factor Valgrind support out and expose it

Now other Stack / StackSource implementations can use the same Valgrind
code. Ref #3.

build.rs

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

src/lib.rs

@@ -18,6 +18,7 @@ mod std { pub use core::*; }
 
 pub mod context;
 pub mod stack;
+pub mod valgrind;
 
 #[cfg(target_arch = "x86_64")]
 mod arch;

src/os.rs

@@ -6,22 +6,14 @@ use self::std::io::Error as IoError;
 use self::libc::{c_void, size_t};
 use core::ptr;
 use stack;
-
-#[allow(non_camel_case_types)]
-type stack_id_t = u32;
-extern "C" {
-  #[link_name = "lwt_stack_register"]
-  fn stack_register(start: *const u8, end: *const u8) -> stack_id_t;
-  #[link_name = "lwt_stack_deregister"]
-  fn stack_deregister(id: stack_id_t);
-}
+use valgrind;
 
 #[allow(raw_pointer_derive)]
 #[derive(Debug)]
 pub struct Stack {
   ptr: *mut u8,
   len: usize,
-  valgrind_id: stack_id_t
+  valgrind_id: valgrind::stack_id_t
 }
 
 pub struct StackSource;
@@ -69,8 +61,9 @@ impl Stack {
                len, IoError::last_os_error())
       }
 
-      let valgrind_id = stack_register(ptr.offset(len as isize) as *const _,
-                                       ptr as *const _);
+      let valgrind_id =
+        valgrind::stack_register(ptr.offset(len as isize) as *const _,
+                                 ptr as *const _);
 
       Stack { ptr: ptr as *mut u8, len: len, valgrind_id: valgrind_id }
     };
@@ -95,7 +88,7 @@ impl Stack {
 impl Drop for Stack {
   fn drop(&mut self) {
     unsafe {
-      stack_deregister(self.valgrind_id);
+      valgrind::stack_deregister(self.valgrind_id);
       if libc::munmap(self.ptr as *mut c_void, self.len as size_t) != 0 {
         panic!("munmap for stack {:p} of size {} failed: {:?}",
                self.ptr, self.len, IoError::last_os_error())

src/valgrind.rs

@@ -0,0 +1,9 @@
+#![allow(non_camel_case_types)]
+
+pub type stack_id_t = u32;
+extern "C" {
+  #[link_name = "lwt_stack_register"]
+  pub fn stack_register(start: *const u8, end: *const u8) -> stack_id_t;
+  #[link_name = "lwt_stack_deregister"]
+  pub fn stack_deregister(id: stack_id_t);
+}