From 758088c673175b70f198b64c02c21d122cbecb4f Mon Sep 17 00:00:00 2001
From: whitequark <whitequark@whitequark.org>
Date: Sun, 17 Jul 2016 01:24:20 +0000
Subject: [PATCH] Fix Stack::new(0).

---
 src/os/mod.rs  | 5 ++++-
 tests/stack.rs | 9 ++++++++-
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/src/os/mod.rs b/src/os/mod.rs
index e977c18..67c7af0 100644
--- a/src/os/mod.rs
+++ b/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;
diff --git a/tests/stack.rs b/tests/stack.rs
index 9315784..6c9f049 100644
--- a/tests/stack.rs
+++ b/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; }