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// SPDX-License-Identifier: GPL-2.0
#![allow(missing_docs)]
use super::{flags::*, AllocError, Allocator, Flags};
use core::alloc::Layout;
use core::cmp;
use core::mem;
use core::ptr;
use core::ptr::NonNull;
pub struct Cmalloc;
pub type Kmalloc = Cmalloc;
pub type Vmalloc = Kmalloc;
pub type KVmalloc = Kmalloc;
extern "C" {
#[link_name = "aligned_alloc"]
fn libc_aligned_alloc(align: usize, size: usize) -> *mut core::ffi::c_void;
#[link_name = "free"]
fn libc_free(ptr: *mut core::ffi::c_void);
}
struct CmallocData {
// The actual size as requested through `Cmalloc::alloc` or `Cmalloc::realloc`.
size: usize,
// The offset from the pointer returned to the caller of `Cmalloc::alloc` or `Cmalloc::realloc`
// to the actual base address of the allocation.
offset: usize,
}
impl Cmalloc {
/// Adjust the size and alignment such that we can additionally store `CmallocData` right
/// before the actual data described by `layout`.
///
/// Example:
///
/// For `CmallocData` assume an alignment of 8 and a size of 16.
/// For `layout` assume and alignment of 16 and a size of 64.
///
/// 0 16 32 96
/// |----------------|----------------|------------------------------------------------|
/// empty CmallocData data
///
/// For this example the returned `Layout` has an alignment of 32 and a size of 96.
fn layout_adjust(layout: Layout) -> Result<Layout, AllocError> {
let layout = layout.pad_to_align();
// Ensure that `CmallocData` fits into half the alignment. Additionally, this guarantees
// that advancing a pointer aligned to `align` by `align / 2` we still satisfy or exceed
// the alignment requested through `layout`.
let align = cmp::max(
layout.align(),
mem::size_of::<CmallocData>().next_power_of_two(),
) * 2;
// Add the additional space required for `CmallocData`.
let size = layout.size() + mem::size_of::<CmallocData>();
Ok(Layout::from_size_align(size, align)
.map_err(|_| AllocError)?
.pad_to_align())
}
fn alloc_store_data(layout: Layout) -> Result<NonNull<u8>, AllocError> {
let requested_size = layout.size();
let layout = Self::layout_adjust(layout)?;
let min_align = layout.align() / 2;
// SAFETY: Returns either NULL or a pointer to a memory allocation that satisfies or
// exceeds the given size and alignment requirements.
let raw_ptr = unsafe { libc_aligned_alloc(layout.align(), layout.size()) } as *mut u8;
let priv_ptr = NonNull::new(raw_ptr).ok_or(AllocError)?;
// SAFETY: Advance the pointer by `min_align`. The adjustments from `Self::layout_adjust`
// ensure that after this operation the original size and alignment requirements are still
// satisfied or exceeded.
let ptr = unsafe { priv_ptr.as_ptr().add(min_align) };
// SAFETY: `min_align` is greater than or equal to the size of `CmallocData`, hence we
// don't exceed the allocation boundaries.
let data_ptr: *mut CmallocData = unsafe { ptr.sub(mem::size_of::<CmallocData>()) }.cast();
let data = CmallocData {
size: requested_size,
offset: min_align,
};
// SAFETY: `data_ptr` is properly aligned and within the allocation boundaries reserved for
// `CmallocData`.
unsafe { data_ptr.write(data) };
NonNull::new(ptr).ok_or(AllocError)
}
/// # Safety
///
/// `ptr` must have been previously allocated with `Self::alloc_store_data`.
unsafe fn data<'a>(ptr: NonNull<u8>) -> &'a CmallocData {
// SAFETY: `Self::alloc_store_data` stores the `CmallocData` right before the address
// returned to callers of `Self::alloc_store_data`.
let data_ptr: *mut CmallocData =
unsafe { ptr.as_ptr().sub(mem::size_of::<CmallocData>()) }.cast();
// SAFETY: The `CmallocData` has been previously stored at this offset with
// `Self::alloc_store_data`.
unsafe { &*data_ptr }
}
/// # Safety
///
/// This function must not be called more than once for the same allocation.
///
/// `ptr` must have been previously allocated with `Self::alloc_store_data`.
unsafe fn free_read_data(ptr: NonNull<u8>) {
// SAFETY: `ptr` has been created by `Self::alloc_store_data`.
let data = unsafe { Self::data(ptr) };
// SAFETY: `ptr` has been created by `Self::alloc_store_data`.
let priv_ptr = unsafe { ptr.as_ptr().sub(data.offset) };
// SAFETY: `priv_ptr` has previously been allocatored with this `Allocator`.
unsafe { libc_free(priv_ptr.cast()) };
}
}
unsafe impl Allocator for Cmalloc {
fn alloc(layout: Layout, flags: Flags) -> Result<NonNull<[u8]>, AllocError> {
if layout.size() == 0 {
return Ok(NonNull::slice_from_raw_parts(NonNull::dangling(), 0));
}
let ptr = Self::alloc_store_data(layout)?;
if flags.contains(__GFP_ZERO) {
// SAFETY: `Self::alloc_store_data` guarantees that `ptr` points to memory of at least
// `layout.size()` bytes.
unsafe { ptr.as_ptr().write_bytes(0, layout.size()) };
}
Ok(NonNull::slice_from_raw_parts(ptr, layout.size()))
}
unsafe fn realloc(
ptr: Option<NonNull<u8>>,
layout: Layout,
flags: Flags,
) -> Result<NonNull<[u8]>, AllocError> {
let src: NonNull<u8> = if let Some(src) = ptr {
src.cast()
} else {
return Self::alloc(layout, flags);
};
if layout.size() == 0 {
// SAFETY: `src` has been created by `Self::alloc_store_data`.
unsafe { Self::free_read_data(src) };
return Ok(NonNull::slice_from_raw_parts(NonNull::dangling(), 0));
}
let dst = Self::alloc(layout, flags)?;
// SAFETY: `src` has been created by `Self::alloc_store_data`.
let data = unsafe { Self::data(src) };
// SAFETY: `src` has previously been allocated with this `Allocator`; `dst` has just been
// newly allocated. Copy up to the smaller of both sizes.
unsafe {
ptr::copy_nonoverlapping(
src.as_ptr(),
dst.as_ptr().cast(),
cmp::min(layout.size(), data.size),
)
};
// SAFETY: `src` has been created by `Self::alloc_store_data`.
unsafe { Self::free_read_data(src) };
Ok(dst)
}
}
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