WIP: Decommission async-support

.gitignore

@@ -1,4 +1,4 @@
-Cargo.lock
-layout.ld
-platform
-target
+/Cargo.lock
+/layout.ld
+/platform
+/target

.travis.yml

@@ -6,7 +6,7 @@ branches:
 
 language: rust
 rust:
-  - nightly-2020-01-16
+  - nightly-2020-04-06
 
 os:
   - linux

CHANGELOG.md

@@ -9,9 +9,10 @@
   - To retrieve the value of an asynchronous `value`, use `value.await`
   - This is only possible within an `async fn`, so either
     - Make the caller `fn` of `.await` an `async fn`
-    - Not recommended: Use `core::executor::block_on(value)` to retrieve the `value`
+    - Not recommended: Use `libtock::executor::block_on(value)` to retrieve the `value`
 - Most API functions, including `main()`, return a `Result<T, TockError>`
 - All drivers can exclusively be retrieved by `retrieve_drivers` which returns a `Drivers` singleton. Drivers can be shared between different tasks only if it is safe to do so.
+- The low-level functions have been moved to a new crate called `libtock-core`. This crate is intended to be less experimental and more stable.
 
 ### Changed APIs
 
@@ -42,6 +43,8 @@
 - Targets without support for atomics can be built
 - The `TockAllocator` is no longer included by default and needs to to be opted-in via `--features=alloc`
 - `hardware_test.rs` is now called `libtock_test.rs` to make clear that the intent is to test the correctness of `libtock-rs`, not the hardware or the kernel
+- The panic handler can now be customized using the `custom_panic_handler` feature
+- The error alloc handler can now be customized using the `custom_alloc_error_handler` feature
 
 ## a8bb4fa9be504517d5533511fd8e607ea61f1750 (0.1.0)
 

Cargo.toml

@@ -12,7 +12,6 @@ custom_alloc_error_handler = ["libtock-core/custom_alloc_error_handler"]
 __internal_disable_gpio_in_integration_test = []
 
 [dependencies]
-core = { package = "async-support", path = "async-support" }
 libtock-core = { path = "core" }
 libtock_codegen = { path = "codegen" }
 futures = { version = "0.3.1", default-features = false, features = ["unstable", "cfg-target-has-atomic"] }
@@ -58,7 +57,6 @@ lto = true
 
 [workspace]
 members = [
-    "async-support",
     "codegen",
     "core",
     "test-runner"

build.rs

@@ -6,21 +6,25 @@ use std::io::BufReader;
 use std::path::Path;
 use std::process;
 
+static LAYOUT_FILE_NAME: &str = "layout.ld";
+
 fn main() {
-    static ENV_VAR: &str = "PLATFORM";
-    static FILE_NAME: &str = "platform";
+    static PLATFORM_ENV_VAR: &str = "PLATFORM";
+    static PLATFORM_FILE_NAME: &str = "platform";
     static APP_HEAP_SIZE: &str = "APP_HEAP_SIZE";
     static KERNEL_HEAP_SIZE: &str = "KERNEL_HEAP_SIZE";
 
-    println!("cargo:rerun-if-env-changed={}", ENV_VAR);
+    println!("cargo:rerun-if-env-changed={}", PLATFORM_ENV_VAR);
     println!("cargo:rerun-if-env-changed={}", APP_HEAP_SIZE);
     println!("cargo:rerun-if-env-changed={}", KERNEL_HEAP_SIZE);
-    println!("cargo:rerun-if-changed={}", FILE_NAME);
+    println!("cargo:rerun-if-changed={}", PLATFORM_FILE_NAME);
+    println!("cargo:rerun-if-changed={}", LAYOUT_FILE_NAME);
 
-    let platform_name = read_env_var(ENV_VAR).or_else(|| read_board_name_from_file(FILE_NAME));
+    let platform_name =
+        read_env_var(PLATFORM_ENV_VAR).or_else(|| read_board_name_from_file(PLATFORM_FILE_NAME));
     if let Some(platform_name) = platform_name {
-        println!("cargo:rustc-env={}={}", ENV_VAR, platform_name);
-        copy_linker_file(&platform_name.trim());
+        println!("cargo:rustc-env={}={}", PLATFORM_ENV_VAR, platform_name);
+        copy_linker_file(platform_name.trim());
     } else {
         println!(
             "cargo:warning=No platform specified. \
@@ -66,5 +70,5 @@ fn copy_linker_file(platform_name: &str) {
         println!("Cannot find layout file {:?}", path);
         process::exit(1);
     }
-    fs::copy(linker_file_name, "layout.ld").unwrap();
+    fs::copy(linker_file_name, LAYOUT_FILE_NAME).unwrap();
 }

codegen/src/lib.rs

@@ -98,7 +98,7 @@ fn try_generate_main_wrapped(
                 MAIN_INVOKED = true;
             }
             let _block = async #block;
-            unsafe {::core::executor::block_on(_block) }
+            unsafe { ::libtock::executor::block_on(_block) }
         }
     ))
 }
@@ -126,7 +126,7 @@ mod tests {
                 let _block = async {
                     method_call().await;
                 };
-                unsafe { ::core::executor::block_on(_block) }
+                unsafe { ::libtock::executor::block_on(_block) }
             }
         ))
         .unwrap();

core/Cargo.toml

@@ -10,5 +10,5 @@ custom_panic_handler = []
 custom_alloc_error_handler = []
 
 [dependencies]
-linked_list_allocator = { optional = true, version = "=0.6.5", default-features = false }
+linked_list_allocator = { optional = true, version = "=0.8.1", default-features = false }
 libtock_codegen = { path = "../codegen" }

core/src/entry_point/start_item_arm.rs

@@ -105,7 +105,7 @@ pub unsafe extern "C" fn _start(
         bl rust_start"
         :                                                              // No output operands
         : "{r0}"(app_start), "{r1}"(mem_start), "{r3}"(app_heap_break) // Input operands
-        : "r0", "r1", "r2", "r3", "r4", "r5", "r6", "r7", "r8", "r12",
+        : "r0", "r1", "r2", "r3", "r4", "r5", "r6", "r8", "r12",
           "cc", "memory"                                               // Clobbers
         : "volatile"                                                   // Options
     );

core/src/syscalls/mod.rs

@@ -10,23 +10,7 @@ use crate::result::SubscribeError;
 use crate::shared_memory::SharedMemory;
 
 pub mod raw {
-    use super::platform;
-
-    pub use platform::*;
-
-    /// # Safety
-    ///
-    /// Yielding in the main function should be safe. Nevertheless, yielding manually is not required as this is already achieved by the `async` runtime.
-    ///
-    /// When yielding in callbacks, two problems can arise:
-    /// - The guarantees of `FnMut` are violated. In this case, make sure your callback has `Fn` behavior.
-    /// - Callbacks can get executed in a nested manner and overflow the stack quickly.
-    ///
-    /// This function is exported as `libtock::syscalls::raw::yieldk`. Do not reference this name directly. Its only purpose is to establish a back-channel from `async-support`, a patched version of `core` to `libtock-rs` via linking. This workaround has been chosen to keep the `core` crate free of dependencies on platform-specific syscall implementations and is expected to get removed as soon as possible.
-    #[export_name = "libtock::syscalls::raw::yieldk"]
-    pub unsafe fn yieldk() {
-        platform::yieldk()
-    }
+    pub use super::platform::*;
 }
 
 pub fn subscribe<C: Consumer<T>, T>(

core/src/syscalls/platform.rs

@@ -3,9 +3,15 @@ use core::cell::RefCell;
 use std::vec::Vec;
 
 /// yield for a callback fired by the kernel
+///
 /// # Safety
-/// Yielding inside a callback conflicts with Rust's safety guarantees. For example,
-/// a FnMut closure could be triggered multiple times making a &mut a shared reference.
+///
+/// Yielding in the main function should be safe. Nevertheless, yielding manually
+/// is not required as this is already achieved by the `async` runtime.
+///
+/// When yielding in callbacks, two problems can arise:
+/// - The guarantees of `FnMut` are violated. In this case, make sure your callback has `Fn` behavior.
+/// - Callbacks can get executed in a nested manner and overflow the stack quickly.
 pub unsafe fn yieldk() {
     EVENTS.with(|e| e.borrow_mut().push(Event::YieldK));
 }

rust-toolchain

@@ -1 +1 @@
-nightly-2020-01-16
+nightly-2020-04-06

src/console.rs

@@ -1,9 +1,9 @@
 use crate::callback::Identity0Consumer;
+use crate::executor;
 use crate::futures;
 use crate::result::TockResult;
 use crate::syscalls;
 use core::cell::Cell;
-use core::executor;
 use core::fmt;
 use core::mem;
 

src/drivers.rs

@@ -5,7 +5,6 @@ use crate::gpio::GpioDriverFactory;
 use crate::leds::LedsDriverFactory;
 use crate::result::OtherError;
 use crate::result::TockError;
-use crate::result::TockResult;
 use crate::rng::RngDriver;
 use crate::sensors::ninedof::NinedofDriver;
 use crate::sensors::AmbientLightSensor;
@@ -37,12 +36,12 @@ pub struct Drivers {
 }
 
 /// Retrieve [Drivers] struct. Returns struct only once.
-pub fn retrieve_drivers() -> TockResult<Drivers> {
+pub fn retrieve_drivers() -> Result<Drivers, DriversAlreadyTakenError> {
     static mut DRIVER_TAKEN: bool = false;
 
     unsafe {
         if DRIVER_TAKEN {
-            Err(TockError::Other(OtherError::DriverAlreadyTaken))
+            Err(DriversAlreadyTakenError)
         } else {
             DRIVER_TAKEN = true;
             Ok(retrieve_drivers_unsafe())
@@ -79,3 +78,11 @@ const DRIVERS: Drivers = Drivers {
     humidity_sensor: HumiditySensor,
     ninedof: NinedofDriver,
 };
+
+pub struct DriversAlreadyTakenError;
+
+impl From<DriversAlreadyTakenError> for TockError {
+    fn from(_: DriversAlreadyTakenError) -> Self {
+        TockError::Other(OtherError::DriversAlreadyTaken)
+    }
+}

src/executor.rs

@@ -0,0 +1,50 @@
+use crate::syscalls;
+use core::pin::Pin;
+use core::ptr;
+use core::task::Context;
+use core::task::Poll;
+use core::task::RawWaker;
+use core::task::RawWakerVTable;
+use core::task::Waker;
+use futures::Future;
+
+/// # Safety
+///
+/// [[block_on]] yields whenever a future cannot make any progress at present. Yielding is considered unsafe.
+pub unsafe fn block_on<T>(mut future: impl Future<Output = T>) -> T {
+    // Contract described in the Rustdoc: "A value, once pinned, must remain pinned forever (...).".
+    // IOW calling Pin::new_unchecked is safe as long as no &mut future is leaked after pinning.
+    let mut pinned_future = Pin::new_unchecked(&mut future);
+
+    loop {
+        match poll(pinned_future.as_mut()) {
+            Poll::Pending => syscalls::raw::yieldk(),
+            Poll::Ready(value) => {
+                return value;
+            }
+        }
+    }
+}
+
+fn poll<F: Future>(pinned_future: Pin<&mut F>) -> Poll<F::Output> {
+    let waker = unsafe { Waker::from_raw(get_dummy_waker()) };
+    let mut context = Context::from_waker(&waker);
+    pinned_future.poll(&mut context)
+}
+
+// Since Tock OS comes with waking-up functionality built-in, we use dummy wakers that do nothing at all.
+fn get_dummy_waker() -> RawWaker {
+    fn clone(_x: *const ()) -> RawWaker {
+        get_dummy_waker()
+    }
+
+    fn do_nothing(_x: *const ()) {}
+
+    // This vtable implements the methods required for managing the lifecycle of the wakers.
+    // Our wakers are dummies, so those functions don't do anything.
+    static DUMMY_WAKER_VTABLE: RawWakerVTable =
+        RawWakerVTable::new(clone, do_nothing, do_nothing, do_nothing);
+
+    // The wakers don't have any implementation, so the instance can simply be null.
+    RawWaker::new(ptr::null(), &DUMMY_WAKER_VTABLE)
+}