Linux-Kernel-Internals

- Linux Kernel Internals: https://ankitkdev.com/blog/
- Char Driver: https://ankitkdev.com/blog/linux-kernel/device-driver/char-driver/
- Ioctl Interface: https://ankitkdev.com/blog/linux-kernel/device-driver/ioctl/
- Proc-Interface: https://ankitkdev.com/blog/linux-kernel/device-driver/proc/
- Completion-Variable: https://ankitkdev.com/blog/linux-kernel/concurrency/completion-variable/
- container_of(): https://ankitkdev.com/blog/linux-kernel/macros/container_of/
- Module Parameters: https://ankitkdev.com/blog/linux-kernel/macros/kernel-module/
- pr_fmt(): https://ankitkdev.com/blog/linux-kernel/macros/pr-family/
- Stringification: https://ankitkdev.com/blog/linux-kernel/macros/string/
- Debugging Macros: https://ankitkdev.com/blog/linux-kernel/macros/debug/
- Error Handling with Pointers: https://ankitkdev.com/blog/kernal-internals/error-handling/
- Kbuild Makefile: https://ankitkdev.com/blog/kernal-internals/kbuild/
- SLUB debug: https://ankitkdev.com/blog/kernel-debugging/debug-slub-memory/
- unsigned :\ 0 Bit-Fields in c: https://ankitkdev.com/blog/c/zero-width-bit-field/
- do { ... } while (0): https://ankitkdev.com/blog/c/do-while-loop/
- Error Handling: https://ankitkdev.com/blog/c/error-handling/
- C Memory Layout: https://ankitkdev.com/blog/c/c-memory-layout/
- Forward Declarations: https://ankitkdev.com/blog/c/forward-declaration-in-c/
- Return value by Macro: https://ankitkdev.com/blog/c/return-by-macro/
- Variadic Macro: https://ankitkdev.com/blog/c/variadic-macro/
- programming concepts: https://ankitkdev.com/blog/theory/
- Build & Install Linux Kernel for BBB: https://ankitkdev.com/blog/misc/build-linux-kernel-BBB/
- Configure U-boot for BBB: https://ankitkdev.com/blog/misc/configure-uboot-bbb/
- Install Ubuntu Server on Qemu: https://ankitkdev.com/blog/misc/install-ubuntu-server-on-qemu/
- Linux Kernel Mentorship Program: https://ankitkdev.com/blog/misc/linux-kernel-mentorship-program/


## Kbuild Makefile

> These aren't plain GNU Make, Kbuild (the kernel's build system) reads them with special meaning when you run `make -C /lib/modules/$(uname -r)/build M=$(pwd) modules`.

```makefile
CFLAGS_main.o := -DDEBUG

ccflags-y := -std=gnu99 -DENABLE_DEBUG

proc_fs_basic-objs := main.o

obj-m := proc_fs_basic.o
```

- **`CFLAGS_main.o`** - per-object compiler flags. Only `main.o` gets `-DDEBUG`; if you had `main.o` and `helper.o`, only the first sees the macro. Useful for debug-gating one file without recompiling the whole module noisily.

- **`ccflags-y`** - flags applied to _every_ `.o` in this Makefile (the module-wide equivalent of `CFLAGS`). Here it forces `gnu99` and defines `ENABLE_DEBUG` globally.

- **`proc_fs_basic-objs`** - when a module is built from more than one source file, this lists what gets linked into the final `.ko`. Pattern is `<module_name>-objs := a.o b.o c.o` (Kbuild also accepts `-y` instead of `-objs` in newer trees).

- **`obj-m`** - the actual build trigger. `obj-m` = build as a loadable module → `proc_fs_basic.ko`. Swap it for `obj-y` and it'd get compiled directly into the kernel image instead.

> Order of resolution: `obj-m` → Kbuild sees `proc_fs_basic.o` is wanted → checks for `proc_fs_basic-objs` → pulls in `main.o` → applies `CFLAGS_main.o` + `ccflags-y` while compiling it.