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Philipp Oppermann
2015-08-25 17:07:40 +02:00
parent 1e831e2266
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_posts/2015-08-18-multiboot-kernel.md
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@@ -281,4 +281,4 @@ In the [next post] we will create a page table and do some CPU configuration to
[Makefile tutorial]: http://mrbook.org/blog/tutorials/make/
[automatic variables]: https://www.gnu.org/software/make/manual/html_node/Automatic-Variables.html
[next post]: {% post_url 2015-08-25-entering-longmode %}
[next post]: {{ site.url }}{{ page.next.url }}

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_posts/2015-08-25-entering-longmode.md
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layout: post
title: 'Entering Long Mode in small steps'
---
In the [last post] we created a minimal multiboot kernel. It just prints `OK` and hangs. Let's extend it! The goal is to call 64-bit [Rust] code. But the CPU is currently in [Protected Mode] and allows only 32-bit instructions and up to 4GiB memory. So we need to setup _Paging_ and switch to the 64-bit [Long Mode] first.
In the [previous post] we created a minimal multiboot kernel. It just prints `OK` and hangs. Let's extend it! The goal is to call 64-bit [Rust] code. But the CPU is currently in [Protected Mode] and allows only 32-bit instructions and up to 4GiB memory. So we need to setup _Paging_ and switch to the 64-bit [Long Mode] first.
I tried to explain everything in detail and to keep the code as simple as possible. If you have any questions, suggestions or other issues, please leave a comment or [create an issue] on Github. The source code is available in a [repository][source code], too.
[last post]: {% post_url 2015-08-18-multiboot-kernel %}
[previous post]: {{ site.url }}{{ page.previous.url }}
[Rust]: http://www.rust-lang.org/
[Real Mode]: http://wiki.osdev.org/Real_Mode
[Protected Mode]: https://en.wikipedia.org/wiki/Protected_mode
@@ -426,8 +426,9 @@ _Congratulations_! You have successfully wrestled through this CPU configuration
- and we can write these 64-bit registers directly to memory using `mov qword` (quad word)
## Whats next?
It's time to leave assembly behind[^leave_assembly_behind] and switch to some higher level language. We won't use any C or C++ (not even a single line). Instead we will use the relatively new [Rust] language. It's a systems language without garbage collections but with guaranteed memory safety. Through a real type system and many abstractions it feels like a high-level language but can still be low-level enough for OS development.
It's time to leave assembly behind[^leave_assembly_behind] and switch to some higher level language. We won't use any C or C++ (not even a single line). Instead we will use the relatively new [Rust] language. It's a systems language without garbage collections but with guaranteed memory safety. Through a real type system and many abstractions it feels like a high-level language but can still be low-level enough for OS development. The [next post] describes the Rust setup.
[Rust]: https://www.rust-lang.org/
[next post]: {{ site.url }}{{ page.next.url }}
[^leave_assembly_behind]: Actually we will still need some assembly in the future, but I'll try to minimize it.