//! The main module and entrypoint
//!
//! The operating system and app also starts in this module. Kernel code starts
//! executing from `entry.asm`, after which [`rust_main()`] is called to
//! initialize various pieces of functionality [`clear_bss()`]. (See its source code for
//! details.)
//!
//! We then call [`println!`] to display `Hello, world!`.

#![deny(missing_docs)]
#![deny(warnings)]
#![no_std]
#![no_main]
#![feature(panic_info_message)]

use core::arch::global_asm;

#[macro_use]
mod console;
mod lang_items;
mod sbi;

global_asm!(include_str!("entry.asm"));

/// clear BSS segment
fn clear_bss() {
    extern "C" {
        fn sbss();
        fn ebss();
    }
    (sbss as usize..ebss as usize).for_each(|a| unsafe { (a as *mut u8).write_volatile(0) });
}

/// the rust entry-point of os
#[no_mangle]
pub fn rust_main() -> ! {
    extern "C" {
        fn stext();
        fn etext();
        fn srodata();
        fn erodata();
        fn sdata();
        fn edata();
        fn sbss();
        fn ebss();
        fn boot_stack();
        fn boot_stack_top();
    }
    clear_bss();
    println!("Hello, world!");
    println!(".text [{:#x}, {:#x})", stext as usize, etext as usize);
    println!(".rodata [{:#x}, {:#x})", srodata as usize, erodata as usize);
    println!(".data [{:#x}, {:#x})", sdata as usize, edata as usize);
    println!(
        "boot_stack [{:#x}, {:#x})",
        boot_stack as usize, boot_stack_top as usize
    );
    println!(".bss [{:#x}, {:#x})", sbss as usize, ebss as usize);
    panic!("Shutdown machine!");
}