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

os4-ref/.cargo/config

@@ -0,0 +1,7 @@
+[build]
+target = "riscv64gc-unknown-none-elf"
+
+[target.riscv64gc-unknown-none-elf]
+rustflags = [
+    "-Clink-arg=-Tsrc/linker.ld", "-Cforce-frame-pointers=yes"
+]

os4-ref/Cargo.toml

@@ -0,0 +1,17 @@
+[package]
+name = "os"
+version = "0.1.0"
+authors = ["Yifan Wu <shinbokuow@163.com>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+bitflags = "1.2.1"
+buddy_system_allocator = "0.6"
+lazy_static = { version = "1.4.0", features = ["spin_no_std"] }
+log = "0.4"
+riscv = { git = "https://gitee.com/rcore-os/riscv", features = ["inline-asm"] }
+spin = "0.9"
+lock_api = "=0.4.6"
+xmas-elf = "0.7.0"

os4-ref/Makefile

@@ -0,0 +1,59 @@
+# Building
+TARGET := riscv64gc-unknown-none-elf
+MODE := release
+KERNEL_ELF := target/$(TARGET)/$(MODE)/os
+KERNEL_BIN := $(KERNEL_ELF).bin
+KERNEL_ASM := $(KERNEL_ELF).asm
+
+# BOARD
+BOARD ?= qemu
+SBI ?= rustsbi
+BOOTLOADER := ../bootloader/$(SBI)-$(BOARD).bin
+
+# KERNEL ENTRY
+KERNEL_ENTRY_PA := 0x80200000
+
+# Binutils
+OBJDUMP := rust-objdump --arch-name=riscv64
+OBJCOPY := rust-objcopy --binary-architecture=riscv64
+
+CHAPTER ?= $(shell git rev-parse --abbrev-ref HEAD | grep -o 'ch[0-9]' | grep -o '[0-9]')
+TEST ?= $(CHAPTER)
+BASE ?= 1
+
+build: env $(KERNEL_BIN)
+
+$(KERNEL_BIN): kernel
+	@$(OBJCOPY) $(KERNEL_ELF) --strip-all -O binary $@
+	@$(OBJDUMP) $(KERNEL_ELF) -S > $(KERNEL_ELF).asm
+
+env:
+	(rustup target list | grep "riscv64gc-unknown-none-elf (installed)") || rustup target add $(TARGET)
+	cargo install cargo-binutils --vers ~0.3
+	rustup component add rust-src
+	rustup component add llvm-tools-preview
+
+$(KERNEL_BIN): kernel
+	@$(OBJCOPY) $(KERNEL_ELF) --strip-all -O binary $@
+
+kernel:
+	@make -C ../user build TEST=$(TEST) CHAPTER=$(CHAPTER) BASE=$(BASE)
+	@cargo build --release
+
+clean:
+	@cargo clean
+
+run: build
+	@qemu-system-riscv64 \
+		-machine virt \
+		-nographic \
+		-bios $(BOOTLOADER) \
+		-device loader,file=$(KERNEL_BIN),addr=$(KERNEL_ENTRY_PA)
+
+debug: build
+	@tmux new-session -d \
+		"qemu-system-riscv64 -machine virt -nographic -bios $(BOOTLOADER) -device loader,file=$(KERNEL_BIN),addr=$(KERNEL_ENTRY_PA) -s -S" && \
+		tmux split-window -h "riscv64-unknown-elf-gdb -ex 'file $(KERNEL_ELF)' -ex 'set arch riscv:rv64' -ex 'target remote localhost:1234'" && \
+		tmux -2 attach-session -d
+
+.PHONY: build env kernel clean run-inner

os4-ref/build.rs

@@ -0,0 +1,60 @@
+//! Building applications linker
+
+use std::fs::{read_dir, File};
+use std::io::{Result, Write};
+
+fn main() {
+    println!("cargo:rerun-if-changed=../user/src/");
+    println!("cargo:rerun-if-changed={}", TARGET_PATH);
+    insert_app_data().unwrap();
+}
+
+static TARGET_PATH: &str = "../user/build/elf/";
+
+/// get app data and build linker
+fn insert_app_data() -> Result<()> {
+    let mut f = File::create("src/link_app.S").unwrap();
+    let mut apps: Vec<_> = read_dir("../user/build/elf/")
+        .unwrap()
+        .into_iter()
+        .map(|dir_entry| {
+            let mut name_with_ext = dir_entry.unwrap().file_name().into_string().unwrap();
+            name_with_ext.drain(name_with_ext.find('.').unwrap()..name_with_ext.len());
+            name_with_ext
+        })
+        .collect();
+    apps.sort();
+
+    writeln!(
+        f,
+        r#"
+    .align 3
+    .section .data
+    .global _num_app
+_num_app:
+    .quad {}"#,
+        apps.len()
+    )?;
+
+    for i in 0..apps.len() {
+        writeln!(f, r#"    .quad app_{}_start"#, i)?;
+    }
+    writeln!(f, r#"    .quad app_{}_end"#, apps.len() - 1)?;
+
+    for (idx, app) in apps.iter().enumerate() {
+        println!("app_{}: {}", idx, app);
+        writeln!(
+            f,
+            r#"
+    .section .data
+    .global app_{0}_start
+    .global app_{0}_end
+    .align 3
+app_{0}_start:
+    .incbin "{2}{1}.elf"
+app_{0}_end:"#,
+            idx, app, TARGET_PATH
+        )?;
+    }
+    Ok(())
+}

os4-ref/src/config.rs

@@ -0,0 +1,20 @@
+//! Constants used in rCore
+
+pub const USER_STACK_SIZE: usize = 4096 * 2;
+pub const KERNEL_STACK_SIZE: usize = 4096 * 2;
+pub const KERNEL_HEAP_SIZE: usize = 0x30_0000;
+pub const MEMORY_END: usize = 0x80800000;
+pub const PAGE_SIZE: usize = 0x1000;
+pub const PAGE_SIZE_BITS: usize = 0xc;
+pub const MAX_SYSCALL_NUM: usize = 500;
+
+pub const TRAMPOLINE: usize = usize::MAX - PAGE_SIZE + 1;
+pub const TRAP_CONTEXT: usize = TRAMPOLINE - PAGE_SIZE;
+/// Return (bottom, top) of a kernel stack in kernel space.
+pub fn kernel_stack_position(app_id: usize) -> (usize, usize) {
+    let top = TRAMPOLINE - app_id * (KERNEL_STACK_SIZE + PAGE_SIZE);
+    let bottom = top - KERNEL_STACK_SIZE;
+    (bottom, top)
+}
+
+pub const CLOCK_FREQ: usize = 12500000;

os4-ref/src/console.rs

@@ -0,0 +1,35 @@
+//! SBI console driver, for text output
+
+use crate::sbi::console_putchar;
+use core::fmt::{self, Write};
+
+struct Stdout;
+
+impl Write for Stdout {
+    fn write_str(&mut self, s: &str) -> fmt::Result {
+        for c in s.chars() {
+            console_putchar(c as usize);
+        }
+        Ok(())
+    }
+}
+
+pub fn print(args: fmt::Arguments) {
+    Stdout.write_fmt(args).unwrap();
+}
+
+#[macro_export]
+/// print string macro
+macro_rules! print {
+    ($fmt: literal $(, $($arg: tt)+)?) => {
+        $crate::console::print(format_args!($fmt $(, $($arg)+)?));
+    }
+}
+
+#[macro_export]
+/// println string macro
+macro_rules! println {
+    ($fmt: literal $(, $($arg: tt)+)?) => {
+        $crate::console::print(format_args!(concat!($fmt, "\n") $(, $($arg)+)?));
+    }
+}

os4-ref/src/entry.asm

@@ -0,0 +1,12 @@
+    .section .text.entry
+    .globl _start
+_start:
+    la sp, boot_stack_top
+    call rust_main
+
+    .section .bss.stack
+    .globl boot_stack
+boot_stack:
+    .space 4096 * 16
+    .globl boot_stack_top
+boot_stack_top:

os4-ref/src/heap_alloc.rs

@@ -0,0 +1,26 @@
+//! The global allocator
+
+use crate::config::KERNEL_HEAP_SIZE;
+use buddy_system_allocator::LockedHeap;
+
+#[global_allocator]
+/// heap allocator instance
+static HEAP_ALLOCATOR: LockedHeap = LockedHeap::empty();
+
+/// heap space ([u8; KERNEL_HEAP_SIZE])
+static mut HEAP_SPACE: [u8; KERNEL_HEAP_SIZE] = [0; KERNEL_HEAP_SIZE];
+
+/// initiate heap allocator
+pub fn init_heap() {
+    unsafe {
+        HEAP_ALLOCATOR
+            .lock()
+            .init(HEAP_SPACE.as_ptr() as usize, KERNEL_HEAP_SIZE);
+    }
+}
+
+#[alloc_error_handler]
+/// panic when heap allocation error occurs
+pub fn handle_alloc_error(layout: core::alloc::Layout) -> ! {
+    panic!("Heap allocation error, layout = {:?}", layout);
+}

os4-ref/src/lang_items.rs

@@ -0,0 +1,20 @@
+//! The panic handler
+
+use crate::sbi::shutdown;
+use core::panic::PanicInfo;
+
+#[panic_handler]
+/// panic handler
+fn panic(info: &PanicInfo) -> ! {
+    if let Some(location) = info.location() {
+        println!(
+            "Panicked at {}:{} {}",
+            location.file(),
+            location.line(),
+            info.message().unwrap()
+        );
+    } else {
+        println!("[kernel] Panicked: {}", info.message().unwrap());
+    }
+    shutdown()
+}

os4-ref/src/linker.ld

@@ -0,0 +1,53 @@
+OUTPUT_ARCH(riscv)
+ENTRY(_start)
+BASE_ADDRESS = 0x80200000;
+
+SECTIONS
+{
+    . = BASE_ADDRESS;
+    skernel = .;
+
+    stext = .;
+    .text : {
+        *(.text.entry)
+        . = ALIGN(4K);
+        strampoline = .;
+        *(.text.trampoline);
+        . = ALIGN(4K);
+        *(.text .text.*)
+    }
+
+    . = ALIGN(4K);
+    etext = .;
+    srodata = .;
+    .rodata : {
+        *(.rodata .rodata.*)
+        *(.srodata .srodata.*)
+    }
+
+    . = ALIGN(4K);
+    erodata = .;
+    sdata = .;
+    .data : {
+        *(.data .data.*)
+        *(.sdata .sdata.*)
+    }
+
+    . = ALIGN(4K);
+    edata = .;
+    sbss_with_stack = .;
+    .bss : {
+        *(.bss.stack)
+        sbss = .;
+        *(.bss .bss.*)
+        *(.sbss .sbss.*)
+    }
+
+    . = ALIGN(4K);
+    ebss = .;
+    ekernel = .;
+
+    /DISCARD/ : {
+        *(.eh_frame)
+    }
+}

os4-ref/src/loader.rs

@@ -0,0 +1,26 @@
+//! Loading user applications into memory
+
+/// Get the total number of applications.
+pub fn get_num_app() -> usize {
+    extern "C" {
+        fn _num_app();
+    }
+    unsafe { (_num_app as usize as *const usize).read_volatile() }
+}
+
+/// get applications data
+pub fn get_app_data(app_id: usize) -> &'static [u8] {
+    extern "C" {
+        fn _num_app();
+    }
+    let num_app_ptr = _num_app as usize as *const usize;
+    let num_app = get_num_app();
+    let app_start = unsafe { core::slice::from_raw_parts(num_app_ptr.add(1), num_app + 1) };
+    assert!(app_id < num_app);
+    unsafe {
+        core::slice::from_raw_parts(
+            app_start[app_id] as *const u8,
+            app_start[app_id + 1] - app_start[app_id],
+        )
+    }
+}

os4-ref/src/logging.rs

@@ -0,0 +1,45 @@
+//! Global logger
+
+use log::{self, Level, LevelFilter, Log, Metadata, Record};
+
+/// a simple logger
+struct SimpleLogger;
+
+impl Log for SimpleLogger {
+    fn enabled(&self, _metadata: &Metadata) -> bool {
+        true
+    }
+    fn log(&self, record: &Record) {
+        if !self.enabled(record.metadata()) {
+            return;
+        }
+        let color = match record.level() {
+            Level::Error => 31, // Red
+            Level::Warn => 93,  // BrightYellow
+            Level::Info => 34,  // Blue
+            Level::Debug => 32, // Green
+            Level::Trace => 90, // BrightBlack
+        };
+        println!(
+            "\u{1B}[{}m[{:>5}] {}\u{1B}[0m",
+            color,
+            record.level(),
+            record.args(),
+        );
+    }
+    fn flush(&self) {}
+}
+
+/// initiate logger
+pub fn init() {
+    static LOGGER: SimpleLogger = SimpleLogger;
+    log::set_logger(&LOGGER).unwrap();
+    log::set_max_level(match option_env!("LOG") {
+        Some("ERROR") => LevelFilter::Error,
+        Some("WARN") => LevelFilter::Warn,
+        Some("INFO") => LevelFilter::Info,
+        Some("DEBUG") => LevelFilter::Debug,
+        Some("TRACE") => LevelFilter::Trace,
+        _ => LevelFilter::Off,
+    });
+}

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!");
+}

os4-ref/src/mm/address.rs

@@ -0,0 +1,245 @@
+//! Implementation of physical and virtual address and page number.
+
+use super::PageTableEntry;
+use crate::config::{PAGE_SIZE, PAGE_SIZE_BITS};
+use core::fmt::{self, Debug, Formatter};
+
+/// physical address
+#[derive(Copy, Clone, Ord, PartialOrd, Eq, PartialEq)]
+pub struct PhysAddr(pub usize);
+
+/// virtual address
+#[derive(Copy, Clone, Ord, PartialOrd, Eq, PartialEq)]
+pub struct VirtAddr(pub usize);
+
+/// physical page number
+#[derive(Copy, Clone, Ord, PartialOrd, Eq, PartialEq)]
+pub struct PhysPageNum(pub usize);
+
+/// virtual page number
+#[derive(Copy, Clone, Ord, PartialOrd, Eq, PartialEq)]
+pub struct VirtPageNum(pub usize);
+
+/// Debugging
+
+impl Debug for VirtAddr {
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        f.write_fmt(format_args!("VA:{:#x}", self.0))
+    }
+}
+impl Debug for VirtPageNum {
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        f.write_fmt(format_args!("VPN:{:#x}", self.0))
+    }
+}
+impl Debug for PhysAddr {
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        f.write_fmt(format_args!("PA:{:#x}", self.0))
+    }
+}
+impl Debug for PhysPageNum {
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        f.write_fmt(format_args!("PPN:{:#x}", self.0))
+    }
+}
+
+/// T: {PhysAddr, VirtAddr, PhysPageNum, VirtPageNum}
+/// T -> usize: T.0
+/// usize -> T: usize.into()
+
+impl From<usize> for PhysAddr {
+    fn from(v: usize) -> Self {
+        Self(v)
+    }
+}
+impl From<usize> for PhysPageNum {
+    fn from(v: usize) -> Self {
+        Self(v)
+    }
+}
+impl From<usize> for VirtAddr {
+    fn from(v: usize) -> Self {
+        Self(v)
+    }
+}
+impl From<usize> for VirtPageNum {
+    fn from(v: usize) -> Self {
+        Self(v)
+    }
+}
+impl From<PhysAddr> for usize {
+    fn from(v: PhysAddr) -> Self {
+        v.0
+    }
+}
+impl From<PhysPageNum> for usize {
+    fn from(v: PhysPageNum) -> Self {
+        v.0
+    }
+}
+impl From<VirtAddr> for usize {
+    fn from(v: VirtAddr) -> Self {
+        v.0
+    }
+}
+impl From<VirtPageNum> for usize {
+    fn from(v: VirtPageNum) -> Self {
+        v.0
+    }
+}
+
+impl VirtAddr {
+    pub fn floor(&self) -> VirtPageNum {
+        VirtPageNum(self.0 / PAGE_SIZE)
+    }
+    pub fn ceil(&self) -> VirtPageNum {
+        VirtPageNum((self.0 - 1 + PAGE_SIZE) / PAGE_SIZE)
+    }
+    pub fn page_offset(&self) -> usize {
+        self.0 & (PAGE_SIZE - 1)
+    }
+    pub fn aligned(&self) -> bool {
+        self.page_offset() == 0
+    }
+}
+impl From<VirtAddr> for VirtPageNum {
+    fn from(v: VirtAddr) -> Self {
+        assert_eq!(v.page_offset(), 0);
+        v.floor()
+    }
+}
+impl From<VirtPageNum> for VirtAddr {
+    fn from(v: VirtPageNum) -> Self {
+        Self(v.0 << PAGE_SIZE_BITS)
+    }
+}
+impl PhysAddr {
+    pub fn floor(&self) -> PhysPageNum {
+        PhysPageNum(self.0 / PAGE_SIZE)
+    }
+    pub fn ceil(&self) -> PhysPageNum {
+        PhysPageNum((self.0 - 1 + PAGE_SIZE) / PAGE_SIZE)
+    }
+    pub fn page_offset(&self) -> usize {
+        self.0 & (PAGE_SIZE - 1)
+    }
+    pub fn aligned(&self) -> bool {
+        self.page_offset() == 0
+    }
+}
+impl From<PhysAddr> for PhysPageNum {
+    fn from(v: PhysAddr) -> Self {
+        assert_eq!(v.page_offset(), 0);
+        v.floor()
+    }
+}
+impl From<PhysPageNum> for PhysAddr {
+    fn from(v: PhysPageNum) -> Self {
+        Self(v.0 << PAGE_SIZE_BITS)
+    }
+}
+
+impl VirtPageNum {
+    pub fn indexes(&self) -> [usize; 3] {
+        let mut vpn = self.0;
+        let mut idx = [0usize; 3];
+        for i in (0..3).rev() {
+            idx[i] = vpn & 511;
+            vpn >>= 9;
+        }
+        idx
+    }
+}
+
+impl PhysPageNum {
+    pub fn get_pte_array(&self) -> &'static mut [PageTableEntry] {
+        let pa: PhysAddr = (*self).into();
+        unsafe { core::slice::from_raw_parts_mut(pa.0 as *mut PageTableEntry, 512) }
+    }
+    pub fn get_bytes_array(&self) -> &'static mut [u8] {
+        let pa: PhysAddr = (*self).into();
+        unsafe { core::slice::from_raw_parts_mut(pa.0 as *mut u8, 4096) }
+    }
+    pub fn get_mut<T>(&self) -> &'static mut T {
+        let pa: PhysAddr = (*self).into();
+        unsafe { (pa.0 as *mut T).as_mut().unwrap() }
+    }
+}
+
+pub trait StepByOne {
+    fn step(&mut self);
+}
+impl StepByOne for VirtPageNum {
+    fn step(&mut self) {
+        self.0 += 1;
+    }
+}
+
+#[derive(Copy, Clone)]
+/// a simple range structure for type T
+pub struct SimpleRange<T>
+where
+    T: StepByOne + Copy + PartialEq + PartialOrd + Debug,
+{
+    l: T,
+    r: T,
+}
+impl<T> SimpleRange<T>
+where
+    T: StepByOne + Copy + PartialEq + PartialOrd + Debug,
+{
+    pub fn new(start: T, end: T) -> Self {
+        assert!(start <= end, "start {:?} > end {:?}!", start, end);
+        Self { l: start, r: end }
+    }
+    pub fn get_start(&self) -> T {
+        self.l
+    }
+    pub fn get_end(&self) -> T {
+        self.r
+    }
+}
+impl<T> IntoIterator for SimpleRange<T>
+where
+    T: StepByOne + Copy + PartialEq + PartialOrd + Debug,
+{
+    type Item = T;
+    type IntoIter = SimpleRangeIterator<T>;
+    fn into_iter(self) -> Self::IntoIter {
+        SimpleRangeIterator::new(self.l, self.r)
+    }
+}
+/// iterator for the simple range structure
+pub struct SimpleRangeIterator<T>
+where
+    T: StepByOne + Copy + PartialEq + PartialOrd + Debug,
+{
+    current: T,
+    end: T,
+}
+impl<T> SimpleRangeIterator<T>
+where
+    T: StepByOne + Copy + PartialEq + PartialOrd + Debug,
+{
+    pub fn new(l: T, r: T) -> Self {
+        Self { current: l, end: r }
+    }
+}
+impl<T> Iterator for SimpleRangeIterator<T>
+where
+    T: StepByOne + Copy + PartialEq + PartialOrd + Debug,
+{
+    type Item = T;
+    fn next(&mut self) -> Option<Self::Item> {
+        if self.current == self.end {
+            None
+        } else {
+            let t = self.current;
+            self.current.step();
+            Some(t)
+        }
+    }
+}
+
+/// a simple range structure for virtual page number
+pub type VPNRange = SimpleRange<VirtPageNum>;

os4-ref/src/mm/frame_allocator.rs

@@ -0,0 +1,136 @@
+//! Implementation of [`FrameAllocator`] which 
+//! controls all the frames in the operating system.
+
+use super::{PhysAddr, PhysPageNum};
+use crate::config::MEMORY_END;
+use crate::sync::UPSafeCell;
+use alloc::vec::Vec;
+use core::fmt::{self, Debug, Formatter};
+use lazy_static::*;
+
+/// manage a frame which has the same lifecycle as the tracker
+pub struct FrameTracker {
+    pub ppn: PhysPageNum,
+}
+
+impl FrameTracker {
+    pub fn new(ppn: PhysPageNum) -> Self {
+        // page cleaning
+        let bytes_array = ppn.get_bytes_array();
+        for i in bytes_array {
+            *i = 0;
+        }
+        Self { ppn }
+    }
+}
+
+impl Debug for FrameTracker {
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        f.write_fmt(format_args!("FrameTracker:PPN={:#x}", self.ppn.0))
+    }
+}
+
+impl Drop for FrameTracker {
+    fn drop(&mut self) {
+        frame_dealloc(self.ppn);
+    }
+}
+
+trait FrameAllocator {
+    fn new() -> Self;
+    fn alloc(&mut self) -> Option<PhysPageNum>;
+    fn dealloc(&mut self, ppn: PhysPageNum);
+}
+
+/// an implementation for frame allocator
+pub struct StackFrameAllocator {
+    current: usize,
+    end: usize,
+    recycled: Vec<usize>,
+}
+
+impl StackFrameAllocator {
+    pub fn init(&mut self, l: PhysPageNum, r: PhysPageNum) {
+        self.current = l.0;
+        self.end = r.0;
+    }
+}
+impl FrameAllocator for StackFrameAllocator {
+    fn new() -> Self {
+        Self {
+            current: 0,
+            end: 0,
+            recycled: Vec::new(),
+        }
+    }
+    fn alloc(&mut self) -> Option<PhysPageNum> {
+        if let Some(ppn) = self.recycled.pop() {
+            Some(ppn.into())
+        } else if self.current == self.end {
+            None
+        } else {
+            self.current += 1;
+            Some((self.current - 1).into())
+        }
+    }
+    fn dealloc(&mut self, ppn: PhysPageNum) {
+        let ppn = ppn.0;
+        // validity check
+        if ppn >= self.current || self.recycled.iter().any(|v| *v == ppn) {
+            panic!("Frame ppn={:#x} has not been allocated!", ppn);
+        }
+        // recycle
+        self.recycled.push(ppn);
+    }
+}
+
+type FrameAllocatorImpl = StackFrameAllocator;
+
+lazy_static! {
+    /// frame allocator instance through lazy_static!
+    pub static ref FRAME_ALLOCATOR: UPSafeCell<FrameAllocatorImpl> =
+        unsafe { UPSafeCell::new(FrameAllocatorImpl::new()) };
+}
+
+/// initiate the frame allocator using `ekernel` and `MEMORY_END`
+pub fn init_frame_allocator() {
+    extern "C" {
+        fn ekernel();
+    }
+    FRAME_ALLOCATOR.exclusive_access().init(
+        PhysAddr::from(ekernel as usize).ceil(),
+        PhysAddr::from(MEMORY_END).floor(),
+    );
+}
+
+/// allocate a frame
+pub fn frame_alloc() -> Option<FrameTracker> {
+    FRAME_ALLOCATOR
+        .exclusive_access()
+        .alloc()
+        .map(FrameTracker::new)
+}
+
+/// deallocate a frame
+fn frame_dealloc(ppn: PhysPageNum) {
+    FRAME_ALLOCATOR.exclusive_access().dealloc(ppn);
+}
+
+#[allow(unused)]
+/// a simple test for frame allocator
+pub fn frame_allocator_test() {
+    let mut v: Vec<FrameTracker> = Vec::new();
+    for i in 0..5 {
+        let frame = frame_alloc().unwrap();
+        info!("{:?}", frame);
+        v.push(frame);
+    }
+    v.clear();
+    for i in 0..5 {
+        let frame = frame_alloc().unwrap();
+        info!("{:?}", frame);
+        v.push(frame);
+    }
+    drop(v);
+    info!("frame_allocator_test passed!");
+}

os4-ref/src/mm/heap_allocator.rs

@@ -0,0 +1,51 @@
+//! The global allocator
+
+use crate::config::KERNEL_HEAP_SIZE;
+use buddy_system_allocator::LockedHeap;
+
+#[global_allocator]
+/// heap allocator instance
+static HEAP_ALLOCATOR: LockedHeap = LockedHeap::empty();
+
+#[alloc_error_handler]
+/// panic when heap allocation error occurs
+pub fn handle_alloc_error(layout: core::alloc::Layout) -> ! {
+    panic!("Heap allocation error, layout = {:?}", layout);
+}
+
+/// heap space ([u8; KERNEL_HEAP_SIZE])
+static mut HEAP_SPACE: [u8; KERNEL_HEAP_SIZE] = [0; KERNEL_HEAP_SIZE];
+
+/// initiate heap allocator
+pub fn init_heap() {
+    unsafe {
+        HEAP_ALLOCATOR
+            .lock()
+            .init(HEAP_SPACE.as_ptr() as usize, KERNEL_HEAP_SIZE);
+    }
+}
+
+#[allow(unused)]
+pub fn heap_test() {
+    use alloc::boxed::Box;
+    use alloc::vec::Vec;
+    extern "C" {
+        fn sbss();
+        fn ebss();
+    }
+    let bss_range = sbss as usize..ebss as usize;
+    let a = Box::new(5);
+    assert_eq!(*a, 5);
+    assert!(bss_range.contains(&(a.as_ref() as *const _ as usize)));
+    drop(a);
+    let mut v: Vec<usize> = Vec::new();
+    for i in 0..500 {
+        v.push(i);
+    }
+    for (i, vi) in v.iter().enumerate().take(500) {
+        assert_eq!(*vi, i);
+    }
+    assert!(bss_range.contains(&(v.as_ptr() as usize)));
+    drop(v);
+    info!("heap_test passed!");
+}

os4-ref/src/mm/memory_set.rs

@@ -0,0 +1,346 @@
+//! Implementation of [`MapArea`] and [`MemorySet`].
+
+use super::{frame_alloc, FrameTracker};
+use super::{PTEFlags, PageTable, PageTableEntry};
+use super::{PhysAddr, PhysPageNum, VirtAddr, VirtPageNum};
+use super::{StepByOne, VPNRange};
+use crate::config::{MEMORY_END, PAGE_SIZE, TRAMPOLINE, TRAP_CONTEXT, USER_STACK_SIZE};
+use alloc::collections::BTreeMap;
+use alloc::sync::Arc;
+use alloc::vec::Vec;
+use lazy_static::*;
+use riscv::register::satp;
+use spin::Mutex;
+
+extern "C" {
+    fn stext();
+    fn etext();
+    fn srodata();
+    fn erodata();
+    fn sdata();
+    fn edata();
+    fn sbss_with_stack();
+    fn ebss();
+    fn ekernel();
+    fn strampoline();
+}
+
+lazy_static! {
+    /// a memory set instance through lazy_static! managing kernel space
+    pub static ref KERNEL_SPACE: Arc<Mutex<MemorySet>> =
+        Arc::new(Mutex::new(MemorySet::new_kernel()));
+}
+
+/// memory set structure, controls virtual-memory space
+pub struct MemorySet {
+    page_table: PageTable,
+    areas: Vec<MapArea>,
+}
+
+impl MemorySet {
+    pub fn new_bare() -> Self {
+        Self {
+            page_table: PageTable::new(),
+            areas: Vec::new(),
+        }
+    }
+    pub fn token(&self) -> usize {
+        self.page_table.token()
+    }
+    /// Assume that no conflicts.
+    pub fn insert_framed_area(
+        &mut self,
+        start_va: VirtAddr,
+        end_va: VirtAddr,
+        permission: MapPermission,
+    ) {
+        self.push(
+            MapArea::new(start_va, end_va, MapType::Framed, permission),
+            None,
+        );
+    }
+    fn push(&mut self, mut map_area: MapArea, data: Option<&[u8]>) {
+        map_area.map(&mut self.page_table);
+        if let Some(data) = data {
+            map_area.copy_data(&mut self.page_table, data);
+        }
+        self.areas.push(map_area);
+    }
+    /// Mention that trampoline is not collected by areas.
+    fn map_trampoline(&mut self) {
+        self.page_table.map(
+            VirtAddr::from(TRAMPOLINE).into(),
+            PhysAddr::from(strampoline as usize).into(),
+            PTEFlags::R | PTEFlags::X,
+        );
+    }
+    /// Without kernel stacks.
+    pub fn new_kernel() -> Self {
+        let mut memory_set = Self::new_bare();
+        // map trampoline
+        memory_set.map_trampoline();
+        // map kernel sections
+        info!(".text [{:#x}, {:#x})", stext as usize, etext as usize);
+        info!(".rodata [{:#x}, {:#x})", srodata as usize, erodata as usize);
+        info!(".data [{:#x}, {:#x})", sdata as usize, edata as usize);
+        info!(
+            ".bss [{:#x}, {:#x})",
+            sbss_with_stack as usize, ebss as usize
+        );
+        info!("mapping .text section");
+        memory_set.push(
+            MapArea::new(
+                (stext as usize).into(),
+                (etext as usize).into(),
+                MapType::Identical,
+                MapPermission::R | MapPermission::X,
+            ),
+            None,
+        );
+        info!("mapping .rodata section");
+        memory_set.push(
+            MapArea::new(
+                (srodata as usize).into(),
+                (erodata as usize).into(),
+                MapType::Identical,
+                MapPermission::R,
+            ),
+            None,
+        );
+        info!("mapping .data section");
+        memory_set.push(
+            MapArea::new(
+                (sdata as usize).into(),
+                (edata as usize).into(),
+                MapType::Identical,
+                MapPermission::R | MapPermission::W,
+            ),
+            None,
+        );
+        info!("mapping .bss section");
+        memory_set.push(
+            MapArea::new(
+                (sbss_with_stack as usize).into(),
+                (ebss as usize).into(),
+                MapType::Identical,
+                MapPermission::R | MapPermission::W,
+            ),
+            None,
+        );
+        info!("mapping physical memory");
+        memory_set.push(
+            MapArea::new(
+                (ekernel as usize).into(),
+                MEMORY_END.into(),
+                MapType::Identical,
+                MapPermission::R | MapPermission::W,
+            ),
+            None,
+        );
+        memory_set
+    }
+    /// Include sections in elf and trampoline and TrapContext and user stack,
+    /// also returns user_sp and entry point.
+    pub fn from_elf(elf_data: &[u8]) -> (Self, usize, usize) {
+        let mut memory_set = Self::new_bare();
+        // map trampoline
+        memory_set.map_trampoline();
+        // map program headers of elf, with U flag
+        let elf = xmas_elf::ElfFile::new(elf_data).unwrap();
+        let elf_header = elf.header;
+        let magic = elf_header.pt1.magic;
+        assert_eq!(magic, [0x7f, 0x45, 0x4c, 0x46], "invalid elf!");
+        let ph_count = elf_header.pt2.ph_count();
+        let mut max_end_vpn = VirtPageNum(0);
+        for i in 0..ph_count {
+            let ph = elf.program_header(i).unwrap();
+            if ph.get_type().unwrap() == xmas_elf::program::Type::Load {
+                let start_va: VirtAddr = (ph.virtual_addr() as usize).into();
+                let end_va: VirtAddr = ((ph.virtual_addr() + ph.mem_size()) as usize).into();
+                let mut map_perm = MapPermission::U;
+                let ph_flags = ph.flags();
+                if ph_flags.is_read() {
+                    map_perm |= MapPermission::R;
+                }
+                if ph_flags.is_write() {
+                    map_perm |= MapPermission::W;
+                }
+                if ph_flags.is_execute() {
+                    map_perm |= MapPermission::X;
+                }
+                let map_area = MapArea::new(start_va, end_va, MapType::Framed, map_perm);
+                max_end_vpn = map_area.vpn_range.get_end();
+                memory_set.push(
+                    map_area,
+                    Some(&elf.input[ph.offset() as usize..(ph.offset() + ph.file_size()) as usize]),
+                );
+            }
+        }
+        // map user stack with U flags
+        let max_end_va: VirtAddr = max_end_vpn.into();
+        let mut user_stack_bottom: usize = max_end_va.into();
+        // guard page
+        user_stack_bottom += PAGE_SIZE;
+        let user_stack_top = user_stack_bottom + USER_STACK_SIZE;
+        memory_set.push(
+            MapArea::new(
+                user_stack_bottom.into(),
+                user_stack_top.into(),
+                MapType::Framed,
+                MapPermission::R | MapPermission::W | MapPermission::U,
+            ),
+            None,
+        );
+        // map TrapContext
+        memory_set.push(
+            MapArea::new(
+                TRAP_CONTEXT.into(),
+                TRAMPOLINE.into(),
+                MapType::Framed,
+                MapPermission::R | MapPermission::W,
+            ),
+            None,
+        );
+        (
+            memory_set,
+            user_stack_top,
+            elf.header.pt2.entry_point() as usize,
+        )
+    }
+    pub fn activate(&self) {
+        let satp = self.page_table.token();
+        unsafe {
+            satp::write(satp);
+            core::arch::asm!("sfence.vma");
+        }
+    }
+    pub fn translate(&self, vpn: VirtPageNum) -> Option<PageTableEntry> {
+        self.page_table.translate(vpn)
+    }
+}
+
+/// map area structure, controls a contiguous piece of virtual memory
+pub struct MapArea {
+    vpn_range: VPNRange,
+    data_frames: BTreeMap<VirtPageNum, FrameTracker>,
+    map_type: MapType,
+    map_perm: MapPermission,
+}
+
+impl MapArea {
+    pub fn new(
+        start_va: VirtAddr,
+        end_va: VirtAddr,
+        map_type: MapType,
+        map_perm: MapPermission,
+    ) -> Self {
+        let start_vpn: VirtPageNum = start_va.floor();
+        let end_vpn: VirtPageNum = end_va.ceil();
+        Self {
+            vpn_range: VPNRange::new(start_vpn, end_vpn),
+            data_frames: BTreeMap::new(),
+            map_type,
+            map_perm,
+        }
+    }
+    pub fn map_one(&mut self, page_table: &mut PageTable, vpn: VirtPageNum) {
+        let ppn: PhysPageNum;
+        match self.map_type {
+            MapType::Identical => {
+                ppn = PhysPageNum(vpn.0);
+            }
+            MapType::Framed => {
+                let frame = frame_alloc().unwrap();
+                ppn = frame.ppn;
+                self.data_frames.insert(vpn, frame);
+            }
+        }
+        let pte_flags = PTEFlags::from_bits(self.map_perm.bits).unwrap();
+        page_table.map(vpn, ppn, pte_flags);
+    }
+    #[allow(unused)]
+    pub fn unmap_one(&mut self, page_table: &mut PageTable, vpn: VirtPageNum) {
+        #[allow(clippy::single_match)]
+        match self.map_type {
+            MapType::Framed => {
+                self.data_frames.remove(&vpn);
+            }
+            _ => {}
+        }
+        page_table.unmap(vpn);
+    }
+    pub fn map(&mut self, page_table: &mut PageTable) {
+        for vpn in self.vpn_range {
+            self.map_one(page_table, vpn);
+        }
+    }
+    #[allow(unused)]
+    pub fn unmap(&mut self, page_table: &mut PageTable) {
+        for vpn in self.vpn_range {
+            self.unmap_one(page_table, vpn);
+        }
+    }
+    /// data: start-aligned but maybe with shorter length
+    /// assume that all frames were cleared before
+    pub fn copy_data(&mut self, page_table: &mut PageTable, data: &[u8]) {
+        assert_eq!(self.map_type, MapType::Framed);
+        let mut start: usize = 0;
+        let mut current_vpn = self.vpn_range.get_start();
+        let len = data.len();
+        loop {
+            let src = &data[start..len.min(start + PAGE_SIZE)];
+            let dst = &mut page_table
+                .translate(current_vpn)
+                .unwrap()
+                .ppn()
+                .get_bytes_array()[..src.len()];
+            dst.copy_from_slice(src);
+            start += PAGE_SIZE;
+            if start >= len {
+                break;
+            }
+            current_vpn.step();
+        }
+    }
+}
+
+#[derive(Copy, Clone, PartialEq, Debug)]
+/// map type for memory set: identical or framed
+pub enum MapType {
+    Identical,
+    Framed,
+}
+
+bitflags! {
+    /// map permission corresponding to that in pte: `R W X U`
+    pub struct MapPermission: u8 {
+        const R = 1 << 1;
+        const W = 1 << 2;
+        const X = 1 << 3;
+        const U = 1 << 4;
+    }
+}
+
+#[allow(unused)]
+pub fn remap_test() {
+    let mut kernel_space = KERNEL_SPACE.lock();
+    let mid_text: VirtAddr = ((stext as usize + etext as usize) / 2).into();
+    let mid_rodata: VirtAddr = ((srodata as usize + erodata as usize) / 2).into();
+    let mid_data: VirtAddr = ((sdata as usize + edata as usize) / 2).into();
+    assert!(!kernel_space
+        .page_table
+        .translate(mid_text.floor())
+        .unwrap()
+        .writable());
+    assert!(!kernel_space
+        .page_table
+        .translate(mid_rodata.floor())
+        .unwrap()
+        .writable());
+    assert!(!kernel_space
+        .page_table
+        .translate(mid_data.floor())
+        .unwrap()
+        .executable());
+    info!("remap_test passed!");
+}

os4-ref/src/mm/mod.rs

@@ -0,0 +1,29 @@
+//! Memory management implementation
+//! 
+//! SV39 page-based virtual-memory architecture for RV64 systems, and
+//! everything about memory management, like frame allocator, page table,
+//! map area and memory set, is implemented here.
+//! 
+//! Every task or process has a memory_set to control its virtual memory.
+
+
+mod address;
+mod frame_allocator;
+mod heap_allocator;
+mod memory_set;
+mod page_table;
+
+pub use address::{PhysAddr, PhysPageNum, VirtAddr, VirtPageNum};
+use address::{StepByOne, VPNRange};
+pub use frame_allocator::{frame_alloc, FrameTracker};
+pub use memory_set::remap_test;
+pub use memory_set::{MapPermission, MemorySet, KERNEL_SPACE};
+pub use page_table::{translated_byte_buffer, PageTableEntry};
+use page_table::{PTEFlags, PageTable};
+
+/// initiate heap allocator, frame allocator and kernel space
+pub fn init() {
+    heap_allocator::init_heap();
+    frame_allocator::init_frame_allocator();
+    KERNEL_SPACE.lock().activate();
+}

os4-ref/src/mm/page_table.rs

@@ -0,0 +1,157 @@
+//! Implementation of [`PageTableEntry`] and [`PageTable`].
+
+use super::{frame_alloc, FrameTracker, PhysPageNum, StepByOne, VirtAddr, VirtPageNum};
+use alloc::vec;
+use alloc::vec::Vec;
+use bitflags::*;
+
+bitflags! {
+    /// page table entry flags
+    pub struct PTEFlags: u8 {
+        const V = 1 << 0;
+        const R = 1 << 1;
+        const W = 1 << 2;
+        const X = 1 << 3;
+        const U = 1 << 4;
+        const G = 1 << 5;
+        const A = 1 << 6;
+        const D = 1 << 7;
+    }
+}
+
+#[derive(Copy, Clone)]
+#[repr(C)]
+/// page table entry structure
+pub struct PageTableEntry {
+    pub bits: usize,
+}
+
+impl PageTableEntry {
+    pub fn new(ppn: PhysPageNum, flags: PTEFlags) -> Self {
+        PageTableEntry {
+            bits: ppn.0 << 10 | flags.bits as usize,
+        }
+    }
+    pub fn empty() -> Self {
+        PageTableEntry { bits: 0 }
+    }
+    pub fn ppn(&self) -> PhysPageNum {
+        (self.bits >> 10 & ((1usize << 44) - 1)).into()
+    }
+    pub fn flags(&self) -> PTEFlags {
+        PTEFlags::from_bits(self.bits as u8).unwrap()
+    }
+    pub fn is_valid(&self) -> bool {
+        (self.flags() & PTEFlags::V) != PTEFlags::empty()
+    }
+    pub fn readable(&self) -> bool {
+        (self.flags() & PTEFlags::R) != PTEFlags::empty()
+    }
+    pub fn writable(&self) -> bool {
+        (self.flags() & PTEFlags::W) != PTEFlags::empty()
+    }
+    pub fn executable(&self) -> bool {
+        (self.flags() & PTEFlags::X) != PTEFlags::empty()
+    }
+}
+
+/// page table structure
+pub struct PageTable {
+    root_ppn: PhysPageNum,
+    frames: Vec<FrameTracker>,
+}
+
+/// Assume that it won't oom when creating/mapping.
+impl PageTable {
+    pub fn new() -> Self {
+        let frame = frame_alloc().unwrap();
+        PageTable {
+            root_ppn: frame.ppn,
+            frames: vec![frame],
+        }
+    }
+    /// Temporarily used to get arguments from user space.
+    pub fn from_token(satp: usize) -> Self {
+        Self {
+            root_ppn: PhysPageNum::from(satp & ((1usize << 44) - 1)),
+            frames: Vec::new(),
+        }
+    }
+    fn find_pte_create(&mut self, vpn: VirtPageNum) -> Option<&mut PageTableEntry> {
+        let mut idxs = vpn.indexes();
+        let mut ppn = self.root_ppn;
+        let mut result: Option<&mut PageTableEntry> = None;
+        for (i, idx) in idxs.iter_mut().enumerate() {
+            let pte = &mut ppn.get_pte_array()[*idx];
+            if i == 2 {
+                result = Some(pte);
+                break;
+            }
+            if !pte.is_valid() {
+                let frame = frame_alloc().unwrap();
+                *pte = PageTableEntry::new(frame.ppn, PTEFlags::V);
+                self.frames.push(frame);
+            }
+            ppn = pte.ppn();
+        }
+        result
+    }
+    fn find_pte(&self, vpn: VirtPageNum) -> Option<&PageTableEntry> {
+        let idxs = vpn.indexes();
+        let mut ppn = self.root_ppn;
+        let mut result: Option<&PageTableEntry> = None;
+        for (i, idx) in idxs.iter().enumerate() {
+            let pte = &ppn.get_pte_array()[*idx];
+            if i == 2 {
+                result = Some(pte);
+                break;
+            }
+            if !pte.is_valid() {
+                return None;
+            }
+            ppn = pte.ppn();
+        }
+        result
+    }
+    #[allow(unused)]
+    pub fn map(&mut self, vpn: VirtPageNum, ppn: PhysPageNum, flags: PTEFlags) {
+        let pte = self.find_pte_create(vpn).unwrap();
+        assert!(!pte.is_valid(), "vpn {:?} is mapped before mapping", vpn);
+        *pte = PageTableEntry::new(ppn, flags | PTEFlags::V);
+    }
+    #[allow(unused)]
+    pub fn unmap(&mut self, vpn: VirtPageNum) {
+        let pte = self.find_pte_create(vpn).unwrap();
+        assert!(pte.is_valid(), "vpn {:?} is invalid before unmapping", vpn);
+        *pte = PageTableEntry::empty();
+    }
+    pub fn translate(&self, vpn: VirtPageNum) -> Option<PageTableEntry> {
+        self.find_pte(vpn).copied()
+    }
+    pub fn token(&self) -> usize {
+        8usize << 60 | self.root_ppn.0
+    }
+}
+
+/// translate a pointer to a mutable u8 Vec through page table
+pub fn translated_byte_buffer(token: usize, ptr: *const u8, len: usize) -> Vec<&'static mut [u8]> {
+    let page_table = PageTable::from_token(token);
+    let mut start = ptr as usize;
+    let end = start + len;
+    let mut v = Vec::new();
+    while start < end {
+        let start_va = VirtAddr::from(start);
+        let mut vpn = start_va.floor();
+        let ppn = page_table.translate(vpn).unwrap().ppn();
+        vpn.step();
+        let mut end_va: VirtAddr = vpn.into();
+        end_va = end_va.min(VirtAddr::from(end));
+        if end_va.page_offset() == 0 {
+            v.push(&mut ppn.get_bytes_array()[start_va.page_offset()..]);
+        } else {
+            v.push(&mut ppn.get_bytes_array()[start_va.page_offset()..end_va.page_offset()]);
+        }
+        start = end_va.into();
+    }
+    v
+}

os4-ref/src/sbi.rs

@@ -0,0 +1,45 @@
+//! SBI call wrappers
+
+#![allow(unused)]
+
+const SBI_SET_TIMER: usize = 0;
+const SBI_CONSOLE_PUTCHAR: usize = 1;
+const SBI_CONSOLE_GETCHAR: usize = 2;
+const SBI_SHUTDOWN: usize = 8;
+
+#[inline(always)]
+/// general sbi call
+fn sbi_call(which: usize, arg0: usize, arg1: usize, arg2: usize) -> usize {
+    let mut ret;
+    unsafe {
+        core::arch::asm!(
+            "ecall",
+            inlateout("x10") arg0 => ret,
+            in("x11") arg1,
+            in("x12") arg2,
+            in("x17") which,
+        );
+    }
+    ret
+}
+
+/// use sbi call to set timer
+pub fn set_timer(timer: usize) {
+    sbi_call(SBI_SET_TIMER, timer, 0, 0);
+}
+
+/// use sbi call to putchar in console (qemu uart handler)
+pub fn console_putchar(c: usize) {
+    sbi_call(SBI_CONSOLE_PUTCHAR, c, 0, 0);
+}
+
+/// use sbi call to getchar from console (qemu uart handler)
+pub fn console_getchar() -> usize {
+    sbi_call(SBI_CONSOLE_GETCHAR, 0, 0, 0)
+}
+
+/// use sbi call to shutdown the kernel
+pub fn shutdown() -> ! {
+    sbi_call(SBI_SHUTDOWN, 0, 0, 0);
+    panic!("It should shutdown!");
+}

os4-ref/src/sync/mod.rs

@@ -0,0 +1,5 @@
+//! Synchronization and interior mutability primitives
+
+mod up;
+
+pub use up::UPSafeCell;

os4-ref/src/sync/up.rs

@@ -0,0 +1,31 @@
+//! Uniprocessor interior mutability primitives
+
+use core::cell::{RefCell, RefMut};
+
+/// Wrap a static data structure inside it so that we are
+/// able to access it without any `unsafe`.
+///
+/// We should only use it in uniprocessor.
+///
+/// In order to get mutable reference of inner data, call
+/// `exclusive_access`.
+pub struct UPSafeCell<T> {
+    /// inner data
+    inner: RefCell<T>,
+}
+
+unsafe impl<T> Sync for UPSafeCell<T> {}
+
+impl<T> UPSafeCell<T> {
+    /// User is responsible to guarantee that inner struct is only used in
+    /// uniprocessor.
+    pub unsafe fn new(value: T) -> Self {
+        Self {
+            inner: RefCell::new(value),
+        }
+    }
+    /// Panic if the data has been borrowed.
+    pub fn exclusive_access(&self) -> RefMut<'_, T> {
+        self.inner.borrow_mut()
+    }
+}

os4-ref/src/syscall/fs.rs

@@ -0,0 +1,21 @@
+//! File and filesystem-related syscalls
+
+use crate::mm::translated_byte_buffer;
+use crate::task::current_user_token;
+
+const FD_STDOUT: usize = 1;
+
+pub fn sys_write(fd: usize, buf: *const u8, len: usize) -> isize {
+    match fd {
+        FD_STDOUT => {
+            let buffers = translated_byte_buffer(current_user_token(), buf, len);
+            for buffer in buffers {
+                print!("{}", core::str::from_utf8(buffer).unwrap());
+            }
+            len as isize
+        }
+        _ => {
+            panic!("Unsupported fd in sys_write!");
+        }
+    }
+}

os4-ref/src/syscall/mod.rs

@@ -0,0 +1,42 @@
+//! Implementation of syscalls
+//!
+//! The single entry point to all system calls, [`syscall()`], is called
+//! whenever userspace wishes to perform a system call using the `ecall`
+//! instruction. In this case, the processor raises an 'Environment call from
+//! U-mode' exception, which is handled as one of the cases in
+//! [`crate::trap::trap_handler`].
+//!
+//! For clarity, each single syscall is implemented as its own function, named
+//! `sys_` then the name of the syscall. You can find functions like this in
+//! submodules, and you should also implement syscalls this way.
+
+const SYSCALL_WRITE: usize = 64;
+const SYSCALL_EXIT: usize = 93;
+const SYSCALL_YIELD: usize = 124;
+const SYSCALL_GET_TIME: usize = 169;
+const SYSCALL_MUNMAP: usize = 215;
+const SYSCALL_MMAP: usize = 222;
+const SYSCALL_SET_PRIORITY: usize = 140;
+const SYSCALL_TASK_INFO: usize = 410;
+
+mod fs;
+mod process;
+
+use fs::*;
+use process::*;
+
+/// handle syscall exception with `syscall_id` and other arguments
+pub fn syscall(syscall_id: usize, args: [usize; 3]) -> isize {
+    // LAB1: You may need to update syscall info here.
+    match syscall_id {
+        SYSCALL_WRITE => sys_write(args[0], args[1] as *const u8, args[2]),
+        SYSCALL_EXIT => sys_exit(args[0] as i32),
+        SYSCALL_YIELD => sys_yield(),
+        SYSCALL_GET_TIME => sys_get_time(args[0] as *mut TimeVal, args[1]),
+        SYSCALL_MMAP => sys_mmap(args[0], args[1], args[2]),
+        SYSCALL_MUNMAP => sys_munmap(args[0], args[1]),
+        SYSCALL_SET_PRIORITY => sys_set_priority(args[0] as isize),
+        SYSCALL_TASK_INFO => sys_task_info(args[0] as *mut TaskInfo),
+        _ => panic!("Unsupported syscall_id: {}", syscall_id),
+    }
+}

os4-ref/src/syscall/process.rs

@@ -0,0 +1,62 @@
+//! Process management syscalls
+
+use crate::config::MAX_SYSCALL_NUM;
+use crate::task::{exit_current_and_run_next, suspend_current_and_run_next, TaskStatus};
+use crate::timer::get_time_us;
+
+#[repr(C)]
+#[derive(Debug)]
+pub struct TimeVal {
+    pub sec: usize,
+    pub usec: usize,
+}
+
+#[derive(Clone, Copy)]
+pub struct TaskInfo {
+    pub status: TaskStatus,
+    pub syscall_times: [u32; MAX_SYSCALL_NUM],
+    pub time: usize,
+}
+
+pub fn sys_exit(exit_code: i32) -> ! {
+    info!("[kernel] Application exited with code {}", exit_code);
+    exit_current_and_run_next();
+    panic!("Unreachable in sys_exit!");
+}
+
+/// current task gives up resources for other tasks
+pub fn sys_yield() -> isize {
+    suspend_current_and_run_next();
+    0
+}
+
+// YOUR JOB: 引入虚地址后重写 sys_get_time
+pub fn sys_get_time(_ts: *mut TimeVal, _tz: usize) -> isize {
+    let _us = get_time_us();
+    // unsafe {
+    //     *ts = TimeVal {
+    //         sec: us / 1_000_000,
+    //         usec: us % 1_000_000,
+    //     };
+    // }
+    0
+}
+
+// CLUE: 从 ch4 开始不再对调度算法进行测试~
+pub fn sys_set_priority(_prio: isize) -> isize {
+    -1
+}
+
+// YOUR JOB: 扩展内核以实现 sys_mmap 和 sys_munmap
+pub fn sys_mmap(_start: usize, _len: usize, _port: usize) -> isize {
+    -1
+}
+
+pub fn sys_munmap(_start: usize, _len: usize) -> isize {
+    -1
+}
+
+// YOUR JOB: 引入虚地址后重写 sys_task_info
+pub fn sys_task_info(ti: *mut TaskInfo) -> isize {
+    -1
+}

os4-ref/src/task/context.rs

@@ -0,0 +1,28 @@
+//! Implementation of [`TaskContext`]
+use crate::trap::trap_return;
+
+#[derive(Copy, Clone)]
+#[repr(C)]
+/// task context structure containing some registers
+pub struct TaskContext {
+    ra: usize,
+    sp: usize,
+    s: [usize; 12],
+}
+
+impl TaskContext {
+    pub fn zero_init() -> Self {
+        Self {
+            ra: 0,
+            sp: 0,
+            s: [0; 12],
+        }
+    }
+    pub fn goto_trap_return(kstack_ptr: usize) -> Self {
+        Self {
+            ra: trap_return as usize,
+            sp: kstack_ptr,
+            s: [0; 12],
+        }
+    }
+}

os4-ref/src/task/mod.rs

@@ -0,0 +1,193 @@
+//! Task management implementation
+//!
+//! Everything about task management, like starting and switching tasks is
+//! implemented here.
+//!
+//! A single global instance of [`TaskManager`] called `TASK_MANAGER` controls
+//! all the tasks in the operating system.
+//!
+//! Be careful when you see [`__switch`]. Control flow around this function
+//! might not be what you expect.
+
+mod context;
+mod switch;
+#[allow(clippy::module_inception)]
+mod task;
+
+use crate::loader::{get_app_data, get_num_app};
+use crate::sync::UPSafeCell;
+use crate::trap::TrapContext;
+use alloc::vec::Vec;
+use lazy_static::*;
+pub use switch::__switch;
+pub use task::{TaskControlBlock, TaskStatus};
+
+pub use context::TaskContext;
+
+/// The task manager, where all the tasks are managed.
+///
+/// Functions implemented on `TaskManager` deals with all task state transitions
+/// and task context switching. For convenience, you can find wrappers around it
+/// in the module level.
+///
+/// Most of `TaskManager` are hidden behind the field `inner`, to defer
+/// borrowing checks to runtime. You can see examples on how to use `inner` in
+/// existing functions on `TaskManager`.
+pub struct TaskManager {
+    /// total number of tasks
+    num_app: usize,
+    /// use inner value to get mutable access
+    inner: UPSafeCell<TaskManagerInner>,
+}
+
+/// The task manager inner in 'UPSafeCell'
+struct TaskManagerInner {
+    /// task list
+    tasks: Vec<TaskControlBlock>,
+    /// id of current `Running` task
+    current_task: usize,
+}
+
+lazy_static! {
+    /// a `TaskManager` instance through lazy_static!
+    pub static ref TASK_MANAGER: TaskManager = {
+        info!("init TASK_MANAGER");
+        let num_app = get_num_app();
+        info!("num_app = {}", num_app);
+        let mut tasks: Vec<TaskControlBlock> = Vec::new();
+        for i in 0..num_app {
+            tasks.push(TaskControlBlock::new(get_app_data(i), i));
+        }
+        TaskManager {
+            num_app,
+            inner: unsafe {
+                UPSafeCell::new(TaskManagerInner {
+                    tasks,
+                    current_task: 0,
+                })
+            },
+        }
+    };
+}
+
+impl TaskManager {
+    /// Run the first task in task list.
+    ///
+    /// Generally, the first task in task list is an idle task (we call it zero process later).
+    /// But in ch4, we load apps statically, so the first task is a real app.
+    fn run_first_task(&self) -> ! {
+        let mut inner = self.inner.exclusive_access();
+        let next_task = &mut inner.tasks[0];
+        next_task.task_status = TaskStatus::Running;
+        let next_task_cx_ptr = &next_task.task_cx as *const TaskContext;
+        drop(inner);
+        let mut _unused = TaskContext::zero_init();
+        // before this, we should drop local variables that must be dropped manually
+        unsafe {
+            __switch(&mut _unused as *mut _, next_task_cx_ptr);
+        }
+        panic!("unreachable in run_first_task!");
+    }
+
+    /// Change the status of current `Running` task into `Ready`.
+    fn mark_current_suspended(&self) {
+        let mut inner = self.inner.exclusive_access();
+        let current = inner.current_task;
+        inner.tasks[current].task_status = TaskStatus::Ready;
+    }
+
+    /// Change the status of current `Running` task into `Exited`.
+    fn mark_current_exited(&self) {
+        let mut inner = self.inner.exclusive_access();
+        let current = inner.current_task;
+        inner.tasks[current].task_status = TaskStatus::Exited;
+    }
+
+    /// Find next task to run and return task id.
+    ///
+    /// In this case, we only return the first `Ready` task in task list.
+    fn find_next_task(&self) -> Option<usize> {
+        let inner = self.inner.exclusive_access();
+        let current = inner.current_task;
+        (current + 1..current + self.num_app + 1)
+            .map(|id| id % self.num_app)
+            .find(|id| inner.tasks[*id].task_status == TaskStatus::Ready)
+    }
+
+    /// Get the current 'Running' task's token.
+    fn get_current_token(&self) -> usize {
+        let inner = self.inner.exclusive_access();
+        inner.tasks[inner.current_task].get_user_token()
+    }
+
+    #[allow(clippy::mut_from_ref)]
+    /// Get the current 'Running' task's trap contexts.
+    fn get_current_trap_cx(&self) -> &mut TrapContext {
+        let inner = self.inner.exclusive_access();
+        inner.tasks[inner.current_task].get_trap_cx()
+    }
+
+    /// Switch current `Running` task to the task we have found,
+    /// or there is no `Ready` task and we can exit with all applications completed
+    fn run_next_task(&self) {
+        if let Some(next) = self.find_next_task() {
+            let mut inner = self.inner.exclusive_access();
+            let current = inner.current_task;
+            inner.tasks[next].task_status = TaskStatus::Running;
+            inner.current_task = next;
+            let current_task_cx_ptr = &mut inner.tasks[current].task_cx as *mut TaskContext;
+            let next_task_cx_ptr = &inner.tasks[next].task_cx as *const TaskContext;
+            drop(inner);
+            // before this, we should drop local variables that must be dropped manually
+            unsafe {
+                __switch(current_task_cx_ptr, next_task_cx_ptr);
+            }
+            // go back to user mode
+        } else {
+            panic!("All applications completed!");
+        }
+    }
+}
+
+/// Run the first task in task list.
+pub fn run_first_task() {
+    TASK_MANAGER.run_first_task();
+}
+
+/// Switch current `Running` task to the task we have found,
+/// or there is no `Ready` task and we can exit with all applications completed
+fn run_next_task() {
+    TASK_MANAGER.run_next_task();
+}
+
+/// Change the status of current `Running` task into `Ready`.
+fn mark_current_suspended() {
+    TASK_MANAGER.mark_current_suspended();
+}
+
+/// Change the status of current `Running` task into `Exited`.
+fn mark_current_exited() {
+    TASK_MANAGER.mark_current_exited();
+}
+
+/// Suspend the current 'Running' task and run the next task in task list.
+pub fn suspend_current_and_run_next() {
+    mark_current_suspended();
+    run_next_task();
+}
+
+/// Exit the current 'Running' task and run the next task in task list.
+pub fn exit_current_and_run_next() {
+    mark_current_exited();
+    run_next_task();
+}
+
+/// Get the current 'Running' task's token.
+pub fn current_user_token() -> usize {
+    TASK_MANAGER.get_current_token()
+}
+
+/// Get the current 'Running' task's trap contexts.
+pub fn current_trap_cx() -> &'static mut TrapContext {
+    TASK_MANAGER.get_current_trap_cx()
+}

os4-ref/src/task/switch.S

@@ -0,0 +1,34 @@
+.altmacro
+.macro SAVE_SN n
+    sd s\n, (\n+2)*8(a0)
+.endm
+.macro LOAD_SN n
+    ld s\n, (\n+2)*8(a1)
+.endm
+    .section .text
+    .globl __switch
+__switch:
+    # __switch(
+    #     current_task_cx_ptr: *mut TaskContext,
+    #     next_task_cx_ptr: *const TaskContext
+    # )
+    # save kernel stack of current task
+    sd sp, 8(a0)
+    # save ra & s0~s11 of current execution
+    sd ra, 0(a0)
+    .set n, 0
+    .rept 12
+        SAVE_SN %n
+        .set n, n + 1
+    .endr
+    # restore ra & s0~s11 of next execution
+    ld ra, 0(a1)
+    .set n, 0
+    .rept 12
+        LOAD_SN %n
+        .set n, n + 1
+    .endr
+    # restore kernel stack of next task
+    ld sp, 8(a1)
+    ret
+

os4-ref/src/task/switch.rs

@@ -0,0 +1,16 @@
+//! Rust wrapper around `__switch`.
+//!
+//! Switching to a different task's context happens here. The actual
+//! implementation must not be in Rust and (essentially) has to be in assembly
+//! language (Do you know why?), so this module really is just a wrapper around
+//! `switch.S`.
+
+core::arch::global_asm!(include_str!("switch.S"));
+
+use super::TaskContext;
+
+extern "C" {
+    /// Switch to the context of `next_task_cx_ptr`, saving the current context
+    /// in `current_task_cx_ptr`.
+    pub fn __switch(current_task_cx_ptr: *mut TaskContext, next_task_cx_ptr: *const TaskContext);
+}

os4-ref/src/task/task.rs

@@ -0,0 +1,64 @@
+//! Types related to task management
+use super::TaskContext;
+use crate::config::{kernel_stack_position, TRAP_CONTEXT};
+use crate::mm::{MapPermission, MemorySet, PhysPageNum, VirtAddr, KERNEL_SPACE};
+use crate::trap::{trap_handler, TrapContext};
+
+/// task control block structure
+pub struct TaskControlBlock {
+    pub task_status: TaskStatus,
+    pub task_cx: TaskContext,
+    pub memory_set: MemorySet,
+    pub trap_cx_ppn: PhysPageNum,
+    pub base_size: usize,
+}
+
+impl TaskControlBlock {
+    pub fn get_trap_cx(&self) -> &'static mut TrapContext {
+        self.trap_cx_ppn.get_mut()
+    }
+    pub fn get_user_token(&self) -> usize {
+        self.memory_set.token()
+    }
+    pub fn new(elf_data: &[u8], app_id: usize) -> Self {
+        // memory_set with elf program headers/trampoline/trap context/user stack
+        let (memory_set, user_sp, entry_point) = MemorySet::from_elf(elf_data);
+        let trap_cx_ppn = memory_set
+            .translate(VirtAddr::from(TRAP_CONTEXT).into())
+            .unwrap()
+            .ppn();
+        let task_status = TaskStatus::Ready;
+        // map a kernel-stack in kernel space
+        let (kernel_stack_bottom, kernel_stack_top) = kernel_stack_position(app_id);
+        KERNEL_SPACE.lock().insert_framed_area(
+            kernel_stack_bottom.into(),
+            kernel_stack_top.into(),
+            MapPermission::R | MapPermission::W,
+        );
+        let task_control_block = Self {
+            task_status,
+            task_cx: TaskContext::goto_trap_return(kernel_stack_top),
+            memory_set,
+            trap_cx_ppn,
+            base_size: user_sp,
+        };
+        // prepare TrapContext in user space
+        let trap_cx = task_control_block.get_trap_cx();
+        *trap_cx = TrapContext::app_init_context(
+            entry_point,
+            user_sp,
+            KERNEL_SPACE.lock().token(),
+            kernel_stack_top,
+            trap_handler as usize,
+        );
+        task_control_block
+    }
+}
+
+#[derive(Copy, Clone, PartialEq)]
+/// task status: UnInit, Ready, Running, Exited
+pub enum TaskStatus {
+    Ready,
+    Running,
+    Exited,
+}

os4-ref/src/timer.rs

@@ -0,0 +1,23 @@
+//! RISC-V timer-related functionality
+
+use crate::config::CLOCK_FREQ;
+use crate::sbi::set_timer;
+use riscv::register::time;
+
+const TICKS_PER_SEC: usize = 100;
+const MICRO_PER_SEC: usize = 1_000_000;
+
+/// read the `mtime` register
+pub fn get_time() -> usize {
+    time::read()
+}
+
+/// get current time in microseconds
+pub fn get_time_us() -> usize {
+    time::read() / (CLOCK_FREQ / MICRO_PER_SEC)
+}
+
+/// set the next timer interrupt
+pub fn set_next_trigger() {
+    set_timer(get_time() + CLOCK_FREQ / TICKS_PER_SEC);
+}

os4-ref/src/trap/context.rs

@@ -0,0 +1,40 @@
+//! Implementation of [`TrapContext`]
+
+use riscv::register::sstatus::{self, Sstatus, SPP};
+
+#[repr(C)]
+/// trap context structure containing sstatus, sepc and registers
+pub struct TrapContext {
+    pub x: [usize; 32],
+    pub sstatus: Sstatus,
+    pub sepc: usize,
+    pub kernel_satp: usize,
+    pub kernel_sp: usize,
+    pub trap_handler: usize,
+}
+
+impl TrapContext {
+    pub fn set_sp(&mut self, sp: usize) {
+        self.x[2] = sp;
+    }
+    pub fn app_init_context(
+        entry: usize,
+        sp: usize,
+        kernel_satp: usize,
+        kernel_sp: usize,
+        trap_handler: usize,
+    ) -> Self {
+        let mut sstatus = sstatus::read();
+        sstatus.set_spp(SPP::User);
+        let mut cx = Self {
+            x: [0; 32],
+            sstatus,
+            sepc: entry,
+            kernel_satp,
+            kernel_sp,
+            trap_handler,
+        };
+        cx.set_sp(sp);
+        cx
+    }
+}

os4-ref/src/trap/mod.rs

@@ -0,0 +1,115 @@
+//! Trap handling functionality
+//!
+//! For rCore, we have a single trap entry point, namely `__alltraps`. At
+//! initialization in [`init()`], we set the `stvec` CSR to point to it.
+//!
+//! All traps go through `__alltraps`, which is defined in `trap.S`. The
+//! assembly language code does just enough work restore the kernel space
+//! context, ensuring that Rust code safely runs, and transfers control to
+//! [`trap_handler()`].
+//!
+//! It then calls different functionality based on what exactly the exception
+//! was. For example, timer interrupts trigger task preemption, and syscalls go
+//! to [`syscall()`].
+mod context;
+
+use crate::config::{TRAMPOLINE, TRAP_CONTEXT};
+use crate::syscall::syscall;
+use crate::task::{
+    current_trap_cx, current_user_token, exit_current_and_run_next, suspend_current_and_run_next,
+};
+use crate::timer::set_next_trigger;
+use riscv::register::{
+    mtvec::TrapMode,
+    scause::{self, Exception, Interrupt, Trap},
+    sie, stval, stvec,
+};
+
+core::arch::global_asm!(include_str!("trap.S"));
+
+pub fn init() {
+    set_kernel_trap_entry();
+}
+
+fn set_kernel_trap_entry() {
+    unsafe {
+        stvec::write(trap_from_kernel as usize, TrapMode::Direct);
+    }
+}
+
+fn set_user_trap_entry() {
+    unsafe {
+        stvec::write(TRAMPOLINE as usize, TrapMode::Direct);
+    }
+}
+
+pub fn enable_timer_interrupt() {
+    unsafe {
+        sie::set_stimer();
+    }
+}
+
+#[no_mangle]
+pub fn trap_handler() -> ! {
+    set_kernel_trap_entry();
+    let cx = current_trap_cx();
+    let scause = scause::read();
+    let stval = stval::read();
+    match scause.cause() {
+        Trap::Exception(Exception::UserEnvCall) => {
+            cx.sepc += 4;
+            cx.x[10] = syscall(cx.x[17], [cx.x[10], cx.x[11], cx.x[12]]) as usize;
+        }
+        Trap::Exception(Exception::StoreFault)
+        | Trap::Exception(Exception::StorePageFault)
+        | Trap::Exception(Exception::LoadPageFault) => {
+            error!("[kernel] PageFault in application, bad addr = {:#x}, bad instruction = {:#x}, core dumped.", stval, cx.sepc);
+            exit_current_and_run_next();
+        }
+        Trap::Exception(Exception::IllegalInstruction) => {
+            error!("[kernel] IllegalInstruction in application, core dumped.");
+            exit_current_and_run_next();
+        }
+        Trap::Interrupt(Interrupt::SupervisorTimer) => {
+            set_next_trigger();
+            suspend_current_and_run_next();
+        }
+        _ => {
+            panic!(
+                "Unsupported trap {:?}, stval = {:#x}!",
+                scause.cause(),
+                stval
+            );
+        }
+    }
+    trap_return();
+}
+
+#[no_mangle]
+pub fn trap_return() -> ! {
+    set_user_trap_entry();
+    let trap_cx_ptr = TRAP_CONTEXT;
+    let user_satp = current_user_token();
+    extern "C" {
+        fn __alltraps();
+        fn __restore();
+    }
+    let restore_va = __restore as usize - __alltraps as usize + TRAMPOLINE;
+    unsafe {
+        core::arch::asm!(
+            "fence.i",
+            "jr {restore_va}",
+            restore_va = in(reg) restore_va,
+            in("a0") trap_cx_ptr,
+            in("a1") user_satp,
+            options(noreturn)
+        );
+    }
+}
+
+#[no_mangle]
+pub fn trap_from_kernel() -> ! {
+    panic!("a trap from kernel!");
+}
+
+pub use context::TrapContext;

os4-ref/src/trap/trap.S

@@ -0,0 +1,69 @@
+.altmacro
+.macro SAVE_GP n
+    sd x\n, \n*8(sp)
+.endm
+.macro LOAD_GP n
+    ld x\n, \n*8(sp)
+.endm
+    .section .text.trampoline
+    .globl __alltraps
+    .globl __restore
+    .align 2
+__alltraps:
+    csrrw sp, sscratch, sp
+    # now sp->*TrapContext in user space, sscratch->user stack
+    # save other general purpose registers
+    sd x1, 1*8(sp)
+    # skip sp(x2), we will save it later
+    sd x3, 3*8(sp)
+    # skip tp(x4), application does not use it
+    # save x5~x31
+    .set n, 5
+    .rept 27
+        SAVE_GP %n
+        .set n, n+1
+    .endr
+    # we can use t0/t1/t2 freely, because they have been saved in TrapContext
+    csrr t0, sstatus
+    csrr t1, sepc
+    sd t0, 32*8(sp)
+    sd t1, 33*8(sp)
+    # read user stack from sscratch and save it in TrapContext
+    csrr t2, sscratch
+    sd t2, 2*8(sp)
+    # load kernel_satp into t0
+    ld t0, 34*8(sp)
+    # load trap_handler into t1
+    ld t1, 36*8(sp)
+    # move to kernel_sp
+    ld sp, 35*8(sp)
+    # switch to kernel space
+    csrw satp, t0
+    sfence.vma
+    # jump to trap_handler
+    jr t1
+
+__restore:
+    # a0: *TrapContext in user space(Constant); a1: user space token
+    # switch to user space
+    csrw satp, a1
+    sfence.vma
+    csrw sscratch, a0
+    mv sp, a0
+    # now sp points to TrapContext in user space, start restoring based on it
+    # restore sstatus/sepc
+    ld t0, 32*8(sp)
+    ld t1, 33*8(sp)
+    csrw sstatus, t0
+    csrw sepc, t1
+    # restore general purpose registers except x0/sp/tp
+    ld x1, 1*8(sp)
+    ld x3, 3*8(sp)
+    .set n, 5
+    .rept 27
+        LOAD_GP %n
+        .set n, n+1
+    .endr
+    # back to user stack
+    ld sp, 2*8(sp)
+    sret