add os[1-8]-ref for os refereces, add guide, add README

os4-ref/src/main.rs

@@ -0,0 +1,74 @@
+//! The main module and entrypoint
+//!
+//! Various facilities of the kernels are implemented as submodules. The most
+//! important ones are:
+//!
+//! - [`trap`]: Handles all cases of switching from userspace to the kernel
+//! - [`task`]: Task management
+//! - [`syscall`]: System call handling and implementation
+//!
+//! The operating system also starts in this module. Kernel code starts
+//! executing from `entry.asm`, after which [`rust_main()`] is called to
+//! initialize various pieces of functionality. (See its source code for
+//! details.)
+//!
+//! We then call [`task::run_first_task()`] and for the first time go to
+//! userspace.
+
+#![no_std]
+#![no_main]
+#![feature(panic_info_message)]
+#![feature(alloc_error_handler)]
+
+#[macro_use]
+extern crate bitflags;
+#[macro_use]
+extern crate log;
+
+extern crate alloc;
+
+#[macro_use]
+mod console;
+mod config;
+mod lang_items;
+mod loader;
+mod logging;
+mod mm;
+mod sbi;
+mod sync;
+pub mod syscall;
+pub mod task;
+mod timer;
+pub mod trap;
+
+core::arch::global_asm!(include_str!("entry.asm"));
+core::arch::global_asm!(include_str!("link_app.S"));
+
+/// clear BSS segment
+fn clear_bss() {
+    extern "C" {
+        fn sbss();
+        fn ebss();
+    }
+    unsafe {
+        core::slice::from_raw_parts_mut(sbss as usize as *mut u8, ebss as usize - sbss as usize)
+            .fill(0);
+    }
+}
+
+#[no_mangle]
+/// the rust entry-point of os
+pub fn rust_main() -> ! {
+    clear_bss();
+    logging::init();
+    println!("[kernel] Hello, world!");
+    mm::init();
+    println!("[kernel] back to world!");
+    mm::remap_test();
+    trap::init();
+    //trap::enable_interrupt();
+    trap::enable_timer_interrupt();
+    timer::set_next_trigger();
+    task::run_first_task();
+    panic!("Unreachable in rust_main!");
+}