michaelkuc6/blog_os
1
0
Fork 0
mirror of https://github.com/phil-opp/blog_os.git synced 2025-12-16 22:37:49 +00:00
Code Issues Projects Releases Wiki Activity

Improve naming and wording

Browse Source
This commit is contained in:
Philipp Oppermann
2015-07-31 19:18:52 +02:00
parent 9588bbe5ff
commit 0e73acda14
1 changed files with 6 additions and 5 deletions
Download Patch File Download Diff File Expand all files Collapse all files

11
_posts/2015-07-22-rust-os-boot.md
View File

@@ -17,9 +17,10 @@ checksum | u32 | -(magic + architecture + header length)
tags | variable | tags | variable |
end tag | (u16, u16, u32) | (0, 0, 8) end tag | (u16, u16, u32) | (0, 0, 8)
Converted to x86 assembly it looks like this (Intel syntax): Converted to a x86 assembly file it looks like this (Intel syntax):
```nasm ```nasm
section .multiboot_header
header_start: header_start:
dd 0xe85250d6 ; magic number (multiboot 2) dd 0xe85250d6 ; magic number (multiboot 2)
dd 0 ; architecture 0 (protected mode i386) dd 0 ; architecture 0 (protected mode i386)
@@ -35,18 +36,18 @@ header_start:
dd 8 ; size dd 8 ; size
header_end: header_end:
``` ```
If you don't know x86 assembly, here is some quick guide: If you don't know x86 assembly, here is some quick guide:
- the header will be written to a section named `.multiboot_header` (we need this later)
- `header_start` and `header_end` are _labels_ that mark a memory location. We use them to calculate the header length easily - `header_start` and `header_end` are _labels_ that mark a memory location. We use them to calculate the header length easily
- `dd` stands for `define double` (32bit) and `dw` stands for `define word` (16bit) - `dd` stands for `define double` (32bit) and `dw` stands for `define word` (16bit)
- the additional `0x100000000` in the checksum calculation is a small hack[^fn-checksum_hack] to avoid a compiler warning - the additional `0x100000000` in the checksum calculation is a small hack[^fn-checksum_hack] to avoid a compiler warning
We can already compile it using `nasm`. As it produces a flat binary by default, the resulting file contains just our 24 bytes (in little endian if you work on a x86 machine): We can already _assemble_ this file (which I called `multiboot_header.asm`) using `nasm`. As it produces a flat binary by default, the resulting file just contains our 24 bytes (in little endian if you work on a x86 machine):
``` ```
> nasm boot.asm > nasm multiboot_header.asm
> hexdump -x boot > hexdump -x multiboot_header
0000000 50d6 e852 0000 0000 0018 0000 af12 17ad 0000000 50d6 e852 0000 0000 0018 0000 af12 17ad
0000010 0000 0000 0008 0000 0000010 0000 0000 0008 0000
0000018 0000018