32 bmap start 58




init: starting sh
$ is the xv6 shell prompt
$


$
peep was called but it still is
$ peep 20
$
totally commented out
CTRL-A X was typed
$ QEMU: Terminated



make[1]: Leaving directory `/home/tcowan/cs3100/lab3/xv6-public' tcowan@tcowan-Ubuntu:~/cs3100/lab3$



















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Hints and Suggestions




Search xv6 for a simple system call and see how it is implemented in the files mentioned above. Suggestion: getpid().



qemu is a complex virtualization software product with a ton of command-line parameters and configuration options. Use make to run it until you know more about what you are doing. See man qemu.



xv6 has documentation! A PDF file is attached to the module containing this assignment in Canvas.



Grading




I use Cucumber scripts to help grade programs. Please note the following:




The cucumber tests will fail if you do not follow the naming instructions, so please be sure that the programs are named correctly. As long as the source file is named correctly, and you have to upload it to Canvas more than once, the displayed name may have a number after it. That is just for display purposes and your file should still be named correctly internally.



Upload the files you modified for this assignment to Canvas when you are ready for me to grade your work. You should upload only the following, using the Firefox web browser in ubuntu:
syscall.c syscall.h sysproc.c trap.c user.h usys.S




It is not necessary to upload your files to icarus for this assignment.



NOTE: Just because cucumber reports a certain number of points for your submission of the assignment, the instructor reserves the right to inspect your code, run your submission with additional tools and manually grade your assignment. The decision of the instructor is final. Test your code thoroughly to ensure all requirements are fully met.




Here is how you earn points for this assignment:




FEATURES
POINTS




Must-Have Features






Files are named correctly and only the following files are uploaded to Canvas:
50
syscall.c syscall.h sysproc.c trap.c user.h usys.S


xv6 compiles and builds a usable kernel and file system without errors or warnings
50
with your implementation of system call getsyscallinfo(), which uses a


kernel integer variable named callCount.


xv6 runs with system call getsyscallinfo() under qemu, displays the $
50
command prompt and accepts and processes shell commands






peep compiles and runs under xv6 with calls to getsyscallinfo(), and each
50
time it is passed an integer 1, displays "Success"






Grand Total
200










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