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Minor wording change

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"so that the calling code cannot overflow `heap_start`" -> "so that `alloc_end` cannot overflow"
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Calvin Lee
2016-09-22 16:03:32 -06:00
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parent 54e02fd6b5
commit 5b9a45674d
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blog/post/08-kernel-heap.md
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@@ -99,7 +99,7 @@ impl BumpAllocator {
} }
``` ```
The `heap_start` and `heap_size` fields just contain the start address and size of our kernel heap. The `next` field contains the next free address and is increased after every allocation. To `allocate` a memory block we align the `next` address using the `align_up` function (described below). Then we add up the desired `size` and make sure that we don't exceed the end of the heap. We use a saturating add so that the calling code cannot overflow `heap_start`, which would cause undefined behaviour. If everything goes well, we update the `next` address and return a pointer to the start address of the allocation. Else, we return `None`. The `heap_start` and `heap_size` fields just contain the start address and size of our kernel heap. The `next` field contains the next free address and is increased after every allocation. To `allocate` a memory block we align the `next` address using the `align_up` function (described below). Then we add up the desired `size` and make sure that we don't exceed the end of the heap. We use a saturating add so that the `alloc_end` cannot overflow, which would cause undefined behaviour. If everything goes well, we update the `next` address and return a pointer to the start address of the allocation. Else, we return `None`.
Note that we need to add a feature flag at the beginning of the file, because we've marked the `new` function as `const`. [Const functions] are unstable, so we need to add the `#![feature(const_fn)]` flag. Note that we need to add a feature flag at the beginning of the file, because we've marked the `new` function as `const`. [Const functions] are unstable, so we need to add the `#![feature(const_fn)]` flag.