Overview
This overview document presents the rou2exOS (aka r2) kernel interface for external applications. Applications should utilize custom programming language libraries provided in the apps repository and statically link them with their source code. Examples on how to use such libraries, how to compile them and link them are provided in directories named by concerned languages.
Privilege Levels
The privilege levels are to be specified and defined in the Global Descriptor Table (GDT) in early boot sequence procedures.
| CPU Ring | Common Interrupt | Target purpose |
|---|---|---|
0 |
* | kernel space |
~~1~~ |
~~0x7d~~ |
kernel tasks, drivers, kernel services |
~~2~~ |
~~0x7e~~ |
privileged user space, services, privileged shell access |
3 |
0x7f |
user space, user programs, common shell |
*Kernel itself handles multiple software (CPU exceptions) and hardware interrupts (e.g. IRQs).
All common interrupts are callable from anywhere, but are handled only when called from the defined CPU ring, therefore are locked to such space.
Syscall Specification
The system call (syscall) is a procedure for requesting or modifying of kernel components, modules and drivers. Syscalls use the software interrupts (int 0x7f) under the hood to notify the CPU and kernel to take an action. Parameters of a syscall are passed using the CPU registers that are listed below.
Please note that all values passed into a syscall must be aligned to 8 bytes (64bit).
| Register | Usage | Example value (64bit) |
|---|---|---|
RAX |
syscall No. | 0x01 |
RDI |
argument No. 1 | 0x01 |
RSI |
argument No. 2 | 0x123abc |
Syscall Return Codes
| Code (uint64) | Meaning |
|---|---|
0x00 |
Okay |
0xfb |
NotImplemented |
0xfc |
InvalidInput |
0xfd |
FilesystemError |
0xfe |
FileNotFound |
0xff |
InvalidSyscall |