Merge branch 'master' into feature/core_convert_id

31 files changed, 1130 insertions, 552 deletions

diff --git a/src/libstd/sys/unix/args.rs b/src/libstd/sys/unix/args.rs
index e1c7ffc19e5..c3c033dfbc7 100644
--- a/src/libstd/sys/unix/args.rs
+++ b/src/libstd/sys/unix/args.rs
@@ -66,7 +66,8 @@ impl DoubleEndedIterator for Args {
           target_os = "emscripten",
           target_os = "haiku",
           target_os = "l4re",
-          target_os = "fuchsia"))]
+          target_os = "fuchsia",
+          target_os = "hermit"))]
 mod imp {
     use os::unix::prelude::*;
     use ptr;
@@ -79,20 +80,20 @@ mod imp {
 
     static mut ARGC: isize = 0;
     static mut ARGV: *const *const u8 = ptr::null();
+    // We never call `ENV_LOCK.init()`, so it is UB to attempt to
+    // acquire this mutex reentrantly!
     static LOCK: Mutex = Mutex::new();
 
     pub unsafe fn init(argc: isize, argv: *const *const u8) {
-        LOCK.lock();
+        let _guard = LOCK.lock();
         ARGC = argc;
         ARGV = argv;
-        LOCK.unlock();
     }
 
     pub unsafe fn cleanup() {
-        LOCK.lock();
+        let _guard = LOCK.lock();
         ARGC = 0;
         ARGV = ptr::null();
-        LOCK.unlock();
     }
 
     pub fn args() -> Args {
@@ -104,13 +105,11 @@ mod imp {
 
     fn clone() -> Vec<OsString> {
         unsafe {
-            LOCK.lock();
-            let ret = (0..ARGC).map(|i| {
+            let _guard = LOCK.lock();
+            (0..ARGC).map(|i| {
                 let cstr = CStr::from_ptr(*ARGV.offset(i) as *const libc::c_char);
                 OsStringExt::from_vec(cstr.to_bytes().to_vec())
-            }).collect();
-            LOCK.unlock();
-            return ret
+            }).collect()
         }
     }
 }
diff --git a/src/libstd/sys/unix/backtrace/tracing/backtrace_fn.rs b/src/libstd/sys/unix/backtrace/tracing/backtrace_fn.rs
index 400d39cd4bd..6293eeb4ed6 100644
--- a/src/libstd/sys/unix/backtrace/tracing/backtrace_fn.rs
+++ b/src/libstd/sys/unix/backtrace/tracing/backtrace_fn.rs
@@ -38,6 +38,7 @@ pub fn unwind_backtrace(frames: &mut [Frame])
         *to = Frame {
             exact_position: *from as *mut u8,
             symbol_addr: *from as *mut u8,
+            inline_context: 0,
         };
     }
     Ok((nb_frames as usize, BacktraceContext))
diff --git a/src/libstd/sys/unix/backtrace/tracing/gcc_s.rs b/src/libstd/sys/unix/backtrace/tracing/gcc_s.rs
index 000c08d2e0d..6e841568679 100644
--- a/src/libstd/sys/unix/backtrace/tracing/gcc_s.rs
+++ b/src/libstd/sys/unix/backtrace/tracing/gcc_s.rs
@@ -68,6 +68,10 @@ pub fn unwind_backtrace(frames: &mut [Frame])
 extern fn trace_fn(ctx: *mut uw::_Unwind_Context,
                    arg: *mut libc::c_void) -> uw::_Unwind_Reason_Code {
     let cx = unsafe { &mut *(arg as *mut Context) };
+    if cx.idx >= cx.frames.len() {
+        return uw::_URC_NORMAL_STOP;
+    }
+
     let mut ip_before_insn = 0;
     let mut ip = unsafe {
         uw::_Unwind_GetIPInfo(ctx, &mut ip_before_insn) as *mut libc::c_void
@@ -94,13 +98,12 @@ extern fn trace_fn(ctx: *mut uw::_Unwind_Context,
         unsafe { uw::_Unwind_FindEnclosingFunction(ip) }
     };
 
-    if cx.idx < cx.frames.len() {
-        cx.frames[cx.idx] = Frame {
-            symbol_addr: symaddr as *mut u8,
-            exact_position: ip as *mut u8,
-        };
-        cx.idx += 1;
-    }
+    cx.frames[cx.idx] = Frame {
+        symbol_addr: symaddr as *mut u8,
+        exact_position: ip as *mut u8,
+        inline_context: 0,
+    };
+    cx.idx += 1;
 
     uw::_URC_NO_REASON
 }
diff --git a/src/libstd/sys/unix/condvar.rs b/src/libstd/sys/unix/condvar.rs
index 4f878d8ad1f..2007da7b1f6 100644
--- a/src/libstd/sys/unix/condvar.rs
+++ b/src/libstd/sys/unix/condvar.rs
@@ -41,13 +41,15 @@ impl Condvar {
     #[cfg(any(target_os = "macos",
               target_os = "ios",
               target_os = "l4re",
-              target_os = "android"))]
+              target_os = "android",
+              target_os = "hermit"))]
     pub unsafe fn init(&mut self) {}
 
     #[cfg(not(any(target_os = "macos",
                   target_os = "ios",
                   target_os = "l4re",
-                  target_os = "android")))]
+                  target_os = "android",
+                  target_os = "hermit")))]
     pub unsafe fn init(&mut self) {
         use mem;
         let mut attr: libc::pthread_condattr_t = mem::uninitialized();
@@ -83,7 +85,10 @@ impl Condvar {
     // where we configure condition variable to use monotonic clock (instead of
     // default system clock). This approach avoids all problems that result
     // from changes made to the system time.
-    #[cfg(not(any(target_os = "macos", target_os = "ios", target_os = "android")))]
+    #[cfg(not(any(target_os = "macos",
+                  target_os = "ios",
+                  target_os = "android",
+                  target_os = "hermit")))]
     pub unsafe fn wait_timeout(&self, mutex: &Mutex, dur: Duration) -> bool {
         use mem;
 
@@ -113,7 +118,7 @@ impl Condvar {
     // This implementation is modeled after libcxx's condition_variable
     // https://github.com/llvm-mirror/libcxx/blob/release_35/src/condition_variable.cpp#L46
     // https://github.com/llvm-mirror/libcxx/blob/release_35/include/__mutex_base#L367
-    #[cfg(any(target_os = "macos", target_os = "ios", target_os = "android"))]
+    #[cfg(any(target_os = "macos", target_os = "ios", target_os = "android", target_os = "hermit"))]
     pub unsafe fn wait_timeout(&self, mutex: &Mutex, mut dur: Duration) -> bool {
         use ptr;
         use time::Instant;
diff --git a/src/libstd/sys/unix/env.rs b/src/libstd/sys/unix/env.rs
index 00cf7eca75d..ad116c57f55 100644
--- a/src/libstd/sys/unix/env.rs
+++ b/src/libstd/sys/unix/env.rs
@@ -172,3 +172,14 @@ pub mod os {
     pub const EXE_SUFFIX: &'static str = "";
     pub const EXE_EXTENSION: &'static str = "";
 }
+
+#[cfg(target_os = "hermit")]
+pub mod os {
+    pub const FAMILY: &'static str = "unix";
+    pub const OS: &'static str = "hermit";
+    pub const DLL_PREFIX: &'static str = "lib";
+    pub const DLL_SUFFIX: &'static str = ".so";
+    pub const DLL_EXTENSION: &'static str = "so";
+    pub const EXE_SUFFIX: &'static str = "";
+    pub const EXE_EXTENSION: &'static str = "";
+}
diff --git a/src/libstd/sys/unix/ext/ffi.rs b/src/libstd/sys/unix/ext/ffi.rs
index fb9984ccbdd..8347145db5a 100644
--- a/src/libstd/sys/unix/ext/ffi.rs
+++ b/src/libstd/sys/unix/ext/ffi.rs
@@ -17,7 +17,9 @@ use mem;
 use sys::os_str::Buf;
 use sys_common::{FromInner, IntoInner, AsInner};
 
-/// Unix-specific extensions to `OsString`.
+/// Unix-specific extensions to [`OsString`].
+///
+/// [`OsString`]: ../../../../std/ffi/struct.OsString.html
 #[stable(feature = "rust1", since = "1.0.0")]
 pub trait OsStringExt {
     /// Creates an [`OsString`] from a byte vector.
@@ -66,7 +68,9 @@ impl OsStringExt for OsString {
     }
 }
 
-/// Unix-specific extensions to `OsStr`.
+/// Unix-specific extensions to [`OsStr`].
+///
+/// [`OsStr`]: ../../../../std/ffi/struct.OsStr.html
 #[stable(feature = "rust1", since = "1.0.0")]
 pub trait OsStrExt {
     #[stable(feature = "rust1", since = "1.0.0")]
diff --git a/src/libstd/sys/unix/ext/fs.rs b/src/libstd/sys/unix/ext/fs.rs
index 2e17fd58e0a..507e9d88171 100644
--- a/src/libstd/sys/unix/ext/fs.rs
+++ b/src/libstd/sys/unix/ext/fs.rs
@@ -41,24 +41,96 @@ pub trait FileExt {
     ///
     /// # Examples
     ///
-    /// ```
-    /// use std::os::unix::prelude::FileExt;
+    /// ```no_run
+    /// use std::io;
     /// use std::fs::File;
+    /// use std::os::unix::prelude::FileExt;
     ///
-    /// # use std::io;
-    /// # fn f() -> io::Result<()> {
-    /// let mut buf = [0u8; 8];
-    /// let file = File::open("foo.txt")?;
+    /// fn main() -> io::Result<()> {
+    ///     let mut buf = [0u8; 8];
+    ///     let file = File::open("foo.txt")?;
     ///
-    /// // We now read 8 bytes from the offset 10.
-    /// let num_bytes_read = file.read_at(&mut buf, 10)?;
-    /// println!("read {} bytes: {:?}", num_bytes_read, buf);
-    /// # Ok(())
-    /// # }
+    ///     // We now read 8 bytes from the offset 10.
+    ///     let num_bytes_read = file.read_at(&mut buf, 10)?;
+    ///     println!("read {} bytes: {:?}", num_bytes_read, buf);
+    ///     Ok(())
+    /// }
     /// ```
     #[stable(feature = "file_offset", since = "1.15.0")]
     fn read_at(&self, buf: &mut [u8], offset: u64) -> io::Result<usize>;
 
+    /// Reads the exact number of byte required to fill `buf` from the given offset.
+    ///
+    /// The offset is relative to the start of the file and thus independent
+    /// from the current cursor.
+    ///
+    /// The current file cursor is not affected by this function.
+    ///
+    /// Similar to [`Read::read_exact`] but uses [`read_at`] instead of `read`.
+    ///
+    /// [`Read::read_exact`]: ../../../../std/io/trait.Read.html#method.read_exact
+    /// [`read_at`]: #tymethod.read_at
+    ///
+    /// # Errors
+    ///
+    /// If this function encounters an error of the kind
+    /// [`ErrorKind::Interrupted`] then the error is ignored and the operation
+    /// will continue.
+    ///
+    /// If this function encounters an "end of file" before completely filling
+    /// the buffer, it returns an error of the kind [`ErrorKind::UnexpectedEof`].
+    /// The contents of `buf` are unspecified in this case.
+    ///
+    /// If any other read error is encountered then this function immediately
+    /// returns. The contents of `buf` are unspecified in this case.
+    ///
+    /// If this function returns an error, it is unspecified how many bytes it
+    /// has read, but it will never read more than would be necessary to
+    /// completely fill the buffer.
+    ///
+    /// [`ErrorKind::Interrupted`]: ../../../../std/io/enum.ErrorKind.html#variant.Interrupted
+    /// [`ErrorKind::UnexpectedEof`]: ../../../../std/io/enum.ErrorKind.html#variant.UnexpectedEof
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// #![feature(rw_exact_all_at)]
+    /// use std::io;
+    /// use std::fs::File;
+    /// use std::os::unix::prelude::FileExt;
+    ///
+    /// fn main() -> io::Result<()> {
+    ///     let mut buf = [0u8; 8];
+    ///     let file = File::open("foo.txt")?;
+    ///
+    ///     // We now read exactly 8 bytes from the offset 10.
+    ///     file.read_exact_at(&mut buf, 10)?;
+    ///     println!("read {} bytes: {:?}", buf.len(), buf);
+    ///     Ok(())
+    /// }
+    /// ```
+    #[unstable(feature = "rw_exact_all_at", issue = "51984")]
+    fn read_exact_at(&self, mut buf: &mut [u8], mut offset: u64) -> io::Result<()> {
+        while !buf.is_empty() {
+            match self.read_at(buf, offset) {
+                Ok(0) => break,
+                Ok(n) => {
+                    let tmp = buf;
+                    buf = &mut tmp[n..];
+                    offset += n as u64;
+                }
+                Err(ref e) if e.kind() == io::ErrorKind::Interrupted => {}
+                Err(e) => return Err(e),
+            }
+        }
+        if !buf.is_empty() {
+            Err(io::Error::new(io::ErrorKind::UnexpectedEof,
+                               "failed to fill whole buffer"))
+        } else {
+            Ok(())
+        }
+    }
+
     /// Writes a number of bytes starting from a given offset.
     ///
     /// Returns the number of bytes written.
@@ -78,21 +150,76 @@ pub trait FileExt {
     ///
     /// # Examples
     ///
-    /// ```
-    /// use std::os::unix::prelude::FileExt;
+    /// ```no_run
     /// use std::fs::File;
+    /// use std::io;
+    /// use std::os::unix::prelude::FileExt;
     ///
-    /// # use std::io;
-    /// # fn f() -> io::Result<()> {
-    /// let file = File::open("foo.txt")?;
+    /// fn main() -> io::Result<()> {
+    ///     let file = File::open("foo.txt")?;
     ///
-    /// // We now write at the offset 10.
-    /// file.write_at(b"sushi", 10)?;
-    /// # Ok(())
-    /// # }
+    ///     // We now write at the offset 10.
+    ///     file.write_at(b"sushi", 10)?;
+    ///     Ok(())
+    /// }
     /// ```
     #[stable(feature = "file_offset", since = "1.15.0")]
     fn write_at(&self, buf: &[u8], offset: u64) -> io::Result<usize>;
+
+    /// Attempts to write an entire buffer starting from a given offset.
+    ///
+    /// The offset is relative to the start of the file and thus independent
+    /// from the current cursor.
+    ///
+    /// The current file cursor is not affected by this function.
+    ///
+    /// This method will continuously call [`write_at`] until there is no more data
+    /// to be written or an error of non-[`ErrorKind::Interrupted`] kind is
+    /// returned. This method will not return until the entire buffer has been
+    /// successfully written or such an error occurs. The first error that is
+    /// not of [`ErrorKind::Interrupted`] kind generated from this method will be
+    /// returned.
+    ///
+    /// # Errors
+    ///
+    /// This function will return the first error of
+    /// non-[`ErrorKind::Interrupted`] kind that [`write_at`] returns.
+    ///
+    /// [`ErrorKind::Interrupted`]: ../../../../std/io/enum.ErrorKind.html#variant.Interrupted
+    /// [`write_at`]: #tymethod.write_at
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// #![feature(rw_exact_all_at)]
+    /// use std::fs::File;
+    /// use std::io;
+    /// use std::os::unix::prelude::FileExt;
+    ///
+    /// fn main() -> io::Result<()> {
+    ///     let file = File::open("foo.txt")?;
+    ///
+    ///     // We now write at the offset 10.
+    ///     file.write_all_at(b"sushi", 10)?;
+    ///     Ok(())
+    /// }
+    /// ```
+    #[unstable(feature = "rw_exact_all_at", issue = "51984")]
+    fn write_all_at(&self, mut buf: &[u8], mut offset: u64) -> io::Result<()> {
+        while !buf.is_empty() {
+            match self.write_at(buf, offset) {
+                Ok(0) => return Err(io::Error::new(io::ErrorKind::WriteZero,
+                                                   "failed to write whole buffer")),
+                Ok(n) => {
+                    buf = &buf[n..];
+                    offset += n as u64
+                }
+                Err(ref e) if e.kind() == io::ErrorKind::Interrupted => {}
+                Err(e) => return Err(e),
+            }
+        }
+        Ok(())
+    }
 }
 
 #[stable(feature = "file_offset", since = "1.15.0")]
@@ -105,7 +232,9 @@ impl FileExt for fs::File {
     }
 }
 
-/// Unix-specific extensions to `Permissions`
+/// Unix-specific extensions to [`fs::Permissions`].
+///
+/// [`fs::Permissions`]: ../../../../std/fs/struct.Permissions.html
 #[stable(feature = "fs_ext", since = "1.1.0")]
 pub trait PermissionsExt {
     /// Returns the underlying raw `st_mode` bits that contain the standard
@@ -117,13 +246,13 @@ pub trait PermissionsExt {
     /// use std::fs::File;
     /// use std::os::unix::fs::PermissionsExt;
     ///
-    /// # fn run() -> std::io::Result<()> {
-    /// let f = File::create("foo.txt")?;
-    /// let metadata = f.metadata()?;
-    /// let permissions = metadata.permissions();
+    /// fn main() -> std::io::Result<()> {
+    ///     let f = File::create("foo.txt")?;
+    ///     let metadata = f.metadata()?;
+    ///     let permissions = metadata.permissions();
     ///
-    /// println!("permissions: {}", permissions.mode());
-    /// # Ok(()) }
+    ///     println!("permissions: {}", permissions.mode());
+    ///     Ok(()) }
     /// ```
     #[stable(feature = "fs_ext", since = "1.1.0")]
     fn mode(&self) -> u32;
@@ -136,14 +265,14 @@ pub trait PermissionsExt {
     /// use std::fs::File;
     /// use std::os::unix::fs::PermissionsExt;
     ///
-    /// # fn run() -> std::io::Result<()> {
-    /// let f = File::create("foo.txt")?;
-    /// let metadata = f.metadata()?;
-    /// let mut permissions = metadata.permissions();
+    /// fn main() -> std::io::Result<()> {
+    ///     let f = File::create("foo.txt")?;
+    ///     let metadata = f.metadata()?;
+    ///     let mut permissions = metadata.permissions();
     ///
-    /// permissions.set_mode(0o644); // Read/write for owner and read for others.
-    /// assert_eq!(permissions.mode(), 0o644);
-    /// # Ok(()) }
+    ///     permissions.set_mode(0o644); // Read/write for owner and read for others.
+    ///     assert_eq!(permissions.mode(), 0o644);
+    ///     Ok(()) }
     /// ```
     #[stable(feature = "fs_ext", since = "1.1.0")]
     fn set_mode(&mut self, mode: u32);
@@ -180,7 +309,9 @@ impl PermissionsExt for Permissions {
     }
 }
 
-/// Unix-specific extensions to `OpenOptions`
+/// Unix-specific extensions to [`fs::OpenOptions`].
+///
+/// [`fs::OpenOptions`]: ../../../../std/fs/struct.OpenOptions.html
 #[stable(feature = "fs_ext", since = "1.1.0")]
 pub trait OpenOptionsExt {
     /// Sets the mode bits that a new file will be created with.
@@ -246,13 +377,9 @@ impl OpenOptionsExt for OpenOptions {
     }
 }
 
-// Hm, why are there casts here to the returned type, shouldn't the types always
-// be the same? Right you are! Turns out, however, on android at least the types
-// in the raw `stat` structure are not the same as the types being returned. Who
-// knew!
-//
-// As a result to make sure this compiles for all platforms we do the manual
-// casts and rely on manual lowering to `stat` if the raw type is desired.
+/// Unix-specific extensions to [`fs::Metadata`].
+///
+/// [`fs::Metadata`]: ../../../../std/fs/struct.Metadata.html
 #[stable(feature = "metadata_ext", since = "1.1.0")]
 pub trait MetadataExt {
     /// Returns the ID of the device containing the file.
@@ -260,15 +387,15 @@ pub trait MetadataExt {
     /// # Examples
     ///
     /// ```no_run
+    /// use std::io;
     /// use std::fs;
     /// use std::os::unix::fs::MetadataExt;
     ///
-    /// # use std::io;
-    /// # fn f() -> io::Result<()> {
-    /// let meta = fs::metadata("some_file")?;
-    /// let dev_id = meta.dev();
-    /// # Ok(())
-    /// # }
+    /// fn main() -> io::Result<()> {
+    ///     let meta = fs::metadata("some_file")?;
+    ///     let dev_id = meta.dev();
+    ///     Ok(())
+    /// }
     /// ```
     #[stable(feature = "metadata_ext", since = "1.1.0")]
     fn dev(&self) -> u64;
@@ -279,13 +406,13 @@ pub trait MetadataExt {
     /// ```no_run
     /// use std::fs;
     /// use std::os::unix::fs::MetadataExt;
+    /// use std::io;
     ///
-    /// # use std::io;
-    /// # fn f() -> io::Result<()> {
-    /// let meta = fs::metadata("some_file")?;
-    /// let inode = meta.ino();
-    /// # Ok(())
-    /// # }
+    /// fn main() -> io::Result<()> {
+    ///     let meta = fs::metadata("some_file")?;
+    ///     let inode = meta.ino();
+    ///     Ok(())
+    /// }
     /// ```
     #[stable(feature = "metadata_ext", since = "1.1.0")]
     fn ino(&self) -> u64;
@@ -296,17 +423,17 @@ pub trait MetadataExt {
     /// ```no_run
     /// use std::fs;
     /// use std::os::unix::fs::MetadataExt;
-    ///
-    /// # use std::io;
-    /// # fn f() -> io::Result<()> {
-    /// let meta = fs::metadata("some_file")?;
-    /// let mode = meta.mode();
-    /// let user_has_write_access      = mode & 0o200;
-    /// let user_has_read_write_access = mode & 0o600;
-    /// let group_has_read_access      = mode & 0o040;
-    /// let others_have_exec_access    = mode & 0o001;
-    /// # Ok(())
-    /// # }
+    /// use std::io;
+    ///
+    /// fn main() -> io::Result<()> {
+    ///     let meta = fs::metadata("some_file")?;
+    ///     let mode = meta.mode();
+    ///     let user_has_write_access      = mode & 0o200;
+    ///     let user_has_read_write_access = mode & 0o600;
+    ///     let group_has_read_access      = mode & 0o040;
+    ///     let others_have_exec_access    = mode & 0o001;
+    ///     Ok(())
+    /// }
     /// ```
     #[stable(feature = "metadata_ext", since = "1.1.0")]
     fn mode(&self) -> u32;
@@ -317,13 +444,13 @@ pub trait MetadataExt {
     /// ```no_run
     /// use std::fs;
     /// use std::os::unix::fs::MetadataExt;
+    ///  use std::io;
     ///
-    /// # use std::io;
-    /// # fn f() -> io::Result<()> {
-    /// let meta = fs::metadata("some_file")?;
-    /// let nb_hard_links = meta.nlink();
-    /// # Ok(())
-    /// # }
+    /// fn main() -> io::Result<()> {
+    ///     let meta = fs::metadata("some_file")?;
+    ///     let nb_hard_links = meta.nlink();
+    ///     Ok(())
+    /// }
     /// ```
     #[stable(feature = "metadata_ext", since = "1.1.0")]
     fn nlink(&self) -> u64;
@@ -334,13 +461,13 @@ pub trait MetadataExt {
     /// ```no_run
     /// use std::fs;
     /// use std::os::unix::fs::MetadataExt;
+    /// use std::io;
     ///
-    /// # use std::io;
-    /// # fn f() -> io::Result<()> {
-    /// let meta = fs::metadata("some_file")?;
-    /// let user_id = meta.uid();
-    /// # Ok(())
-    /// # }
+    /// fn main() -> io::Result<()> {
+    ///     let meta = fs::metadata("some_file")?;
+    ///     let user_id = meta.uid();
+    ///     Ok(())
+    /// }
     /// ```
     #[stable(feature = "metadata_ext", since = "1.1.0")]
     fn uid(&self) -> u32;
@@ -351,13 +478,13 @@ pub trait MetadataExt {
     /// ```no_run
     /// use std::fs;
     /// use std::os::unix::fs::MetadataExt;
+    /// use std::io;
     ///
-    /// # use std::io;
-    /// # fn f() -> io::Result<()> {
-    /// let meta = fs::metadata("some_file")?;
-    /// let group_id = meta.gid();
-    /// # Ok(())
-    /// # }
+    /// fn main() -> io::Result<()> {
+    ///     let meta = fs::metadata("some_file")?;
+    ///     let group_id = meta.gid();
+    ///     Ok(())
+    /// }
     /// ```
     #[stable(feature = "metadata_ext", since = "1.1.0")]
     fn gid(&self) -> u32;
@@ -368,13 +495,13 @@ pub trait MetadataExt {
     /// ```no_run
     /// use std::fs;
     /// use std::os::unix::fs::MetadataExt;
+    /// use std::io;
     ///
-    /// # use std::io;
-    /// # fn f() -> io::Result<()> {
-    /// let meta = fs::metadata("some_file")?;
-    /// let device_id = meta.rdev();
-    /// # Ok(())
-    /// # }
+    /// fn main() -> io::Result<()> {
+    ///     let meta = fs::metadata("some_file")?;
+    ///     let device_id = meta.rdev();
+    ///     Ok(())
+    /// }
     /// ```
     #[stable(feature = "metadata_ext", since = "1.1.0")]
     fn rdev(&self) -> u64;
@@ -385,13 +512,13 @@ pub trait MetadataExt {
     /// ```no_run
     /// use std::fs;
     /// use std::os::unix::fs::MetadataExt;
+    /// use std::io;
     ///
-    /// # use std::io;
-    /// # fn f() -> io::Result<()> {
-    /// let meta = fs::metadata("some_file")?;
-    /// let file_size = meta.size();
-    /// # Ok(())
-    /// # }
+    /// fn main() -> io::Result<()> {
+    ///     let meta = fs::metadata("some_file")?;
+    ///     let file_size = meta.size();
+    ///     Ok(())
+    /// }
     /// ```
     #[stable(feature = "metadata_ext", since = "1.1.0")]
     fn size(&self) -> u64;
@@ -402,13 +529,13 @@ pub trait MetadataExt {
     /// ```no_run
     /// use std::fs;
     /// use std::os::unix::fs::MetadataExt;
+    /// use std::io;
     ///
-    /// # use std::io;
-    /// # fn f() -> io::Result<()> {
-    /// let meta = fs::metadata("some_file")?;
-    /// let last_access_time = meta.atime();
-    /// # Ok(())
-    /// # }
+    /// fn main() -> io::Result<()> {
+    ///     let meta = fs::metadata("some_file")?;
+    ///     let last_access_time = meta.atime();
+    ///     Ok(())
+    /// }
     /// ```
     #[stable(feature = "metadata_ext", since = "1.1.0")]
     fn atime(&self) -> i64;
@@ -419,13 +546,13 @@ pub trait MetadataExt {
     /// ```no_run
     /// use std::fs;
     /// use std::os::unix::fs::MetadataExt;
+    /// use std::io;
     ///
-    /// # use std::io;
-    /// # fn f() -> io::Result<()> {
-    /// let meta = fs::metadata("some_file")?;
-    /// let nano_last_access_time = meta.atime_nsec();
-    /// # Ok(())
-    /// # }
+    /// fn main() -> io::Result<()> {
+    ///     let meta = fs::metadata("some_file")?;
+    ///     let nano_last_access_time = meta.atime_nsec();
+    ///     Ok(())
+    /// }
     /// ```
     #[stable(feature = "metadata_ext", since = "1.1.0")]
     fn atime_nsec(&self) -> i64;
@@ -436,13 +563,13 @@ pub trait MetadataExt {
     /// ```no_run
     /// use std::fs;
     /// use std::os::unix::fs::MetadataExt;
+    /// use std::io;
     ///
-    /// # use std::io;
-    /// # fn f() -> io::Result<()> {
-    /// let meta = fs::metadata("some_file")?;
-    /// let last_modification_time = meta.mtime();
-    /// # Ok(())
-    /// # }
+    /// fn main() -> io::Result<()> {
+    ///     let meta = fs::metadata("some_file")?;
+    ///     let last_modification_time = meta.mtime();
+    ///     Ok(())
+    /// }
     /// ```
     #[stable(feature = "metadata_ext", since = "1.1.0")]
     fn mtime(&self) -> i64;
@@ -453,13 +580,13 @@ pub trait MetadataExt {
     /// ```no_run
     /// use std::fs;
     /// use std::os::unix::fs::MetadataExt;
+    /// use std::io;
     ///
-    /// # use std::io;
-    /// # fn f() -> io::Result<()> {
-    /// let meta = fs::metadata("some_file")?;
-    /// let nano_last_modification_time = meta.mtime_nsec();
-    /// # Ok(())
-    /// # }
+    /// fn main() -> io::Result<()> {
+    ///     let meta = fs::metadata("some_file")?;
+    ///     let nano_last_modification_time = meta.mtime_nsec();
+    ///     Ok(())
+    /// }
     /// ```
     #[stable(feature = "metadata_ext", since = "1.1.0")]
     fn mtime_nsec(&self) -> i64;
@@ -470,13 +597,13 @@ pub trait MetadataExt {
     /// ```no_run
     /// use std::fs;
     /// use std::os::unix::fs::MetadataExt;
+    /// use std::io;
     ///
-    /// # use std::io;
-    /// # fn f() -> io::Result<()> {
-    /// let meta = fs::metadata("some_file")?;
-    /// let last_status_change_time = meta.ctime();
-    /// # Ok(())
-    /// # }
+    /// fn main() -> io::Result<()> {
+    ///     let meta = fs::metadata("some_file")?;
+    ///     let last_status_change_time = meta.ctime();
+    ///     Ok(())
+    /// }
     /// ```
     #[stable(feature = "metadata_ext", since = "1.1.0")]
     fn ctime(&self) -> i64;
@@ -487,13 +614,13 @@ pub trait MetadataExt {
     /// ```no_run
     /// use std::fs;
     /// use std::os::unix::fs::MetadataExt;
+    /// use std::io;
     ///
-    /// # use std::io;
-    /// # fn f() -> io::Result<()> {
-    /// let meta = fs::metadata("some_file")?;
-    /// let nano_last_status_change_time = meta.ctime_nsec();
-    /// # Ok(())
-    /// # }
+    /// fn main() -> io::Result<()> {
+    ///     let meta = fs::metadata("some_file")?;
+    ///     let nano_last_status_change_time = meta.ctime_nsec();
+    ///     Ok(())
+    /// }
     /// ```
     #[stable(feature = "metadata_ext", since = "1.1.0")]
     fn ctime_nsec(&self) -> i64;
@@ -504,13 +631,13 @@ pub trait MetadataExt {
     /// ```no_run
     /// use std::fs;
     /// use std::os::unix::fs::MetadataExt;
+    /// use std::io;
     ///
-    /// # use std::io;
-    /// # fn f() -> io::Result<()> {
-    /// let meta = fs::metadata("some_file")?;
-    /// let blocksize = meta.blksize();
-    /// # Ok(())
-    /// # }
+    /// fn main() -> io::Result<()> {
+    ///     let meta = fs::metadata("some_file")?;
+    ///     let blocksize = meta.blksize();
+    ///     Ok(())
+    /// }
     /// ```
     #[stable(feature = "metadata_ext", since = "1.1.0")]
     fn blksize(&self) -> u64;
@@ -523,13 +650,13 @@ pub trait MetadataExt {
     /// ```no_run
     /// use std::fs;
     /// use std::os::unix::fs::MetadataExt;
+    /// use std::io;
     ///
-    /// # use std::io;
-    /// # fn f() -> io::Result<()> {
-    /// let meta = fs::metadata("some_file")?;
-    /// let blocks = meta.blocks();
-    /// # Ok(())
-    /// # }
+    /// fn main() -> io::Result<()> {
+    ///     let meta = fs::metadata("some_file")?;
+    ///     let blocks = meta.blocks();
+    ///     Ok(())
+    /// }
     /// ```
     #[stable(feature = "metadata_ext", since = "1.1.0")]
     fn blocks(&self) -> u64;
@@ -555,24 +682,29 @@ impl MetadataExt for fs::Metadata {
     fn blocks(&self) -> u64 { self.st_blocks() }
 }
 
-/// Add support for special unix types (block/char device, fifo and socket).
+/// Unix-specific extensions for [`FileType`].
+///
+/// Adds support for special Unix file types such as block/character devices,
+/// pipes, and sockets.
+///
+/// [`FileType`]: ../../../../std/fs/struct.FileType.html
 #[stable(feature = "file_type_ext", since = "1.5.0")]
 pub trait FileTypeExt {
     /// Returns whether this file type is a block device.
     ///
     /// # Examples
     ///
-    /// ```
+    /// ```no_run
     /// use std::fs;
     /// use std::os::unix::fs::FileTypeExt;
+    /// use std::io;
     ///
-    /// # use std::io;
-    /// # fn f() -> io::Result<()> {
-    /// let meta = fs::metadata("block_device_file")?;
-    /// let file_type = meta.file_type();
-    /// assert!(file_type.is_block_device());
-    /// # Ok(())
-    /// # }
+    /// fn main() -> io::Result<()> {
+    ///     let meta = fs::metadata("block_device_file")?;
+    ///     let file_type = meta.file_type();
+    ///     assert!(file_type.is_block_device());
+    ///     Ok(())
+    /// }
     /// ```
     #[stable(feature = "file_type_ext", since = "1.5.0")]
     fn is_block_device(&self) -> bool;
@@ -580,17 +712,17 @@ pub trait FileTypeExt {
     ///
     /// # Examples
     ///
-    /// ```
+    /// ```no_run
     /// use std::fs;
     /// use std::os::unix::fs::FileTypeExt;
+    /// use std::io;
     ///
-    /// # use std::io;
-    /// # fn f() -> io::Result<()> {
-    /// let meta = fs::metadata("char_device_file")?;
-    /// let file_type = meta.file_type();
-    /// assert!(file_type.is_char_device());
-    /// # Ok(())
-    /// # }
+    /// fn main() -> io::Result<()> {
+    ///     let meta = fs::metadata("char_device_file")?;
+    ///     let file_type = meta.file_type();
+    ///     assert!(file_type.is_char_device());
+    ///     Ok(())
+    /// }
     /// ```
     #[stable(feature = "file_type_ext", since = "1.5.0")]
     fn is_char_device(&self) -> bool;
@@ -598,17 +730,17 @@ pub trait FileTypeExt {
     ///
     /// # Examples
     ///
-    /// ```
+    /// ```no_run
     /// use std::fs;
     /// use std::os::unix::fs::FileTypeExt;
+    /// use std::io;
     ///
-    /// # use std::io;
-    /// # fn f() -> io::Result<()> {
-    /// let meta = fs::metadata("fifo_file")?;
-    /// let file_type = meta.file_type();
-    /// assert!(file_type.is_fifo());
-    /// # Ok(())
-    /// # }
+    /// fn main() -> io::Result<()> {
+    ///     let meta = fs::metadata("fifo_file")?;
+    ///     let file_type = meta.file_type();
+    ///     assert!(file_type.is_fifo());
+    ///     Ok(())
+    /// }
     /// ```
     #[stable(feature = "file_type_ext", since = "1.5.0")]
     fn is_fifo(&self) -> bool;
@@ -616,17 +748,17 @@ pub trait FileTypeExt {
     ///
     /// # Examples
     ///
-    /// ```
+    /// ```no_run
     /// use std::fs;
     /// use std::os::unix::fs::FileTypeExt;
+    /// use std::io;
     ///
-    /// # use std::io;
-    /// # fn f() -> io::Result<()> {
-    /// let meta = fs::metadata("unix.socket")?;
-    /// let file_type = meta.file_type();
-    /// assert!(file_type.is_socket());
-    /// # Ok(())
-    /// # }
+    /// fn main() -> io::Result<()> {
+    ///     let meta = fs::metadata("unix.socket")?;
+    ///     let file_type = meta.file_type();
+    ///     assert!(file_type.is_socket());
+    ///     Ok(())
+    /// }
     /// ```
     #[stable(feature = "file_type_ext", since = "1.5.0")]
     fn is_socket(&self) -> bool;
@@ -687,13 +819,13 @@ impl DirEntryExt for fs::DirEntry {
 ///
 /// # Examples
 ///
-/// ```
+/// ```no_run
 /// use std::os::unix::fs;
 ///
-/// # fn foo() -> std::io::Result<()> {
-/// fs::symlink("a.txt", "b.txt")?;
-/// # Ok(())
-/// # }
+/// fn main() -> std::io::Result<()> {
+///     fs::symlink("a.txt", "b.txt")?;
+///     Ok(())
+/// }
 /// ```
 #[stable(feature = "symlink", since = "1.1.0")]
 pub fn symlink<P: AsRef<Path>, Q: AsRef<Path>>(src: P, dst: Q) -> io::Result<()>
@@ -701,10 +833,10 @@ pub fn symlink<P: AsRef<Path>, Q: AsRef<Path>>(src: P, dst: Q) -> io::Result<()>
     sys::fs::symlink(src.as_ref(), dst.as_ref())
 }
 
-#[stable(feature = "dir_builder", since = "1.6.0")]
-/// An extension trait for [`fs::DirBuilder`] for unix-specific options.
+/// Unix-specific extensions to [`fs::DirBuilder`].
 ///
 /// [`fs::DirBuilder`]: ../../../../std/fs/struct.DirBuilder.html
+#[stable(feature = "dir_builder", since = "1.6.0")]
 pub trait DirBuilderExt {
     /// Sets the mode to create new directories with. This option defaults to
     /// 0o777.
diff --git a/src/libstd/sys/unix/ext/mod.rs b/src/libstd/sys/unix/ext/mod.rs
index c221f7c8cfe..88e4237f8e2 100644
--- a/src/libstd/sys/unix/ext/mod.rs
+++ b/src/libstd/sys/unix/ext/mod.rs
@@ -35,6 +35,7 @@
 
 #![stable(feature = "rust1", since = "1.0.0")]
 #![doc(cfg(unix))]
+#![allow(missing_docs)]
 
 pub mod io;
 pub mod ffi;
diff --git a/src/libstd/sys/unix/ext/net.rs b/src/libstd/sys/unix/ext/net.rs
index 86b0f35be92..55f43ccd7db 100644
--- a/src/libstd/sys/unix/ext/net.rs
+++ b/src/libstd/sys/unix/ext/net.rs
@@ -51,13 +51,11 @@ use libc::MSG_NOSIGNAL;
 const MSG_NOSIGNAL: libc::c_int = 0x0;
 
 fn sun_path_offset() -> usize {
-    unsafe {
-        // Work with an actual instance of the type since using a null pointer is UB
-        let addr: libc::sockaddr_un = mem::uninitialized();
-        let base = &addr as *const _ as usize;
-        let path = &addr.sun_path as *const _ as usize;
-        path - base
-    }
+    // Work with an actual instance of the type since using a null pointer is UB
+    let addr: libc::sockaddr_un = unsafe { mem::uninitialized() };
+    let base = &addr as *const _ as usize;
+    let path = &addr.sun_path as *const _ as usize;
+    path - base
 }
 
 unsafe fn sockaddr_un(path: &Path) -> io::Result<(libc::sockaddr_un, libc::socklen_t)> {
@@ -216,7 +214,10 @@ impl SocketAddr {
         let path = unsafe { mem::transmute::<&[libc::c_char], &[u8]>(&self.addr.sun_path) };
 
         // macOS seems to return a len of 16 and a zeroed sun_path for unnamed addresses
-        if len == 0 || (cfg!(not(target_os = "linux")) && self.addr.sun_path[0] == 0) {
+        if len == 0
+            || (cfg!(not(any(target_os = "linux", target_os = "android")))
+                && self.addr.sun_path[0] == 0)
+        {
             AddressKind::Unnamed
         } else if self.addr.sun_path[0] == 0 {
             AddressKind::Abstract(&path[1..len])
@@ -387,10 +388,11 @@ impl UnixStream {
     /// Sets the read timeout for the socket.
     ///
     /// If the provided value is [`None`], then [`read`] calls will block
-    /// indefinitely. It is an error to pass the zero [`Duration`] to this
+    /// indefinitely. An [`Err`] is returned if the zero [`Duration`] is passed to this
     /// method.
     ///
     /// [`None`]: ../../../../std/option/enum.Option.html#variant.None
+    /// [`Err`]: ../../../../std/result/enum.Result.html#variant.Err
     /// [`read`]: ../../../../std/io/trait.Read.html#tymethod.read
     /// [`Duration`]: ../../../../std/time/struct.Duration.html
     ///
@@ -403,6 +405,20 @@ impl UnixStream {
     /// let socket = UnixStream::connect("/tmp/sock").unwrap();
     /// socket.set_read_timeout(Some(Duration::new(1, 0))).expect("Couldn't set read timeout");
     /// ```
+    ///
+    /// An [`Err`] is returned if the zero [`Duration`] is passed to this
+    /// method:
+    ///
+    /// ```no_run
+    /// use std::io;
+    /// use std::os::unix::net::UnixStream;
+    /// use std::time::Duration;
+    ///
+    /// let socket = UnixStream::connect("/tmp/sock").unwrap();
+    /// let result = socket.set_read_timeout(Some(Duration::new(0, 0)));
+    /// let err = result.unwrap_err();
+    /// assert_eq!(err.kind(), io::ErrorKind::InvalidInput)
+    /// ```
     #[stable(feature = "unix_socket", since = "1.10.0")]
     pub fn set_read_timeout(&self, timeout: Option<Duration>) -> io::Result<()> {
         self.0.set_timeout(timeout, libc::SO_RCVTIMEO)
@@ -411,11 +427,12 @@ impl UnixStream {
     /// Sets the write timeout for the socket.
     ///
     /// If the provided value is [`None`], then [`write`] calls will block
-    /// indefinitely. It is an error to pass the zero [`Duration`] to this
-    /// method.
+    /// indefinitely. An [`Err`] is returned if the zero [`Duration`] is
+    /// passed to this method.
     ///
     /// [`None`]: ../../../../std/option/enum.Option.html#variant.None
-    /// [`read`]: ../../../../std/io/trait.Write.html#tymethod.write
+    /// [`Err`]: ../../../../std/result/enum.Result.html#variant.Err
+    /// [`write`]: ../../../../std/io/trait.Write.html#tymethod.write
     /// [`Duration`]: ../../../../std/time/struct.Duration.html
     ///
     /// # Examples
@@ -427,6 +444,20 @@ impl UnixStream {
     /// let socket = UnixStream::connect("/tmp/sock").unwrap();
     /// socket.set_write_timeout(Some(Duration::new(1, 0))).expect("Couldn't set write timeout");
     /// ```
+    ///
+    /// An [`Err`] is returned if the zero [`Duration`] is passed to this
+    /// method:
+    ///
+    /// ```no_run
+    /// use std::io;
+    /// use std::net::UdpSocket;
+    /// use std::time::Duration;
+    ///
+    /// let socket = UdpSocket::bind("127.0.0.1:34254").unwrap();
+    /// let result = socket.set_write_timeout(Some(Duration::new(0, 0)));
+    /// let err = result.unwrap_err();
+    /// assert_eq!(err.kind(), io::ErrorKind::InvalidInput)
+    /// ```
     #[stable(feature = "unix_socket", since = "1.10.0")]
     pub fn set_write_timeout(&self, timeout: Option<Duration>) -> io::Result<()> {
         self.0.set_timeout(timeout, libc::SO_SNDTIMEO)
@@ -493,6 +524,9 @@ impl UnixStream {
     ///     println!("Got error: {:?}", err);
     /// }
     /// ```
+    ///
+    /// # Platform specific
+    /// On Redox this always returns None.
     #[stable(feature = "unix_socket", since = "1.10.0")]
     pub fn take_error(&self) -> io::Result<Option<io::Error>> {
         self.0.take_error()
@@ -815,6 +849,9 @@ impl UnixListener {
     ///     println!("Got error: {:?}", err);
     /// }
     /// ```
+    ///
+    /// # Platform specific
+    /// On Redox this always returns None.
     #[stable(feature = "unix_socket", since = "1.10.0")]
     pub fn take_error(&self) -> io::Result<Option<io::Error>> {
         self.0.take_error()
@@ -1250,10 +1287,11 @@ impl UnixDatagram {
     /// Sets the read timeout for the socket.
     ///
     /// If the provided value is [`None`], then [`recv`] and [`recv_from`] calls will
-    /// block indefinitely. It is an error to pass the zero [`Duration`] to this
-    /// method.
+    /// block indefinitely. An [`Err`] is returned if the zero [`Duration`]
+    /// is passed to this method.
     ///
     /// [`None`]: ../../../../std/option/enum.Option.html#variant.None
+    /// [`Err`]: ../../../../std/result/enum.Result.html#variant.Err
     /// [`recv`]: #method.recv
     /// [`recv_from`]: #method.recv_from
     /// [`Duration`]: ../../../../std/time/struct.Duration.html
@@ -1267,6 +1305,20 @@ impl UnixDatagram {
     /// let sock = UnixDatagram::unbound().unwrap();
     /// sock.set_read_timeout(Some(Duration::new(1, 0))).expect("set_read_timeout function failed");
     /// ```
+    ///
+    /// An [`Err`] is returned if the zero [`Duration`] is passed to this
+    /// method:
+    ///
+    /// ```no_run
+    /// use std::io;
+    /// use std::os::unix::net::UnixDatagram;
+    /// use std::time::Duration;
+    ///
+    /// let socket = UnixDatagram::unbound().unwrap();
+    /// let result = socket.set_read_timeout(Some(Duration::new(0, 0)));
+    /// let err = result.unwrap_err();
+    /// assert_eq!(err.kind(), io::ErrorKind::InvalidInput)
+    /// ```
     #[stable(feature = "unix_socket", since = "1.10.0")]
     pub fn set_read_timeout(&self, timeout: Option<Duration>) -> io::Result<()> {
         self.0.set_timeout(timeout, libc::SO_RCVTIMEO)
@@ -1275,7 +1327,7 @@ impl UnixDatagram {
     /// Sets the write timeout for the socket.
     ///
     /// If the provided value is [`None`], then [`send`] and [`send_to`] calls will
-    /// block indefinitely. It is an error to pass the zero [`Duration`] to this
+    /// block indefinitely. An [`Err`] is returned if the zero [`Duration`] is passed to this
     /// method.
     ///
     /// [`None`]: ../../../../std/option/enum.Option.html#variant.None
@@ -1293,6 +1345,20 @@ impl UnixDatagram {
     /// sock.set_write_timeout(Some(Duration::new(1, 0)))
     ///     .expect("set_write_timeout function failed");
     /// ```
+    ///
+    /// An [`Err`] is returned if the zero [`Duration`] is passed to this
+    /// method:
+    ///
+    /// ```no_run
+    /// use std::io;
+    /// use std::os::unix::net::UnixDatagram;
+    /// use std::time::Duration;
+    ///
+    /// let socket = UnixDatagram::unbound().unwrap();
+    /// let result = socket.set_write_timeout(Some(Duration::new(0, 0)));
+    /// let err = result.unwrap_err();
+    /// assert_eq!(err.kind(), io::ErrorKind::InvalidInput)
+    /// ```
     #[stable(feature = "unix_socket", since = "1.10.0")]
     pub fn set_write_timeout(&self, timeout: Option<Duration>) -> io::Result<()> {
         self.0.set_timeout(timeout, libc::SO_SNDTIMEO)
@@ -1410,7 +1476,7 @@ impl IntoRawFd for UnixDatagram {
 #[cfg(all(test, not(target_os = "emscripten")))]
 mod test {
     use thread;
-    use io;
+    use io::{self, ErrorKind};
     use io::prelude::*;
     use time::Duration;
     use sys_common::io::test::tmpdir;
@@ -1613,6 +1679,27 @@ mod test {
         assert!(kind == io::ErrorKind::WouldBlock || kind == io::ErrorKind::TimedOut);
     }
 
+    // Ensure the `set_read_timeout` and `set_write_timeout` calls return errors
+    // when passed zero Durations
+    #[test]
+    fn test_unix_stream_timeout_zero_duration() {
+        let dir = tmpdir();
+        let socket_path = dir.path().join("sock");
+
+        let listener = or_panic!(UnixListener::bind(&socket_path));
+        let stream = or_panic!(UnixStream::connect(&socket_path));
+
+        let result = stream.set_write_timeout(Some(Duration::new(0, 0)));
+        let err = result.unwrap_err();
+        assert_eq!(err.kind(), ErrorKind::InvalidInput);
+
+        let result = stream.set_read_timeout(Some(Duration::new(0, 0)));
+        let err = result.unwrap_err();
+        assert_eq!(err.kind(), ErrorKind::InvalidInput);
+
+        drop(listener);
+    }
+
     #[test]
     fn test_unix_datagram() {
         let dir = tmpdir();
@@ -1712,6 +1799,24 @@ mod test {
         thread.join().unwrap();
     }
 
+    // Ensure the `set_read_timeout` and `set_write_timeout` calls return errors
+    // when passed zero Durations
+    #[test]
+    fn test_unix_datagram_timeout_zero_duration() {
+        let dir = tmpdir();
+        let path = dir.path().join("sock");
+
+        let datagram = or_panic!(UnixDatagram::bind(&path));
+
+        let result = datagram.set_write_timeout(Some(Duration::new(0, 0)));
+        let err = result.unwrap_err();
+        assert_eq!(err.kind(), ErrorKind::InvalidInput);
+
+        let result = datagram.set_read_timeout(Some(Duration::new(0, 0)));
+        let err = result.unwrap_err();
+        assert_eq!(err.kind(), ErrorKind::InvalidInput);
+    }
+
     #[test]
     fn abstract_namespace_not_allowed() {
         assert!(UnixStream::connect("\0asdf").is_err());
diff --git a/src/libstd/sys/unix/ext/process.rs b/src/libstd/sys/unix/ext/process.rs
index 60309bec6d4..21630ae9746 100644
--- a/src/libstd/sys/unix/ext/process.rs
+++ b/src/libstd/sys/unix/ext/process.rs
@@ -18,7 +18,9 @@ use process;
 use sys;
 use sys_common::{AsInnerMut, AsInner, FromInner, IntoInner};
 
-/// Unix-specific extensions to the `std::process::Command` builder
+/// Unix-specific extensions to the [`process::Command`] builder.
+///
+/// [`process::Command`]: ../../../../std/process/struct.Command.html
 #[stable(feature = "rust1", since = "1.0.0")]
 pub trait CommandExt {
     /// Sets the child process's user id. This translates to a
@@ -117,7 +119,9 @@ impl CommandExt for process::Command {
     }
 }
 
-/// Unix-specific extensions to `std::process::ExitStatus`
+/// Unix-specific extensions to [`process::ExitStatus`].
+///
+/// [`process::ExitStatus`]: ../../../../std/process/struct.ExitStatus.html
 #[stable(feature = "rust1", since = "1.0.0")]
 pub trait ExitStatusExt {
     /// Creates a new `ExitStatus` from the raw underlying `i32` return value of
@@ -193,7 +197,7 @@ impl IntoRawFd for process::ChildStderr {
 }
 
 /// Returns the OS-assigned process identifier associated with this process's parent.
-#[unstable(feature = "unix_ppid", issue = "46104")]
+#[stable(feature = "unix_ppid", since = "1.27.0")]
 pub fn parent_id() -> u32 {
     ::sys::os::getppid()
 }
diff --git a/src/libstd/sys/unix/ext/thread.rs b/src/libstd/sys/unix/ext/thread.rs
index fe2a48764dc..8dadf29945c 100644
--- a/src/libstd/sys/unix/ext/thread.rs
+++ b/src/libstd/sys/unix/ext/thread.rs
@@ -21,7 +21,9 @@ use thread::JoinHandle;
 #[allow(deprecated)]
 pub type RawPthread = pthread_t;
 
-/// Unix-specific extensions to `std::thread::JoinHandle`
+/// Unix-specific extensions to [`thread::JoinHandle`].
+///
+/// [`thread::JoinHandle`]: ../../../../std/thread/struct.JoinHandle.html
 #[stable(feature = "thread_extensions", since = "1.9.0")]
 pub trait JoinHandleExt {
     /// Extracts the raw pthread_t without taking ownership
diff --git a/src/libstd/sys/unix/fast_thread_local.rs b/src/libstd/sys/unix/fast_thread_local.rs
index 6cdbe5df75d..c13a0fea1e0 100644
--- a/src/libstd/sys/unix/fast_thread_local.rs
+++ b/src/libstd/sys/unix/fast_thread_local.rs
@@ -20,7 +20,7 @@
 // fallback implementation to use as well.
 //
 // Due to rust-lang/rust#18804, make sure this is not generic!
-#[cfg(target_os = "linux")]
+#[cfg(any(target_os = "linux", target_os = "fuchsia", target_os = "hermit"))]
 pub unsafe fn register_dtor(t: *mut u8, dtor: unsafe extern fn(*mut u8)) {
     use libc;
     use mem;
@@ -55,11 +55,6 @@ pub unsafe fn register_dtor(t: *mut u8, dtor: unsafe extern fn(*mut u8)) {
     _tlv_atexit(dtor, t);
 }
 
-// Just use the thread_local fallback implementation, at least until there's
-// a more direct implementation.
-#[cfg(target_os = "fuchsia")]
-pub use sys_common::thread_local::register_dtor_fallback as register_dtor;
-
 pub fn requires_move_before_drop() -> bool {
     // The macOS implementation of TLS apparently had an odd aspect to it
     // where the pointer we have may be overwritten while this destructor
diff --git a/src/libstd/sys/unix/fd.rs b/src/libstd/sys/unix/fd.rs
index 5dafc3251e7..4830e38d6a9 100644
--- a/src/libstd/sys/unix/fd.rs
+++ b/src/libstd/sys/unix/fd.rs
@@ -75,8 +75,15 @@ impl FileDesc {
         unsafe fn cvt_pread64(fd: c_int, buf: *mut c_void, count: usize, offset: i64)
             -> io::Result<isize>
         {
+            use convert::TryInto;
             use libc::pread64;
-            cvt(pread64(fd, buf, count, offset as i32))
+            // pread64 on emscripten actually takes a 32 bit offset
+            if let Ok(o) = offset.try_into() {
+                cvt(pread64(fd, buf, count, o))
+            } else {
+                Err(io::Error::new(io::ErrorKind::InvalidInput,
+                                   "cannot pread >2GB"))
+            }
         }
 
         #[cfg(not(any(target_os = "android", target_os = "emscripten")))]
@@ -116,8 +123,15 @@ impl FileDesc {
         unsafe fn cvt_pwrite64(fd: c_int, buf: *const c_void, count: usize, offset: i64)
             -> io::Result<isize>
         {
+            use convert::TryInto;
             use libc::pwrite64;
-            cvt(pwrite64(fd, buf, count, offset as i32))
+            // pwrite64 on emscripten actually takes a 32 bit offset
+            if let Ok(o) = offset.try_into() {
+                cvt(pwrite64(fd, buf, count, o))
+            } else {
+                Err(io::Error::new(io::ErrorKind::InvalidInput,
+                                   "cannot pwrite >2GB"))
+            }
         }
 
         #[cfg(not(any(target_os = "android", target_os = "emscripten")))]
@@ -140,6 +154,13 @@ impl FileDesc {
         }
     }
 
+    #[cfg(target_os = "linux")]
+    pub fn get_cloexec(&self) -> io::Result<bool> {
+        unsafe {
+            Ok((cvt(libc::fcntl(self.fd, libc::F_GETFD))? & libc::FD_CLOEXEC) != 0)
+        }
+    }
+
     #[cfg(not(any(target_env = "newlib",
                   target_os = "solaris",
                   target_os = "emscripten",
diff --git a/src/libstd/sys/unix/fs.rs b/src/libstd/sys/unix/fs.rs
index a1ca839dc18..7a89d9857bb 100644
--- a/src/libstd/sys/unix/fs.rs
+++ b/src/libstd/sys/unix/fs.rs
@@ -25,8 +25,12 @@ use sys_common::{AsInner, FromInner};
 
 #[cfg(any(target_os = "linux", target_os = "emscripten", target_os = "l4re"))]
 use libc::{stat64, fstat64, lstat64, off64_t, ftruncate64, lseek64, dirent64, readdir64_r, open64};
+#[cfg(any(target_os = "linux", target_os = "emscripten"))]
+use libc::fstatat64;
+#[cfg(any(target_os = "linux", target_os = "emscripten", target_os = "android"))]
+use libc::dirfd;
 #[cfg(target_os = "android")]
-use libc::{stat as stat64, fstat as fstat64, lstat as lstat64, lseek64,
+use libc::{stat as stat64, fstat as fstat64, fstatat as fstatat64, lstat as lstat64, lseek64,
            dirent as dirent64, open as open64};
 #[cfg(not(any(target_os = "linux",
               target_os = "emscripten",
@@ -48,9 +52,16 @@ pub struct FileAttr {
     stat: stat64,
 }
 
-pub struct ReadDir {
+// all DirEntry's will have a reference to this struct
+struct InnerReadDir {
     dirp: Dir,
-    root: Arc<PathBuf>,
+    root: PathBuf,
+}
+
+#[derive(Clone)]
+pub struct ReadDir {
+    inner: Arc<InnerReadDir>,
+    end_of_stream: bool,
 }
 
 struct Dir(*mut libc::DIR);
@@ -60,8 +71,8 @@ unsafe impl Sync for Dir {}
 
 pub struct DirEntry {
     entry: dirent64,
-    root: Arc<PathBuf>,
-    // We need to store an owned copy of the directory name
+    dir: ReadDir,
+    // We need to store an owned copy of the entry name
     // on Solaris and Fuchsia because a) it uses a zero-length
     // array to store the name, b) its lifetime between readdir
     // calls is not guaranteed.
@@ -207,7 +218,7 @@ impl fmt::Debug for ReadDir {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         // This will only be called from std::fs::ReadDir, which will add a "ReadDir()" frame.
         // Thus the result will be e g 'ReadDir("/home")'
-        fmt::Debug::fmt(&*self.root, f)
+        fmt::Debug::fmt(&*self.inner.root, f)
     }
 }
 
@@ -223,7 +234,7 @@ impl Iterator for ReadDir {
                 // is safe to use in threaded applications and it is generally preferred
                 // over the readdir_r(3C) function.
                 super::os::set_errno(0);
-                let entry_ptr = libc::readdir(self.dirp.0);
+                let entry_ptr = libc::readdir(self.inner.dirp.0);
                 if entry_ptr.is_null() {
                     // NULL can mean either the end is reached or an error occurred.
                     // So we had to clear errno beforehand to check for an error now.
@@ -240,7 +251,7 @@ impl Iterator for ReadDir {
                     entry: *entry_ptr,
                     name: ::slice::from_raw_parts(name as *const u8,
                                                   namelen as usize).to_owned().into_boxed_slice(),
-                    root: self.root.clone()
+                    dir: self.clone()
                 };
                 if ret.name_bytes() != b"." && ret.name_bytes() != b".." {
                     return Some(Ok(ret))
@@ -251,14 +262,25 @@ impl Iterator for ReadDir {
 
     #[cfg(not(any(target_os = "solaris", target_os = "fuchsia")))]
     fn next(&mut self) -> Option<io::Result<DirEntry>> {
+        if self.end_of_stream {
+            return None;
+        }
+
         unsafe {
             let mut ret = DirEntry {
                 entry: mem::zeroed(),
-                root: self.root.clone()
+                dir: self.clone(),
             };
             let mut entry_ptr = ptr::null_mut();
             loop {
-                if readdir64_r(self.dirp.0, &mut ret.entry, &mut entry_ptr) != 0 {
+                if readdir64_r(self.inner.dirp.0, &mut ret.entry, &mut entry_ptr) != 0 {
+                    if entry_ptr.is_null() {
+                        // We encountered an error (which will be returned in this iteration), but
+                        // we also reached the end of the directory stream. The `end_of_stream`
+                        // flag is enabled to make sure that we return `None` in the next iteration
+                        // (instead of looping forever)
+                        self.end_of_stream = true;
+                    }
                     return Some(Err(Error::last_os_error()))
                 }
                 if entry_ptr.is_null() {
@@ -281,23 +303,34 @@ impl Drop for Dir {
 
 impl DirEntry {
     pub fn path(&self) -> PathBuf {
-        self.root.join(OsStr::from_bytes(self.name_bytes()))
+        self.dir.inner.root.join(OsStr::from_bytes(self.name_bytes()))
     }
 
     pub fn file_name(&self) -> OsString {
         OsStr::from_bytes(self.name_bytes()).to_os_string()
     }
 
+    #[cfg(any(target_os = "linux", target_os = "emscripten", target_os = "android"))]
+    pub fn metadata(&self) -> io::Result<FileAttr> {
+        let fd = cvt(unsafe {dirfd(self.dir.inner.dirp.0)})?;
+        let mut stat: stat64 = unsafe { mem::zeroed() };
+        cvt(unsafe {
+            fstatat64(fd, self.entry.d_name.as_ptr(), &mut stat, libc::AT_SYMLINK_NOFOLLOW)
+        })?;
+        Ok(FileAttr { stat: stat })
+    }
+
+    #[cfg(not(any(target_os = "linux", target_os = "emscripten", target_os = "android")))]
     pub fn metadata(&self) -> io::Result<FileAttr> {
         lstat(&self.path())
     }
 
-    #[cfg(any(target_os = "solaris", target_os = "haiku"))]
+    #[cfg(any(target_os = "solaris", target_os = "haiku", target_os = "hermit"))]
     pub fn file_type(&self) -> io::Result<FileType> {
         lstat(&self.path()).map(|m| m.file_type())
     }
 
-    #[cfg(not(any(target_os = "solaris", target_os = "haiku")))]
+    #[cfg(not(any(target_os = "solaris", target_os = "haiku", target_os = "hermit")))]
     pub fn file_type(&self) -> io::Result<FileType> {
         match self.entry.d_type {
             libc::DT_CHR => Ok(FileType { mode: libc::S_IFCHR }),
@@ -319,7 +352,8 @@ impl DirEntry {
               target_os = "solaris",
               target_os = "haiku",
               target_os = "l4re",
-              target_os = "fuchsia"))]
+              target_os = "fuchsia",
+              target_os = "hermit"))]
     pub fn ino(&self) -> u64 {
         self.entry.d_ino as u64
     }
@@ -350,7 +384,8 @@ impl DirEntry {
               target_os = "linux",
               target_os = "emscripten",
               target_os = "l4re",
-              target_os = "haiku"))]
+              target_os = "haiku",
+              target_os = "hermit"))]
     fn name_bytes(&self) -> &[u8] {
         unsafe {
             CStr::from_ptr(self.entry.d_name.as_ptr()).to_bytes()
@@ -441,15 +476,48 @@ impl File {
 
         // Currently the standard library supports Linux 2.6.18 which did not
         // have the O_CLOEXEC flag (passed above). If we're running on an older
-        // Linux kernel then the flag is just ignored by the OS, so we continue
-        // to explicitly ask for a CLOEXEC fd here.
+        // Linux kernel then the flag is just ignored by the OS. After we open
+        // the first file, we check whether it has CLOEXEC set. If it doesn't,
+        // we will explicitly ask for a CLOEXEC fd for every further file we
+        // open, if it does, we will skip that step.
         //
         // The CLOEXEC flag, however, is supported on versions of macOS/BSD/etc
         // that we support, so we only do this on Linux currently.
-        if cfg!(target_os = "linux") {
-            fd.set_cloexec()?;
+        #[cfg(target_os = "linux")]
+        fn ensure_cloexec(fd: &FileDesc) -> io::Result<()> {
+            use sync::atomic::{AtomicUsize, Ordering};
+
+            const OPEN_CLOEXEC_UNKNOWN: usize = 0;
+            const OPEN_CLOEXEC_SUPPORTED: usize = 1;
+            const OPEN_CLOEXEC_NOTSUPPORTED: usize = 2;
+            static OPEN_CLOEXEC: AtomicUsize = AtomicUsize::new(OPEN_CLOEXEC_UNKNOWN);
+
+            let need_to_set;
+            match OPEN_CLOEXEC.load(Ordering::Relaxed) {
+                OPEN_CLOEXEC_UNKNOWN => {
+                    need_to_set = !fd.get_cloexec()?;
+                    OPEN_CLOEXEC.store(if need_to_set {
+                        OPEN_CLOEXEC_NOTSUPPORTED
+                    } else {
+                        OPEN_CLOEXEC_SUPPORTED
+                    }, Ordering::Relaxed);
+                },
+                OPEN_CLOEXEC_SUPPORTED => need_to_set = false,
+                OPEN_CLOEXEC_NOTSUPPORTED => need_to_set = true,
+                _ => unreachable!(),
+            }
+            if need_to_set {
+                fd.set_cloexec()?;
+            }
+            Ok(())
+        }
+
+        #[cfg(not(target_os = "linux"))]
+        fn ensure_cloexec(_: &FileDesc) -> io::Result<()> {
+            Ok(())
         }
 
+        ensure_cloexec(&fd)?;
         Ok(File(fd))
     }
 
@@ -631,14 +699,18 @@ impl fmt::Debug for File {
 }
 
 pub fn readdir(p: &Path) -> io::Result<ReadDir> {
-    let root = Arc::new(p.to_path_buf());
+    let root = p.to_path_buf();
     let p = cstr(p)?;
     unsafe {
         let ptr = libc::opendir(p.as_ptr());
         if ptr.is_null() {
             Err(Error::last_os_error())
         } else {
-            Ok(ReadDir { dirp: Dir(ptr), root: root })
+            let inner = InnerReadDir { dirp: Dir(ptr), root };
+            Ok(ReadDir{
+                inner: Arc::new(inner),
+                end_of_stream: false,
+            })
         }
     }
 }
@@ -733,7 +805,7 @@ pub fn stat(p: &Path) -> io::Result<FileAttr> {
     let p = cstr(p)?;
     let mut stat: stat64 = unsafe { mem::zeroed() };
     cvt(unsafe {
-        stat64(p.as_ptr(), &mut stat as *mut _ as *mut _)
+        stat64(p.as_ptr(), &mut stat)
     })?;
     Ok(FileAttr { stat: stat })
 }
@@ -742,7 +814,7 @@ pub fn lstat(p: &Path) -> io::Result<FileAttr> {
     let p = cstr(p)?;
     let mut stat: stat64 = unsafe { mem::zeroed() };
     cvt(unsafe {
-        lstat64(p.as_ptr(), &mut stat as *mut _ as *mut _)
+        lstat64(p.as_ptr(), &mut stat)
     })?;
     Ok(FileAttr { stat: stat })
 }
@@ -761,8 +833,9 @@ pub fn canonicalize(p: &Path) -> io::Result<PathBuf> {
     Ok(PathBuf::from(OsString::from_vec(buf)))
 }
 
+#[cfg(not(any(target_os = "linux", target_os = "android")))]
 pub fn copy(from: &Path, to: &Path) -> io::Result<u64> {
-    use fs::{File, set_permissions};
+    use fs::File;
     if !from.is_file() {
         return Err(Error::new(ErrorKind::InvalidInput,
                               "the source path is not an existing regular file"))
@@ -773,6 +846,100 @@ pub fn copy(from: &Path, to: &Path) -> io::Result<u64> {
     let perm = reader.metadata()?.permissions();
 
     let ret = io::copy(&mut reader, &mut writer)?;
-    set_permissions(to, perm)?;
+    writer.set_permissions(perm)?;
     Ok(ret)
 }
+
+#[cfg(any(target_os = "linux", target_os = "android"))]
+pub fn copy(from: &Path, to: &Path) -> io::Result<u64> {
+    use cmp;
+    use fs::File;
+    use sync::atomic::{AtomicBool, Ordering};
+
+    // Kernel prior to 4.5 don't have copy_file_range
+    // We store the availability in a global to avoid unneccessary syscalls
+    static HAS_COPY_FILE_RANGE: AtomicBool = AtomicBool::new(true);
+
+    unsafe fn copy_file_range(
+        fd_in: libc::c_int,
+        off_in: *mut libc::loff_t,
+        fd_out: libc::c_int,
+        off_out: *mut libc::loff_t,
+        len: libc::size_t,
+        flags: libc::c_uint,
+    ) -> libc::c_long {
+        libc::syscall(
+            libc::SYS_copy_file_range,
+            fd_in,
+            off_in,
+            fd_out,
+            off_out,
+            len,
+            flags,
+        )
+    }
+
+    if !from.is_file() {
+        return Err(Error::new(ErrorKind::InvalidInput,
+                              "the source path is not an existing regular file"))
+    }
+
+    let mut reader = File::open(from)?;
+    let mut writer = File::create(to)?;
+    let (perm, len) = {
+        let metadata = reader.metadata()?;
+        (metadata.permissions(), metadata.size())
+    };
+
+    let has_copy_file_range = HAS_COPY_FILE_RANGE.load(Ordering::Relaxed);
+    let mut written = 0u64;
+    while written < len {
+        let copy_result = if has_copy_file_range {
+            let bytes_to_copy = cmp::min(len - written, usize::max_value() as u64) as usize;
+            let copy_result = unsafe {
+                // We actually don't have to adjust the offsets,
+                // because copy_file_range adjusts the file offset automatically
+                cvt(copy_file_range(reader.as_raw_fd(),
+                                    ptr::null_mut(),
+                                    writer.as_raw_fd(),
+                                    ptr::null_mut(),
+                                    bytes_to_copy,
+                                    0)
+                    )
+            };
+            if let Err(ref copy_err) = copy_result {
+                match copy_err.raw_os_error() {
+                    Some(libc::ENOSYS) | Some(libc::EPERM) => {
+                        HAS_COPY_FILE_RANGE.store(false, Ordering::Relaxed);
+                    }
+                    _ => {}
+                }
+            }
+            copy_result
+        } else {
+            Err(io::Error::from_raw_os_error(libc::ENOSYS))
+        };
+        match copy_result {
+            Ok(ret) => written += ret as u64,
+            Err(err) => {
+                match err.raw_os_error() {
+                    Some(os_err) if os_err == libc::ENOSYS
+                                 || os_err == libc::EXDEV
+                                 || os_err == libc::EPERM => {
+                        // Try fallback io::copy if either:
+                        // - Kernel version is < 4.5 (ENOSYS)
+                        // - Files are mounted on different fs (EXDEV)
+                        // - copy_file_range is disallowed, for example by seccomp (EPERM)
+                        assert_eq!(written, 0);
+                        let ret = io::copy(&mut reader, &mut writer)?;
+                        writer.set_permissions(perm)?;
+                        return Ok(ret)
+                    },
+                    _ => return Err(err),
+                }
+            }
+        }
+    }
+    writer.set_permissions(perm)?;
+    Ok(written)
+}
diff --git a/src/libstd/sys/unix/l4re.rs b/src/libstd/sys/unix/l4re.rs
index c3e8d0b7d95..21218489679 100644
--- a/src/libstd/sys/unix/l4re.rs
+++ b/src/libstd/sys/unix/l4re.rs
@@ -437,9 +437,5 @@ pub mod net {
     pub fn lookup_host(_: &str) -> io::Result<LookupHost> {
         unimpl!();
     }
-
-    pub fn res_init_if_glibc_before_2_26() -> io::Result<()> {
-        unimpl!();
-    }
 }
 
diff --git a/src/libstd/sys/unix/mod.rs b/src/libstd/sys/unix/mod.rs
index 9bdea945ea4..c738003caf1 100644
--- a/src/libstd/sys/unix/mod.rs
+++ b/src/libstd/sys/unix/mod.rs
@@ -28,6 +28,7 @@ use libc;
 #[cfg(all(not(dox), target_os = "emscripten"))] pub use os::emscripten as platform;
 #[cfg(all(not(dox), target_os = "fuchsia"))]   pub use os::fuchsia as platform;
 #[cfg(all(not(dox), target_os = "l4re"))]      pub use os::linux as platform;
+#[cfg(all(not(dox), target_os = "hermit"))]    pub use os::hermit as platform;
 
 pub use self::rand::hashmap_random_keys;
 pub use libc::strlen;
@@ -80,11 +81,11 @@ pub fn init() {
         reset_sigpipe();
     }
 
-    #[cfg(not(any(target_os = "emscripten", target_os="fuchsia")))]
+    #[cfg(not(any(target_os = "emscripten", target_os = "fuchsia")))]
     unsafe fn reset_sigpipe() {
         assert!(signal(libc::SIGPIPE, libc::SIG_IGN) != libc::SIG_ERR);
     }
-    #[cfg(any(target_os = "emscripten", target_os="fuchsia"))]
+    #[cfg(any(target_os = "emscripten", target_os = "fuchsia"))]
     unsafe fn reset_sigpipe() {}
 }
 
diff --git a/src/libstd/sys/unix/mutex.rs b/src/libstd/sys/unix/mutex.rs
index 52cf3f97c5c..1d447de1134 100644
--- a/src/libstd/sys/unix/mutex.rs
+++ b/src/libstd/sys/unix/mutex.rs
@@ -25,8 +25,10 @@ unsafe impl Sync for Mutex {}
 #[allow(dead_code)] // sys isn't exported yet
 impl Mutex {
     pub const fn new() -> Mutex {
-        // Might be moved and address is changing it is better to avoid
-        // initialization of potentially opaque OS data before it landed
+        // Might be moved to a different address, so it is better to avoid
+        // initialization of potentially opaque OS data before it landed.
+        // Be very careful using this newly constructed `Mutex`, reentrant
+        // locking is undefined behavior until `init` is called!
         Mutex { inner: UnsafeCell::new(libc::PTHREAD_MUTEX_INITIALIZER) }
     }
     #[inline]
@@ -49,9 +51,6 @@ impl Mutex {
         // references, we instead create the mutex with type
         // PTHREAD_MUTEX_NORMAL which is guaranteed to deadlock if we try to
         // re-lock it from the same thread, thus avoiding undefined behavior.
-        //
-        // We can't do anything for StaticMutex, but that type is deprecated
-        // anyways.
         let mut attr: libc::pthread_mutexattr_t = mem::uninitialized();
         let r = libc::pthread_mutexattr_init(&mut attr);
         debug_assert_eq!(r, 0);
diff --git a/src/libstd/sys/unix/net.rs b/src/libstd/sys/unix/net.rs
index e775f857f2b..04d9f0b06d3 100644
--- a/src/libstd/sys/unix/net.rs
+++ b/src/libstd/sys/unix/net.rs
@@ -51,6 +51,10 @@ pub fn cvt_gai(err: c_int) -> io::Result<()> {
     if err == 0 {
         return Ok(())
     }
+
+    // We may need to trigger a glibc workaround. See on_resolver_failure() for details.
+    on_resolver_failure();
+
     if err == EAI_SYSTEM {
         return Err(io::Error::last_os_error())
     }
@@ -377,43 +381,22 @@ impl IntoInner<c_int> for Socket {
 // res_init unconditionally, we call it only when we detect we're linking
 // against glibc version < 2.26. (That is, when we both know its needed and
 // believe it's thread-safe).
-pub fn res_init_if_glibc_before_2_26() -> io::Result<()> {
+#[cfg(target_env = "gnu")]
+fn on_resolver_failure() {
+    use sys;
+
     // If the version fails to parse, we treat it the same as "not glibc".
-    if let Some(Ok(version_str)) = glibc_version_cstr().map(CStr::to_str) {
-        if let Some(version) = parse_glibc_version(version_str) {
-            if version < (2, 26) {
-                let ret = unsafe { libc::res_init() };
-                if ret != 0 {
-                    return Err(io::Error::last_os_error());
-                }
-            }
+    if let Some(version) = sys::os::glibc_version() {
+        if version < (2, 26) {
+            unsafe { libc::res_init() };
         }
     }
-    Ok(())
 }
 
-fn glibc_version_cstr() -> Option<&'static CStr> {
-    weak! {
-        fn gnu_get_libc_version() -> *const libc::c_char
-    }
-    if let Some(f) = gnu_get_libc_version.get() {
-        unsafe { Some(CStr::from_ptr(f())) }
-    } else {
-        None
-    }
-}
-
-// Returns Some((major, minor)) if the string is a valid "x.y" version,
-// ignoring any extra dot-separated parts. Otherwise return None.
-fn parse_glibc_version(version: &str) -> Option<(usize, usize)> {
-    let mut parsed_ints = version.split(".").map(str::parse::<usize>).fuse();
-    match (parsed_ints.next(), parsed_ints.next()) {
-        (Some(Ok(major)), Some(Ok(minor))) => Some((major, minor)),
-        _ => None
-    }
-}
+#[cfg(not(target_env = "gnu"))]
+fn on_resolver_failure() {}
 
-#[cfg(test)]
+#[cfg(all(test, taget_env = "gnu"))]
 mod test {
     use super::*;
 
diff --git a/src/libstd/sys/unix/os.rs b/src/libstd/sys/unix/os.rs
index a46e855b4a6..f8f0bbd5bc2 100644
--- a/src/libstd/sys/unix/os.rs
+++ b/src/libstd/sys/unix/os.rs
@@ -33,6 +33,8 @@ use sys::fd;
 use vec;
 
 const TMPBUF_SZ: usize = 128;
+// We never call `ENV_LOCK.init()`, so it is UB to attempt to
+// acquire this mutex reentrantly!
 static ENV_LOCK: Mutex = Mutex::new();
 
 
@@ -47,6 +49,7 @@ extern {
                    target_os = "netbsd",
                    target_os = "openbsd",
                    target_os = "android",
+                   target_os = "hermit",
                    target_env = "newlib"),
                link_name = "__errno")]
     #[cfg_attr(target_os = "solaris", link_name = "___errno")]
@@ -376,7 +379,7 @@ pub fn current_exe() -> io::Result<PathBuf> {
     }
 }
 
-#[cfg(any(target_os = "fuchsia", target_os = "l4re"))]
+#[cfg(any(target_os = "fuchsia", target_os = "l4re", target_os = "hermit"))]
 pub fn current_exe() -> io::Result<PathBuf> {
     use io::ErrorKind;
     Err(io::Error::new(ErrorKind::Other, "Not yet implemented!"))
@@ -409,26 +412,19 @@ pub unsafe fn environ() -> *mut *const *const c_char {
 /// environment variables of the current process.
 pub fn env() -> Env {
     unsafe {
-        ENV_LOCK.lock();
+        let _guard = ENV_LOCK.lock();
         let mut environ = *environ();
-        if environ == ptr::null() {
-            ENV_LOCK.unlock();
-            panic!("os::env() failure getting env string from OS: {}",
-                   io::Error::last_os_error());
-        }
         let mut result = Vec::new();
-        while *environ != ptr::null() {
+        while environ != ptr::null() && *environ != ptr::null() {
             if let Some(key_value) = parse(CStr::from_ptr(*environ).to_bytes()) {
                 result.push(key_value);
             }
             environ = environ.offset(1);
         }
-        let ret = Env {
+        return Env {
             iter: result.into_iter(),
             _dont_send_or_sync_me: PhantomData,
-        };
-        ENV_LOCK.unlock();
-        return ret
+        }
     }
 
     fn parse(input: &[u8]) -> Option<(OsString, OsString)> {
@@ -452,15 +448,14 @@ pub fn getenv(k: &OsStr) -> io::Result<Option<OsString>> {
     // always None as well
     let k = CString::new(k.as_bytes())?;
     unsafe {
-        ENV_LOCK.lock();
+        let _guard = ENV_LOCK.lock();
         let s = libc::getenv(k.as_ptr()) as *const libc::c_char;
         let ret = if s.is_null() {
             None
         } else {
             Some(OsStringExt::from_vec(CStr::from_ptr(s).to_bytes().to_vec()))
         };
-        ENV_LOCK.unlock();
-        return Ok(ret)
+        Ok(ret)
     }
 }
 
@@ -469,10 +464,8 @@ pub fn setenv(k: &OsStr, v: &OsStr) -> io::Result<()> {
     let v = CString::new(v.as_bytes())?;
 
     unsafe {
-        ENV_LOCK.lock();
-        let ret = cvt(libc::setenv(k.as_ptr(), v.as_ptr(), 1)).map(|_| ());
-        ENV_LOCK.unlock();
-        return ret
+        let _guard = ENV_LOCK.lock();
+        cvt(libc::setenv(k.as_ptr(), v.as_ptr(), 1)).map(|_| ())
     }
 }
 
@@ -480,10 +473,8 @@ pub fn unsetenv(n: &OsStr) -> io::Result<()> {
     let nbuf = CString::new(n.as_bytes())?;
 
     unsafe {
-        ENV_LOCK.lock();
-        let ret = cvt(libc::unsetenv(nbuf.as_ptr())).map(|_| ());
-        ENV_LOCK.unlock();
-        return ret
+        let _guard = ENV_LOCK.lock();
+        cvt(libc::unsetenv(nbuf.as_ptr())).map(|_| ())
     }
 }
 
@@ -546,3 +537,35 @@ pub fn getpid() -> u32 {
 pub fn getppid() -> u32 {
     unsafe { libc::getppid() as u32 }
 }
+
+#[cfg(target_env = "gnu")]
+pub fn glibc_version() -> Option<(usize, usize)> {
+    if let Some(Ok(version_str)) = glibc_version_cstr().map(CStr::to_str) {
+        parse_glibc_version(version_str)
+    } else {
+        None
+    }
+}
+
+#[cfg(target_env = "gnu")]
+fn glibc_version_cstr() -> Option<&'static CStr> {
+    weak! {
+        fn gnu_get_libc_version() -> *const libc::c_char
+    }
+    if let Some(f) = gnu_get_libc_version.get() {
+        unsafe { Some(CStr::from_ptr(f())) }
+    } else {
+        None
+    }
+}
+
+// Returns Some((major, minor)) if the string is a valid "x.y" version,
+// ignoring any extra dot-separated parts. Otherwise return None.
+#[cfg(target_env = "gnu")]
+fn parse_glibc_version(version: &str) -> Option<(usize, usize)> {
+    let mut parsed_ints = version.split('.').map(str::parse::<usize>).fuse();
+    match (parsed_ints.next(), parsed_ints.next()) {
+        (Some(Ok(major)), Some(Ok(minor))) => Some((major, minor)),
+        _ => None
+    }
+}
diff --git a/src/libstd/sys/unix/os_str.rs b/src/libstd/sys/unix/os_str.rs
index e0349387998..01c0fb830aa 100644
--- a/src/libstd/sys/unix/os_str.rs
+++ b/src/libstd/sys/unix/os_str.rs
@@ -19,7 +19,7 @@ use rc::Rc;
 use sync::Arc;
 use sys_common::{AsInner, IntoInner};
 use sys_common::bytestring::debug_fmt_bytestring;
-use std_unicode::lossy::Utf8Lossy;
+use core::str::lossy::Utf8Lossy;
 
 #[derive(Clone, Hash)]
 pub struct Buf {
@@ -104,6 +104,11 @@ impl Buf {
         self.inner.shrink_to_fit()
     }
 
+    #[inline]
+    pub fn shrink_to(&mut self, min_capacity: usize) {
+        self.inner.shrink_to(min_capacity)
+    }
+
     pub fn as_slice(&self) -> &Slice {
         unsafe { mem::transmute(&*self.inner) }
     }
diff --git a/src/libstd/sys/unix/pipe.rs b/src/libstd/sys/unix/pipe.rs
index ec9b6f17dca..0a5dccdddda 100644
--- a/src/libstd/sys/unix/pipe.rs
+++ b/src/libstd/sys/unix/pipe.rs
@@ -100,24 +100,6 @@ pub fn read2(p1: AnonPipe,
         // wait for either pipe to become readable using `poll`
         cvt_r(|| unsafe { libc::poll(fds.as_mut_ptr(), 2, -1) })?;
 
-        // Read as much as we can from each pipe, ignoring EWOULDBLOCK or
-        // EAGAIN. If we hit EOF, then this will happen because the underlying
-        // reader will return Ok(0), in which case we'll see `Ok` ourselves. In
-        // this case we flip the other fd back into blocking mode and read
-        // whatever's leftover on that file descriptor.
-        let read = |fd: &FileDesc, dst: &mut Vec<u8>| {
-            match fd.read_to_end(dst) {
-                Ok(_) => Ok(true),
-                Err(e) => {
-                    if e.raw_os_error() == Some(libc::EWOULDBLOCK) ||
-                       e.raw_os_error() == Some(libc::EAGAIN) {
-                        Ok(false)
-                    } else {
-                        Err(e)
-                    }
-                }
-            }
-        };
         if fds[0].revents != 0 && read(&p1, v1)? {
             p2.set_nonblocking(false)?;
             return p2.read_to_end(v2).map(|_| ());
@@ -127,4 +109,23 @@ pub fn read2(p1: AnonPipe,
             return p1.read_to_end(v1).map(|_| ());
         }
     }
+
+    // Read as much as we can from each pipe, ignoring EWOULDBLOCK or
+    // EAGAIN. If we hit EOF, then this will happen because the underlying
+    // reader will return Ok(0), in which case we'll see `Ok` ourselves. In
+    // this case we flip the other fd back into blocking mode and read
+    // whatever's leftover on that file descriptor.
+    fn read(fd: &FileDesc, dst: &mut Vec<u8>) -> Result<bool, io::Error> {
+        match fd.read_to_end(dst) {
+            Ok(_) => Ok(true),
+            Err(e) => {
+                if e.raw_os_error() == Some(libc::EWOULDBLOCK) ||
+                   e.raw_os_error() == Some(libc::EAGAIN) {
+                    Ok(false)
+                } else {
+                    Err(e)
+                }
+            }
+        }
+    }
 }
diff --git a/src/libstd/sys/unix/process/mod.rs b/src/libstd/sys/unix/process/mod.rs
index 2a331069bc2..d8ac26c45b1 100644
--- a/src/libstd/sys/unix/process/mod.rs
+++ b/src/libstd/sys/unix/process/mod.rs
@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-pub use self::process_common::{Command, ExitStatus, Stdio, StdioPipes};
+pub use self::process_common::{Command, ExitStatus, ExitCode, Stdio, StdioPipes};
 pub use self::process_inner::Process;
 
 mod process_common;
diff --git a/src/libstd/sys/unix/process/process_common.rs b/src/libstd/sys/unix/process/process_common.rs
index c53bcdbf8e3..77f125f3c5b 100644
--- a/src/libstd/sys/unix/process/process_common.rs
+++ b/src/libstd/sys/unix/process/process_common.rs
@@ -13,7 +13,7 @@ use os::unix::prelude::*;
 use ffi::{OsString, OsStr, CString, CStr};
 use fmt;
 use io;
-use libc::{self, c_int, gid_t, uid_t, c_char};
+use libc::{self, c_int, gid_t, uid_t, c_char, EXIT_SUCCESS, EXIT_FAILURE};
 use ptr;
 use sys::fd::FileDesc;
 use sys::fs::{File, OpenOptions};
@@ -45,19 +45,25 @@ pub struct Command {
     // other keys.
     program: CString,
     args: Vec<CString>,
-    argv: Vec<*const c_char>,
+    argv: Argv,
     env: CommandEnv<DefaultEnvKey>,
 
     cwd: Option<CString>,
     uid: Option<uid_t>,
     gid: Option<gid_t>,
     saw_nul: bool,
-    closures: Vec<Box<FnMut() -> io::Result<()> + Send + Sync>>,
+    closures: Vec<Box<dyn FnMut() -> io::Result<()> + Send + Sync>>,
     stdin: Option<Stdio>,
     stdout: Option<Stdio>,
     stderr: Option<Stdio>,
 }
 
+// Create a new type for argv, so that we can make it `Send`
+struct Argv(Vec<*const c_char>);
+
+// It is safe to make Argv Send, because it contains pointers to memory owned by `Command.args`
+unsafe impl Send for Argv {}
+
 // passed back to std::process with the pipes connected to the child, if any
 // were requested
 pub struct StdioPipes {
@@ -92,7 +98,7 @@ impl Command {
         let mut saw_nul = false;
         let program = os2c(program, &mut saw_nul);
         Command {
-            argv: vec![program.as_ptr(), ptr::null()],
+            argv: Argv(vec![program.as_ptr(), ptr::null()]),
             program,
             args: Vec::new(),
             env: Default::default(),
@@ -111,8 +117,8 @@ impl Command {
         // Overwrite the trailing NULL pointer in `argv` and then add a new null
         // pointer.
         let arg = os2c(arg, &mut self.saw_nul);
-        self.argv[self.args.len() + 1] = arg.as_ptr();
-        self.argv.push(ptr::null());
+        self.argv.0[self.args.len() + 1] = arg.as_ptr();
+        self.argv.0.push(ptr::null());
 
         // Also make sure we keep track of the owned value to schedule a
         // destructor for this memory.
@@ -133,7 +139,7 @@ impl Command {
         self.saw_nul
     }
     pub fn get_argv(&self) -> &Vec<*const c_char> {
-        &self.argv
+        &self.argv.0
     }
 
     #[allow(dead_code)]
@@ -149,12 +155,12 @@ impl Command {
         self.gid
     }
 
-    pub fn get_closures(&mut self) -> &mut Vec<Box<FnMut() -> io::Result<()> + Send + Sync>> {
+    pub fn get_closures(&mut self) -> &mut Vec<Box<dyn FnMut() -> io::Result<()> + Send + Sync>> {
         &mut self.closures
     }
 
     pub fn before_exec(&mut self,
-                       f: Box<FnMut() -> io::Result<()> + Send + Sync>) {
+                       f: Box<dyn FnMut() -> io::Result<()> + Send + Sync>) {
         self.closures.push(f);
     }
 
@@ -178,6 +184,10 @@ impl Command {
         let maybe_env = self.env.capture_if_changed();
         maybe_env.map(|env| construct_envp(env, &mut self.saw_nul))
     }
+    #[allow(dead_code)]
+    pub fn env_saw_path(&self) -> bool {
+        self.env.have_changed_path()
+    }
 
     pub fn setup_io(&self, default: Stdio, needs_stdin: bool)
                 -> io::Result<(StdioPipes, ChildPipes)> {
@@ -387,6 +397,19 @@ impl fmt::Display for ExitStatus {
     }
 }
 
+#[derive(PartialEq, Eq, Clone, Copy, Debug)]
+pub struct ExitCode(u8);
+
+impl ExitCode {
+    pub const SUCCESS: ExitCode = ExitCode(EXIT_SUCCESS as _);
+    pub const FAILURE: ExitCode = ExitCode(EXIT_FAILURE as _);
+
+    #[inline]
+    pub fn as_i32(&self) -> i32 {
+        self.0 as i32
+    }
+}
+
 #[cfg(all(test, not(target_os = "emscripten")))]
 mod tests {
     use super::*;
diff --git a/src/libstd/sys/unix/process/process_fuchsia.rs b/src/libstd/sys/unix/process/process_fuchsia.rs
index 06c0540fec0..fa48001179e 100644
--- a/src/libstd/sys/unix/process/process_fuchsia.rs
+++ b/src/libstd/sys/unix/process/process_fuchsia.rs
@@ -56,68 +56,49 @@ impl Command {
                       -> io::Result<zx_handle_t> {
         use sys::process::zircon::*;
 
-        let job_handle = zx_job_default();
         let envp = match maybe_envp {
             Some(envp) => envp.as_ptr(),
             None => ptr::null(),
         };
 
-        // To make sure launchpad_destroy gets called on the launchpad if this function fails
-        struct LaunchpadDestructor(*mut launchpad_t);
-        impl Drop for LaunchpadDestructor {
-            fn drop(&mut self) { unsafe { launchpad_destroy(self.0); } }
-        }
-
-        // Duplicate the job handle
-        let mut job_copy: zx_handle_t = ZX_HANDLE_INVALID;
-        zx_cvt(zx_handle_duplicate(job_handle, ZX_RIGHT_SAME_RIGHTS, &mut job_copy))?;
-        // Create a launchpad
-        let mut launchpad: *mut launchpad_t = ptr::null_mut();
-        zx_cvt(launchpad_create(job_copy, self.get_argv()[0], &mut launchpad))?;
-        let launchpad_destructor = LaunchpadDestructor(launchpad);
-
-        // Set the process argv
-        zx_cvt(launchpad_set_args(launchpad, self.get_argv().len() as i32 - 1,
-                                  self.get_argv().as_ptr()))?;
-        // Setup the environment vars
-        zx_cvt(launchpad_set_environ(launchpad, envp))?;
-        zx_cvt(launchpad_add_vdso_vmo(launchpad))?;
-        // Load the executable
-        zx_cvt(launchpad_elf_load(launchpad, launchpad_vmo_from_file(self.get_argv()[0])))?;
-        zx_cvt(launchpad_load_vdso(launchpad, ZX_HANDLE_INVALID))?;
-        zx_cvt(launchpad_clone(launchpad, LP_CLONE_FDIO_NAMESPACE | LP_CLONE_FDIO_CWD))?;
+        let transfer_or_clone = |opt_fd, target_fd| if let Some(local_fd) = opt_fd {
+            fdio_spawn_action_t {
+                action: FDIO_SPAWN_ACTION_TRANSFER_FD,
+                local_fd,
+                target_fd,
+                ..Default::default()
+            }
+        } else {
+            fdio_spawn_action_t {
+                action: FDIO_SPAWN_ACTION_CLONE_FD,
+                local_fd: target_fd,
+                target_fd,
+                ..Default::default()
+            }
+        };
 
         // Clone stdin, stdout, and stderr
-        if let Some(fd) = stdio.stdin.fd() {
-            zx_cvt(launchpad_transfer_fd(launchpad, fd, 0))?;
-        } else {
-            zx_cvt(launchpad_clone_fd(launchpad, 0, 0))?;
-        }
-        if let Some(fd) = stdio.stdout.fd() {
-            zx_cvt(launchpad_transfer_fd(launchpad, fd, 1))?;
-        } else {
-            zx_cvt(launchpad_clone_fd(launchpad, 1, 1))?;
-        }
-        if let Some(fd) = stdio.stderr.fd() {
-            zx_cvt(launchpad_transfer_fd(launchpad, fd, 2))?;
-        } else {
-            zx_cvt(launchpad_clone_fd(launchpad, 2, 2))?;
-        }
+        let action1 = transfer_or_clone(stdio.stdin.fd(), 0);
+        let action2 = transfer_or_clone(stdio.stdout.fd(), 1);
+        let action3 = transfer_or_clone(stdio.stderr.fd(), 2);
+        let actions = [action1, action2, action3];
 
-        // We don't want FileDesc::drop to be called on any stdio. It would close their fds. The
-        // fds will be closed once the child process finishes.
+        // We don't want FileDesc::drop to be called on any stdio. fdio_spawn_etc
+        // always consumes transferred file descriptors.
         mem::forget(stdio);
 
         for callback in self.get_closures().iter_mut() {
             callback()?;
         }
 
-        // `launchpad_go` destroys the launchpad, so we must not
-        mem::forget(launchpad_destructor);
-
         let mut process_handle: zx_handle_t = 0;
-        let mut err_msg: *const libc::c_char = ptr::null();
-        zx_cvt(launchpad_go(launchpad, &mut process_handle, &mut err_msg))?;
+        zx_cvt(fdio_spawn_etc(
+            0,
+            FDIO_SPAWN_CLONE_JOB | FDIO_SPAWN_CLONE_LDSVC | FDIO_SPAWN_CLONE_NAMESPACE,
+            self.get_argv()[0], self.get_argv().as_ptr(), envp, 3, actions.as_ptr(),
+            &mut process_handle,
+            ptr::null_mut(),
+        ))?;
         // FIXME: See if we want to do something with that err_msg
 
         Ok(process_handle)
diff --git a/src/libstd/sys/unix/process/process_unix.rs b/src/libstd/sys/unix/process/process_unix.rs
index 189280a4ba9..9d6d607e3f3 100644
--- a/src/libstd/sys/unix/process/process_unix.rs
+++ b/src/libstd/sys/unix/process/process_unix.rs
@@ -34,6 +34,11 @@ impl Command {
         }
 
         let (ours, theirs) = self.setup_io(default, needs_stdin)?;
+
+        if let Some(ret) = self.posix_spawn(&theirs, envp.as_ref())? {
+            return Ok((ret, ours))
+        }
+
         let (input, output) = sys::pipe::anon_pipe()?;
 
         let pid = unsafe {
@@ -229,6 +234,119 @@ impl Command {
         libc::execvp(self.get_argv()[0], self.get_argv().as_ptr());
         io::Error::last_os_error()
     }
+
+    #[cfg(not(any(target_os = "macos", target_os = "freebsd",
+                  all(target_os = "linux", target_env = "gnu"))))]
+    fn posix_spawn(&mut self, _: &ChildPipes, _: Option<&CStringArray>)
+        -> io::Result<Option<Process>>
+    {
+        Ok(None)
+    }
+
+    // Only support platforms for which posix_spawn() can return ENOENT
+    // directly.
+    #[cfg(any(target_os = "macos", target_os = "freebsd",
+              all(target_os = "linux", target_env = "gnu")))]
+    fn posix_spawn(&mut self, stdio: &ChildPipes, envp: Option<&CStringArray>)
+        -> io::Result<Option<Process>>
+    {
+        use mem;
+        use sys;
+
+        if self.get_cwd().is_some() ||
+            self.get_gid().is_some() ||
+            self.get_uid().is_some() ||
+            self.env_saw_path() ||
+            self.get_closures().len() != 0 {
+            return Ok(None)
+        }
+
+        // Only glibc 2.24+ posix_spawn() supports returning ENOENT directly.
+        #[cfg(all(target_os = "linux", target_env = "gnu"))]
+        {
+            if let Some(version) = sys::os::glibc_version() {
+                if version < (2, 24) {
+                    return Ok(None)
+                }
+            } else {
+                return Ok(None)
+            }
+        }
+
+        let mut p = Process { pid: 0, status: None };
+
+        struct PosixSpawnFileActions(libc::posix_spawn_file_actions_t);
+
+        impl Drop for PosixSpawnFileActions {
+            fn drop(&mut self) {
+                unsafe {
+                    libc::posix_spawn_file_actions_destroy(&mut self.0);
+                }
+            }
+        }
+
+        struct PosixSpawnattr(libc::posix_spawnattr_t);
+
+        impl Drop for PosixSpawnattr {
+            fn drop(&mut self) {
+                unsafe {
+                    libc::posix_spawnattr_destroy(&mut self.0);
+                }
+            }
+        }
+
+        unsafe {
+            let mut file_actions = PosixSpawnFileActions(mem::uninitialized());
+            let mut attrs = PosixSpawnattr(mem::uninitialized());
+
+            libc::posix_spawnattr_init(&mut attrs.0);
+            libc::posix_spawn_file_actions_init(&mut file_actions.0);
+
+            if let Some(fd) = stdio.stdin.fd() {
+                cvt(libc::posix_spawn_file_actions_adddup2(&mut file_actions.0,
+                                                           fd,
+                                                           libc::STDIN_FILENO))?;
+            }
+            if let Some(fd) = stdio.stdout.fd() {
+                cvt(libc::posix_spawn_file_actions_adddup2(&mut file_actions.0,
+                                                           fd,
+                                                           libc::STDOUT_FILENO))?;
+            }
+            if let Some(fd) = stdio.stderr.fd() {
+                cvt(libc::posix_spawn_file_actions_adddup2(&mut file_actions.0,
+                                                           fd,
+                                                           libc::STDERR_FILENO))?;
+            }
+
+            let mut set: libc::sigset_t = mem::uninitialized();
+            cvt(libc::sigemptyset(&mut set))?;
+            cvt(libc::posix_spawnattr_setsigmask(&mut attrs.0,
+                                                 &set))?;
+            cvt(libc::sigaddset(&mut set, libc::SIGPIPE))?;
+            cvt(libc::posix_spawnattr_setsigdefault(&mut attrs.0,
+                                                    &set))?;
+
+            let flags = libc::POSIX_SPAWN_SETSIGDEF |
+                libc::POSIX_SPAWN_SETSIGMASK;
+            cvt(libc::posix_spawnattr_setflags(&mut attrs.0, flags as _))?;
+
+            let envp = envp.map(|c| c.as_ptr())
+                .unwrap_or(*sys::os::environ() as *const _);
+            let ret = libc::posix_spawnp(
+                &mut p.pid,
+                self.get_argv()[0],
+                &file_actions.0,
+                &attrs.0,
+                self.get_argv().as_ptr() as *const _,
+                envp as *const _,
+            );
+            if ret == 0 {
+                Ok(Some(p))
+            } else {
+                Err(io::Error::from_raw_os_error(ret))
+            }
+        }
+    }
 }
 
 ////////////////////////////////////////////////////////////////////////////////
diff --git a/src/libstd/sys/unix/process/zircon.rs b/src/libstd/sys/unix/process/zircon.rs
index 90864e6ef3f..a06c73ee263 100644
--- a/src/libstd/sys/unix/process/zircon.rs
+++ b/src/libstd/sys/unix/process/zircon.rs
@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![allow(non_camel_case_types)]
+#![allow(non_camel_case_types, unused)]
 
 use convert::TryInto;
 use io;
@@ -117,75 +117,36 @@ extern {
                               avail: *mut size_t) -> zx_status_t;
 }
 
-// From `enum special_handles` in system/ulib/launchpad/launchpad.c
-// HND_LOADER_SVC = 0
-// HND_EXEC_VMO = 1
-// HND_SEGMENTS_VMAR = 2
-const HND_SPECIAL_COUNT: c_int = 3;
-
+#[derive(Default)]
 #[repr(C)]
-pub struct launchpad_t {
-    argc: u32,
-    envc: u32,
-    args: *const c_char,
-    args_len: size_t,
-    env: *const c_char,
-    env_len: size_t,
-
-    handles: *mut zx_handle_t,
-    handles_info: *mut u32,
-    handle_count: size_t,
-    handle_alloc: size_t,
-
-    entry: zx_vaddr_t,
-    base: zx_vaddr_t,
-    vdso_base: zx_vaddr_t,
-
-    stack_size: size_t,
-
-    special_handles: [zx_handle_t; HND_SPECIAL_COUNT as usize],
-    loader_message: bool,
+pub struct fdio_spawn_action_t {
+    pub action: u32,
+    pub reserved0: u32,
+    pub local_fd: i32,
+    pub target_fd: i32,
+    pub reserved1: u64,
 }
 
 extern {
-    pub fn launchpad_create(job: zx_handle_t, name: *const c_char,
-                            lp: *mut *mut launchpad_t) -> zx_status_t;
-
-    pub fn launchpad_go(lp: *mut launchpad_t,
-                        proc_handle: *mut zx_handle_t,
-                        err_msg: *mut *const c_char) -> zx_status_t;
-
-    pub fn launchpad_destroy(lp: *mut launchpad_t);
-
-    pub fn launchpad_set_args(lp: *mut launchpad_t, argc: c_int,
-                               argv: *const *const c_char) -> zx_status_t;
-
-    pub fn launchpad_set_environ(lp: *mut launchpad_t, envp: *const *const c_char) -> zx_status_t;
-
-    pub fn launchpad_clone(lp: *mut launchpad_t, what: u32) -> zx_status_t;
-
-    pub fn launchpad_clone_fd(lp: *mut launchpad_t, fd: c_int, target_fd: c_int) -> zx_status_t;
-
-    pub fn launchpad_transfer_fd(lp: *mut launchpad_t, fd: c_int, target_fd: c_int) -> zx_status_t;
-
-    pub fn launchpad_elf_load(lp: *mut launchpad_t, vmo: zx_handle_t) -> zx_status_t;
-
-    pub fn launchpad_add_vdso_vmo(lp: *mut launchpad_t) -> zx_status_t;
+    pub fn fdio_spawn_etc(job: zx_handle_t, flags: u32, path: *const c_char,
+                          argv: *const *const c_char, envp: *const *const c_char,
+                          action_count: u64, actions: *const fdio_spawn_action_t,
+                          process: *mut zx_handle_t, err_msg: *mut c_char) -> zx_status_t;
+}
 
-    pub fn launchpad_load_vdso(lp: *mut launchpad_t, vmo: zx_handle_t) -> zx_status_t;
+// fdio_spawn_etc flags
 
-    pub fn launchpad_vmo_from_file(filename: *const c_char) -> zx_handle_t;
-}
+pub const FDIO_SPAWN_CLONE_JOB: u32 = 0x0001;
+pub const FDIO_SPAWN_CLONE_LDSVC: u32 = 0x0002;
+pub const FDIO_SPAWN_CLONE_NAMESPACE: u32 = 0x0004;
+pub const FDIO_SPAWN_CLONE_STDIO: u32 = 0x0008;
+pub const FDIO_SPAWN_CLONE_ENVIRON: u32 = 0x0010;
+pub const FDIO_SPAWN_CLONE_ALL: u32 = 0xFFFF;
 
-// Launchpad clone constants
+// fdio_spawn_etc actions
 
-pub const LP_CLONE_FDIO_NAMESPACE: u32 = 0x0001;
-pub const LP_CLONE_FDIO_CWD: u32 = 0x0002;
-// LP_CLONE_FDIO_STDIO = 0x0004
-// LP_CLONE_FDIO_ALL = 0x00FF
-// LP_CLONE_ENVIRON = 0x0100
-// LP_CLONE_DEFAULT_JOB = 0x0200
-// LP_CLONE_ALL = 0xFFFF
+pub const FDIO_SPAWN_ACTION_CLONE_FD: u32 = 0x0001;
+pub const FDIO_SPAWN_ACTION_TRANSFER_FD: u32 = 0x0002;
 
 // Errors
 
diff --git a/src/libstd/sys/unix/rand.rs b/src/libstd/sys/unix/rand.rs
index caa18945765..01c0ada4ffb 100644
--- a/src/libstd/sys/unix/rand.rs
+++ b/src/libstd/sys/unix/rand.rs
@@ -183,35 +183,10 @@ mod imp {
 mod imp {
     #[link(name = "zircon")]
     extern {
-        fn zx_cprng_draw(buffer: *mut u8, len: usize, actual: *mut usize) -> i32;
-    }
-
-    fn getrandom(buf: &mut [u8]) -> Result<usize, i32> {
-        unsafe {
-            let mut actual = 0;
-            let status = zx_cprng_draw(buf.as_mut_ptr(), buf.len(), &mut actual);
-            if status == 0 {
-                Ok(actual)
-            } else {
-                Err(status)
-            }
-        }
+        fn zx_cprng_draw(buffer: *mut u8, len: usize);
     }
 
     pub fn fill_bytes(v: &mut [u8]) {
-        let mut buf = v;
-        while !buf.is_empty() {
-            let ret = getrandom(buf);
-            match ret {
-                Err(err) => {
-                    panic!("kernel zx_cprng_draw call failed! (returned {}, buf.len() {})",
-                        err, buf.len())
-                }
-                Ok(actual) => {
-                    let move_buf = buf;
-                    buf = &mut move_buf[(actual as usize)..];
-                }
-            }
-        }
+        unsafe { zx_cprng_draw(v.as_mut_ptr(), v.len()) }
     }
 }
diff --git a/src/libstd/sys/unix/stack_overflow.rs b/src/libstd/sys/unix/stack_overflow.rs
index 51adbc24ae0..40453f9b8a1 100644
--- a/src/libstd/sys/unix/stack_overflow.rs
+++ b/src/libstd/sys/unix/stack_overflow.rs
@@ -57,9 +57,6 @@ mod imp {
     use sys_common::thread_info;
 
 
-    // This is initialized in init() and only read from after
-    static mut PAGE_SIZE: usize = 0;
-
     #[cfg(any(target_os = "linux", target_os = "android"))]
     unsafe fn siginfo_si_addr(info: *mut libc::siginfo_t) -> usize {
         #[repr(C)]
@@ -102,12 +99,12 @@ mod imp {
                                     _data: *mut libc::c_void) {
         use sys_common::util::report_overflow;
 
-        let guard = thread_info::stack_guard().unwrap_or(0);
+        let guard = thread_info::stack_guard().unwrap_or(0..0);
         let addr = siginfo_si_addr(info);
 
         // If the faulting address is within the guard page, then we print a
         // message saying so and abort.
-        if guard != 0 && guard - PAGE_SIZE <= addr && addr < guard {
+        if guard.start <= addr && addr < guard.end {
             report_overflow();
             rtabort!("stack overflow");
         } else {
@@ -123,8 +120,6 @@ mod imp {
     static mut MAIN_ALTSTACK: *mut libc::c_void = ptr::null_mut();
 
     pub unsafe fn init() {
-        PAGE_SIZE = ::sys::os::page_size();
-
         let mut action: sigaction = mem::zeroed();
         action.sa_flags = SA_SIGINFO | SA_ONSTACK;
         action.sa_sigaction = signal_handler as sighandler_t;
diff --git a/src/libstd/sys/unix/stdio.rs b/src/libstd/sys/unix/stdio.rs
index e9b3d4affc7..87ba2aef4f1 100644
--- a/src/libstd/sys/unix/stdio.rs
+++ b/src/libstd/sys/unix/stdio.rs
@@ -75,3 +75,7 @@ pub fn is_ebadf(err: &io::Error) -> bool {
 }
 
 pub const STDIN_BUF_SIZE: usize = ::sys_common::io::DEFAULT_BUF_SIZE;
+
+pub fn stderr_prints_nothing() -> bool {
+    false
+}
diff --git a/src/libstd/sys/unix/thread.rs b/src/libstd/sys/unix/thread.rs
index cb249af4254..f3a45d24657 100644
--- a/src/libstd/sys/unix/thread.rs
+++ b/src/libstd/sys/unix/thread.rs
@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-use alloc::boxed::FnBox;
+use boxed::FnBox;
 use cmp;
 use ffi::CStr;
 use io;
@@ -49,7 +49,7 @@ unsafe fn pthread_attr_setstacksize(_attr: *mut libc::pthread_attr_t,
 }
 
 impl Thread {
-    pub unsafe fn new<'a>(stack: usize, p: Box<FnBox() + 'a>)
+    pub unsafe fn new<'a>(stack: usize, p: Box<dyn FnBox() + 'a>)
                           -> io::Result<Thread> {
         let p = box p;
         let mut native: libc::pthread_t = mem::zeroed();
@@ -138,7 +138,8 @@ impl Thread {
               target_os = "solaris",
               target_os = "haiku",
               target_os = "l4re",
-              target_os = "emscripten"))]
+              target_os = "emscripten",
+              target_os = "hermit"))]
     pub fn set_name(_name: &CStr) {
         // Newlib, Illumos, Haiku, and Emscripten have no way to set a thread name.
     }
@@ -205,8 +206,11 @@ impl Drop for Thread {
           not(target_os = "solaris")))]
 #[cfg_attr(test, allow(dead_code))]
 pub mod guard {
-    pub unsafe fn current() -> Option<usize> { None }
-    pub unsafe fn init() -> Option<usize> { None }
+    use ops::Range;
+    pub type Guard = Range<usize>;
+    pub unsafe fn current() -> Option<Guard> { None }
+    pub unsafe fn init() -> Option<Guard> { None }
+    pub unsafe fn deinit() {}
 }
 
 
@@ -220,16 +224,45 @@ pub mod guard {
 #[cfg_attr(test, allow(dead_code))]
 pub mod guard {
     use libc;
-    use libc::mmap;
-    use libc::{PROT_NONE, MAP_PRIVATE, MAP_ANON, MAP_FAILED, MAP_FIXED};
+    use libc::{mmap, mprotect};
+    use libc::{PROT_NONE, PROT_READ, PROT_WRITE, MAP_PRIVATE, MAP_ANON, MAP_FAILED, MAP_FIXED};
+    use ops::Range;
     use sys::os;
 
-    #[cfg(any(target_os = "macos",
-              target_os = "bitrig",
-              target_os = "openbsd",
-              target_os = "solaris"))]
+    // This is initialized in init() and only read from after
+    static mut PAGE_SIZE: usize = 0;
+
+    pub type Guard = Range<usize>;
+
+    #[cfg(target_os = "solaris")]
+    unsafe fn get_stack_start() -> Option<*mut libc::c_void> {
+        let mut current_stack: libc::stack_t = ::mem::zeroed();
+        assert_eq!(libc::stack_getbounds(&mut current_stack), 0);
+        Some(current_stack.ss_sp)
+    }
+
+    #[cfg(target_os = "macos")]
+    unsafe fn get_stack_start() -> Option<*mut libc::c_void> {
+        let stackaddr = libc::pthread_get_stackaddr_np(libc::pthread_self()) as usize -
+             libc::pthread_get_stacksize_np(libc::pthread_self());
+        Some(stackaddr as *mut libc::c_void)
+    }
+
+    #[cfg(any(target_os = "openbsd", target_os = "bitrig"))]
     unsafe fn get_stack_start() -> Option<*mut libc::c_void> {
-        current().map(|s| s as *mut libc::c_void)
+        let mut current_stack: libc::stack_t = ::mem::zeroed();
+        assert_eq!(libc::pthread_stackseg_np(libc::pthread_self(),
+                                             &mut current_stack), 0);
+
+        let extra = if cfg!(target_os = "bitrig") {3} else {1} * PAGE_SIZE;
+        let stackaddr = if libc::pthread_main_np() == 1 {
+            // main thread
+            current_stack.ss_sp as usize - current_stack.ss_size + extra
+        } else {
+            // new thread
+            current_stack.ss_sp as usize - current_stack.ss_size
+        };
+        Some(stackaddr as *mut libc::c_void)
     }
 
     #[cfg(any(target_os = "android", target_os = "freebsd",
@@ -253,9 +286,10 @@ pub mod guard {
         ret
     }
 
-    pub unsafe fn init() -> Option<usize> {
-        let psize = os::page_size();
-        let mut stackaddr = get_stack_start()?;
+    // Precondition: PAGE_SIZE is initialized.
+    unsafe fn get_stack_start_aligned() -> Option<*mut libc::c_void> {
+        assert!(PAGE_SIZE != 0);
+        let stackaddr = get_stack_start()?;
 
         // Ensure stackaddr is page aligned! A parent process might
         // have reset RLIMIT_STACK to be non-page aligned. The
@@ -263,11 +297,18 @@ pub mod guard {
         // stackaddr < stackaddr + stacksize, so if stackaddr is not
         // page-aligned, calculate the fix such that stackaddr <
         // new_page_aligned_stackaddr < stackaddr + stacksize
-        let remainder = (stackaddr as usize) % psize;
-        if remainder != 0 {
-            stackaddr = ((stackaddr as usize) + psize - remainder)
-                as *mut libc::c_void;
-        }
+        let remainder = (stackaddr as usize) % PAGE_SIZE;
+        Some(if remainder == 0 {
+            stackaddr
+        } else {
+            ((stackaddr as usize) + PAGE_SIZE - remainder) as *mut libc::c_void
+        })
+    }
+
+    pub unsafe fn init() -> Option<Guard> {
+        PAGE_SIZE = os::page_size();
+
+        let stackaddr = get_stack_start_aligned()?;
 
         if cfg!(target_os = "linux") {
             // Linux doesn't allocate the whole stack right away, and
@@ -280,60 +321,71 @@ pub mod guard {
             // Instead, we'll just note where we expect rlimit to start
             // faulting, so our handler can report "stack overflow", and
             // trust that the kernel's own stack guard will work.
-            Some(stackaddr as usize)
+            let stackaddr = stackaddr as usize;
+            Some(stackaddr - PAGE_SIZE..stackaddr)
         } else {
             // Reallocate the last page of the stack.
             // This ensures SIGBUS will be raised on
             // stack overflow.
-            let result = mmap(stackaddr, psize, PROT_NONE,
+            // Systems which enforce strict PAX MPROTECT do not allow
+            // to mprotect() a mapping with less restrictive permissions
+            // than the initial mmap() used, so we mmap() here with
+            // read/write permissions and only then mprotect() it to
+            // no permissions at all. See issue #50313.
+            let result = mmap(stackaddr, PAGE_SIZE, PROT_READ | PROT_WRITE,
                               MAP_PRIVATE | MAP_ANON | MAP_FIXED, -1, 0);
-
             if result != stackaddr || result == MAP_FAILED {
                 panic!("failed to allocate a guard page");
             }
 
+            let result = mprotect(stackaddr, PAGE_SIZE, PROT_NONE);
+            if result != 0 {
+                panic!("failed to protect the guard page");
+            }
+
+            let guardaddr = stackaddr as usize;
             let offset = if cfg!(target_os = "freebsd") {
                 2
             } else {
                 1
             };
 
-            Some(stackaddr as usize + offset * psize)
+            Some(guardaddr..guardaddr + offset * PAGE_SIZE)
         }
     }
 
-    #[cfg(target_os = "solaris")]
-    pub unsafe fn current() -> Option<usize> {
-        let mut current_stack: libc::stack_t = ::mem::zeroed();
-        assert_eq!(libc::stack_getbounds(&mut current_stack), 0);
-        Some(current_stack.ss_sp as usize)
-    }
-
-    #[cfg(target_os = "macos")]
-    pub unsafe fn current() -> Option<usize> {
-        Some((libc::pthread_get_stackaddr_np(libc::pthread_self()) as usize -
-              libc::pthread_get_stacksize_np(libc::pthread_self())))
+    pub unsafe fn deinit() {
+        if !cfg!(target_os = "linux") {
+            if let Some(stackaddr) = get_stack_start_aligned() {
+                // Remove the protection on the guard page.
+                // FIXME: we cannot unmap the page, because when we mmap()
+                // above it may be already mapped by the OS, which we can't
+                // detect from mmap()'s return value. If we unmap this page,
+                // it will lead to failure growing stack size on platforms like
+                // macOS. Instead, just restore the page to a writable state.
+                // This ain't Linux, so we probably don't need to care about
+                // execstack.
+                let result = mprotect(stackaddr, PAGE_SIZE, PROT_READ | PROT_WRITE);
+
+                if result != 0 {
+                    panic!("unable to reset the guard page");
+                }
+            }
+        }
     }
 
-    #[cfg(any(target_os = "openbsd", target_os = "bitrig"))]
-    pub unsafe fn current() -> Option<usize> {
-        let mut current_stack: libc::stack_t = ::mem::zeroed();
-        assert_eq!(libc::pthread_stackseg_np(libc::pthread_self(),
-                                             &mut current_stack), 0);
-
-        let extra = if cfg!(target_os = "bitrig") {3} else {1} * os::page_size();
-        Some(if libc::pthread_main_np() == 1 {
-            // main thread
-            current_stack.ss_sp as usize - current_stack.ss_size + extra
-        } else {
-            // new thread
-            current_stack.ss_sp as usize - current_stack.ss_size
-        })
+    #[cfg(any(target_os = "macos",
+              target_os = "bitrig",
+              target_os = "openbsd",
+              target_os = "solaris"))]
+    pub unsafe fn current() -> Option<Guard> {
+        let stackaddr = get_stack_start()? as usize;
+        Some(stackaddr - PAGE_SIZE..stackaddr)
     }
 
     #[cfg(any(target_os = "android", target_os = "freebsd",
               target_os = "linux", target_os = "netbsd", target_os = "l4re"))]
-    pub unsafe fn current() -> Option<usize> {
+    pub unsafe fn current() -> Option<Guard> {
         let mut ret = None;
         let mut attr: libc::pthread_attr_t = ::mem::zeroed();
         assert_eq!(libc::pthread_attr_init(&mut attr), 0);
@@ -352,12 +404,23 @@ pub mod guard {
             assert_eq!(libc::pthread_attr_getstack(&attr, &mut stackaddr,
                                                    &mut size), 0);
 
+            let stackaddr = stackaddr as usize;
             ret = if cfg!(target_os = "freebsd") {
-                Some(stackaddr as usize - guardsize)
+                // FIXME does freebsd really fault *below* the guard addr?
+                let guardaddr = stackaddr - guardsize;
+                Some(guardaddr - PAGE_SIZE..guardaddr)
             } else if cfg!(target_os = "netbsd") {
-                Some(stackaddr as usize)
+                Some(stackaddr - guardsize..stackaddr)
+            } else if cfg!(all(target_os = "linux", target_env = "gnu")) {
+                // glibc used to include the guard area within the stack, as noted in the BUGS
+                // section of `man pthread_attr_getguardsize`.  This has been corrected starting
+                // with glibc 2.27, and in some distro backports, so the guard is now placed at the
+                // end (below) the stack.  There's no easy way for us to know which we have at
+                // runtime, so we'll just match any fault in the range right above or below the
+                // stack base to call that fault a stack overflow.
+                Some(stackaddr - guardsize..stackaddr + guardsize)
             } else {
-                Some(stackaddr as usize + guardsize)
+                Some(stackaddr..stackaddr + guardsize)
             };
         }
         assert_eq!(libc::pthread_attr_destroy(&mut attr), 0);
diff --git a/src/libstd/sys/unix/time.rs b/src/libstd/sys/unix/time.rs
index 83127935909..0b1fb726357 100644
--- a/src/libstd/sys/unix/time.rs
+++ b/src/libstd/sys/unix/time.rs
@@ -289,7 +289,7 @@ mod inner {
 
         pub fn sub_instant(&self, other: &Instant) -> Duration {
             self.t.sub_timespec(&other.t).unwrap_or_else(|_| {
-                panic!("other was less than the current instant")
+                panic!("specified instant was later than self")
             })
         }
 
@@ -345,9 +345,9 @@ mod inner {
         }
     }
 
-    #[cfg(not(target_os = "dragonfly"))]
+    #[cfg(not(any(target_os = "dragonfly", target_os = "hermit")))]
     pub type clock_t = libc::c_int;
-    #[cfg(target_os = "dragonfly")]
+    #[cfg(any(target_os = "dragonfly", target_os = "hermit"))]
     pub type clock_t = libc::c_ulong;
 
     fn now(clock: clock_t) -> Timespec {