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// SPDX-License-Identifier: GPL-2.0
//! Allocator support.
use core::alloc::{GlobalAlloc, Layout};
use core::ptr;
use crate::bindings;
struct KernelAllocator;
/// Calls `krealloc` with a proper size to alloc a new object aligned to `new_layout`'s alignment.
///
/// # Safety
///
/// - `ptr` can be either null or a pointer which has been allocated by this allocator.
/// - `new_layout` must have a non-zero size.
unsafe fn krealloc_aligned(ptr: *mut u8, new_layout: Layout, flags: bindings::gfp_t) -> *mut u8 {
// Customized layouts from `Layout::from_size_align()` can have size < align, so pad first.
let layout = new_layout.pad_to_align();
let mut size = layout.size();
if layout.align() > bindings::BINDINGS_ARCH_SLAB_MINALIGN {
// The alignment requirement exceeds the slab guarantee, thus try to enlarge the size
// to use the "power-of-two" size/alignment guarantee (see comments in `kmalloc()` for
// more information).
//
// Note that `layout.size()` (after padding) is guaranteed to be a multiple of
// `layout.align()`, so `next_power_of_two` gives enough alignment guarantee.
size = size.next_power_of_two();
}
// SAFETY:
// - `ptr` is either null or a pointer returned from a previous `k{re}alloc()` by the
// function safety requirement.
// - `size` is greater than 0 since it's either a `layout.size()` (which cannot be zero
// according to the function safety requirement) or a result from `next_power_of_two()`.
unsafe { bindings::krealloc(ptr as *const core::ffi::c_void, size, flags) as *mut u8 }
}
unsafe impl GlobalAlloc for KernelAllocator {
unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
// `krealloc()` is used instead of `kmalloc()` because the latter is
// an inline function and cannot be bound to as a result.
unsafe { bindings::krealloc(ptr::null(), layout.size(), bindings::GFP_KERNEL) as *mut u8 }
}
unsafe fn dealloc(&self, ptr: *mut u8, _layout: Layout) {
unsafe {
bindings::kfree(ptr as *const core::ffi::c_void);
}
}
}
#[global_allocator]
static ALLOCATOR: KernelAllocator = KernelAllocator;
// `rustc` only generates these for some crate types. Even then, we would need
// to extract the object file that has them from the archive. For the moment,
// let's generate them ourselves instead.
//
// Note: Although these are *safe* functions, they are called by the compiler
// with parameters that obey the same `GlobalAlloc` function safety
// requirements: size and align should form a valid layout, and size is
// greater than 0.
//
// Note that `#[no_mangle]` implies exported too, nowadays.
#[no_mangle]
fn __rust_alloc(size: usize, align: usize) -> *mut u8 {
// SAFETY: See assumption above.
let layout = unsafe { Layout::from_size_align_unchecked(size, align) };
// SAFETY: `ptr::null_mut()` is null, per assumption above the size of `layout` is greater
// than 0.
unsafe { krealloc_aligned(ptr::null_mut(), layout, bindings::GFP_KERNEL) }
}
#[no_mangle]
fn __rust_dealloc(ptr: *mut u8, _size: usize, _align: usize) {
unsafe { bindings::kfree(ptr as *const core::ffi::c_void) };
}
#[no_mangle]
fn __rust_realloc(ptr: *mut u8, _old_size: usize, align: usize, new_size: usize) -> *mut u8 {
// SAFETY: See assumption above.
let new_layout = unsafe { Layout::from_size_align_unchecked(new_size, align) };
// SAFETY: Per assumption above, `ptr` is allocated by `__rust_*` before, and the size of
// `new_layout` is greater than 0.
unsafe { krealloc_aligned(ptr, new_layout, bindings::GFP_KERNEL) }
}
#[no_mangle]
fn __rust_alloc_zeroed(size: usize, align: usize) -> *mut u8 {
// SAFETY: See assumption above.
let layout = unsafe { Layout::from_size_align_unchecked(size, align) };
// SAFETY: `ptr::null_mut()` is null, per assumption above the size of `layout` is greater
// than 0.
unsafe {
krealloc_aligned(
ptr::null_mut(),
layout,
bindings::GFP_KERNEL | bindings::__GFP_ZERO,
)
}
}
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