sel4_newlib/
heap.rs

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1//
2// Copyright 2023, Colias Group, LLC
3//
4// SPDX-License-Identifier: BSD-2-Clause
5//
6
7use core::cell::UnsafeCell;
8use core::ffi::{c_int, c_void};
9use core::sync::atomic::{AtomicIsize, Ordering};
10
11use sel4_panicking_env::abort;
12
13use crate::errno;
14
15// NOTE(rustc_wishlist) use SyncUnsafeCell once #![feature(sync_unsafe_cell)] stabilizes
16#[repr(align(4096))] // no real reason for this
17struct BackingMemory<const N: usize>(UnsafeCell<[u8; N]>);
18
19unsafe impl<const N: usize> Sync for BackingMemory<N> {}
20
21impl<const N: usize> BackingMemory<N> {
22    const fn new() -> Self {
23        Self(UnsafeCell::new([0; N]))
24    }
25
26    const fn start(&self) -> *mut u8 {
27        self.0.get().cast()
28    }
29
30    const fn size(&self) -> usize {
31        N
32    }
33}
34
35#[doc(hidden)]
36pub struct StaticHeap<const N: usize> {
37    memory: BackingMemory<N>,
38    watermark: AtomicIsize,
39}
40
41unsafe impl<const N: usize> Sync for StaticHeap<N> {}
42
43impl<const N: usize> StaticHeap<N> {
44    pub const fn new() -> Self {
45        Self {
46            memory: BackingMemory::new(),
47            watermark: AtomicIsize::new(0),
48        }
49    }
50
51    // TODO handle overflowing atomic
52    pub fn sbrk(&self, incr: c_int) -> *mut c_void {
53        #[cfg(feature = "log")]
54        {
55            log::trace!("_sbrk({})", incr);
56        }
57        let incr = incr.try_into().unwrap_or_else(|_| abort!());
58        let old = self.watermark.fetch_add(incr, Ordering::SeqCst);
59        let new = old + incr;
60        if new < 0 {
61            abort!("program break below data segment start")
62        }
63        if new > self.memory.size().try_into().unwrap_or_else(|_| abort!()) {
64            self.watermark.fetch_sub(incr, Ordering::SeqCst);
65            errno::set_errno(errno::values::ENOMEM);
66            return usize::MAX as *mut c_void;
67        }
68        self.memory.start().wrapping_offset(old).cast::<c_void>()
69    }
70}
71
72impl<const N: usize> Default for StaticHeap<N> {
73    fn default() -> Self {
74        Self::new()
75    }
76}
77
78#[macro_export]
79macro_rules! declare_sbrk_with_static_heap {
80    ($n:expr) => {
81        #[no_mangle]
82        extern "C" fn _sbrk(incr: core::ffi::c_int) -> *mut core::ffi::c_void {
83            static HEAP: $crate::StaticHeap<{ $n }> = $crate::StaticHeap::new();
84            HEAP.sbrk(incr)
85        }
86    };
87}
sel4_newlib/heap.rs

sel4_newlib/
heap.rs
