projects/linux·blob 4a95bc12 · refs

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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 // ISO C (ISO/IEC 9899:2011) defines `aligned_alloc`:
66 //
67 // > The value of alignment shall be a valid alignment supported by the implementation
68 // [...].
69 //
70 // As an example of the "supported by the implementation" requirement, POSIX.1-2001 (IEEE
71 // 1003.1-2001) defines `posix_memalign`:
72 //
73 // > The value of alignment shall be a power of two multiple of sizeof (void *).
74 //
75 // and POSIX-based implementations of `aligned_alloc` inherit this requirement. At the time
76 // of writing, this is known to be the case on macOS (but not in glibc).
77 //
78 // Satisfy the stricter requirement to avoid spurious test failures on some platforms.
79 let min_align = core::mem::size_of::<*const crate::ffi::c_void>();
80 let layout = layout.align_to(min_align).map_err(|_| AllocError)?;
81 let layout = layout.pad_to_align();
82
83 // SAFETY: Returns either NULL or a pointer to a memory allocation that satisfies or
84 // exceeds the given size and alignment requirements.
85 let dst = unsafe { libc_aligned_alloc(layout.align(), layout.size()) } as *mut u8;
86 let dst = NonNull::new(dst).ok_or(AllocError)?;
87
88 if flags.contains(__GFP_ZERO) {
89 // SAFETY: The preceding calls to `libc_aligned_alloc` and `NonNull::new`
90 // guarantee that `dst` points to memory of at least `layout.size()` bytes.
91 unsafe { dst.as_ptr().write_bytes(0, layout.size()) };
92 }
93
94 if !src.is_null() {
95 // SAFETY:
96 // - `src` has previously been allocated with this `Allocator`; `dst` has just been
97 // newly allocated, hence the memory regions do not overlap.
98 // - both` src` and `dst` are properly aligned and valid for reads and writes
99 unsafe {
100 ptr::copy_nonoverlapping(
101 src,
102 dst.as_ptr(),
103 cmp::min(layout.size(), old_layout.size()),
104 )
105 };
106 }
107
108 // SAFETY: `src` is either NULL or was previously allocated with this `Allocator`
109 unsafe { libc_free(src.cast()) };
110
111 Ok(NonNull::slice_from_raw_parts(dst, layout.size()))
112 }
113}