1// SPDX-License-Identifier: GPL-2.0
 2
 3//! So far the kernel's `Box` and `Vec` types can't be used by userspace test cases, since all users
 4//! of those types (e.g. `CString`) use kernel allocators for instantiation.
 5//!
 6//! In order to allow userspace test cases to make use of such types as well, implement the
 7//! `Cmalloc` allocator within the allocator_test module and type alias all kernel allocators to
 8//! `Cmalloc`. The `Cmalloc` allocator uses libc's `realloc()` function as allocator backend.
 9
10#![allow(missing_docs)]
11
12use super::{flags::*, AllocError, Allocator, Flags};
13use core::alloc::Layout;
14use core::cmp;
15use core::ptr;
16use core::ptr::NonNull;
17
18/// The userspace allocator based on libc.
19pub struct Cmalloc;
20
21pub type Kmalloc = Cmalloc;
22pub type Vmalloc = Kmalloc;
23pub type KVmalloc = Kmalloc;
24
25extern "C" {
26    #[link_name = "aligned_alloc"]
27    fn libc_aligned_alloc(align: usize, size: usize) -> *mut crate::ffi::c_void;
28
29    #[link_name = "free"]
30    fn libc_free(ptr: *mut crate::ffi::c_void);
31}
32
33// SAFETY:
34// - memory remains valid until it is explicitly freed,
35// - passing a pointer to a valid memory allocation created by this `Allocator` is always OK,
36// - `realloc` provides the guarantees as provided in the `# Guarantees` section.
37unsafe impl Allocator for Cmalloc {
38    unsafe fn realloc(
39        ptr: Option<NonNull<u8>>,
40        layout: Layout,
41        old_layout: Layout,
42        flags: Flags,
43    ) -> Result<NonNull<[u8]>, AllocError> {
44        let src = match ptr {
45            Some(src) => {
46                if old_layout.size() == 0 {
47                    ptr::null_mut()
48                } else {
49                    src.as_ptr()
50                }
51            }
52            None => ptr::null_mut(),
53        };
54
55        if layout.size() == 0 {
56            // SAFETY: `src` is either NULL or was previously allocated with this `Allocator`
57            unsafe { libc_free(src.cast()) };
58
59            return Ok(NonNull::slice_from_raw_parts(
60                crate::alloc::dangling_from_layout(layout),
61                0,
62            ));
63        }
64
65        // SAFETY: Returns either NULL or a pointer to a memory allocation that satisfies or
66        // exceeds the given size and alignment requirements.
67        let dst = unsafe { libc_aligned_alloc(layout.align(), layout.size()) } as *mut u8;
68        let dst = NonNull::new(dst).ok_or(AllocError)?;
69
70        if flags.contains(__GFP_ZERO) {
71            // SAFETY: The preceding calls to `libc_aligned_alloc` and `NonNull::new`
72            // guarantee that `dst` points to memory of at least `layout.size()` bytes.
73            unsafe { dst.as_ptr().write_bytes(0, layout.size()) };
74        }
75
76        if !src.is_null() {
77            // SAFETY:
78            // - `src` has previously been allocated with this `Allocator`; `dst` has just been
79            //   newly allocated, hence the memory regions do not overlap.
80            // - both` src` and `dst` are properly aligned and valid for reads and writes
81            unsafe {
82                ptr::copy_nonoverlapping(
83                    src,
84                    dst.as_ptr(),
85                    cmp::min(layout.size(), old_layout.size()),
86                )
87            };
88        }
89
90        // SAFETY: `src` is either NULL or was previously allocated with this `Allocator`
91        unsafe { libc_free(src.cast()) };
92
93        Ok(NonNull::slice_from_raw_parts(dst, layout.size()))
94    }
95}