Syscall Symphony (CSE522S Final Project)

Authors: William Gozlan, Meagan Konst, Diva Harsoor

About

This is the full version of the final version of Syscall Symphony, our final project for CSE522S. This project was prepared on the Raspberry Pi 3B+ running the Raspberry Pi OS. See the project report for more details.

Setup, Build, and Run Instructions:

1.) Clone the main branch of this repository in your root directory. The commands to do so are as follows. Note this will require sudo privileges.

cd /
git clone https://github.com/willgozlan/syscall-symphony.git  

2.) Verify dependencies:

• Ensure you have gawk and bison installed as these are dependencies (sudo apt install gawk bison)
• Ensure you have the aplay utility to play wav files from command line. Check in /usr/bin/aplay. If you don't have it, you can install it with sudo apt-get install alsa-utils
• Right now, assumptions are made that the repo is cloned into the root directory, as this allows many users to link with glibc-symphony. See report for more details.

3.) The project directory syscall-symphony/contains 5 sub-directories as follows:

• examples/: This contains an example program to test our modifications to glibc, as well as a Makefile to build and link against our version of glibc.
• finding_syscalls/: This contains example programs that call a simple system call, then return. The included Makefile links against normal glibc. We used this along with gdb to find where specific system calls are implemented. See project report for more details.
• glibc-symphony/: This is the main directory for our modifed glibc version to make changes to the glibc source code as well as build and run it. There are 3 directories, as follows:
  • glibc/: glibc source code, where we make our modifications
  • glibc-build/: Initially empty directory where glibc will be built
  • local/: Initially empty directory where the headers/library files get installed after build, and the linker path should point to link with glibc-symphony.
• pid-tools/: This contains source files for the add_pid and remove_pid programs, along with a Makefile to build them. Additional files are dependencies to build these 2 programs.
• sounds/: The wav files for the specific syscalls reside here.

Gain a sudo terminal through sudo su. Therefore, the following commands execute with root privileges.

Navigate into the /syscall-symphony/glibc-symphony/glibc-build directory and run the following, where PATH is the absolute path to syscall-symphony/glibc-symphony/local.

../glibc/configure --prefix=PATH

Since you should have cloned into root, the command should be as follows: ../glibc/configure --prefix=/syscall-symphony/glibc-symphony/local

4.) From the same directory (/syscall-symphony/glibc-symphony/glibc-build), compile with make -j4. Note, you could also make clean, if you wanted to clean up leftover artifacts in future builds. Expect this to take around 40 minutes on the RaspberryPi.

5.) Still within the same directory (/syscall-symphony/glibc-symphony/glibc-build), install everything into the /syscall-symphony/glibc-symphony/local by running: make -j4 install. This should be quicker than the last step, but still take about 20 minutes on the RaspberryPi.

6.) Navigate to the pid-tools directory in /syscall-symphony/pid-tools. From there, run make to compile the PID user tools you need to add and remove files from the pid list.

You are done compiling and setting up our version of glibc!

7.) Finally, to test this modifed version of glibc, navigate into the /syscall-symphony/examples directory. Run make to build the sample programs with the provided Makefile, which links against glibc-symphony. Finally, there are several programs you can run to see this works.

• The programs with a system call as a name (open, close, read, write, sleep, fork) and glibc functions (malloc, free) print the PID, then block on a call to getc for stdin. To use these, run the executable; then, from another terminal, navigate to /syscall-symphony/pid-tools and run add_pid with the PID as an argument to add it to the PID list. Then, in the other terminal that is waiting for standard input, press any key to continue and watch the system call play a sound then continue to run as normal! Upon the programs exit, you can run remove_pid with the PID as an argument to remove it from the PID list.
• The programs big_example and parallel_dense_mm add and remove the PID's automaitically from the list by envoking a call to system to execute add_pid and remove_pid. You can run them as normal and the sounds should play. Note that parallel_dense_mm was adopted from CSE422S studios.

Note: The first line of the Makefile in the /syscall-symphony/examples directory contains a variable on the first line called testglibc, which points to where /syscall-symphony/glibc-symphony/local is on your system, using an absolute path.

Troubleshooting

1.) Problem: Audio doesn't come through

Solution: - Ensure an audio device is plugged into the RaspberryPi, and it is on. - Ensure the audio out is set to the correct location by running sudo raspi-config, then going to System Options -> Audio -> Headphones -> OK -> Finish. Alternatively you could set this to HDMI if you are using an HDMI device with speakers. - You can verify ALSA's aplay is working by navigating to syscall-symphony/sounds/ and playing the open.wav file by running aplay open.wav.

2.) Problem: No such file or directory for either /usr/bin/aplay or /syscall-symphony/sounds/open.wav

Solution: See step 2 above, and ensure the repository is cloned into / directory.

3.) Problem: -bash: ./: No such file or directory in step 6, even though the executable is there

Solution: See the note in step 6. The testglibc variable is set to the wrong place (it must be an absolute path to /syscall-symphony/glibc-symphony/local).

Known Bugs

See project report for more details on this.

Segmentation fault when perror or printf is called by a program linked with glibc-symphony (our modified version of glibc)

This is due to infinite recursion from the write syscall wrapper, which we modified to check if the calling process has sound privileges. This check uses modified syscall wrappers, which then check if the calling process has sound privileges…and so on. To fix, we should remove all calls to perror and printf and replace with functions that call the write syscall using the manifest constant instead of the glibc wrapper.

Race condition with remove_pid temporary file

The executable created from remove_pid.c creates a temporary file named temp, whose creation and deletion is not included in the critical section protected by flock(). To fix, we should either expand the critical section to include the temporary file or we should give each concurrent process a temporary file with a unique name.