commit: 78e705c5466813f02a8f12aff1879fd78a7b6572
parent 2895b07f02891013c3306a33cccc831071aa40b0
Author: Drew DeVault <sir@cmpwn.com>
Date: Mon, 13 Jun 2022 14:20:16 +0200
Helios
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1 file changed, 93 insertions(+), 0 deletions(-)
diff --git a/content/blog/helios.md b/content/blog/helios.md
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+---
+title: The Helios microkernel
+date: 2022-06-13
+---
+
+I've been working on a cool project lately that I'd like to introduce you to:
+[the Helios microkernel][Helios]. Helios is written in [Hare] and currently
+targets x86\_64, and riscv64 and aarch64 are on the way. It's very much a
+work-in-progress: don't expect to pick this up and start building anything with
+it today.
+
+[Helios]: https://sr.ht/~sircmpwn/helios
+[Hare]: https://harelang.org
+[seL4]: https://sel4.systems
+
+
+
+Again, drawing some inspiration from seL4, Helios uses a capability-based design
+for isolation and security. The kernel offers primitives for allocating physical
+pages, mapping them into address spaces, and managing tasks, plus features like
+platform-specific I/O (e.g. reading and writing x86 ports). The entire system is
+written in Hare, plus some necessary assembly for the platform bits (e.g.
+configuring the GDT or IDT).
+
+Things are still quite early, but I'm pretty excited about this project. I
+haven't had this much fun hacking in some time :) We have several kernel
+services working, including memory management and virtual address spaces, and
+I've written a couple of simple drivers in userspace (serial and BIOS VGA
+consoles). Next up is preemptive multi-tasking — we already have
+interrupts working reliably, including the PIT, so all that's left for
+multi-tasking is to actually implement the context switch. I'd like to aim for
+an seL4-style single-stack system, though some finageling will be required
+to make that work.
+
+Much of the design comes from seL4, but unlike seL4, we intend to build upon
+this kernel and develop a userspace as well. Each of the planned components is
+named after celestial bodies, getting further from the sun as they get
+higher-level:
+
+- Helios: the kernel
+- Mercury: low-level userspace services & service bus
+- Venus: real-world driver collection
+- Gaia: high-level programming environment
+- Ares: a complete operating system; package management, GUI, etc
+
+A few other components are planned — "Vulcan" is the userspace kernel
+testing framework, named for the (now disproved) hypothetical planet between
+Mercury and the Sun, and "Luna" is the planned POSIX compatibility layer. One of
+the goals is to be practical for use on real-world hardware. I've been testing
+it continuously on my ThinkPads to ensure real-world hardware support, and I
+plan on writing drivers for its devices — Intel HD graphics, HD Audio, and
+Intel Gigabit Ethernet at the least. A basic AMD graphics driver is also likely
+to appear, and perhaps drivers for some SoC's, like Raspberry Pi's VideoCore. I
+have some neat ideas for the higher-level components as well, but I'll save
+those for later.
+
+Why build a new operating system? Well, for a start, it's really fun. But I also
+take most of my projects pretty seriously and aim for real-world usability,
+though it remains to be seen if this will be achieved. This is a hugely
+ambitious project, or, in other words, my favorite kind of project. Even if it's
+not ultimately useful, it will drive the development of a lot of useful stuff.
+We're planning to design a debugger that will be ported to Linux as well, and
+we'll be developing DWARF support for Hare to facilitate this. The GUI toolkit
+we want to build for Ares will also be generally applicable. And Helios and
+Mercury together have a reasonably small scope and makes for an interesting and
+useful platform in their own right, even if the rest of the stack never
+completely materializes. If nothing else, it will probably be able to run DOOM
+fairly soon.
+
+The kernel *is* a microkernel, so it is fairly narrow in scope and will probably
+be more-or-less complete in the foreseeable future. The next to-do items are
+context switching, so we can set up multi-tasking, IPC, fault handling, and
+userspace support for interrupts. We'll also need to parse the ACPI tables and
+bring up PCI in the kernel before handing it off to userspace. Once these things
+are in place, the kernel is essentially ready to be used to write most drivers,
+and the focus will move to fleshing out Mercury and Venus, followed by a small
+version of Gaia that can at least support an interactive shell. There are some
+longer-term features which will be nice to have in the kernel at some point,
+though, such as SMP, IOMMU, or VT-x support.
+
+Feel free to pull down the code and check it out, though remember my warning
+that it doesn't do too much yet. You can download the [latest ISO] from the CI,
+if you want to reproduce the picture at the top of this post, and write it to a
+flash drive to stick in the x86\_64 computer of your choice (boot via legacy
+BIOS). If you want to mess with the code, you could play around with the Vulcan
+system to get simple programs running in userspace. The kernel serial driver is
+write-only, but a serial driver written in userspace could easily be made to
+support interactive programs. If you're feeling extra adventureous, it probably
+wouldn't be too difficult to get a framebuffer online and draw some pixels
+— ping me in #helios on Libera Chat for a few words of guidance if you
+want to try it.
+
+[latest ISO]: https://builds.sr.ht/~sircmpwn/helios/commits/master
