aesophor / valkyrie

VALKYRIE

A UNIX-like toy kernel built from scratch (for AArch64)

Kernel Features

• Capable of running on a real Raspberry Pi 3B+
• AArch64 kernel with (user & kernel) preemptive multi-threading
• Copy-on-write fork()
• Virtual memory
• Virtual filesystem (VFS)
• FAT32 filesystem (supports long filenames)
• /dev, /proc, /tmp filesystem
• Self-made C++ standard library

Syscalls

int sys_read(int fd, void __user *buf, size_t count);
int sys_write(int fd, const void __user *buf, size_t count);
int sys_open(const char __user *pathname, int options);
int sys_close(int fd);
int sys_fork();
int sys_exec(const char __user *name, const char __user *argv[]);
[[noreturn]] void sys_exit(int error_code);
int sys_getpid();
int sys_wait(int __user *wstatus);
int sys_sched_yield();
long sys_kill(pid_t pid, int signal);
int sys_signal(int signal, void(__user *handler)());
int sys_access(const char __user *pathname, int options);
int sys_chdir(const char __user *pathname);
int sys_mkdir(const char __user *pathname);
int sys_rmdir(const char __user *pathname);
int sys_unlink(const char __user *pathname);
int sys_mount(const char __user *device_name, const char __user *mountpoint,
              const char __user *fs_name);
int sys_umount(const char __user *mountpoint);
int sys_mknod(const char __user *pathname, mode_t mode, dev_t dev);
int sys_getcwd(char __user *buf);
void __user *sys_mmap(void __user *addr, size_t len, int prot, int flags, int fd,
                      int file_offset);
int sys_munmap(void __user *addr, size_t len);  // unfinished

User Programs

• init
• login
• sh
• ls
• cat
• mkdir
• touch
• fork_test
• page_fault_test
• procfs_test
• vfs_test_dev
• vfs_test_mnt
• vfs_test_orw
• mmap_illegal_read
• mmap_illegal_write

Build valkyrie

Build requirements

• GNU make
• aarch64 (cross) compiler toolchain
• qemu-system-aarch64

Installing ARMv8 (cross) compiler toolchain and QEMU

# Arch Linux (x86_64)
sudo pacman -S aarch64-linux-gnu-gcc aarch64-linux-gnu-gdb qemu-arch-extra

# macOS (x86_64)
brew tap messense/macos-cross-toolchains
brew install aarch64-unknown-linux-gnu qemu

# macOS (Apple Silicon)
brew install aarch64-elf-gcc aarch64-elf-binutils qemu

Building valkyrie

git clone https://github.com/aesophor/valkyrie
cd valkyrie
make

Run valkyrie

Download sd.img from here.

The sd.img file contains:

• The boot partition (in which kernel8.img resides).
• The root partition (consists of /bin, /usr, etc).
• If you wish to run valkyrie in QEMU, then place sd.img under the project's root dir.
• If you wish to run valkyrie on a real rpi3b+, then flash it to your SD card with dd.

Running valkyrie in QEMU

make run

Running valkyrie on a real rpi3b+

Set up the USB-TO-TTL (USB-TO-SERIAL) Converter

1. Flash sd.img to the SD card (download)
2. Mount the SD card and replace the kernel8.img on the SD card with the latest build.
3. Eject the SD card and plug it into RPI3.
4. Plug in the USB-TO-TTL converter to your computer
   • for macOS, run screen /dev/tty.usbserial-0001 115200
   • for linux, run screen /dev/ttyUSB0 115200

References

• 國立陽明交通大學 資訊科學與工程研究所, Operating System Capstone, Spring 2021
• Linux
• SerenityOS
• OS67

License

GNU General Public License v3