Add the simplest heap

.github/workflows/ci.yml

@@ -58,6 +58,7 @@ jobs:
       - run: qemu-system-arm --version
       - run: cargo run --target thumbv7m-none-eabi --example llff_integration_test --all-features
       - run: cargo run --target thumbv7m-none-eabi --example tlsf_integration_test --all-features
+      - run: cargo run --target thumbv7m-none-eabi --example simplest_integration_test --all-features
 
   clippy:
     name: Clippy

Cargo.toml

@@ -29,8 +29,10 @@ allocator_api = []
 
 # Use the Two-Level Segregated Fit allocator
 tlsf = ["rlsf", "const-default"]
- # Use the LinkedList first-fit allocator
+# Use the LinkedList first-fit allocator
 llff = ["linked_list_allocator"]
+# Use the simplest allocator
+simplest = []
 
 [dependencies]
 critical-section = "1.0"
@@ -56,6 +58,10 @@ required-features = ["allocator_api", "llff"]
 name = "tlsf_integration_test"
 required-features = ["allocator_api", "tlsf"]
 
+[[example]]
+name = "simplest_integration_test"
+required-features = ["allocator_api", "simplest"]
+
 [[example]]
 name = "global_alloc"
 required-features = ["llff"]

examples/global_alloc.rs

@@ -10,6 +10,7 @@ use cortex_m_rt::entry;
 use embedded_alloc::LlffHeap as Heap;
 // Two-Level Segregated Fit Heap allocator (feature = "tlsf")
 // use embedded_alloc::TlsfHeap as Heap;
+// use embedded_alloc::SimplestHeap as Heap;
 
 #[global_allocator]
 static HEAP: Heap = Heap::empty();

examples/simplest_integration_test.rs

@@ -0,0 +1,88 @@
+//! This is a very basic smoke test that runs in QEMU
+//! Reference the QEMU section of the [Embedded Rust Book] for more information
+//!
+//! This only tests integration of the allocator on an embedded target.
+//! Comprehensive allocator tests are located in the allocator dependency.
+//!
+//! After toolchain installation this test can be run with:
+//!
+//! ```bash
+//! cargo +nightly run --target thumbv7m-none-eabi --example simplest_integration_test --all-features
+//! ```
+//!
+//! [Embedded Rust Book]: https://docs.rust-embedded.org/book/intro/index.html
+
+#![feature(allocator_api)]
+#![no_main]
+#![no_std]
+
+extern crate alloc;
+extern crate panic_semihosting;
+
+use alloc::vec::Vec;
+use core::mem::{size_of, MaybeUninit};
+use cortex_m_rt::entry;
+use cortex_m_semihosting::{debug, hprintln};
+use embedded_alloc::SimplestHeap as Heap;
+
+#[global_allocator]
+static HEAP: Heap = Heap::empty();
+
+fn test_global_heap() {
+    assert_eq!(HEAP.used(), 0);
+
+    let mut xs: Vec<i32> = alloc::vec![1];
+    xs.push(2);
+    xs.extend(&[3, 4]);
+
+    // do not optimize xs
+    core::hint::black_box(&mut xs);
+
+    assert_eq!(xs.as_slice(), &[1, 2, 3, 4]);
+    assert!(HEAP.used() >= size_of::<i32>() * xs.len());
+}
+
+fn test_allocator_api() {
+    // small local heap
+    const HEAP_SIZE: usize = 16;
+    let mut heap_mem: [MaybeUninit<u8>; HEAP_SIZE] = [MaybeUninit::uninit(); HEAP_SIZE];
+    let local_heap: Heap = Heap::empty();
+    unsafe { local_heap.init(&raw mut heap_mem as usize, HEAP_SIZE) }
+
+    assert_eq!(local_heap.used(), 0);
+
+    let mut v: Vec<u16, Heap> = Vec::new_in(local_heap);
+    v.push(0xCAFE);
+    v.extend(&[0xDEAD, 0xFEED]);
+
+    // do not optimize v
+    core::hint::black_box(&mut v);
+
+    assert_eq!(v.as_slice(), &[0xCAFE, 0xDEAD, 0xFEED]);
+}
+
+#[entry]
+fn main() -> ! {
+    {
+        const HEAP_SIZE: usize = 1024;
+        static mut HEAP_MEM: [MaybeUninit<u8>; HEAP_SIZE] = [MaybeUninit::uninit(); HEAP_SIZE];
+        unsafe { HEAP.init(&raw mut HEAP_MEM as usize, HEAP_SIZE) }
+    }
+
+    #[allow(clippy::type_complexity)]
+    let tests: &[(fn() -> (), &'static str)] = &[
+        (test_global_heap, "test_global_heap"),
+        (test_allocator_api, "test_allocator_api"),
+    ];
+
+    for (test_fn, test_name) in tests {
+        hprintln!("{}: start", test_name);
+        test_fn();
+        hprintln!("{}: pass", test_name);
+    }
+
+    // exit QEMU with a success status
+    debug::exit(debug::EXIT_SUCCESS);
+    #[allow(clippy::empty_loop)]
+    loop {}
+}

src/lib.rs

@@ -5,10 +5,14 @@
 
 #[cfg(feature = "llff")]
 mod llff;
+#[cfg(feature = "simplest")]
+mod simplest;
 #[cfg(feature = "tlsf")]
 mod tlsf;
 
 #[cfg(feature = "llff")]
 pub use llff::Heap as LlffHeap;
+#[cfg(feature = "simplest")]
+pub use simplest::Heap as SimplestHeap;
 #[cfg(feature = "tlsf")]
 pub use tlsf::Heap as TlsfHeap;

src/simplest.rs

@@ -0,0 +1,135 @@
+use core::alloc::{GlobalAlloc, Layout};
+use core::cell::RefCell;
+use core::ptr;
+use critical_section::Mutex;
+
+/// The simplest possible heap.
+///
+/// # Safety
+///
+/// This heap does **NOT** free allocated memory.
+pub struct Heap {
+    heap: Mutex<RefCell<SimplestHeap>>,
+}
+
+impl Heap {
+    /// Create a new UNINITIALIZED heap allocator
+    ///
+    /// You must initialize this heap using the
+    /// [`init`](Self::init) method before using the allocator.
+    pub const fn empty() -> Heap {
+        Heap {
+            heap: Mutex::new(RefCell::new(SimplestHeap::empty())),
+        }
+    }
+
+    /// Initializes the heap
+    ///
+    /// This function must be called BEFORE you run any code that makes use of the
+    /// allocator.
+    ///
+    /// `start_addr` is the address where the heap will be located.
+    ///
+    /// `size` is the size of the heap in bytes.
+    ///
+    /// # Safety
+    ///
+    /// Obey these or Bad Stuff will happen.
+    ///
+    /// - This function must be called exactly ONCE.
+    /// - `size > 0`
+    pub unsafe fn init(&self, start_addr: usize, size: usize) {
+        critical_section::with(|cs| {
+            self.heap
+                .borrow(cs)
+                .borrow_mut()
+                .init(start_addr as *mut u8, size);
+        });
+    }
+
+    /// Returns an estimate of the amount of bytes in use.
+    pub fn used(&self) -> usize {
+        critical_section::with(|cs| self.heap.borrow(cs).borrow().used())
+    }
+
+    /// Returns an estimate of the amount of bytes available.
+    pub fn free(&self) -> usize {
+        critical_section::with(|cs| self.heap.borrow(cs).borrow().free())
+    }
+}
+
+unsafe impl GlobalAlloc for Heap {
+    unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
+        critical_section::with(|cs| self.heap.borrow(cs).borrow_mut().alloc(layout))
+    }
+
+    unsafe fn dealloc(&self, _ptr: *mut u8, _layout: Layout) {}
+}
+
+#[cfg(feature = "allocator_api")]
+mod allocator_api {
+    use super::*;
+    use core::alloc::{AllocError, Allocator};
+    use core::ptr::NonNull;
+
+    unsafe impl Allocator for Heap {
+        fn allocate(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
+            match layout.size() {
+                0 => Ok(NonNull::slice_from_raw_parts(layout.dangling(), 0)),
+                size => critical_section::with(|cs| {
+                    let rst = NonNull::new(self.heap.borrow(cs).borrow_mut().alloc(layout))
+                        .ok_or(AllocError)?;
+                    Ok(NonNull::slice_from_raw_parts(rst, size))
+                }),
+            }
+        }
+
+        unsafe fn deallocate(&self, _ptr: NonNull<u8>, _layout: Layout) {}
+    }
+}
+
+struct SimplestHeap {
+    arena: *mut u8,
+    remaining: usize,
+    size: usize,
+}
+
+unsafe impl Send for SimplestHeap {}
+
+impl SimplestHeap {
+    const fn empty() -> Self {
+        Self {
+            arena: ptr::null_mut(),
+            remaining: 0,
+            size: 0,
+        }
+    }
+
+    fn init(&mut self, start_addr: *mut u8, size: usize) {
+        self.arena = start_addr;
+        self.remaining = size;
+        self.size = size;
+    }
+
+    fn free(&self) -> usize {
+        self.remaining
+    }
+
+    fn used(&self) -> usize {
+        self.size - self.remaining
+    }
+
+    fn alloc(&mut self, layout: Layout) -> *mut u8 {
+        if layout.size() > self.remaining {
+            return ptr::null_mut();
+        }
+
+        // `Layout` contract forbids making a `Layout` with align=0, or align not power of 2.
+        // So we can safely use a mask to ensure alignment without worrying about UB.
+        let align_mask_to_round_down = !(layout.align() - 1);
+
+        self.remaining -= layout.size();
+        self.remaining &= align_mask_to_round_down;
+        self.arena.wrapping_add(self.remaining)
+    }
+}