Avoid mem::uninitialized() in std::sys::unix

For `libc` types that will be initialized in FFI calls, we can just use
`MaybeUninit` and then pass around raw pointers.

For `sun_path_offset()`, which really wants `offset_of`, all callers
have a real `sockaddr_un` available, so we can use that reference.

src/libstd/sys/unix/condvar.rs

@@ -40,15 +40,15 @@ impl Condvar {
                   target_os = "android",
                   target_os = "hermit")))]
     pub unsafe fn init(&mut self) {
-        use crate::mem;
-        let mut attr: libc::pthread_condattr_t = mem::uninitialized();
-        let r = libc::pthread_condattr_init(&mut attr);
+        use crate::mem::MaybeUninit;
+        let mut attr = MaybeUninit::<libc::pthread_condattr_t>::uninit();
+        let r = libc::pthread_condattr_init(attr.as_mut_ptr());
         assert_eq!(r, 0);
-        let r = libc::pthread_condattr_setclock(&mut attr, libc::CLOCK_MONOTONIC);
+        let r = libc::pthread_condattr_setclock(attr.as_mut_ptr(), libc::CLOCK_MONOTONIC);
         assert_eq!(r, 0);
-        let r = libc::pthread_cond_init(self.inner.get(), &attr);
+        let r = libc::pthread_cond_init(self.inner.get(), attr.as_ptr());
         assert_eq!(r, 0);
-        let r = libc::pthread_condattr_destroy(&mut attr);
+        let r = libc::pthread_condattr_destroy(attr.as_mut_ptr());
         assert_eq!(r, 0);
     }
 

src/libstd/sys/unix/ext/net.rs

@@ -40,10 +40,9 @@ use libc::MSG_NOSIGNAL;
               target_os = "haiku")))]
 const MSG_NOSIGNAL: libc::c_int = 0x0;
 
-fn sun_path_offset() -> usize {
+fn sun_path_offset(addr: &libc::sockaddr_un) -> usize {
     // 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 base = addr as *const _ as usize;
     let path = &addr.sun_path as *const _ as usize;
     path - base
 }
@@ -69,7 +68,7 @@ unsafe fn sockaddr_un(path: &Path) -> io::Result<(libc::sockaddr_un, libc::sockl
     // null byte for pathname addresses is already there because we zeroed the
     // struct
 
-    let mut len = sun_path_offset() + bytes.len();
+    let mut len = sun_path_offset(&addr) + bytes.len();
     match bytes.get(0) {
         Some(&0) | None => {}
         Some(_) => len += 1,
@@ -122,7 +121,7 @@ impl SocketAddr {
         if len == 0 {
             // When there is a datagram from unnamed unix socket
             // linux returns zero bytes of address
-            len = sun_path_offset() as libc::socklen_t;  // i.e., zero-length address
+            len = sun_path_offset(&addr) as libc::socklen_t;  // i.e., zero-length address
         } else if addr.sun_family != libc::AF_UNIX as libc::sa_family_t {
             return Err(io::Error::new(io::ErrorKind::InvalidInput,
                                       "file descriptor did not correspond to a Unix socket"));
@@ -200,7 +199,7 @@ impl SocketAddr {
     }
 
     fn address<'a>(&'a self) -> AddressKind<'a> {
-        let len = self.len as usize - sun_path_offset();
+        let len = self.len as usize - sun_path_offset(&self.addr);
         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

src/libstd/sys/unix/mutex.rs

@@ -1,5 +1,5 @@
 use crate::cell::UnsafeCell;
-use crate::mem;
+use crate::mem::MaybeUninit;
 
 pub struct Mutex { inner: UnsafeCell<libc::pthread_mutex_t> }
 
@@ -40,14 +40,14 @@ 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.
-        let mut attr: libc::pthread_mutexattr_t = mem::uninitialized();
-        let r = libc::pthread_mutexattr_init(&mut attr);
+        let mut attr = MaybeUninit::<libc::pthread_mutexattr_t>::uninit();
+        let r = libc::pthread_mutexattr_init(attr.as_mut_ptr());
         debug_assert_eq!(r, 0);
-        let r = libc::pthread_mutexattr_settype(&mut attr, libc::PTHREAD_MUTEX_NORMAL);
+        let r = libc::pthread_mutexattr_settype(attr.as_mut_ptr(), libc::PTHREAD_MUTEX_NORMAL);
         debug_assert_eq!(r, 0);
-        let r = libc::pthread_mutex_init(self.inner.get(), &attr);
+        let r = libc::pthread_mutex_init(self.inner.get(), attr.as_ptr());
         debug_assert_eq!(r, 0);
-        let r = libc::pthread_mutexattr_destroy(&mut attr);
+        let r = libc::pthread_mutexattr_destroy(attr.as_mut_ptr());
         debug_assert_eq!(r, 0);
     }
     #[inline]
@@ -89,19 +89,19 @@ unsafe impl Sync for ReentrantMutex {}
 
 impl ReentrantMutex {
     pub unsafe fn uninitialized() -> ReentrantMutex {
-        ReentrantMutex { inner: mem::uninitialized() }
+        ReentrantMutex { inner: UnsafeCell::new(libc::PTHREAD_MUTEX_INITIALIZER) }
     }
 
     pub unsafe fn init(&mut self) {
-        let mut attr: libc::pthread_mutexattr_t = mem::uninitialized();
-        let result = libc::pthread_mutexattr_init(&mut attr as *mut _);
+        let mut attr = MaybeUninit::<libc::pthread_mutexattr_t>::uninit();
+        let result = libc::pthread_mutexattr_init(attr.as_mut_ptr());
         debug_assert_eq!(result, 0);
-        let result = libc::pthread_mutexattr_settype(&mut attr as *mut _,
+        let result = libc::pthread_mutexattr_settype(attr.as_mut_ptr(),
                                                     libc::PTHREAD_MUTEX_RECURSIVE);
         debug_assert_eq!(result, 0);
-        let result = libc::pthread_mutex_init(self.inner.get(), &attr as *const _);
+        let result = libc::pthread_mutex_init(self.inner.get(), attr.as_ptr());
         debug_assert_eq!(result, 0);
-        let result = libc::pthread_mutexattr_destroy(&mut attr as *mut _);
+        let result = libc::pthread_mutexattr_destroy(attr.as_mut_ptr());
         debug_assert_eq!(result, 0);
     }
 

src/libstd/sys/unix/process/process_common.rs

@@ -466,11 +466,11 @@ mod tests {
             // Test to make sure that a signal mask does not get inherited.
             let mut cmd = Command::new(OsStr::new("cat"));
 
-            let mut set: libc::sigset_t = mem::uninitialized();
-            let mut old_set: libc::sigset_t = mem::uninitialized();
-            t!(cvt(sigemptyset(&mut set)));
-            t!(cvt(sigaddset(&mut set, libc::SIGINT)));
-            t!(cvt(libc::pthread_sigmask(libc::SIG_SETMASK, &set, &mut old_set)));
+            let mut set = mem::MaybeUninit::<libc::sigset_t>::uninit();
+            let mut old_set = mem::MaybeUninit::<libc::sigset_t>::uninit();
+            t!(cvt(sigemptyset(set.as_mut_ptr())));
+            t!(cvt(sigaddset(set.as_mut_ptr(), libc::SIGINT)));
+            t!(cvt(libc::pthread_sigmask(libc::SIG_SETMASK, set.as_ptr(), old_set.as_mut_ptr())));
 
             cmd.stdin(Stdio::MakePipe);
             cmd.stdout(Stdio::MakePipe);
@@ -479,7 +479,7 @@ mod tests {
             let stdin_write = pipes.stdin.take().unwrap();
             let stdout_read = pipes.stdout.take().unwrap();
 
-            t!(cvt(libc::pthread_sigmask(libc::SIG_SETMASK, &old_set,
+            t!(cvt(libc::pthread_sigmask(libc::SIG_SETMASK, old_set.as_ptr(),
                                          ptr::null_mut())));
 
             t!(cvt(libc::kill(cat.id() as libc::pid_t, libc::SIGINT)));

src/libstd/sys/unix/process/process_unix.rs

@@ -202,7 +202,7 @@ impl Command {
         // emscripten has no signal support.
         #[cfg(not(any(target_os = "emscripten")))]
         {
-            use crate::mem;
+            use crate::mem::{self, MaybeUninit};
             // Reset signal handling so the child process starts in a
             // standardized state. libstd ignores SIGPIPE, and signal-handling
             // libraries often set a mask. Child processes inherit ignored
@@ -210,18 +210,18 @@ impl Command {
             // UNIX programs do not reset these things on their own, so we
             // need to clean things up now to avoid confusing the program
             // we're about to run.
-            let mut set: libc::sigset_t = mem::uninitialized();
+            let mut set = MaybeUninit::<libc::sigset_t>::uninit();
             if cfg!(target_os = "android") {
                 // Implementing sigemptyset allow us to support older Android
                 // versions. See the comment about Android and sig* functions in
                 // process_common.rs
-                libc::memset(&mut set as *mut _ as *mut _,
+                libc::memset(set.as_mut_ptr() as *mut _,
                              0,
                              mem::size_of::<libc::sigset_t>());
             } else {
-                cvt(libc::sigemptyset(&mut set))?;
+                cvt(libc::sigemptyset(set.as_mut_ptr()))?;
             }
-            cvt(libc::pthread_sigmask(libc::SIG_SETMASK, &set,
+            cvt(libc::pthread_sigmask(libc::SIG_SETMASK, set.as_ptr(),
                                          ptr::null_mut()))?;
             let ret = sys::signal(libc::SIGPIPE, libc::SIG_DFL);
             if ret == libc::SIG_ERR {
@@ -273,7 +273,7 @@ impl Command {
     fn posix_spawn(&mut self, stdio: &ChildPipes, envp: Option<&CStringArray>)
         -> io::Result<Option<Process>>
     {
-        use crate::mem;
+        use crate::mem::MaybeUninit;
         use crate::sys;
 
         if self.get_gid().is_some() ||
@@ -315,63 +315,63 @@ impl Command {
 
         let mut p = Process { pid: 0, status: None };
 
-        struct PosixSpawnFileActions(libc::posix_spawn_file_actions_t);
+        struct PosixSpawnFileActions(MaybeUninit<libc::posix_spawn_file_actions_t>);
 
         impl Drop for PosixSpawnFileActions {
             fn drop(&mut self) {
                 unsafe {
-                    libc::posix_spawn_file_actions_destroy(&mut self.0);
+                    libc::posix_spawn_file_actions_destroy(self.0.as_mut_ptr());
                 }
             }
         }
 
-        struct PosixSpawnattr(libc::posix_spawnattr_t);
+        struct PosixSpawnattr(MaybeUninit<libc::posix_spawnattr_t>);
 
         impl Drop for PosixSpawnattr {
             fn drop(&mut self) {
                 unsafe {
-                    libc::posix_spawnattr_destroy(&mut self.0);
+                    libc::posix_spawnattr_destroy(self.0.as_mut_ptr());
                 }
             }
         }
 
         unsafe {
-            let mut file_actions = PosixSpawnFileActions(mem::uninitialized());
-            let mut attrs = PosixSpawnattr(mem::uninitialized());
+            let mut file_actions = PosixSpawnFileActions(MaybeUninit::uninit());
+            let mut attrs = PosixSpawnattr(MaybeUninit::uninit());
 
-            libc::posix_spawnattr_init(&mut attrs.0);
-            libc::posix_spawn_file_actions_init(&mut file_actions.0);
+            libc::posix_spawnattr_init(attrs.0.as_mut_ptr());
+            libc::posix_spawn_file_actions_init(file_actions.0.as_mut_ptr());
 
             if let Some(fd) = stdio.stdin.fd() {
-                cvt(libc::posix_spawn_file_actions_adddup2(&mut file_actions.0,
+                cvt(libc::posix_spawn_file_actions_adddup2(file_actions.0.as_mut_ptr(),
                                                            fd,
                                                            libc::STDIN_FILENO))?;
             }
             if let Some(fd) = stdio.stdout.fd() {
-                cvt(libc::posix_spawn_file_actions_adddup2(&mut file_actions.0,
+                cvt(libc::posix_spawn_file_actions_adddup2(file_actions.0.as_mut_ptr(),
                                                            fd,
                                                            libc::STDOUT_FILENO))?;
             }
             if let Some(fd) = stdio.stderr.fd() {
-                cvt(libc::posix_spawn_file_actions_adddup2(&mut file_actions.0,
+                cvt(libc::posix_spawn_file_actions_adddup2(file_actions.0.as_mut_ptr(),
                                                            fd,
                                                            libc::STDERR_FILENO))?;
             }
             if let Some((f, cwd)) = addchdir {
-                cvt(f(&mut file_actions.0, cwd.as_ptr()))?;
+                cvt(f(file_actions.0.as_mut_ptr(), cwd.as_ptr()))?;
             }
 
-            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 mut set = MaybeUninit::<libc::sigset_t>::uninit();
+            cvt(libc::sigemptyset(set.as_mut_ptr()))?;
+            cvt(libc::posix_spawnattr_setsigmask(attrs.0.as_mut_ptr(),
+                                                 set.as_ptr()))?;
+            cvt(libc::sigaddset(set.as_mut_ptr(), libc::SIGPIPE))?;
+            cvt(libc::posix_spawnattr_setsigdefault(attrs.0.as_mut_ptr(),
+                                                    set.as_ptr()))?;
 
             let flags = libc::POSIX_SPAWN_SETSIGDEF |
                 libc::POSIX_SPAWN_SETSIGMASK;
-            cvt(libc::posix_spawnattr_setflags(&mut attrs.0, flags as _))?;
+            cvt(libc::posix_spawnattr_setflags(attrs.0.as_mut_ptr(), flags as _))?;
 
             // Make sure we synchronize access to the global `environ` resource
             let _env_lock = sys::os::env_lock();
@@ -380,8 +380,8 @@ impl Command {
             let ret = libc::posix_spawnp(
                 &mut p.pid,
                 self.get_argv()[0],
-                &file_actions.0,
-                &attrs.0,
+                file_actions.0.as_ptr(),
+                attrs.0.as_ptr(),
                 self.get_argv().as_ptr() as *const _,
                 envp as *const _,
             );