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Philipp Oppermann
2015-10-29 19:36:04 +01:00
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_posts/2015-08-25-entering-longmode.md
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@@ -279,7 +279,7 @@ setup_page_tables:
ret
```
Maybe I first explain how an assembly loop works. We use the `ecx` register as a counter variable, just like `i` in a or loop. After mapping the `ecx-th` entry, we increase `ecx` by one and jump to `.map_p2_table` again if it's still smaller 512.
Maybe I first explain how an assembly loop works. We use the `ecx` register as a counter variable, just like `i` in a for loop. After mapping the `ecx-th` entry, we increase `ecx` by one and jump to `.map_p2_table` again if it's still smaller 512.
To map a P2 entry we first calculate the start address of its page in `eax`: The `ecx-th` entry needs to be mapped to `ecx * 2MiB`. Then we set the `present`, `writable`, and `huge page` bits and write it to the P2 entry. The address of the `ecx-th` entry in P2 is `p2_table + ecx * 8`, because each entry is 8 bytes large.