parent
3efe54169e
commit
0e3857ca50
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use memory::paging::{self, Page, PageIter, ActivePageTable};
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use memory::{PAGE_SIZE, FrameAllocator};
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pub struct StackAllocator {
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range: PageIter,
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}
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impl StackAllocator {
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pub fn new(page_range: PageIter) -> StackAllocator {
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StackAllocator { range: page_range }
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}
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}
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impl StackAllocator {
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pub fn alloc_stack<FA: FrameAllocator>(&mut self,
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active_table: &mut ActivePageTable,
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frame_allocator: &mut FA,
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size_in_pages: usize)
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-> Option<Stack> {
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if size_in_pages == 0 {
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return None; /* a zero sized stack makes no sense */
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}
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// clone the range, since we only want to change it on success
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let mut range = self.range.clone();
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// try to allocate the stack pages and a guard page
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let guard_page = range.next();
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let stack_start = range.next();
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let stack_end = if size_in_pages == 1 {
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stack_start
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} else {
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// choose the (size_in_pages-2)th element, since index
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// starts at 0 and we already allocated the start page
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range.nth(size_in_pages - 2)
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};
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match (guard_page, stack_start, stack_end) {
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(Some(_), Some(start), Some(end)) => {
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// success! write back updated range
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self.range = range;
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// map stack pages to physical frames
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for page in Page::range_inclusive(start, end) {
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active_table.map(page, paging::WRITABLE, frame_allocator);
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}
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// create a new stack
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let top_of_stack = end.start_address() + PAGE_SIZE;
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Some(Stack::new(top_of_stack, start.start_address()))
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}
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_ => None, /* not enough pages */
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}
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}
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}
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#[derive(Debug)]
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pub struct Stack {
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top: usize,
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bottom: usize,
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}
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impl Stack {
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fn new(top: usize, bottom: usize) -> Stack {
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assert!(top > bottom);
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Stack {
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top: top,
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bottom: bottom,
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}
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}
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pub fn top(&self) -> usize {
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self.top
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}
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pub fn bottom(&self) -> usize {
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self.bottom
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}
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}
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