Exercise 3

Part 1

Modify dumptask.stp and dumptask.d so it will print information on successful binary load by execve() and before process exit. Write a simple program lab3.c:

#include 
#include 
#include 

int main(int argc, char* argv[]) {
    while(--argc > 0) {
        memset(argv[argc], 'X', strlen(argv[argc]));
    }
    
    open("/etc/passwd", O_RDONLY);
    return 0;
}

# gcc lab3.c -o lab3

Run changed scripts and run your program in different ways:

• Run it with argument:

  # ./lab3 arg1

• Create a symbolic link and run a program through it:

  # ln -s lab3 lab3-1
  # ./lab3-1

• Created chrooted environment and run lab3 inside it:

  # mkdir -p /tmp/chroot/bin /tmp/chroot/lib64 /tmp/chroot/lib
  # mount --bind /lib64 /tmp/chroot/lib64         (in Linux)
  # mount -F lofs /lib /tmp/chroot/lib            (in Solaris)
  # cp lab3 /tmp/chroot/bin
  # chroot /tmp/chroot/ /bin/lab3

Q: What data output has been changed? Try to explain these changes.

Part 2

Shell scripts have overhead caused by need to spawn new processes for basic operations, and thus calling fork() and execve(). Write SystemTap and DTrace scripts that measure following characteristics:

• time, spent for fork() and execve() system calls;
• time, spent for child process initialization in userspace: closing files and resetting signals –- it is time interval between finish of fork() call in child context and calling of execve();
• own program time after it was loaded with execve() and before it was exited.

To be more correct, we should also measure time spent by ld.so loader and subtract it from own program time, but it involves complex tracing of userspace, so we leave it out of the scope of this exercise.

Measure all time periods in microseconds and save them to an aggregations using process executable name and its program arguments.

Use proc_starter experiment to demonstrate written script. This module starts sh shell (which can be overridden with shell parameter), uses PS1 environment variable to reset prompt, and simulates real user entering commands by passing them through pseudo-terminal. Commands are represented as probability map command.