auto merge of #11762 : alexcrichton/rust/guard_pages, r=alexcrichton

Rebasing of the previous PRs, I believe I've found the problems.

9 files changed, 284 insertions, 107 deletions

diff --git a/src/libgreen/context.rs b/src/libgreen/context.rs
index 5916557abdb..4e626b3bec7 100644
--- a/src/libgreen/context.rs
+++ b/src/libgreen/context.rs
@@ -12,10 +12,9 @@ use std::libc::c_void;
 use std::uint;
 use std::cast::{transmute, transmute_mut_unsafe,
                 transmute_region, transmute_mut_region};
+use stack::Stack;
 use std::unstable::stack;
 
-use stack::StackSegment;
-
 // FIXME #7761: Registers is boxed so that it is 16-byte aligned, for storing
 // SSE regs.  It would be marginally better not to do this. In C++ we
 // use an attribute on a struct.
@@ -41,7 +40,7 @@ impl Context {
     }
 
     /// Create a new context that will resume execution by running proc()
-    pub fn new(start: proc(), stack: &mut StackSegment) -> Context {
+    pub fn new(start: proc(), stack: &mut Stack) -> Context {
         // The C-ABI function that is the task entry point
         //
         // Note that this function is a little sketchy. We're taking a
@@ -79,6 +78,7 @@ impl Context {
         // be passed to the spawn function.  Another unfortunate
         // allocation
         let start = ~start;
+
         initialize_call_frame(&mut *regs,
                               task_start_wrapper as *c_void,
                               unsafe { transmute(&*start) },
diff --git a/src/libgreen/coroutine.rs b/src/libgreen/coroutine.rs
index 7bc5d0accfe..c001d40a246 100644
--- a/src/libgreen/coroutine.rs
+++ b/src/libgreen/coroutine.rs
@@ -14,7 +14,7 @@
 use std::rt::env;
 
 use context::Context;
-use stack::{StackPool, StackSegment};
+use stack::{StackPool, Stack};
 
 /// A coroutine is nothing more than a (register context, stack) pair.
 pub struct Coroutine {
@@ -24,7 +24,7 @@ pub struct Coroutine {
     ///
     /// Servo needs this to be public in order to tell SpiderMonkey
     /// about the stack bounds.
-    current_stack_segment: StackSegment,
+    current_stack_segment: Stack,
 
     /// Always valid if the task is alive and not running.
     saved_context: Context
@@ -39,7 +39,7 @@ impl Coroutine {
             Some(size) => size,
             None => env::min_stack()
         };
-        let mut stack = stack_pool.take_segment(stack_size);
+        let mut stack = stack_pool.take_stack(stack_size);
         let initial_context = Context::new(start, &mut stack);
         Coroutine {
             current_stack_segment: stack,
@@ -49,7 +49,7 @@ impl Coroutine {
 
     pub fn empty() -> Coroutine {
         Coroutine {
-            current_stack_segment: StackSegment::new(0),
+            current_stack_segment: unsafe { Stack::dummy_stack() },
             saved_context: Context::empty()
         }
     }
@@ -57,6 +57,6 @@ impl Coroutine {
     /// Destroy coroutine and try to reuse std::stack segment.
     pub fn recycle(self, stack_pool: &mut StackPool) {
         let Coroutine { current_stack_segment, .. } = self;
-        stack_pool.give_segment(current_stack_segment);
+        stack_pool.give_stack(current_stack_segment);
     }
 }
diff --git a/src/libgreen/stack.rs b/src/libgreen/stack.rs
index 7e6dd02dd67..bc2c199b83f 100644
--- a/src/libgreen/stack.rs
+++ b/src/libgreen/stack.rs
@@ -8,46 +8,113 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-use std::vec;
-use std::libc::{c_uint, uintptr_t};
+use std::rt::env::max_cached_stacks;
+use std::os::{errno, page_size, MemoryMap, MapReadable, MapWritable,
+              MapNonStandardFlags, MapVirtual};
+use std::libc;
 
-pub struct StackSegment {
-    priv buf: ~[u8],
-    priv valgrind_id: c_uint
+/// A task's stack. The name "Stack" is a vestige of segmented stacks.
+pub struct Stack {
+    priv buf: MemoryMap,
+    priv min_size: uint,
+    priv valgrind_id: libc::c_uint,
 }
 
-impl StackSegment {
-    pub fn new(size: uint) -> StackSegment {
-        unsafe {
-            // Crate a block of uninitialized values
-            let mut stack = vec::with_capacity(size);
-            stack.set_len(size);
+// Try to use MAP_STACK on platforms that support it (it's what we're doing
+// anyway), but some platforms don't support it at all. For example, it appears
+// that there's a bug in freebsd that MAP_STACK implies MAP_FIXED (so it always
+// fails): http://lists.freebsd.org/pipermail/freebsd-bugs/2011-July/044840.html
+#[cfg(not(windows), not(target_os = "freebsd"))]
+static STACK_FLAGS: libc::c_int = libc::MAP_STACK | libc::MAP_PRIVATE |
+                                  libc::MAP_ANON;
+#[cfg(target_os = "freebsd")]
+static STACK_FLAGS: libc::c_int = libc::MAP_PRIVATE | libc::MAP_ANON;
+#[cfg(windows)]
+static STACK_FLAGS: libc::c_int = 0;
 
-            let mut stk = StackSegment {
-                buf: stack,
-                valgrind_id: 0
-            };
+impl Stack {
+    /// Allocate a new stack of `size`. If size = 0, this will fail. Use
+    /// `dummy_stack` if you want a zero-sized stack.
+    pub fn new(size: uint) -> Stack {
+        // Map in a stack. Eventually we might be able to handle stack
+        // allocation failure, which would fail to spawn the task. But there's
+        // not many sensible things to do on OOM.  Failure seems fine (and is
+        // what the old stack allocation did).
+        let stack = match MemoryMap::new(size, [MapReadable, MapWritable,
+                                         MapNonStandardFlags(STACK_FLAGS)]) {
+            Ok(map) => map,
+            Err(e) => fail!("mmap for stack of size {} failed: {}", size, e)
+        };
 
-            // XXX: Using the FFI to call a C macro. Slow
-            stk.valgrind_id = rust_valgrind_stack_register(stk.start(), stk.end());
-            return stk;
+        // Change the last page to be inaccessible. This is to provide safety;
+        // when an FFI function overflows it will (hopefully) hit this guard
+        // page. It isn't guaranteed, but that's why FFI is unsafe. buf.data is
+        // guaranteed to be aligned properly.
+        if !protect_last_page(&stack) {
+            fail!("Could not memory-protect guard page. stack={:?}, errno={}",
+                  stack, errno());
+        }
+
+        let mut stk = Stack {
+            buf: stack,
+            min_size: size,
+            valgrind_id: 0
+        };
+
+        // XXX: Using the FFI to call a C macro. Slow
+        stk.valgrind_id = unsafe {
+            rust_valgrind_stack_register(stk.start(), stk.end())
+        };
+        return stk;
+    }
+
+    /// Create a 0-length stack which starts (and ends) at 0.
+    pub unsafe fn dummy_stack() -> Stack {
+        Stack {
+            buf: MemoryMap { data: 0 as *mut u8, len: 0, kind: MapVirtual },
+            min_size: 0,
+            valgrind_id: 0
         }
     }
 
     /// Point to the low end of the allocated stack
     pub fn start(&self) -> *uint {
-        self.buf.as_ptr() as *uint
+        self.buf.data as *uint
     }
 
-    /// Point one word beyond the high end of the allocated stack
+    /// Point one uint beyond the high end of the allocated stack
     pub fn end(&self) -> *uint {
         unsafe {
-            self.buf.as_ptr().offset(self.buf.len() as int) as *uint
+            self.buf.data.offset(self.buf.len as int) as *uint
         }
     }
 }
 
-impl Drop for StackSegment {
+#[cfg(unix)]
+fn protect_last_page(stack: &MemoryMap) -> bool {
+    unsafe {
+        // This may seem backwards: the start of the segment is the last page?
+        // Yes! The stack grows from higher addresses (the end of the allocated
+        // block) to lower addresses (the start of the allocated block).
+        let last_page = stack.data as *libc::c_void;
+        libc::mprotect(last_page, page_size() as libc::size_t,
+                       libc::PROT_NONE) != -1
+    }
+}
+
+#[cfg(windows)]
+fn protect_last_page(stack: &MemoryMap) -> bool {
+    unsafe {
+        // see above
+        let last_page = stack.data as *mut libc::c_void;
+        let mut old_prot: libc::DWORD = 0;
+        libc::VirtualProtect(last_page, page_size() as libc::SIZE_T,
+                             libc::PAGE_NOACCESS,
+                             &mut old_prot as libc::LPDWORD) != 0
+    }
+}
+
+impl Drop for Stack {
     fn drop(&mut self) {
         unsafe {
             // XXX: Using the FFI to call a C macro. Slow
@@ -56,20 +123,36 @@ impl Drop for StackSegment {
     }
 }
 
-pub struct StackPool(());
+pub struct StackPool {
+    // Ideally this would be some datastructure that preserved ordering on
+    // Stack.min_size.
+    priv stacks: ~[Stack],
+}
 
 impl StackPool {
-    pub fn new() -> StackPool { StackPool(()) }
+    pub fn new() -> StackPool {
+        StackPool {
+            stacks: ~[],
+        }
+    }
 
-    pub fn take_segment(&self, min_size: uint) -> StackSegment {
-        StackSegment::new(min_size)
+    pub fn take_stack(&mut self, min_size: uint) -> Stack {
+        // Ideally this would be a binary search
+        match self.stacks.iter().position(|s| s.min_size < min_size) {
+            Some(idx) => self.stacks.swap_remove(idx),
+            None      => Stack::new(min_size)
+        }
     }
 
-    pub fn give_segment(&self, _stack: StackSegment) {
+    pub fn give_stack(&mut self, stack: Stack) {
+        if self.stacks.len() <= max_cached_stacks() {
+            self.stacks.push(stack)
+        }
     }
 }
 
 extern {
-    fn rust_valgrind_stack_register(start: *uintptr_t, end: *uintptr_t) -> c_uint;
-    fn rust_valgrind_stack_deregister(id: c_uint);
+    fn rust_valgrind_stack_register(start: *libc::uintptr_t,
+                                    end: *libc::uintptr_t) -> libc::c_uint;
+    fn rust_valgrind_stack_deregister(id: libc::c_uint);
 }
diff --git a/src/libstd/libc.rs b/src/libstd/libc.rs
index a398835824b..d5f185880fa 100644
--- a/src/libstd/libc.rs
+++ b/src/libstd/libc.rs
@@ -2863,6 +2863,7 @@ pub mod consts {
             pub static MAP_PRIVATE : c_int = 0x0002;
             pub static MAP_FIXED : c_int = 0x0010;
             pub static MAP_ANON : c_int = 0x1000;
+            pub static MAP_STACK : c_int = 0;
 
             pub static MAP_FAILED : *c_void = -1 as *c_void;
 
diff --git a/src/libstd/os.rs b/src/libstd/os.rs
index 1b55427fc2d..457d58ae464 100644
--- a/src/libstd/os.rs
+++ b/src/libstd/os.rs
@@ -33,13 +33,13 @@ use container::Container;
 #[cfg(target_os = "macos")]
 use iter::range;
 use libc;
-use libc::{c_char, c_void, c_int, size_t};
+use libc::{c_char, c_void, c_int};
 use option::{Some, None};
 use os;
 use prelude::*;
 use ptr;
 use str;
-use to_str;
+use fmt;
 use unstable::finally::Finally;
 use sync::atomics::{AtomicInt, INIT_ATOMIC_INT, SeqCst};
 
@@ -59,7 +59,7 @@ pub fn getcwd() -> Path {
 
     let mut buf = [0 as c_char, ..BUF_BYTES];
     unsafe {
-        if libc::getcwd(buf.as_mut_ptr(), buf.len() as size_t).is_null() {
+        if libc::getcwd(buf.as_mut_ptr(), buf.len() as libc::size_t).is_null() {
             fail!()
         }
         Path::new(CString::new(buf.as_ptr(), false))
@@ -350,14 +350,16 @@ pub fn self_exe_name() -> Option<Path> {
             let mib = ~[CTL_KERN as c_int,
                         KERN_PROC as c_int,
                         KERN_PROC_PATHNAME as c_int, -1 as c_int];
-            let mut sz: size_t = 0;
+            let mut sz: libc::size_t = 0;
             let err = sysctl(mib.as_ptr(), mib.len() as ::libc::c_uint,
-                             ptr::mut_null(), &mut sz, ptr::null(), 0u as size_t);
+                             ptr::mut_null(), &mut sz, ptr::null(),
+                             0u as libc::size_t);
             if err != 0 { return None; }
             if sz == 0 { return None; }
             let mut v: ~[u8] = vec::with_capacity(sz as uint);
             let err = sysctl(mib.as_ptr(), mib.len() as ::libc::c_uint,
-                             v.as_mut_ptr() as *mut c_void, &mut sz, ptr::null(), 0u as size_t);
+                             v.as_mut_ptr() as *mut c_void, &mut sz, ptr::null(),
+                             0u as libc::size_t);
             if err != 0 { return None; }
             if sz == 0 { return None; }
             v.set_len(sz as uint - 1); // chop off trailing NUL
@@ -593,12 +595,12 @@ pub fn last_os_error() -> ~str {
         #[cfg(target_os = "macos")]
         #[cfg(target_os = "android")]
         #[cfg(target_os = "freebsd")]
-        fn strerror_r(errnum: c_int, buf: *mut c_char, buflen: size_t)
+        fn strerror_r(errnum: c_int, buf: *mut c_char, buflen: libc::size_t)
                       -> c_int {
             #[nolink]
             extern {
-                fn strerror_r(errnum: c_int, buf: *mut c_char, buflen: size_t)
-                              -> c_int;
+                fn strerror_r(errnum: c_int, buf: *mut c_char,
+                              buflen: libc::size_t) -> c_int;
             }
             unsafe {
                 strerror_r(errnum, buf, buflen)
@@ -609,12 +611,13 @@ pub fn last_os_error() -> ~str {
         // and requires macros to instead use the POSIX compliant variant.
         // So we just use __xpg_strerror_r which is always POSIX compliant
         #[cfg(target_os = "linux")]
-        fn strerror_r(errnum: c_int, buf: *mut c_char, buflen: size_t) -> c_int {
+        fn strerror_r(errnum: c_int, buf: *mut c_char,
+                      buflen: libc::size_t) -> c_int {
             #[nolink]
             extern {
                 fn __xpg_strerror_r(errnum: c_int,
                                     buf: *mut c_char,
-                                    buflen: size_t)
+                                    buflen: libc::size_t)
                                     -> c_int;
             }
             unsafe {
@@ -626,7 +629,7 @@ pub fn last_os_error() -> ~str {
 
         let p = buf.as_mut_ptr();
         unsafe {
-            if strerror_r(errno() as c_int, p, buf.len() as size_t) < 0 {
+            if strerror_r(errno() as c_int, p, buf.len() as libc::size_t) < 0 {
                 fail!("strerror_r failure");
             }
 
@@ -829,13 +832,14 @@ pub fn page_size() -> uint {
     }
 }
 
-/// A memory mapped file or chunk of memory. This is a very system-specific interface to the OS's
-/// memory mapping facilities (`mmap` on POSIX, `VirtualAlloc`/`CreateFileMapping` on win32). It
-/// makes no attempt at abstracting platform differences, besides in error values returned. Consider
+/// A memory mapped file or chunk of memory. This is a very system-specific
+/// interface to the OS's memory mapping facilities (`mmap` on POSIX,
+/// `VirtualAlloc`/`CreateFileMapping` on win32). It makes no attempt at
+/// abstracting platform differences, besides in error values returned. Consider
 /// yourself warned.
 ///
-/// The memory map is released (unmapped) when the destructor is run, so don't let it leave scope by
-/// accident if you want it to stick around.
+/// The memory map is released (unmapped) when the destructor is run, so don't
+/// let it leave scope by accident if you want it to stick around.
 pub struct MemoryMap {
     /// Pointer to the memory created or modified by this map.
     data: *mut u8,
@@ -847,11 +851,12 @@ pub struct MemoryMap {
 
 /// Type of memory map
 pub enum MemoryMapKind {
-    /// Memory-mapped file. On Windows, the inner pointer is a handle to the mapping, and
-    /// corresponds to `CreateFileMapping`. Elsewhere, it is null.
+    /// Virtual memory map. Usually used to change the permissions of a given
+    /// chunk of memory.  Corresponds to `VirtualAlloc` on Windows.
     MapFile(*u8),
-    /// Virtual memory map. Usually used to change the permissions of a given chunk of memory.
-    /// Corresponds to `VirtualAlloc` on Windows.
+    /// Virtual memory map. Usually used to change the permissions of a given
+    /// chunk of memory, or for allocation. Corresponds to `VirtualAlloc` on
+    /// Windows.
     MapVirtual
 }
 
@@ -863,81 +868,119 @@ pub enum MapOption {
     MapWritable,
     /// The memory should be executable
     MapExecutable,
-    /// Create a map for a specific address range. Corresponds to `MAP_FIXED` on POSIX.
+    /// Create a map for a specific address range. Corresponds to `MAP_FIXED` on
+    /// POSIX.
     MapAddr(*u8),
     /// Create a memory mapping for a file with a given fd.
     MapFd(c_int),
-    /// When using `MapFd`, the start of the map is `uint` bytes from the start of the file.
-    MapOffset(uint)
+    /// When using `MapFd`, the start of the map is `uint` bytes from the start
+    /// of the file.
+    MapOffset(uint),
+    /// On POSIX, this can be used to specify the default flags passed to
+    /// `mmap`. By default it uses `MAP_PRIVATE` and, if not using `MapFd`,
+    /// `MAP_ANON`. This will override both of those. This is platform-specific
+    /// (the exact values used) and ignored on Windows.
+    MapNonStandardFlags(c_int),
 }
 
 /// Possible errors when creating a map.
 pub enum MapError {
     /// ## The following are POSIX-specific
     ///
-    /// fd was not open for reading or, if using `MapWritable`, was not open for writing.
+    /// fd was not open for reading or, if using `MapWritable`, was not open for
+    /// writing.
     ErrFdNotAvail,
     /// fd was not valid
     ErrInvalidFd,
-    /// Either the address given by `MapAddr` or offset given by `MapOffset` was not a multiple of
-    /// `MemoryMap::granularity` (unaligned to page size).
+    /// Either the address given by `MapAddr` or offset given by `MapOffset` was
+    /// not a multiple of `MemoryMap::granularity` (unaligned to page size).
     ErrUnaligned,
     /// With `MapFd`, the fd does not support mapping.
     ErrNoMapSupport,
-    /// If using `MapAddr`, the address + `min_len` was outside of the process's address space. If
-    /// using `MapFd`, the target of the fd didn't have enough resources to fulfill the request.
+    /// If using `MapAddr`, the address + `min_len` was outside of the process's
+    /// address space. If using `MapFd`, the target of the fd didn't have enough
+    /// resources to fulfill the request.
     ErrNoMem,
+    /// A zero-length map was requested. This is invalid according to
+    /// [POSIX](http://pubs.opengroup.org/onlinepubs/9699919799/functions/mmap.html).
+    /// Not all platforms obey this, but this wrapper does.
+    ErrZeroLength,
     /// Unrecognized error. The inner value is the unrecognized errno.
     ErrUnknown(int),
     /// ## The following are win32-specific
     ///
-    /// Unsupported combination of protection flags (`MapReadable`/`MapWritable`/`MapExecutable`).
+    /// Unsupported combination of protection flags
+    /// (`MapReadable`/`MapWritable`/`MapExecutable`).
     ErrUnsupProt,
-    /// When using `MapFd`, `MapOffset` was given (Windows does not support this at all)
+    /// When using `MapFd`, `MapOffset` was given (Windows does not support this
+    /// at all)
     ErrUnsupOffset,
     /// When using `MapFd`, there was already a mapping to the file.
     ErrAlreadyExists,
-    /// Unrecognized error from `VirtualAlloc`. The inner value is the return value of GetLastError.
+    /// Unrecognized error from `VirtualAlloc`. The inner value is the return
+    /// value of GetLastError.
     ErrVirtualAlloc(uint),
-    /// Unrecognized error from `CreateFileMapping`. The inner value is the return value of
-    /// `GetLastError`.
+    /// Unrecognized error from `CreateFileMapping`. The inner value is the
+    /// return value of `GetLastError`.
     ErrCreateFileMappingW(uint),
-    /// Unrecognized error from `MapViewOfFile`. The inner value is the return value of
-    /// `GetLastError`.
+    /// Unrecognized error from `MapViewOfFile`. The inner value is the return
+    /// value of `GetLastError`.
     ErrMapViewOfFile(uint)
 }
 
-impl to_str::ToStr for MapError {
-    fn to_str(&self) -> ~str {
-        match *self {
-            ErrFdNotAvail => ~"fd not available for reading or writing",
-            ErrInvalidFd => ~"Invalid fd",
-            ErrUnaligned => ~"Unaligned address, invalid flags, \
-                              negative length or unaligned offset",
-            ErrNoMapSupport=> ~"File doesn't support mapping",
-            ErrNoMem => ~"Invalid address, or not enough available memory",
-            ErrUnknown(code) => format!("Unknown error={}", code),
-            ErrUnsupProt => ~"Protection mode unsupported",
-            ErrUnsupOffset => ~"Offset in virtual memory mode is unsupported",
-            ErrAlreadyExists => ~"File mapping for specified file already exists",
-            ErrVirtualAlloc(code) => format!("VirtualAlloc failure={}", code),
-            ErrCreateFileMappingW(code) => format!("CreateFileMappingW failure={}", code),
-            ErrMapViewOfFile(code) => format!("MapViewOfFile failure={}", code)
-        }
+impl fmt::Default for MapError {
+    fn fmt(val: &MapError, out: &mut fmt::Formatter) {
+        let str = match *val {
+            ErrFdNotAvail => "fd not available for reading or writing",
+            ErrInvalidFd => "Invalid fd",
+            ErrUnaligned => {
+                "Unaligned address, invalid flags, negative length or \
+                 unaligned offset"
+            }
+            ErrNoMapSupport=> "File doesn't support mapping",
+            ErrNoMem => "Invalid address, or not enough available memory",
+            ErrUnsupProt => "Protection mode unsupported",
+            ErrUnsupOffset => "Offset in virtual memory mode is unsupported",
+            ErrAlreadyExists => "File mapping for specified file already exists",
+            ErrZeroLength => "Zero-length mapping not allowed",
+            ErrUnknown(code) => {
+                write!(out.buf, "Unknown error = {}", code);
+                return
+            },
+            ErrVirtualAlloc(code) => {
+                write!(out.buf, "VirtualAlloc failure = {}", code);
+                return
+            },
+            ErrCreateFileMappingW(code) => {
+                format!("CreateFileMappingW failure = {}", code);
+                return
+            },
+            ErrMapViewOfFile(code) => {
+                write!(out.buf, "MapViewOfFile failure = {}", code);
+                return
+            }
+        };
+        write!(out.buf, "{}", str);
     }
 }
 
 #[cfg(unix)]
 impl MemoryMap {
-    /// Create a new mapping with the given `options`, at least `min_len` bytes long.
+    /// Create a new mapping with the given `options`, at least `min_len` bytes
+    /// long. `min_len` must be greater than zero; see the note on
+    /// `ErrZeroLength`.
     pub fn new(min_len: uint, options: &[MapOption]) -> Result<MemoryMap, MapError> {
         use libc::off_t;
 
+        if min_len == 0 {
+            return Err(ErrZeroLength)
+        }
         let mut addr: *u8 = ptr::null();
         let mut prot = 0;
         let mut flags = libc::MAP_PRIVATE;
         let mut fd = -1;
         let mut offset = 0;
+        let mut custom_flags = false;
         let len = round_up(min_len, page_size());
 
         for &o in options.iter() {
@@ -953,13 +996,15 @@ impl MemoryMap {
                     flags |= libc::MAP_FILE;
                     fd = fd_;
                 },
-                MapOffset(offset_) => { offset = offset_ as off_t; }
+                MapOffset(offset_) => { offset = offset_ as off_t; },
+                MapNonStandardFlags(f) => { custom_flags = true; flags = f },
             }
         }
-        if fd == -1 { flags |= libc::MAP_ANON; }
+        if fd == -1 && !custom_flags { flags |= libc::MAP_ANON; }
 
         let r = unsafe {
-            libc::mmap(addr as *c_void, len as size_t, prot, flags, fd, offset)
+            libc::mmap(addr as *c_void, len as libc::size_t, prot, flags, fd,
+                       offset)
         };
         if r.equiv(&libc::MAP_FAILED) {
             Err(match errno() as c_int {
@@ -983,7 +1028,8 @@ impl MemoryMap {
         }
     }
 
-    /// Granularity that the offset or address must be for `MapOffset` and `MapAddr` respectively.
+    /// Granularity that the offset or address must be for `MapOffset` and
+    /// `MapAddr` respectively.
     pub fn granularity() -> uint {
         page_size()
     }
@@ -993,6 +1039,8 @@ impl MemoryMap {
 impl Drop for MemoryMap {
     /// Unmap the mapping. Fails the task if `munmap` fails.
     fn drop(&mut self) {
+        if self.len == 0 { /* workaround for dummy_stack */ return; }
+
         unsafe {
             match libc::munmap(self.data as *c_void, self.len as libc::size_t) {
                 0 => (),
@@ -1027,7 +1075,11 @@ impl MemoryMap {
                 MapExecutable => { executable = true; }
                 MapAddr(addr_) => { lpAddress = addr_ as LPVOID; },
                 MapFd(fd_) => { fd = fd_; },
-                MapOffset(offset_) => { offset = offset_; }
+                MapOffset(offset_) => { offset = offset_; },
+                MapNonStandardFlags(f) => {
+                    info!("MemoryMap::new: MapNonStandardFlags used on \
+                           Windows: {}", f)
+                }
             }
         }
 
@@ -1113,18 +1165,18 @@ impl MemoryMap {
 
 #[cfg(windows)]
 impl Drop for MemoryMap {
-    /// Unmap the mapping. Fails the task if any of `VirtualFree`, `UnmapViewOfFile`, or
-    /// `CloseHandle` fail.
+    /// Unmap the mapping. Fails the task if any of `VirtualFree`,
+    /// `UnmapViewOfFile`, or `CloseHandle` fail.
     fn drop(&mut self) {
         use libc::types::os::arch::extra::{LPCVOID, HANDLE};
         use libc::consts::os::extra::FALSE;
+        if self.len == 0 { return }
 
         unsafe {
             match self.kind {
                 MapVirtual => {
-                    if libc::VirtualFree(self.data as *mut c_void,
-                                         self.len as size_t,
-                                         libc::MEM_RELEASE) == FALSE {
+                    if libc::VirtualFree(self.data as *mut c_void, 0,
+                                         libc::MEM_RELEASE) == 0 {
                         error!("VirtualFree failed: {}", errno());
                     }
                 },
@@ -1429,7 +1481,7 @@ mod tests {
             os::MapWritable
         ]) {
             Ok(chunk) => chunk,
-            Err(msg) => fail!(msg.to_str())
+            Err(msg) => fail!("{}", msg)
         };
         assert!(chunk.len >= 16);
 
@@ -1479,7 +1531,7 @@ mod tests {
             MapOffset(size / 2)
         ]) {
             Ok(chunk) => chunk,
-            Err(msg) => fail!(msg.to_str())
+            Err(msg) => fail!("{}", msg)
         };
         assert!(chunk.len > 0);
 
diff --git a/src/libstd/rt/env.rs b/src/libstd/rt/env.rs
index f3fa482b18c..729e377e1af 100644
--- a/src/libstd/rt/env.rs
+++ b/src/libstd/rt/env.rs
@@ -10,7 +10,7 @@
 
 //! Runtime environment settings
 
-use from_str::FromStr;
+use from_str::from_str;
 use option::{Some, None};
 use os;
 
@@ -18,18 +18,25 @@ use os;
 // They are expected to be initialized once then left alone.
 
 static mut MIN_STACK: uint = 2 * 1024 * 1024;
+/// This default corresponds to 20M of cache per scheduler (at the default size).
+static mut MAX_CACHED_STACKS: uint = 10;
 static mut DEBUG_BORROW: bool = false;
 static mut POISON_ON_FREE: bool = false;
 
 pub fn init() {
     unsafe {
         match os::getenv("RUST_MIN_STACK") {
-            Some(s) => match FromStr::from_str(s) {
+            Some(s) => match from_str(s) {
                 Some(i) => MIN_STACK = i,
                 None => ()
             },
             None => ()
         }
+        match os::getenv("RUST_MAX_CACHED_STACKS") {
+            Some(max) => MAX_CACHED_STACKS = from_str(max).expect("expected positive integer in \
+                                                                   RUST_MAX_CACHED_STACKS"),
+            None => ()
+        }
         match os::getenv("RUST_DEBUG_BORROW") {
             Some(_) => DEBUG_BORROW = true,
             None => ()
@@ -45,6 +52,10 @@ pub fn min_stack() -> uint {
     unsafe { MIN_STACK }
 }
 
+pub fn max_cached_stacks() -> uint {
+    unsafe { MAX_CACHED_STACKS }
+}
+
 pub fn debug_borrow() -> bool {
     unsafe { DEBUG_BORROW }
 }
diff --git a/src/test/bench/silly-test-spawn.rs b/src/test/bench/silly-test-spawn.rs
new file mode 100644
index 00000000000..900796efe33
--- /dev/null
+++ b/src/test/bench/silly-test-spawn.rs
@@ -0,0 +1,16 @@
+// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Useful smoketest for scheduler performance.
+fn main() {
+    for _ in range(1, 100_000) {
+        do spawn { }
+    }
+}
diff --git a/src/test/bench/spawnone.rs b/src/test/bench/spawnone.rs
new file mode 100644
index 00000000000..75485a7fb9e
--- /dev/null
+++ b/src/test/bench/spawnone.rs
@@ -0,0 +1,14 @@
+// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Useful for checking syscall usage of baseline scheduler usage
+fn main() {
+    do spawn { }
+}
diff --git a/src/test/bench/task-perf-one-million.rs b/src/test/bench/task-perf-one-million.rs
index cdbec1784b9..e9a9ed19474 100644
--- a/src/test/bench/task-perf-one-million.rs
+++ b/src/test/bench/task-perf-one-million.rs
@@ -56,7 +56,7 @@ fn main() {
         args
     };
 
-    let children = from_str::<uint>(args[1]).get();
+    let children = from_str::<uint>(args[1]).unwrap();
     let (wait_port, wait_chan) = stream();
     do task::spawn {
         calc(children, &wait_chan);
@@ -66,5 +66,5 @@ fn main() {
     let (sum_port, sum_chan) = stream::<int>();
     start_chan.send(sum_chan);
     let sum = sum_port.recv();
-    error!("How many tasks? %d tasks.", sum);
+    error!("How many tasks? {} tasks.", sum);
 }