separate all the libc interaction out per OS

We're now handling more of this ourselves, and leaving less to libstd.
Hopefully, we'll eventually break free of libstd, leaving a
highly-focused low-level library that retains all its conveniences in
freestanding environments.

src/lib.rs

@@ -1,6 +1,6 @@
 #![feature(no_std)]
 #![feature(asm, core)]
-#![feature(libc, page_size)]
+#![feature(libc)]
 #![no_std]
 
 #[macro_use]

src/os.rs

@@ -1,13 +1,12 @@
-extern crate libc;
 extern crate std;
-use self::std::prelude::v1::*;
-use self::std::env;
+use core::prelude::*;
 use self::std::io::Error as IoError;
-use self::libc::{c_void, size_t};
-use core::ptr;
 use stack;
 use valgrind;
 
+#[cfg(unix)]
+#[path = "os/unix.rs"] mod sys;
+
 #[allow(raw_pointer_derive)]
 #[derive(Debug)]
 pub struct Stack {
@@ -34,32 +33,27 @@ impl stack::Stack for Stack {
 
   fn limit(&self) -> *const u8 {
     unsafe {
-      self.ptr.offset(env::page_size() as isize)
+      self.ptr.offset(sys::page_size() as isize)
     }
   }
 }
 
 impl Stack {
   fn new(size: usize) -> Stack {
-    let page_size = env::page_size();
+    let page_size = sys::page_size();
 
     // round the page size up,
     // using the fact that it is a power of two
     let len = (size + page_size - 1) & !(page_size - 1);
 
-    const STACK_PROT: libc::c_int = libc::PROT_READ | libc::PROT_WRITE;
-    const STACK_FLAGS: libc::c_int = libc::MAP_STACK
-                                   | libc::MAP_PRIVATE
-                                   | libc::MAP_ANON;
-
     let stack = unsafe {
-      let ptr = libc::mmap(ptr::null_mut(), len as size_t,
-                           STACK_PROT, STACK_FLAGS, -1, 0);
-
-      if ptr == libc::MAP_FAILED {
-        panic!("mmap for stack of size {} failed: {:?}",
-               len, IoError::last_os_error())
-      }
+      let ptr = match sys::map_stack(size) {
+        None => {
+          panic!("mmap for stack of size {} failed: {:?}",
+                 len, IoError::last_os_error())
+        }
+        Some(ptr) => ptr
+      };
 
       let valgrind_id =
         valgrind::stack_register(ptr as *const _,
@@ -68,20 +62,14 @@ impl Stack {
       Stack { ptr: ptr as *mut u8, len: len, valgrind_id: valgrind_id }
     };
 
-    stack.protect();
-
-    stack
-  }
-
-  fn protect(&self) {
     unsafe {
-      if libc::mprotect(self.ptr as *mut c_void,
-                        env::page_size() as libc::size_t,
-                        libc::PROT_NONE) != 0 {
+      if !sys::protect_stack(stack.ptr) {
         panic!("mprotect for guard page of stack {:p} failed: {:?}",
-               self.ptr, IoError::last_os_error());
+               stack.ptr, IoError::last_os_error());
       }
     }
+
+    stack
   }
 }
 
@@ -89,7 +77,7 @@ impl Drop for Stack {
   fn drop(&mut self) {
     unsafe {
       valgrind::stack_deregister(self.valgrind_id);
-      if libc::munmap(self.ptr as *mut c_void, self.len as size_t) != 0 {
+      if !sys::unmap_stack(self.ptr, self.len) {
         panic!("munmap for stack {:p} of size {} failed: {:?}",
                self.ptr, self.len, IoError::last_os_error())
       }

src/os/unix.rs

@@ -0,0 +1,39 @@
+extern crate libc;
+use core::prelude::*;
+pub use self::libc::{c_void, c_int, size_t};
+pub use self::libc::{mmap, mprotect, munmap};
+pub use self::libc::MAP_FAILED;
+
+use core::ptr;
+
+pub fn page_size() -> usize {
+  unsafe {
+    libc::sysconf(libc::_SC_PAGESIZE) as usize
+  }
+}
+
+pub const GUARD_PROT:  c_int = libc::PROT_NONE;
+pub const STACK_PROT:  c_int = libc::PROT_READ
+                             | libc::PROT_WRITE;
+pub const STACK_FLAGS: c_int = libc::MAP_STACK
+                             | libc::MAP_PRIVATE
+                             | libc::MAP_ANON;
+
+pub unsafe fn map_stack(len: usize) -> Option<*mut u8> {
+  let ptr = mmap(ptr::null_mut(), len as size_t,
+                 STACK_PROT, STACK_FLAGS, -1, 0);
+  if ptr != MAP_FAILED {
+    Some(ptr as *mut u8)
+  }
+  else {
+    None
+  }
+}
+
+pub unsafe fn protect_stack(ptr: *mut u8) -> bool {
+  mprotect(ptr as *mut c_void, page_size() as size_t, GUARD_PROT) == 0
+}
+
+pub unsafe fn unmap_stack(ptr: *mut u8, len: usize) -> bool {
+  munmap(ptr as *mut c_void, len as size_t) == 0
+}