Cleanup, use spinlock for allocator

alloc/bump_allocator/Cargo.toml

@@ -1,3 +1,6 @@
 [package]
 name = "bump_allocator"
 version = "0.1.0"
+
+[dependencies]
+"spin" = "*"

alloc/bump_allocator/src/lib.rs

@@ -1,24 +1,23 @@
 //! A simple allocator that never frees, for testing
+//! Some code borrowed from [Phil Opp's Blog](http://os.phil-opp.com/kernel-heap.html)
 
 #![feature(allocator)]
+#![feature(const_fn)]
 #![allocator]
 #![no_std]
 
-pub static mut HEAP: usize = 10*1024*1024;
+use spin::Mutex;
+
+extern crate spin;
+
+pub const HEAP_START: usize = 0o_000_001_000_000_0000;
+pub const HEAP_SIZE: usize = 100 * 1024; // 100 KiB
+
+static BUMP_ALLOCATOR: Mutex<BumpAllocator> = Mutex::new(BumpAllocator::new(HEAP_START, HEAP_SIZE));
 
 #[no_mangle]
 pub extern fn __rust_allocate(size: usize, align: usize) -> *mut u8 {
-    unsafe {
-        let mut ret = HEAP;
-        if align.is_power_of_two() {
-            ret += (align - 1);
-            ret &= !(align - 1);
-        } else {
-            assert_eq!(align, 0);
-        }
-        HEAP = ret + size;
-        ret as *mut u8
-    }
+    BUMP_ALLOCATOR.lock().allocate(size, align).expect("out of memory")
 }
 
 #[no_mangle]
@@ -45,3 +44,53 @@ pub extern fn __rust_reallocate(ptr: *mut u8, size: usize, new_size: usize, alig
 pub extern fn __rust_reallocate_inplace(ptr: *mut u8, size: usize, new_size: usize, align: usize) -> usize {
     size
 }
+
+/// Align downwards. Returns the greatest x with alignment `align`
+/// so that x <= addr. The alignment must be a power of 2.
+pub fn align_down(addr: usize, align: usize) -> usize {
+    if align.is_power_of_two() {
+        addr & !(align - 1)
+    } else if align == 0 {
+        addr
+    } else {
+        panic!("`align` must be a power of 2");
+    }
+}
+
+/// Align upwards. Returns the smallest x with alignment `align`
+/// so that x >= addr. The alignment must be a power of 2.
+pub fn align_up(addr: usize, align: usize) -> usize {
+    align_down(addr + align - 1, align)
+}
+
+#[derive(Debug)]
+struct BumpAllocator {
+    heap_start: usize,
+    heap_size: usize,
+    next: usize,
+}
+
+impl BumpAllocator {
+    /// Create a new allocator, which uses the memory in the
+    /// range [heap_start, heap_start + heap_size).
+    const fn new(heap_start: usize, heap_size: usize) -> BumpAllocator {
+        BumpAllocator {
+            heap_start: heap_start,
+            heap_size: heap_size,
+            next: heap_start,
+        }
+    }
+
+    /// Allocates a block of memory with the given size and alignment.
+    fn allocate(&mut self, size: usize, align: usize) -> Option<*mut u8> {
+    	let alloc_start = align_up(self.next, align);
+        let alloc_end = alloc_start + size;
+
+        if alloc_end <= self.heap_start + self.heap_size {
+            self.next = alloc_end;
+            Some(alloc_start as *mut u8)
+        } else {
+            None
+        }
+    }
+}