Implement libstd for CloudABI.

Though CloudABI is strongly inspired by POSIX, its absence of features
that don't work well with capability-based sandboxing makes it different
enough that adding bits to sys/unix will make things a mess. This change
therefore adds CloudABI specific platform code under sys/cloudabi and
borrows parts from sys/unix that can be used without changes.

One of the goals of this implementation is to build as much as possible
directly on top of CloudABI's system call layer, as opposed to using the
C library. This is preferred, as the system call layer is supposed to be
stable, whereas the C library ABI technically is not. An advantage of
this approach is that it allows us to implement certain interfaces, such
as mutexes and condition variables more optimally. They can be lighter
than the ones provided by pthreads.

This change disables some modules that cannot realistically be
implemented right now. For example, libstd's pathname abstraction is not
designed with POSIX *at() (e.g., openat()) in mind. The *at() functions
are the only set of file system APIs available on CloudABI. There is no
global file system namespace, nor a process working directory.
Discussions on how to port these modules over are outside the scope of
this change.

Apart from this change, there are still some other minor fixups that
need to be made to platform independent code to make things build. These
will be sent out separately, so they can be reviewed more thoroughly.

src/libstd/lib.rs

@@ -473,16 +473,21 @@ pub mod f64;
 pub mod thread;
 pub mod ascii;
 pub mod collections;
+#[cfg(not(target_os = "cloudabi"))]
 pub mod env;
 pub mod error;
 pub mod ffi;
+#[cfg(not(target_os = "cloudabi"))]
 pub mod fs;
 pub mod io;
+#[cfg(not(target_os = "cloudabi"))]
 pub mod net;
 pub mod num;
 pub mod os;
 pub mod panic;
+#[cfg(not(target_os = "cloudabi"))]
 pub mod path;
+#[cfg(not(target_os = "cloudabi"))]
 pub mod process;
 pub mod sync;
 pub mod time;

src/libstd/sys/cloudabi/abi/mod.rs

@@ -0,0 +1,13 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#[allow(warnings)]
+mod cloudabi;
+pub use self::cloudabi::*;

src/libstd/sys/cloudabi/args.rs

@@ -0,0 +1,15 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#[allow(dead_code)]
+pub fn init(_: isize, _: *const *const u8) {}
+
+#[allow(dead_code)]
+pub fn cleanup() {}

src/libstd/sys/cloudabi/backtrace.rs

@@ -0,0 +1,121 @@
+// Copyright 2014-2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use error::Error;
+use ffi::CStr;
+use intrinsics;
+use io;
+use libc;
+use sys_common::backtrace::Frame;
+use unwind as uw;
+
+pub struct BacktraceContext;
+
+struct Context<'a> {
+    idx: usize,
+    frames: &'a mut [Frame],
+}
+
+#[derive(Debug)]
+struct UnwindError(uw::_Unwind_Reason_Code);
+
+impl Error for UnwindError {
+    fn description(&self) -> &'static str {
+        "unexpected return value while unwinding"
+    }
+}
+
+impl ::fmt::Display for UnwindError {
+    fn fmt(&self, f: &mut ::fmt::Formatter) -> ::fmt::Result {
+        write!(f, "{}: {:?}", self.description(), self.0)
+    }
+}
+
+#[inline(never)] // if we know this is a function call, we can skip it when
+                 // tracing
+pub fn unwind_backtrace(frames: &mut [Frame]) -> io::Result<(usize, BacktraceContext)> {
+    let mut cx = Context { idx: 0, frames };
+    let result_unwind =
+        unsafe { uw::_Unwind_Backtrace(trace_fn, &mut cx as *mut Context as *mut libc::c_void) };
+    // See libunwind:src/unwind/Backtrace.c for the return values.
+    // No, there is no doc.
+    match result_unwind {
+        // These return codes seem to be benign and need to be ignored for backtraces
+        // to show up properly on all tested platforms.
+        uw::_URC_END_OF_STACK | uw::_URC_FATAL_PHASE1_ERROR | uw::_URC_FAILURE => {
+            Ok((cx.idx, BacktraceContext))
+        }
+        _ => Err(io::Error::new(
+            io::ErrorKind::Other,
+            UnwindError(result_unwind),
+        )),
+    }
+}
+
+extern "C" 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) };
+    let mut ip_before_insn = 0;
+    let mut ip = unsafe { uw::_Unwind_GetIPInfo(ctx, &mut ip_before_insn) as *mut libc::c_void };
+    if !ip.is_null() && ip_before_insn == 0 {
+        // this is a non-signaling frame, so `ip` refers to the address
+        // after the calling instruction. account for that.
+        ip = (ip as usize - 1) as *mut _;
+    }
+
+    let symaddr = 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;
+    }
+
+    uw::_URC_NO_REASON
+}
+
+pub fn foreach_symbol_fileline<F>(_: Frame, _: F, _: &BacktraceContext) -> io::Result<bool>
+where
+    F: FnMut(&[u8], u32) -> io::Result<()>,
+{
+    // No way to obtain this information on CloudABI.
+    Ok(false)
+}
+
+pub fn resolve_symname<F>(frame: Frame, callback: F, _: &BacktraceContext) -> io::Result<()>
+where
+    F: FnOnce(Option<&str>) -> io::Result<()>,
+{
+    unsafe {
+        let mut info: Dl_info = intrinsics::init();
+        let symname =
+            if dladdr(frame.exact_position as *mut _, &mut info) == 0 || info.dli_sname.is_null() {
+                None
+            } else {
+                CStr::from_ptr(info.dli_sname).to_str().ok()
+            };
+        callback(symname)
+    }
+}
+
+#[repr(C)]
+struct Dl_info {
+    dli_fname: *const libc::c_char,
+    dli_fbase: *mut libc::c_void,
+    dli_sname: *const libc::c_char,
+    dli_saddr: *mut libc::c_void,
+}
+
+extern "C" {
+    fn dladdr(addr: *const libc::c_void, info: *mut Dl_info) -> libc::c_int;
+}

src/libstd/sys/cloudabi/condvar.rs

@@ -0,0 +1,169 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use cell::UnsafeCell;
+use mem;
+use sync::atomic::{AtomicU32, Ordering};
+use sys::cloudabi::abi;
+use sys::mutex::{self, Mutex};
+use sys::time::dur2intervals;
+use time::Duration;
+
+extern "C" {
+    #[thread_local]
+    static __pthread_thread_id: abi::tid;
+}
+
+pub struct Condvar {
+    condvar: UnsafeCell<AtomicU32>,
+}
+
+unsafe impl Send for Condvar {}
+unsafe impl Sync for Condvar {}
+
+impl Condvar {
+    pub const fn new() -> Condvar {
+        Condvar {
+            condvar: UnsafeCell::new(AtomicU32::new(abi::CONDVAR_HAS_NO_WAITERS.0)),
+        }
+    }
+
+    pub unsafe fn init(&mut self) {}
+
+    pub unsafe fn notify_one(&self) {
+        let condvar = self.condvar.get();
+        if (*condvar).load(Ordering::Relaxed) != abi::CONDVAR_HAS_NO_WAITERS.0 {
+            let ret = abi::condvar_signal(condvar as *mut abi::condvar, abi::scope::PRIVATE, 1);
+            assert_eq!(
+                ret,
+                abi::errno::SUCCESS,
+                "Failed to signal on condition variable"
+            );
+        }
+    }
+
+    pub unsafe fn notify_all(&self) {
+        let condvar = self.condvar.get();
+        if (*condvar).load(Ordering::Relaxed) != abi::CONDVAR_HAS_NO_WAITERS.0 {
+            let ret = abi::condvar_signal(
+                condvar as *mut abi::condvar,
+                abi::scope::PRIVATE,
+                abi::nthreads::max_value(),
+            );
+            assert_eq!(
+                ret,
+                abi::errno::SUCCESS,
+                "Failed to broadcast on condition variable"
+            );
+        }
+    }
+
+    pub unsafe fn wait(&self, mutex: &Mutex) {
+        let mutex = mutex::raw(mutex);
+        assert_eq!(
+            (*mutex).load(Ordering::Relaxed) & !abi::LOCK_KERNEL_MANAGED.0,
+            __pthread_thread_id.0 | abi::LOCK_WRLOCKED.0,
+            "This lock is not write-locked by this thread"
+        );
+
+        // Call into the kernel to wait on the condition variable.
+        let condvar = self.condvar.get();
+        let subscription = abi::subscription {
+            type_: abi::eventtype::CONDVAR,
+            union: abi::subscription_union {
+                condvar: abi::subscription_condvar {
+                    condvar: condvar as *mut abi::condvar,
+                    condvar_scope: abi::scope::PRIVATE,
+                    lock: mutex as *mut abi::lock,
+                    lock_scope: abi::scope::PRIVATE,
+                },
+            },
+            ..mem::zeroed()
+        };
+        let mut event: abi::event = mem::uninitialized();
+        let mut nevents: usize = mem::uninitialized();
+        let ret = abi::poll(&subscription, &mut event, 1, &mut nevents);
+        assert_eq!(
+            ret,
+            abi::errno::SUCCESS,
+            "Failed to wait on condition variable"
+        );
+        assert_eq!(
+            event.error,
+            abi::errno::SUCCESS,
+            "Failed to wait on condition variable"
+        );
+    }
+
+    pub unsafe fn wait_timeout(&self, mutex: &Mutex, dur: Duration) -> bool {
+        let mutex = mutex::raw(mutex);
+        assert_eq!(
+            (*mutex).load(Ordering::Relaxed) & !abi::LOCK_KERNEL_MANAGED.0,
+            __pthread_thread_id.0 | abi::LOCK_WRLOCKED.0,
+            "This lock is not write-locked by this thread"
+        );
+
+        // Call into the kernel to wait on the condition variable.
+        let condvar = self.condvar.get();
+        let subscriptions = [
+            abi::subscription {
+                type_: abi::eventtype::CONDVAR,
+                union: abi::subscription_union {
+                    condvar: abi::subscription_condvar {
+                        condvar: condvar as *mut abi::condvar,
+                        condvar_scope: abi::scope::PRIVATE,
+                        lock: mutex as *mut abi::lock,
+                        lock_scope: abi::scope::PRIVATE,
+                    },
+                },
+                ..mem::zeroed()
+            },
+            abi::subscription {
+                type_: abi::eventtype::CLOCK,
+                union: abi::subscription_union {
+                    clock: abi::subscription_clock {
+                        clock_id: abi::clockid::MONOTONIC,
+                        timeout: dur2intervals(&dur),
+                        ..mem::zeroed()
+                    },
+                },
+                ..mem::zeroed()
+            },
+        ];
+        let mut events: [abi::event; 2] = mem::uninitialized();
+        let mut nevents: usize = mem::uninitialized();
+        let ret = abi::poll(subscriptions.as_ptr(), events.as_mut_ptr(), 2, &mut nevents);
+        assert_eq!(
+            ret,
+            abi::errno::SUCCESS,
+            "Failed to wait on condition variable"
+        );
+        for i in 0..nevents {
+            assert_eq!(
+                events[i].error,
+                abi::errno::SUCCESS,
+                "Failed to wait on condition variable"
+            );
+            if events[i].type_ == abi::eventtype::CONDVAR {
+                return true;
+            }
+        }
+        false
+    }
+
+    pub unsafe fn destroy(&self) {
+        let condvar = self.condvar.get();
+        assert_eq!(
+            (*condvar).load(Ordering::Relaxed),
+            abi::CONDVAR_HAS_NO_WAITERS.0,
+            "Attempted to destroy a condition variable with blocked threads"
+        );
+    }
+}