From c6ece101e2787873ec70788c36eb1042964a8555 Mon Sep 17 00:00:00 2001
From: whitequark <whitequark@whitequark.org>
Date: Fri, 2 Sep 2016 22:14:07 +0000
Subject: [PATCH] Expose fringe::STACK_ALIGNMENT, and make OwnedStack respect
 it.

---
 src/arch/or1k.rs   |  2 ++
 src/arch/x86.rs    |  2 ++
 src/arch/x86_64.rs |  2 ++
 src/lib.rs         |  6 +++++-
 src/owned_stack.rs | 14 +++++++++-----
 src/slice_stack.rs |  6 ++++--
 src/stack.rs       | 10 +++++-----
 7 files changed, 29 insertions(+), 13 deletions(-)

diff --git a/src/arch/or1k.rs b/src/arch/or1k.rs
index ab94d0b..c5af1c0 100644
--- a/src/arch/or1k.rs
+++ b/src/arch/or1k.rs
@@ -40,6 +40,8 @@
 //   when unwinding as well as returning normally, because LLVM does not do it for us.
 use stack::Stack;
 
+pub const STACK_ALIGNMENT: usize = 4;
+
 #[derive(Debug, Clone)]
 pub struct StackPointer(*mut usize);
 
diff --git a/src/arch/x86.rs b/src/arch/x86.rs
index 3753506..69e86bf 100644
--- a/src/arch/x86.rs
+++ b/src/arch/x86.rs
@@ -41,6 +41,8 @@
 //   when unwinding as well as returning normally, because LLVM does not do it for us.
 use stack::Stack;
 
+pub const STACK_ALIGNMENT: usize = 16;
+
 #[derive(Debug, Clone)]
 pub struct StackPointer(*mut usize);
 
diff --git a/src/arch/x86_64.rs b/src/arch/x86_64.rs
index b4b4b1b..efa057b 100644
--- a/src/arch/x86_64.rs
+++ b/src/arch/x86_64.rs
@@ -45,6 +45,8 @@
 //   when unwinding as well as returning normally, because LLVM does not do it for us.
 use stack::Stack;
 
+pub const STACK_ALIGNMENT: usize = 16;
+
 #[derive(Debug, Clone)]
 pub struct StackPointer(*mut usize);
 
diff --git a/src/lib.rs b/src/lib.rs
index 02b12e7..1242efe 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -5,7 +5,7 @@
 // http://opensource.org/licenses/MIT>, at your option. This file may not be
 // copied, modified, or distributed except according to those terms.
 #![feature(asm, naked_functions, cfg_target_vendor)]
-#![cfg_attr(feature = "alloc", feature(alloc))]
+#![cfg_attr(feature = "alloc", feature(alloc, heap_api))]
 #![cfg_attr(test, feature(test, thread_local, const_fn))]
 #![no_std]
 
@@ -45,6 +45,10 @@ pub use owned_stack::OwnedStack;
 pub use os::Stack as OsStack;
 
 mod arch;
+
+/// Minimum alignment of a stack base address on the target platform.
+pub const STACK_ALIGNMENT: usize = arch::STACK_ALIGNMENT;
+
 mod debug;
 
 mod context;
diff --git a/src/owned_stack.rs b/src/owned_stack.rs
index d3db64f..e914690 100644
--- a/src/owned_stack.rs
+++ b/src/owned_stack.rs
@@ -3,18 +3,22 @@
 // See the LICENSE file included in this distribution.
 extern crate alloc;
 
-use self::alloc::raw_vec::RawVec;
+use core::slice;
+use self::alloc::heap;
 use self::alloc::boxed::Box;
 
-/// OwnedStack allocates on heap and owns a non-guarded stack.
+/// OwnedStack holds a non-guarded, heap-allocated stack.
 #[derive(Debug)]
 pub struct OwnedStack(Box<[u8]>);
 
 impl OwnedStack {
-    /// Allocates a new stack with exactly `size` accessible bytes using
-    /// the default Rust allocator.
+    /// Allocates a new stack with exactly `size` accessible bytes and alignment appropriate
+    /// for the current platform using the default Rust allocator.
     pub fn new(size: usize) -> OwnedStack {
-        OwnedStack(unsafe { RawVec::with_capacity(size).into_box() })
+        unsafe {
+            let ptr = heap::allocate(size, ::STACK_ALIGNMENT);
+            OwnedStack(Box::from_raw(slice::from_raw_parts_mut(ptr, size)))
+        }
     }
 }
 
diff --git a/src/slice_stack.rs b/src/slice_stack.rs
index 2ac0a82..0af9502 100644
--- a/src/slice_stack.rs
+++ b/src/slice_stack.rs
@@ -2,8 +2,10 @@
 // Copyright (c) whitequark <whitequark@whitequark.org>
 // See the LICENSE file included in this distribution.
 
-/// SliceStack holds a non-guarded stack allocated elsewhere and provided as a mutable
-/// slice.
+/// SliceStack holds a non-guarded stack allocated elsewhere and provided as a mutable slice.
+///
+/// Any slice used in a SliceStack must adhere to the [Stack contract][contract].
+/// [contract]: trait.Stack.html
 #[derive(Debug)]
 pub struct SliceStack<'a>(pub &'a mut [u8]);
 
diff --git a/src/stack.rs b/src/stack.rs
index dfd05bc..39afc39 100644
--- a/src/stack.rs
+++ b/src/stack.rs
@@ -11,17 +11,17 @@
 /// To preserve memory safety, an implementation of this trait must fulfill
 /// the following contract:
 ///
-///   * The base of the stack must be aligned to a platform-specific boundary.
+///   * The base address of the stack must be aligned to
+///     a [`STACK_ALIGNMENT`][align]-byte boundary.
 ///   * Every address between the base and the limit must be readable and writable.
 ///
-/// On any platform supported by libfringe, it is safe to align the stack to a 16-byte boundary.
-/// The platform ABI document lists the specific alignment requirement.
+/// [align]: constant.STACK_ALIGNMENT.html
 pub trait Stack {
-  /// Returns the base of the stack.
+  /// Returns the base address of the stack.
   /// On all modern architectures, the stack grows downwards,
   /// so this is the highest address.
   fn base(&self) -> *mut u8;
-  /// Returns the limit of the stack.
+  /// Returns the limit address of the stack.
   /// On all modern architectures, the stack grows downwards,
   /// so this is the lowest address.
   fn limit(&self) -> *mut u8;