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extend booting section

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Philipp Oppermann
2015-07-31 19:22:21 +02:00
parent 5b0a8cf468
commit fe9e7e9eae
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_posts/2015-07-22-rust-os-boot.md
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@@ -161,10 +161,22 @@ grub-mkrescue -o os.iso isofiles
```
## Booting
Now it's time to boot our OS. We will use [QEMU]:
```
qemu-system-x86_64 -hda os.iso
```
![qemu output]({{ site.url }}/images/qemu-ok.png)
Notice the green `OK` in the upper left corner. It works! Let's summarize what happens:
1. the BIOS loads the bootloader (GRUB) from the virtual hard drive (the ISO)
2. the bootloader reads the kernel executable and finds the Multiboot header
3. it copies the `.boot` and `.text` section to memory (at addresses `0x100000` and `0x100020`)
4. it jumps to the entry point
5. our kernel writes the green `OK` and stops the CPU
You can test it on real hardware, too. Just burn the ISO to a disk or USB stick and boot from it.
[^fn-checksum_hack]: The formula from the table, `-(magic + architecture + header length)`, creates a negative value that doesn't fit into 32bit. By subtracting from `0x100000000` instead, we keep the value positive without changing its truncated value. Without the additional sign bit(s) the result fits into 32bit and the compiler is happy.

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