michaelkuc6/blog_os
1
0
Fork 0
mirror of https://github.com/phil-opp/blog_os.git synced 2025-12-17 06:47:49 +00:00
Code Issues Projects Releases Wiki Activity

Move footnotes to the bottom

Browse Source
This commit is contained in:
Philipp Oppermann
2017-05-03 19:02:47 +02:00
parent 7e63bf08ff
commit 7744a08212
7 changed files with 26 additions and 22 deletions
Download Patch File Download Diff File Expand all files Collapse all files

5
blog/content/posts/06-page-tables/index.md
View File

@@ -346,8 +346,6 @@ _What happens if we call them on a P1 table?_
Well, they would calculate the address of the next table (which does not exist) and treat it as a page table. Either they construct an invalid address (if `XXX < 400`)[^fn-invalid-address] or access the mapped page itself. That way, we could easily corrupt memory or cause CPU exceptions by accident. So these two functions are not _safe_ in Rust terms. Thus we need to make them `unsafe` functions unless we find some clever solution.
[^fn-invalid-address]: If the `XXX` part of the address is smaller than `0o400`, it's binary representation doesn't start with `1`. But the sign extension bits, which should be a copy of that bit, are `1` instead of `0`. Thus the address is not valid.
## Some Clever Solution
We can use Rust's type system to statically guarantee that the `next_table` methods can only be called on P4, P3, and P2 tables, but not on a P1 table. The idea is to add a `Level` parameter to the `Table` type and implement the `next_table` methods only for level 4, 3, and 2.
@@ -887,4 +885,7 @@ Afterwards, we will use this paging module to build a heap allocator. This will
<small>Image sources: [^virtual_physical_translation_source]</small>
## Footnotes
[^fn-invalid-address]: If the `XXX` part of the address is smaller than `0o400`, it's binary representation doesn't start with `1`. But the sign extension bits, which should be a copy of that bit, are `1` instead of `0`. Thus the address is not valid.
[^virtual_physical_translation_source]: Image sources: Modified versions of an image from [Wikipedia](https://commons.wikimedia.org/wiki/File:X86_Paging_64bit.svg). The modified files are licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.