Fix Stack::new(0).

src/os/mod.rs

@@ -28,9 +28,12 @@ impl Stack {
   pub fn new(size: usize) -> Result<Stack, IoError> {
     let page_size = sys::page_size();
 
+    // Stacks have to be at least one page long.
+    let len = if size == 0 { page_size } else { size };
+
     // Round the length one page size up, using the fact that the page size
     // is a power of two.
-    let len = (size + page_size - 1) & !(page_size - 1);
+    let len = (len + page_size - 1) & !(page_size - 1);
 
     // Increase the length to fit the guard page.
     let len = len + page_size;

tests/stack.rs

@@ -6,7 +6,14 @@ extern crate fringe;
 use fringe::{Stack, OsStack};
 
 #[test]
-fn stack_accessible() {
+fn default_stack() {
+  let stack = OsStack::new(0).unwrap();
+  // Make sure the topmost page of the stack, at least, is accessible.
+  unsafe { *(stack.top().offset(-1)) = 0; }
+}
+
+#[test]
+fn one_page_stack() {
   let stack = OsStack::new(4096).unwrap();
   // Make sure the topmost page of the stack, at least, is accessible.
   unsafe { *(stack.top().offset(-1)) = 0; }