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Add paragraph about Multiboot

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Philipp Oppermann
2018-02-10 16:04:27 +01:00
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blog/content/second-edition/posts/02-minimal-rust-kernel/index.md
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@@ -50,10 +50,30 @@ Writing a bootloader is a bit cumbersome as it requires assembly language and a
If you are interested in building your own bootloader: Stay tuned, a set of posts on this topic is already planned! <!-- , check out our “_[Writing a Bootloader]_” posts, where we explain in detail how a bootloader is built. --> If you are interested in building your own bootloader: Stay tuned, a set of posts on this topic is already planned! <!-- , check out our “_[Writing a Bootloader]_” posts, where we explain in detail how a bootloader is built. -->
#### The Multiboot Standard
To avoid that every operating system implements its own bootloader, which is only compatible with a single OS, the Free Software Foundation created an open bootloader standard called [Multiboot] in 1995. The standard defines an interface between the bootloader and operating system, so that any Multiboot compliant bootloader can load any Multiboot compliant operating system. The reference implementation is [GNU GRUB], which is the most popular bootloader for Linux systems.
### The Multiboot Standard [Multiboot]: https://wiki.osdev.org/Multiboot
[GNU GRUB]: https://en.wikipedia.org/wiki/GNU_GRUB
TODO To make a kernel Multiboot compliant, one just need to insert a so-called [Multiboot header] at the beginning of the kernel file. This makes it very easy to boot an OS in GRUB. However, GRUB and the the Multiboot standard have some problems too:
[Multiboot header]: https://www.gnu.org/software/grub/manual/multiboot/multiboot.html#OS-image-format
- They support only the 32-bit protected mode. This means that you still have to do the CPU configuration to switch to the 64-bit long mode.
- The newest version of the standard, [Multiboot 2.0], supports kernels in the 64-bit ELF format, but requires a [adjusting the default page size].
- The development of the standard and GRUB is highly interleaved. For example, I'm not aware of an other bootloader that is Multiboot compliant. As a result, one often has to look into the GRUB source code when the standard is not clear enough.
- The standard is written for the C programming language. That means lots of C-typical structures such as linked lists in the [boot information].
- Both GRUB and the Multiboot standard are only sparsely documented.
- GRUB needs to be installed on the host system to create a bootable disk image from the kernel file. This makes development on Windows or Mac more difficult.
[boot information]: https://www.gnu.org/software/grub/manual/multiboot/multiboot.html#Boot-information-format
[Multiboot 2.0]: https://www.gnu.org/software/grub/manual/multiboot2/multiboot.html
[adjusting the default page size]: https://wiki.osdev.org/Multiboot#Multiboot_2
Because of these drawbacks we decided to not use GRUB or the Multiboot standard. However, we plan to add Multiboot support to our [bootimage] tool, so that it's possible to load your kernel on a GRUB system too. If you're interested in writing a Multiboot compliant kernel, check out the [first edition] of this blog series.
[first edition]: ./first-edition/_index.md
### UEFI ### UEFI