0b2df134ce
The bootloader relied on the kernel to know which parts of memory to not allocate over. For the future shift of having the init process load other processes instead of the kernel, the bootloader needs a mechanism to just hand the kernel a list of allocations. This is now done through the new bootloader allocator, which all allocation goes through. Pool memory will not be tracked, and so can be overwritten - this means the args structure and its other structures like programs need to be handled right away, or copied by the kernel. - Add bootloader allocator - Implement a new linked-list based set of pages that act as allocation registers - Allow for operator new in the bootloader, which goes through the global allocator for pool memory - Split memory map and frame accouting code in the bootloader into separate memory_map.* files - Remove many includes that could be replaced by forward declaration in the bootloader - Add a new global template type, `counted`, which replaces the bootloader's `buffer` type, and updated kernel args structure to use it. - Move bootloader's pointer_manipulation.h to the global include dir - Make offset_iterator try to return references instead of pointers to make it more consistent with static array iteration - Implement a stub atexit() in the bootloader to satisfy clang
The jsix operating system
jsix is a custom multi-core x64 operating system that I am building from scratch. It's far from finished, or even being usable - see the Status and Roadmap section, below.
The design goals of the project are:
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Modernity - I'm not interested in designing for legacy systems, or running on all hardware out there. My target is only 64 bit architecutres, and modern commodity hardware. Currently that means x64 systems with Nehalem or newer CPUs and UEFI firmware. (See this list for the currently required CPU features.) Eventually I'd like to work on an AArch64 port, partly to force myself to factor out the architecture-dependent pieces of the code base.
-
Modularity - I'd like to pull as much of the system out into separate processes as possible, in the microkernel fashion. A sub-goal of this is to explore where the bottlenecks of such a microkernel are now, and whether eschewing legacy hardware will let me design a system that's less bogged down by the traditional microkernel problems.
-
Exploration - I'm really mostly doing this to have fun learning and exploring modern OS development. Initial feature implementations may temporarily throw away modular design to allow for exploration of the related hardware.
A note on the name: This kernel was originally named Popcorn, but I have since
discovered that the Popcorn Linux project is also developing a kernel with that
name, started around the same time as this project. So I've renamed this kernel
jsix (Always styled jsix or j6, never capitalized) as an homage to L4, xv6,
and my wonderful wife.
Status and Roadmap
The following major feature areas are targets for jsix development:
UEFI boot loader
Done. The bootloader loads the kernel and initial userspace programs, and sets up necessary kernel arguments about the memory map and EFI GOP framebuffer. Possible future ideas:
- take over more init-time functions from the kernel
- rewrite it in Zig
Memory
Virtual memory: Sufficient. The kernel manages virtual memory with a number
of kinds of vm_area objects representing mapped areas, which can belong to
one or more vm_space objects which represent a whole virtual memory space.
(Each process has a vm_space, and so does the kernel itself.)
Remaining to do:
- TLB shootdowns
- Page swapping
Physical page allocation: Sufficient. The current physical page allocator implementation suses a group of block representing up-to-1GiB areas of usable memory as defined by the bootloader. Each block has a three-level bitmap denoting free/used pages.
Multitasking
Sufficient. The global scheduler object keeps separate ready/blocked lists per core. Cores periodically attempt to balance load via work stealing.
User-space tasks are able to create threads as well as other processes.
Several kernel-only tasks exist, though I'm trying to reduce that. Eventually only the timekeeping task should be a separate kernel-only thread.
API
In progress. User-space tasks are able to make syscalls to the kernel via fast SYSCALL/SYSRET instructions.
Major tasks still to do:
- The process initialization protocol needs to be re-built entirely.
- Processes' handles to kernel objects need the ability to check capabilities
Hardware Support
- Framebuffer driver: In progress. Currently on machines with a video device accessible by UEFI, jsix starts a user-space framebuffer driver that only prints out kernel logs.
- Serial driver: To do. Machines without a video device should have a user-space log output task like the framebuffer driver, but currently this is done inside the kernel.
- USB driver: To do
- AHCI (SATA) driver: To do
Building
jsix uses the Ninja build tool, and generates the build files for it with a custom tool called Bonnibel. Bonnibel can be installed with Cargo, or downloaded as a prebuilt binary from its Github repository.
Requrirements:
- bonnibel
- ninja
- clang
- nasm
- mtools
- curl for downloading the toolchain
Setting up the cross toolchain
Running pb sync will download and unpack the toolchain into sysroot.
Compiling the toolchain yourself
If you have clang and curl installed, runing the scripts/build_sysroot.sh
script will download and build a LLVM toolchain configured for building jsix
host binaries.
Building and running jsix
Once the toolchain has been set up, running Bonnibel's pb init command will
set up the build configuration, and pb build will actually run the build. If
you have qemu-system-x86_64 installed, the qemu.sh script will to run jsix
in QEMU -nographic mode.
I personally run this either from a real debian amd64 testing/buster machine or a windows WSL debian testing/buster installation. The following should be enough to set up such a system to build the kernel:
sudo apt install qemu-system-x86 nasm clang-10 mtools curl ninja-build
sudo update-alternatives /usr/bin/clang clang /usr/bin/clang-10 1000
sudo update-alternatives /usr/bin/clang++ clang++ /usr/bin/clang++-10 1000
curl -L -o pb https://github.com/justinian/bonnibel_rs/releases/download/v2.3.0/pb-linux-amd64 && chmod a+x pb