projects/linux·blob ea78c190 · 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
25impl Cmalloc {
26 /// Returns a [`Layout`] that makes [`Kmalloc`] fulfill the requested size and alignment of
27 /// `layout`.
28 pub fn aligned_layout(layout: Layout) -> Layout {
29 // Note that `layout.size()` (after padding) is guaranteed to be a multiple of
30 // `layout.align()` which together with the slab guarantees means that `Kmalloc` will return
31 // a properly aligned object (see comments in `kmalloc()` for more information).
32 layout.pad_to_align()
33 }
34}
35
36extern "C" {
37 #[link_name = "aligned_alloc"]
38 fn libc_aligned_alloc(align: usize, size: usize) -> *mut crate::ffi::c_void;
39
40 #[link_name = "free"]
41 fn libc_free(ptr: *mut crate::ffi::c_void);
42}
43
44// SAFETY:
45// - memory remains valid until it is explicitly freed,
46// - passing a pointer to a valid memory allocation created by this `Allocator` is always OK,
47// - `realloc` provides the guarantees as provided in the `# Guarantees` section.
48unsafe impl Allocator for Cmalloc {
49 unsafe fn realloc(
50 ptr: Option<NonNull<u8>>,
51 layout: Layout,
52 old_layout: Layout,
53 flags: Flags,
54 ) -> Result<NonNull<[u8]>, AllocError> {
55 let src = match ptr {
56 Some(src) => {
57 if old_layout.size() == 0 {
58 ptr::null_mut()
59 } else {
60 src.as_ptr()
61 }
62 }
63 None => ptr::null_mut(),
64 };
65
66 if layout.size() == 0 {
67 // SAFETY: `src` is either NULL or was previously allocated with this `Allocator`
68 unsafe { libc_free(src.cast()) };
69
70 return Ok(NonNull::slice_from_raw_parts(
71 crate::alloc::dangling_from_layout(layout),
72 0,
73 ));
74 }
75
76 // ISO C (ISO/IEC 9899:2011) defines `aligned_alloc`:
77 //
78 // > The value of alignment shall be a valid alignment supported by the implementation
79 // [...].
80 //
81 // As an example of the "supported by the implementation" requirement, POSIX.1-2001 (IEEE
82 // 1003.1-2001) defines `posix_memalign`:
83 //
84 // > The value of alignment shall be a power of two multiple of sizeof (void *).
85 //
86 // and POSIX-based implementations of `aligned_alloc` inherit this requirement. At the time
87 // of writing, this is known to be the case on macOS (but not in glibc).
88 //
89 // Satisfy the stricter requirement to avoid spurious test failures on some platforms.
90 let min_align = core::mem::size_of::<*const crate::ffi::c_void>();
91 let layout = layout.align_to(min_align).map_err(|_| AllocError)?;
92 let layout = layout.pad_to_align();
93
94 // SAFETY: Returns either NULL or a pointer to a memory allocation that satisfies or
95 // exceeds the given size and alignment requirements.
96 let dst = unsafe { libc_aligned_alloc(layout.align(), layout.size()) }.cast::<u8>();
97 let dst = NonNull::new(dst).ok_or(AllocError)?;
98
99 if flags.contains(__GFP_ZERO) {
100 // SAFETY: The preceding calls to `libc_aligned_alloc` and `NonNull::new`
101 // guarantee that `dst` points to memory of at least `layout.size()` bytes.
102 unsafe { dst.as_ptr().write_bytes(0, layout.size()) };
103 }
104
105 if !src.is_null() {
106 // SAFETY:
107 // - `src` has previously been allocated with this `Allocator`; `dst` has just been
108 // newly allocated, hence the memory regions do not overlap.
109 // - both` src` and `dst` are properly aligned and valid for reads and writes
110 unsafe {
111 ptr::copy_nonoverlapping(
112 src,
113 dst.as_ptr(),
114 cmp::min(layout.size(), old_layout.size()),
115 )
116 };
117 }
118
119 // SAFETY: `src` is either NULL or was previously allocated with this `Allocator`
120 unsafe { libc_free(src.cast()) };
121
122 Ok(NonNull::slice_from_raw_parts(dst, layout.size()))
123 }
124}