move Valgrind handling into Context

fix #3
This takes all Valgrind functionality private again.
Valgrind stack registrations are now associated with a Context, not with
a Stack. This makes sense, since it's only actually a stack when a
Context is running on it. Perhaps Valgrind will even be able to detect
early stack frees now.

build.rs

@@ -1,5 +1,5 @@
 extern crate gcc;
 
 fn main() {
-  gcc::compile_library("libvalgrind.a", &["src/valgrind.c"]);
+  gcc::compile_library("libvalgrind.a", &["src/debug/valgrind.c"]);
 }

src/context.rs

@@ -1,9 +1,11 @@
 use core::prelude::*;
 use arch::Registers;
 use stack;
+use debug::StackId;
 
 pub struct Context<Stack: stack::Stack> {
   regs: Registers,
+  _stack_id: StackId,
   stack: Stack
 }
 
@@ -11,9 +13,11 @@ impl<Stack> Context<Stack> where Stack: stack::Stack {
   #[inline]
   pub unsafe fn new<F>(mut stack: Stack, f: F) -> Context<Stack>
     where F: FnOnce() + Send + 'static {
+    let stack_id = StackId::register(&mut stack);
     let regs = Registers::new(&mut stack, f);
     Context {
       regs: regs,
+      _stack_id: stack_id,
       stack: stack
     }
   }

src/debug/mod.rs

@@ -0,0 +1,24 @@
+use core::prelude::*;
+use stack;
+
+mod valgrind;
+
+pub struct StackId(valgrind::stack_id_t);
+
+impl StackId {
+  #[inline(always)]
+  pub fn register<Stack: stack::Stack>(stack: &mut Stack) -> StackId {
+    StackId(unsafe {
+      valgrind::stack_register(stack.limit(), stack.top())
+    })
+  }
+}
+
+impl Drop for StackId {
+  #[inline(always)]
+  fn drop(&mut self) {
+    unsafe {
+      valgrind::stack_deregister(self.0)
+    }
+  }
+}

src/debug/valgrind.rs

@@ -12,11 +12,6 @@ extern "C" {
   /// `start < end`.
   pub fn stack_register(start: *const u8, end: *const u8) -> stack_id_t;
 
-  #[link_name = "valgrind_stack_change"]
-  /// Change the size or location of a stack registered with Valgrind.
-  /// `start < end`.
-  pub fn stack_change(id: stack_id_t, start: *const u8, end: *const u8) -> stack_id_t;
-
   #[link_name = "valgrind_stack_deregister"]
   /// Deregister a stack from Valgrind. Takes the integer ID that was returned
   /// on registration.

src/lib.rs

@@ -18,7 +18,8 @@ mod std { pub use core::*; }
 
 pub mod context;
 pub mod stack;
-pub mod valgrind;
+
+mod debug;
 
 #[cfg(target_arch = "x86_64")]
 mod arch;

src/os.rs

@@ -2,7 +2,6 @@ extern crate std;
 use core::prelude::*;
 use self::std::io::Error as IoError;
 use stack;
-use valgrind;
 
 #[cfg(unix)]
 #[path = "os/unix.rs"] mod sys;
@@ -11,8 +10,7 @@ use valgrind;
 #[derive(Debug)]
 pub struct Stack {
   ptr: *mut u8,
-  len: usize,
+  len: usize
-  valgrind_id: valgrind::stack_id_t
 }
 
 pub struct StackSource;
@@ -55,11 +53,7 @@ impl Stack {
         Some(ptr) => ptr
       };
 
-      let valgrind_id =
+      Stack { ptr: ptr as *mut u8, len: len }
-        valgrind::stack_register(ptr as *const _,
-                                 ptr.offset(len as isize) as *const _);
-
-      Stack { ptr: ptr as *mut u8, len: len, valgrind_id: valgrind_id }
     };
 
     unsafe {
@@ -76,7 +70,6 @@ impl Stack {
 impl Drop for Stack {
   fn drop(&mut self) {
     unsafe {
-      valgrind::stack_deregister(self.valgrind_id);
       if !sys::unmap_stack(self.ptr, self.len) {
         panic!("munmap for stack {:p} of size {} failed: {}",
                self.ptr, self.len, IoError::last_os_error())