add arena allocator

kernel/src/allocator/arena.c

@@ -0,0 +1,17 @@
+/* An Arena allocator is a very basic allocator that simply discards free() calls. */
+
+#include "arena.h"
+#include <hal/ops.h>
+
+void* arena_alloc(struct arena_allocator* alloc, size_t len, size_t align) {
+    if(alloc->begin % align) {
+        alloc->begin += (align - alloc->begin % align);
+    }
+    if(alloc->length < len) {
+        PANIC("Attempt to allocate more memory than is available");
+    }
+    void* retval = (void*)alloc->begin;
+    alloc->begin += len;
+    alloc->length -= len;
+    return retval;
+}

kernel/src/allocator/arena.h

@@ -0,0 +1,8 @@
+#include <stddef.h>
+
+struct arena_allocator {
+    size_t begin;
+    size_t length;
+};
+
+void *arena_alloc(struct arena_allocator* alloc, size_t length, size_t align);