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Notes: 01-21 Welcome

·839 words·4 mins·

Welcome to 4310
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  • Instructor: Nat Tuck
  • Course: CS4310 Operating Systems

Where does this course fit in?

  • You’re a CS major
  • You can write computer programs.
  • In this course, we explore some of the details of how actual programs run on concrete computers.

The plot:

  • To do things, programs need to use hardware resources.
  • 1980 personal computer: one program at a time.
  • Two programs at a time means conflicts (who gets input from keyboard? don’t want to mix output to line printer!)
  • Add a dedicated program to talk the hardware: the OS. Other programs ask the OS to access shared resources for them.
  • To ask the OS to do stuff for you, you make a system call.
  • This class is about;
    • Writing programs that use system calls.
    • Implementing system calls.
  • System calls are different on different operating systems, so we need to pick a specific one to use.
  • We’re using Linux. More specifically, a modern Debian-family Linux.
  • Even with an OS, programs are still written to target a specific hardware architecture.
  • Compiled programs are binary data - machine code - and different kinds of processors have different machine codes.
  • We’ll looking at two different processor architectures:
    • AMD64, common for non-mac desktops, laptops, and servers.
    • RISCV, an open source architecture primarily used in embedded systems but slowly getting more popular.
  • A platform is the combination of processor architecture and OS. We’ll look at AMD64 Linux and RISCV Linux.

Course Resources
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Syllabus
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  • There’s a schedule. It may resemble what happens.
  • Grades: Homeworks, Final Exam
  • Homework: These are difficult programming assignments.
    • Some may be extra hard and worth double points.
    • Some may be in-class exercises.
  • Exam: On paper. Paper (including printed) notes allowed.

Cheating

  • Don’t submit other people’s code as your own.
  • Don’t share solutions with other students.

AI

  • You shouldn’t be turning in AI generated code unless explicitly allowed by the HW assignment.
  • You can use AI tools all you want to analyze code and answer questions about it.

Inkfish
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  • Show Inkfish
  • Show hw01a / hw01b

HW01a: Local Linux VM
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  • The easiest way to do programming work is to have the development environment installed locally on your personal computer.
  • For Linux systems programming, Linux is our development environment.
  • Having it installed as your main OS is probably best.
  • But, for consistent ency, the assignment is for everyone to install exactly Mint 22.3 AMD64 in a virtual machine.
  • If you aren’t developing on the VM and you run into weird problems later in the semester, use this VM to rule out configuration issues.

HW01b: Dev Setup
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Programming homework:

  • Download starter code.
  • Write some simple C and ASM code.
  • Really write them by hand. Don’t have AI do it. Don’t use the compiler to generate the assembly.
  • Make sure it compiles and runs.
  • Pack it back up and submit.

This assignment is mostly about structure, process, and getting annoyed at the autograder.

Keep in mind:

  • A C (or asm) program is a collection of functions.
  • These functions can be in one source file or in a bunch of different files.
  • C functions and ASM functions are the same thing. You can mix them together in the same program.
  • It’s easiest if each file is all-C or all-ASM.

Object file example:

  • add1.c
  • add2.c
  • main.c
gcc -c -o add1.o add1.c
gcc -c -o add2.c add2.c
...
gcc -o example add1.o add2.o main.o

C -> ASM
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  • “Programming” means “writing C code”.
  • On Linux-like (UNIX, *nix, POSIX) systems, the operating system API is primarily exposed to C programs through the system C library.
  • The hardware doesn’t run C though - it runs amd64 machine code (on your laptop) or ARM machine code (on your phone) or maybe some other machine code.
  • Machine code is for machines, not humans, so it’s hard to read.
  • Machine code is a series of instructions. If you write the instructions down as text, you get assembly language.
  • To run a C program, you need to translate to machine code (or “binary”).
  • Conceptually, and historically, you first translate C -> ASM, then ASM -> binary.
  • You can still do this if you explicitly ask for it.

Note: For the first few homeworks you will be writing ASM programs. You should not have a compiler do this for you. Submitting compiler output for an assembly assignment is worth zero points.

Example:

// A C program is a collection of functions.
// Here's a minimal program with one function
int
main(int argc, char* argv[])
{
  printf("Hello C program\n");
  return 0;
}

# Direct C => binary
$ gcc -o hello hello.c
$ ./hello

# C => asm
$ gcc -S -o hello.s hello.c
# take a look at hello.s

# asm => binary
$ gcc -o hello hello.s
$ ./hello

Interesting stuff in hello.s:

  • The string is there, but no newline.
  • The main function exists
    • Starts at label “main”
    • Ends at “ret”.
    • Declared “.globl”
  • In the main function another function is called - not printf, but puts.
Nat Tuck
Author
Nat Tuck