113 lines
4.3 KiB
Rust
113 lines
4.3 KiB
Rust
// SPDX-License-Identifier: GPL-2.0
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//! So far the kernel's `Box` and `Vec` types can't be used by userspace test cases, since all users
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//! of those types (e.g. `CString`) use kernel allocators for instantiation.
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//!
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//! In order to allow userspace test cases to make use of such types as well, implement the
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//! `Cmalloc` allocator within the allocator_test module and type alias all kernel allocators to
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//! `Cmalloc`. The `Cmalloc` allocator uses libc's `realloc()` function as allocator backend.
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#![allow(missing_docs)]
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use super::{flags::*, AllocError, Allocator, Flags};
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use core::alloc::Layout;
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use core::cmp;
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use core::ptr;
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use core::ptr::NonNull;
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/// The userspace allocator based on libc.
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pub struct Cmalloc;
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pub type Kmalloc = Cmalloc;
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pub type Vmalloc = Kmalloc;
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pub type KVmalloc = Kmalloc;
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extern "C" {
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#[link_name = "aligned_alloc"]
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fn libc_aligned_alloc(align: usize, size: usize) -> *mut crate::ffi::c_void;
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#[link_name = "free"]
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fn libc_free(ptr: *mut crate::ffi::c_void);
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}
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// SAFETY:
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// - memory remains valid until it is explicitly freed,
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// - passing a pointer to a valid memory allocation created by this `Allocator` is always OK,
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// - `realloc` provides the guarantees as provided in the `# Guarantees` section.
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unsafe impl Allocator for Cmalloc {
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unsafe fn realloc(
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ptr: Option<NonNull<u8>>,
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layout: Layout,
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old_layout: Layout,
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flags: Flags,
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) -> Result<NonNull<[u8]>, AllocError> {
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let src = match ptr {
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Some(src) => {
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if old_layout.size() == 0 {
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ptr::null_mut()
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} else {
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src.as_ptr()
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}
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}
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None => ptr::null_mut(),
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};
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if layout.size() == 0 {
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// SAFETY: `src` is either NULL or was previously allocated with this `Allocator`
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unsafe { libc_free(src.cast()) };
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return Ok(NonNull::slice_from_raw_parts(
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crate::alloc::dangling_from_layout(layout),
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0,
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));
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}
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// ISO C (ISO/IEC 9899:2011) defines `aligned_alloc`:
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//
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// > The value of alignment shall be a valid alignment supported by the implementation
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// [...].
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//
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// As an example of the "supported by the implementation" requirement, POSIX.1-2001 (IEEE
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// 1003.1-2001) defines `posix_memalign`:
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//
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// > The value of alignment shall be a power of two multiple of sizeof (void *).
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//
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// and POSIX-based implementations of `aligned_alloc` inherit this requirement. At the time
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// of writing, this is known to be the case on macOS (but not in glibc).
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//
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// Satisfy the stricter requirement to avoid spurious test failures on some platforms.
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let min_align = core::mem::size_of::<*const crate::ffi::c_void>();
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let layout = layout.align_to(min_align).map_err(|_| AllocError)?;
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let layout = layout.pad_to_align();
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// SAFETY: Returns either NULL or a pointer to a memory allocation that satisfies or
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// exceeds the given size and alignment requirements.
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let dst = unsafe { libc_aligned_alloc(layout.align(), layout.size()) } as *mut u8;
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let dst = NonNull::new(dst).ok_or(AllocError)?;
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if flags.contains(__GFP_ZERO) {
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// SAFETY: The preceding calls to `libc_aligned_alloc` and `NonNull::new`
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// guarantee that `dst` points to memory of at least `layout.size()` bytes.
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unsafe { dst.as_ptr().write_bytes(0, layout.size()) };
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}
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if !src.is_null() {
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// SAFETY:
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// - `src` has previously been allocated with this `Allocator`; `dst` has just been
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// newly allocated, hence the memory regions do not overlap.
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// - both` src` and `dst` are properly aligned and valid for reads and writes
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unsafe {
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ptr::copy_nonoverlapping(
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src,
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dst.as_ptr(),
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cmp::min(layout.size(), old_layout.size()),
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)
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};
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}
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// SAFETY: `src` is either NULL or was previously allocated with this `Allocator`
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unsafe { libc_free(src.cast()) };
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Ok(NonNull::slice_from_raw_parts(dst, layout.size()))
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}
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}
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