Comments for "https://os.phil-opp.com/minimal-rust-kernel/"

[utterances-bot]

This is a general purpose comment thread for the “A Minimal Rust Kernel” post.

[Redrield]

I'm not really a fan of using this magic utility to turn our blob of Rust into a bootable image. The parts in raw assembly in the first edition were a bit tedious but I liked how they gave us a deeper understanding about how the process worked. I hope that this utility won't be sticking around for the post on UEFI booting...

[pixelherodev]

"They are designed to make the bootloader simple instead of the kernel. For example, the kernel needs to be linked with an adjusted default page size, because GRUB can't find the Multiboot header otherwise."

WRONG!

That is true of Multiboot2, a later standard which is less used and NOT multiboot-compatible.

However, the actual Multiboot standard does not have that problem at all.

[phil-opp]

@Redrield Fair point. On the other hand we already used grub-mkrescue as such a magic utility in the first edition, which did exactly the same thing (transforming a Rust binary into a bootable image). The only difference was that GRUB only put us into protected mode, so we had to do the last steps ourselves.

Apart from a less tedious start, the new bootloader gives us an opportunity for an even deeper understanding of the boot process than before: We're planning to write several posts on how the tool and the underlying bootloader works, in a similar fashion as the other posts (i.e. every line of code is in the post and you can follow along). Thus, we can hide the complexity at the beginning of the main post series and directly start with the more interesting part, but also provide resources to those who want to understand it all the way down.

[phil-opp]

@pixelherodev Huh? I was under the impression that Multiboot2 was the successor of Multiboot? Either way, Multiboot 1 is not a better solution for us since it does have other problems (if I remember correctly it does not support 64-bit ELF files at all).

[pixelherodev]

Fair enough. Multiboot 2 is essentially the spiritual successor to multiboot IIRC. I also remember multiboot being easier to get started with, but that's neither here nor there :p Honestly, while I don't think ignoring multiboot was a good idea, I can understand why you did so.

[phil-opp]

Honestly, while I don't think ignoring multiboot was a good idea, I can understand why you did so.

Yeah, there are clear tradeoffs in this case. I really like the idea behind multiboot, but the standard and the implementation not so much. I plan to add grub compatibility to the bootimage tool, so that you can boot it in a multi-OS setting too.

First of all, great tutorial, thanks a lot for the effort!
If you're on Ubuntu, like me, and building openssl-sys when trying to cargo install bootimage fails, make sure you have libssl-dev installed!

[phil-opp]

@FuzzyHerbivore Thanks a lot! I added a hint to the post in 5f195a8.

[kylegalloway]

Disclaimer: I'm on Windows.

There is a problem with running qemu-system-x86_64 -drive format=raw,file=bootimage.bin on windows. QEMU opens and flashes but doesn't display the "Hello World!" text.

Also, converting to a VDI for VirtualBox doesn't seem to work. I get:

$ VBoxManage convertdd .\bootimage.bin bootimage.vdi --format VDI
Converting from raw image file=".\bootimage.bin" to file="bootimage.vdi"...
Creating dynamic image with size 86016 bytes (1MB)...
VBoxManage.exe: error: Cannot create the disk image "bootimage.vdi": VERR_VD_INVALID_SIZE

[AaronCoad]

@kyle I'm also using Windows with cargo 1.26.0 nightly and xargo 0.3.11. Are these the same versions for you? I'm stuck with building using xargo:

xargo build --target hyenaos results in error: multiple input filenames provided
set RUST_TARGET_PATH=cd xargo build --target hyenaos results in nothing (including no build folder) as does RUST_TARGET_PATH=cd xargo build --target hyenaos.

Using cargo 1.26.0 nightly and xargo 0.3.11.

[AaronCoad]

@kylegalloway sorry

[AaronCoad]

Feeling a little silly, still stuck on the above, but realised I was setting the path incorrectly. The following steps still fail:

set RUST_TARGET_PATH=C:\HyenaOS\ or set RUST_TARGET_PATH=C:\HyenaOS
xargo build --target hyenaos or xargo build --target C:\HyenaOS\hyenaos

These are always with the multiple input filenames provided error.

Apologies for the multiple posts.

[phil-opp]

@kylegalloway

There is a problem with running qemu-system-x86_64 -drive format=raw,file=bootimage.bin on windows. QEMU opens and flashes but doesn't display the "Hello World!" text.

I pushed a new version of the bootloader yesterday, seems like this is the cause of the error. I reverted the change for now, so it should work again. Thanks for reporting!

Also, converting to a VDI for VirtualBox doesn't seem to work. I get:

Hmm, I have no idea about this error. I only found https://forum.lede-project.org/t/error-convert-img-to-vdi/152, which indicates that the image needs to be padded somehow before converting.