Kernel Development Learning Pipeline

Lecture 07: 31 September 2024

What ways can your program crash? Has anyone written a C program that crashed? what happened?

Crash type iceberg:

• SIGSEGV
• SIGFPE
• SIGBUS
• SIGILL

try and write some assembly code that executes illegal or privileged instructions. What happens?

What mechanism underlies this

traps exceptions interrupts aborts

https://kdlp.underground.software/articles/kernel_basics.html

OLD L06:

1. Processes (35m)
2. PID, TGID kernel vs userspace lingo
3. parent/child relationships
4. PID 1, subreapers (prctl(PR_SET_CHILD_SUBREAPER)), and orphans
5. PID namespaces, unshare, containers
6. file descriptors & syscalls (35m)
7. what is a file descriptor
8. usage in syscalls
9. everything is a file (descriptor)
10. fopen vs open: beyond the libc
11. signals: SIGCHLD, SIGPIPE

What is a file?

• references open file on disk (could refer to a directory or a symlink too)
• even unix had seeds of something else (block and char devices, sockets and fifos)
• the real answer is a handle to some sort of kernel resource What is a signal?
• naive answer is asynchronous notification that calls a function
• really just an upcall from kernel space to userspace
• actually not nessecarily a function call, or asynchronous (signalfd) What is a syscall?
• naive answer is magic function call that invokes the kernel
• could write a program that invokes no syscalls, but its results would not be obvservable (caveat, maybe?)
• really it is the atom of observable computing
• not even really a function call (io_uring) What is a process, what is a thread?
• naive answer is fork and pthread create,
• in reality they are points within a multidimensional space governed by unshare