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Map page 0 instead of page 0x1000 because of bootloader 0.8.0

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Bootloader 0.8.0 maps the page at 0x1000 itself.
This commit is contained in:
Philipp Oppermann
2019-09-14 17:41:01 +02:00
parent 7104014c27
commit 820bc0cab3
1 changed files with 3 additions and 3 deletions
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6
blog/content/second-edition/posts/09-paging-implementation/index.md
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@@ -782,8 +782,8 @@ fn kernel_main(boot_info: &'static BootInfo) -> ! {
let mut mapper = unsafe { memory::init(boot_info.physical_memory_offset) };
let mut frame_allocator = memory::EmptyFrameAllocator;
// map a previously unmapped page
let page = Page::containing_address(VirtAddr::new(0x1000));
// map an unused page
let page = Page::containing_address(VirtAddr::new(0));
memory::create_example_mapping(page, &mut mapper, &mut frame_allocator);
// write the string `New!` to the screen through the new mapping
@@ -794,7 +794,7 @@ fn kernel_main(boot_info: &'static BootInfo) -> ! {
}
```
We first create the mapping for the page at `0x1000` by calling our `create_example_mapping` function with a mutable reference to the `mapper` and the `frame_allocator` instances. This maps the page `0x1000` to the VGA text buffer frame, so we should see any write to it on the screen.
We first create the mapping for the page at address `0` by calling our `create_example_mapping` function with a mutable reference to the `mapper` and the `frame_allocator` instances. This maps the page to the VGA text buffer frame, so we should see any write to it on the screen.
Then we convert the page to a raw pointer and write a value to offset `400`. We don't write to the start of the page because the top line of the VGA buffer is directly shifted off the screen by the next `println`. We write the value `0x_f021_f077_f065_f04e`, which represents the string _"New!"_ on white background. As we learned [in the _“VGA Text Mode”_ post], writes to the VGA buffer should be volatile, so we use the [`write_volatile`] method.