(2) System Tools
COP-3402, Spring 2024

mkdir newdir
touch emptyfile.txt
cd newdir
pwd
ls
cd ../
cd ~/
rmdir newdir
rm newdir/empty
rmdir newdir
mkdir targetdir
cp emptyfile.txt targetdir
ls -R
ls targetdir/
touch filetomove.txt
mv filetomove.txt targetdir
ls -R
cd targetdir
mv filetomove.txt ../
cd ../
ls -R

ls <tab><tab>n<tab>
touch none.txt
ls <tab><tab>n<tab><tab>o<tab>

tree # to show hierarchy
ls /<tab><tab>v<tab><tab>
pwd
cd subdir
# absolute vs relative paths
cd ../ # parent dir
cd ./ # current dir
ls ./ # current dir
cat ./newfile.txt # same as cat newfile.txt
ls -la

ls > lsoutput.txt
gcc -o printer printer.c  # fprintf(stdout/stderr)
./printer > out  # ./printer 1> out
./printer 2> err
./printer > out 2> err
./print >out 2>&1

• Redirections stdio between processes (instead of just files)

cat file
cat file | grep "hello"
cat file | grep "hello" | cut c2-

ps
ps -aux
ps -aux | grep paul
ls
top
htop
echo $?

man cat
man atoi
man -a exec

tar -cvf packagename.tar file1 file2
tar -tvf packagename.tar
tar -xvf packagename.tar

• nano, emacs, vim

• Show differences between text files

• Show raw bytes of a file

1. Enter your virtual machine, which should have been setup according to these instructions

   cd cop3402spring24
   vagrant ssh
   

2. Create the ssh key

   ssh-keygen -b 4096
   # can just hit enter a few times for an empty password, but generally adding a password is a good idea
   

3. View your public key (be sure to have the .pub extension or you will reveal your private key!)

   cat ~/.ssh/id_rsa.pub  # .pub is important!
   

4. Add your public key to github according to their directions

5. Configure git with your name and email, replacing "Your Name" with your name and "youremail@yourdomain.com" with your the email address you use for GitHub.

   git config --global user.name "Your Name"
   git config --global user.email "youremail@yourdomain.com"
   

6. Add the key to your ssh key manager (optional, but avoids prompt for ssh key password)

   eval $(keychain --eval)  # add to keychain
   ssh-add ~/.ssh/id_rsa
   

   If keychain fails to run, then be sure your virtual machine has been provisioned

7. Clone your repository into the mapped vagrant folder

   cd /vagrant
   

   Clone your repository (replacing USERNAME with your GitHub user name). If this is your first time connecting with GitHub, it will ask you to confirm that server key matches GitHub's server key. If your keys are setup properly, you should see this succeed without error.

   git clone git@github.com:cop3402/toy-compiler-1-USERNAME.git # github username
   

   Enter your repository directory:

   cd toy-compiler-1-USERNAME
   

git status # check what files have been modified or are not yet added
git add filetoadd # only needed if file hasn't been added yet
git commit filetocommit  # enter a commit message in the editor
git log # see your new commit in the log
git push # sync your local and remote repos

git add parser.c
git commit parser.c
# write a commit message in the editor that opens
git push

cpp -o file.i file.c

gcc -S -O0 hello.c
file hello.s

as -o hello.o hello.c
file hello.o

https://www.agix.com.au/creating-a-hello-world-program-in-assembly-language-in-5-minutes/

gcc -o hello.exe -v hello.o # shows linker
file hello.exe

https://systemoverlord.com/2017/03/19/got-and-plt-for-pwning.html

https://stackoverflow.com/questions/5469274/what-does-plt-mean-here

http://dustin.schultz.io/how-is-glibc-loaded-at-runtime.html

• Preprocessor: file.c -> file.i
• Compiler: file.i -> file.asm
• Assembler: file.asm -> file.o
• Linker: file.o, libraries -> file.exe

https://thecustomizewindows.com/2012/07/kernel-of-operating-system/

• Hardware access protection (processor, mem, I/O)
  • No (intentional) direct access to hardware
• Library of system calls (syscalls) for applications
• Resource management among running programs
  • Processes, illusion of simultaneous execution

• Use an agreed-on binary file format, e.g., ELF for *nix
• Provide the location of the first thing to run: _start by convention for C
• Use the exec-family and exit syscalls to start and stop our program

• Dynamic linking
• Signals
• I/O
• Memory management
• Process management

• Brings binary file into memory
• Begins execution
• Can take argc/argv, environment variables, pass along to process
• Sets up file, I/O

(exec ./hello.exe)

• Defines entrypoint _start
• crt sets up: signals, stdio, args (from loader), exit code (syscall)
• Calls main, passing argc/argv
• Takes main's return value passes it to the exit syscall
  • This is why main has a return value
  • The

https://web.archive.org/web/20230321203036/https://wiki.osdev.org/How_kernel,_compiler,_and_C_library_work_together https://web.archive.org/web/20230411170432/https://wiki.osdev.org/Creating_a_C_Library

• Compiler toolchain: file.c -> file.exe
• Loader: file.exe -> running process in RAM

• https://lwn.net/Articles/630727/
• https://lwn.net/Articles/631631/

• .o files symbol tables have missing entries
• Linker resolves missing entries

gcc -c caller.c
gcc -c callee.c
objdump -t caller.o
objdump -t callee.o
gcc -c main.c
objdump -t main.o
gcc -o main.exe main.o caller.o callee.o # link
objdump -t main.exe
readelf -a caller.o
readelf -a main.exe

Moving common declarations of external functions to a .h file.

• Conventions: all, clean (phony)
• built-in rules
• (Diagram) dependency graph

SRC := \
        caller.c \
        callee.c \
        main.c

OBJ := $(SRC:%.c=%.o)

.PHONY: all clean

all: main

main: $(OBJ)
        gcc -o $@ $^

%.o: %.c
        gcc -c $@ $<

clean:
        rm -f $(OBJ) main

• https://overthewire.org/wargames/
• https://ryanstutorials.net/linuxtutorial/commandline.php
• http://www.linuxcommand.org/lc3_learning_the_shell.php

• https://www3.ntu.edu.sg/home/ehchua/programming/cpp/gcc_make.html
• https://randu.org/tutorials/c/make.php
• https://stackoverflow.com/questions/6666805/what-does-each-column-of-objdumps-symbol-table-mean
• https://www.gnu.org/software/make/manual/html_node/Automatic-Variables.html

• https://guides.github.com/activities/hello-world/
• https://rogerdudler.github.io/git-guide/
• https://www.atlassian.com/git/tutorials/using-branches
• https://www.atlassian.com/git/tutorials/comparing-workflows