init

src/allocator.rs

@@ -0,0 +1,50 @@
+use crate::constants::PAGE_SIZE;
+use crate::errors::VmError;
+use crate::util::align_up;
+
+#[derive(Debug, Clone)]
+pub struct Allocator {
+    base: u64,
+    size: u64,
+    offset: u64,
+}
+
+impl Allocator {
+    pub fn new(base: u64, size: u64) -> Self {
+        Self {
+            base,
+            size,
+            offset: 0,
+        }
+    }
+
+    pub fn alloc(&mut self, request: u64) -> Result<u64, VmError> {
+        let length = align_up(request.max(1), PAGE_SIZE);
+        let address = self.base + self.offset;
+        let next = self.offset.saturating_add(length);
+        if next > self.size {
+            return Err(VmError::AllocatorOom {
+                base: self.base,
+                size: self.size,
+                request,
+            });
+        }
+        self.offset = next;
+        Ok(address)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::Allocator;
+
+    #[test]
+    fn allocator_aligns_to_pages() {
+        let mut allocator = Allocator::new(0x1000_0000, 0x20_000);
+        let a = allocator.alloc(1).expect("alloc 1");
+        let b = allocator.alloc(0x1500).expect("alloc 2");
+
+        assert_eq!(a, 0x1000_0000);
+        assert_eq!(b, 0x1000_1000);
+    }
+}