projects/linux·blob v6.6-rc3 · refs

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1// SPDX-License-Identifier: Apache-2.0 OR MIT
2
3//! Memory allocation APIs
4
5#![stable(feature = "alloc_module", since = "1.28.0")]
6
7#[cfg(not(test))]
8use core::intrinsics;
9use core::intrinsics::{min_align_of_val, size_of_val};
10
11use core::ptr::Unique;
12#[cfg(not(test))]
13use core::ptr::{self, NonNull};
14
15#[stable(feature = "alloc_module", since = "1.28.0")]
16#[doc(inline)]
17pub use core::alloc::*;
18
19#[cfg(test)]
20mod tests;
21
22extern "Rust" {
23 // These are the magic symbols to call the global allocator. rustc generates
24 // them to call `__rg_alloc` etc. if there is a `#[global_allocator]` attribute
25 // (the code expanding that attribute macro generates those functions), or to call
26 // the default implementations in std (`__rdl_alloc` etc. in `library/std/src/alloc.rs`)
27 // otherwise.
28 // The rustc fork of LLVM 14 and earlier also special-cases these function names to be able to optimize them
29 // like `malloc`, `realloc`, and `free`, respectively.
30 #[rustc_allocator]
31 #[rustc_nounwind]
32 fn __rust_alloc(size: usize, align: usize) -> *mut u8;
33 #[rustc_deallocator]
34 #[rustc_nounwind]
35 fn __rust_dealloc(ptr: *mut u8, size: usize, align: usize);
36 #[rustc_reallocator]
37 #[rustc_nounwind]
38 fn __rust_realloc(ptr: *mut u8, old_size: usize, align: usize, new_size: usize) -> *mut u8;
39 #[rustc_allocator_zeroed]
40 #[rustc_nounwind]
41 fn __rust_alloc_zeroed(size: usize, align: usize) -> *mut u8;
42
43 #[cfg(not(bootstrap))]
44 static __rust_no_alloc_shim_is_unstable: u8;
45}
46
47/// The global memory allocator.
48///
49/// This type implements the [`Allocator`] trait by forwarding calls
50/// to the allocator registered with the `#[global_allocator]` attribute
51/// if there is one, or the `std` crate’s default.
52///
53/// Note: while this type is unstable, the functionality it provides can be
54/// accessed through the [free functions in `alloc`](self#functions).
55#[unstable(feature = "allocator_api", issue = "32838")]
56#[derive(Copy, Clone, Default, Debug)]
57#[cfg(not(test))]
58pub struct Global;
59
60#[cfg(test)]
61pub use std::alloc::Global;
62
63/// Allocate memory with the global allocator.
64///
65/// This function forwards calls to the [`GlobalAlloc::alloc`] method
66/// of the allocator registered with the `#[global_allocator]` attribute
67/// if there is one, or the `std` crate’s default.
68///
69/// This function is expected to be deprecated in favor of the `alloc` method
70/// of the [`Global`] type when it and the [`Allocator`] trait become stable.
71///
72/// # Safety
73///
74/// See [`GlobalAlloc::alloc`].
75///
76/// # Examples
77///
78/// ```
79/// use std::alloc::{alloc, dealloc, handle_alloc_error, Layout};
80///
81/// unsafe {
82/// let layout = Layout::new::<u16>();
83/// let ptr = alloc(layout);
84/// if ptr.is_null() {
85/// handle_alloc_error(layout);
86/// }
87///
88/// *(ptr as *mut u16) = 42;
89/// assert_eq!(*(ptr as *mut u16), 42);
90///
91/// dealloc(ptr, layout);
92/// }
93/// ```
94#[stable(feature = "global_alloc", since = "1.28.0")]
95#[must_use = "losing the pointer will leak memory"]
96#[inline]
97pub unsafe fn alloc(layout: Layout) -> *mut u8 {
98 unsafe {
99 // Make sure we don't accidentally allow omitting the allocator shim in
100 // stable code until it is actually stabilized.
101 #[cfg(not(bootstrap))]
102 core::ptr::read_volatile(&__rust_no_alloc_shim_is_unstable);
103
104 __rust_alloc(layout.size(), layout.align())
105 }
106}
107
108/// Deallocate memory with the global allocator.
109///
110/// This function forwards calls to the [`GlobalAlloc::dealloc`] method
111/// of the allocator registered with the `#[global_allocator]` attribute
112/// if there is one, or the `std` crate’s default.
113///
114/// This function is expected to be deprecated in favor of the `dealloc` method
115/// of the [`Global`] type when it and the [`Allocator`] trait become stable.
116///
117/// # Safety
118///
119/// See [`GlobalAlloc::dealloc`].
120#[stable(feature = "global_alloc", since = "1.28.0")]
121#[inline]
122pub unsafe fn dealloc(ptr: *mut u8, layout: Layout) {
123 unsafe { __rust_dealloc(ptr, layout.size(), layout.align()) }
124}
125
126/// Reallocate memory with the global allocator.
127///
128/// This function forwards calls to the [`GlobalAlloc::realloc`] method
129/// of the allocator registered with the `#[global_allocator]` attribute
130/// if there is one, or the `std` crate’s default.
131///
132/// This function is expected to be deprecated in favor of the `realloc` method
133/// of the [`Global`] type when it and the [`Allocator`] trait become stable.
134///
135/// # Safety
136///
137/// See [`GlobalAlloc::realloc`].
138#[stable(feature = "global_alloc", since = "1.28.0")]
139#[must_use = "losing the pointer will leak memory"]
140#[inline]
141pub unsafe fn realloc(ptr: *mut u8, layout: Layout, new_size: usize) -> *mut u8 {
142 unsafe { __rust_realloc(ptr, layout.size(), layout.align(), new_size) }
143}
144
145/// Allocate zero-initialized memory with the global allocator.
146///
147/// This function forwards calls to the [`GlobalAlloc::alloc_zeroed`] method
148/// of the allocator registered with the `#[global_allocator]` attribute
149/// if there is one, or the `std` crate’s default.
150///
151/// This function is expected to be deprecated in favor of the `alloc_zeroed` method
152/// of the [`Global`] type when it and the [`Allocator`] trait become stable.
153///
154/// # Safety
155///
156/// See [`GlobalAlloc::alloc_zeroed`].
157///
158/// # Examples
159///
160/// ```
161/// use std::alloc::{alloc_zeroed, dealloc, Layout};
162///
163/// unsafe {
164/// let layout = Layout::new::<u16>();
165/// let ptr = alloc_zeroed(layout);
166///
167/// assert_eq!(*(ptr as *mut u16), 0);
168///
169/// dealloc(ptr, layout);
170/// }
171/// ```
172#[stable(feature = "global_alloc", since = "1.28.0")]
173#[must_use = "losing the pointer will leak memory"]
174#[inline]
175pub unsafe fn alloc_zeroed(layout: Layout) -> *mut u8 {
176 unsafe { __rust_alloc_zeroed(layout.size(), layout.align()) }
177}
178
179#[cfg(not(test))]
180impl Global {
181 #[inline]
182 fn alloc_impl(&self, layout: Layout, zeroed: bool) -> Result<NonNull<[u8]>, AllocError> {
183 match layout.size() {
184 0 => Ok(NonNull::slice_from_raw_parts(layout.dangling(), 0)),
185 // SAFETY: `layout` is non-zero in size,
186 size => unsafe {
187 let raw_ptr = if zeroed { alloc_zeroed(layout) } else { alloc(layout) };
188 let ptr = NonNull::new(raw_ptr).ok_or(AllocError)?;
189 Ok(NonNull::slice_from_raw_parts(ptr, size))
190 },
191 }
192 }
193
194 // SAFETY: Same as `Allocator::grow`
195 #[inline]
196 unsafe fn grow_impl(
197 &self,
198 ptr: NonNull<u8>,
199 old_layout: Layout,
200 new_layout: Layout,
201 zeroed: bool,
202 ) -> Result<NonNull<[u8]>, AllocError> {
203 debug_assert!(
204 new_layout.size() >= old_layout.size(),
205 "`new_layout.size()` must be greater than or equal to `old_layout.size()`"
206 );
207
208 match old_layout.size() {
209 0 => self.alloc_impl(new_layout, zeroed),
210
211 // SAFETY: `new_size` is non-zero as `old_size` is greater than or equal to `new_size`
212 // as required by safety conditions. Other conditions must be upheld by the caller
213 old_size if old_layout.align() == new_layout.align() => unsafe {
214 let new_size = new_layout.size();
215
216 // `realloc` probably checks for `new_size >= old_layout.size()` or something similar.
217 intrinsics::assume(new_size >= old_layout.size());
218
219 let raw_ptr = realloc(ptr.as_ptr(), old_layout, new_size);
220 let ptr = NonNull::new(raw_ptr).ok_or(AllocError)?;
221 if zeroed {
222 raw_ptr.add(old_size).write_bytes(0, new_size - old_size);
223 }
224 Ok(NonNull::slice_from_raw_parts(ptr, new_size))
225 },
226
227 // SAFETY: because `new_layout.size()` must be greater than or equal to `old_size`,
228 // both the old and new memory allocation are valid for reads and writes for `old_size`
229 // bytes. Also, because the old allocation wasn't yet deallocated, it cannot overlap
230 // `new_ptr`. Thus, the call to `copy_nonoverlapping` is safe. The safety contract
231 // for `dealloc` must be upheld by the caller.
232 old_size => unsafe {
233 let new_ptr = self.alloc_impl(new_layout, zeroed)?;
234 ptr::copy_nonoverlapping(ptr.as_ptr(), new_ptr.as_mut_ptr(), old_size);
235 self.deallocate(ptr, old_layout);
236 Ok(new_ptr)
237 },
238 }
239 }
240}
241
242#[unstable(feature = "allocator_api", issue = "32838")]
243#[cfg(not(test))]
244unsafe impl Allocator for Global {
245 #[inline]
246 fn allocate(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
247 self.alloc_impl(layout, false)
248 }
249
250 #[inline]
251 fn allocate_zeroed(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
252 self.alloc_impl(layout, true)
253 }
254
255 #[inline]
256 unsafe fn deallocate(&self, ptr: NonNull<u8>, layout: Layout) {
257 if layout.size() != 0 {
258 // SAFETY: `layout` is non-zero in size,
259 // other conditions must be upheld by the caller
260 unsafe { dealloc(ptr.as_ptr(), layout) }
261 }
262 }
263
264 #[inline]
265 unsafe fn grow(
266 &self,
267 ptr: NonNull<u8>,
268 old_layout: Layout,
269 new_layout: Layout,
270 ) -> Result<NonNull<[u8]>, AllocError> {
271 // SAFETY: all conditions must be upheld by the caller
272 unsafe { self.grow_impl(ptr, old_layout, new_layout, false) }
273 }
274
275 #[inline]
276 unsafe fn grow_zeroed(
277 &self,
278 ptr: NonNull<u8>,
279 old_layout: Layout,
280 new_layout: Layout,
281 ) -> Result<NonNull<[u8]>, AllocError> {
282 // SAFETY: all conditions must be upheld by the caller
283 unsafe { self.grow_impl(ptr, old_layout, new_layout, true) }
284 }
285
286 #[inline]
287 unsafe fn shrink(
288 &self,
289 ptr: NonNull<u8>,
290 old_layout: Layout,
291 new_layout: Layout,
292 ) -> Result<NonNull<[u8]>, AllocError> {
293 debug_assert!(
294 new_layout.size() <= old_layout.size(),
295 "`new_layout.size()` must be smaller than or equal to `old_layout.size()`"
296 );
297
298 match new_layout.size() {
299 // SAFETY: conditions must be upheld by the caller
300 0 => unsafe {
301 self.deallocate(ptr, old_layout);
302 Ok(NonNull::slice_from_raw_parts(new_layout.dangling(), 0))
303 },
304
305 // SAFETY: `new_size` is non-zero. Other conditions must be upheld by the caller
306 new_size if old_layout.align() == new_layout.align() => unsafe {
307 // `realloc` probably checks for `new_size <= old_layout.size()` or something similar.
308 intrinsics::assume(new_size <= old_layout.size());
309
310 let raw_ptr = realloc(ptr.as_ptr(), old_layout, new_size);
311 let ptr = NonNull::new(raw_ptr).ok_or(AllocError)?;
312 Ok(NonNull::slice_from_raw_parts(ptr, new_size))
313 },
314
315 // SAFETY: because `new_size` must be smaller than or equal to `old_layout.size()`,
316 // both the old and new memory allocation are valid for reads and writes for `new_size`
317 // bytes. Also, because the old allocation wasn't yet deallocated, it cannot overlap
318 // `new_ptr`. Thus, the call to `copy_nonoverlapping` is safe. The safety contract
319 // for `dealloc` must be upheld by the caller.
320 new_size => unsafe {
321 let new_ptr = self.allocate(new_layout)?;
322 ptr::copy_nonoverlapping(ptr.as_ptr(), new_ptr.as_mut_ptr(), new_size);
323 self.deallocate(ptr, old_layout);
324 Ok(new_ptr)
325 },
326 }
327 }
328}
329
330/// The allocator for unique pointers.
331#[cfg(all(not(no_global_oom_handling), not(test)))]
332#[lang = "exchange_malloc"]
333#[inline]
334unsafe fn exchange_malloc(size: usize, align: usize) -> *mut u8 {
335 let layout = unsafe { Layout::from_size_align_unchecked(size, align) };
336 match Global.allocate(layout) {
337 Ok(ptr) => ptr.as_mut_ptr(),
338 Err(_) => handle_alloc_error(layout),
339 }
340}
341
342#[cfg_attr(not(test), lang = "box_free")]
343#[inline]
344// This signature has to be the same as `Box`, otherwise an ICE will happen.
345// When an additional parameter to `Box` is added (like `A: Allocator`), this has to be added here as
346// well.
347// For example if `Box` is changed to `struct Box<T: ?Sized, A: Allocator>(Unique<T>, A)`,
348// this function has to be changed to `fn box_free<T: ?Sized, A: Allocator>(Unique<T>, A)` as well.
349pub(crate) unsafe fn box_free<T: ?Sized, A: Allocator>(ptr: Unique<T>, alloc: A) {
350 unsafe {
351 let size = size_of_val(ptr.as_ref());
352 let align = min_align_of_val(ptr.as_ref());
353 let layout = Layout::from_size_align_unchecked(size, align);
354 alloc.deallocate(From::from(ptr.cast()), layout)
355 }
356}
357
358// # Allocation error handler
359
360#[cfg(not(no_global_oom_handling))]
361extern "Rust" {
362 // This is the magic symbol to call the global alloc error handler. rustc generates
363 // it to call `__rg_oom` if there is a `#[alloc_error_handler]`, or to call the
364 // default implementations below (`__rdl_oom`) otherwise.
365 fn __rust_alloc_error_handler(size: usize, align: usize) -> !;
366}
367
368/// Abort on memory allocation error or failure.
369///
370/// Callers of memory allocation APIs wishing to abort computation
371/// in response to an allocation error are encouraged to call this function,
372/// rather than directly invoking `panic!` or similar.
373///
374/// The default behavior of this function is to print a message to standard error
375/// and abort the process.
376/// It can be replaced with [`set_alloc_error_hook`] and [`take_alloc_error_hook`].
377///
378/// [`set_alloc_error_hook`]: ../../std/alloc/fn.set_alloc_error_hook.html
379/// [`take_alloc_error_hook`]: ../../std/alloc/fn.take_alloc_error_hook.html
380#[stable(feature = "global_alloc", since = "1.28.0")]
381#[rustc_const_unstable(feature = "const_alloc_error", issue = "92523")]
382#[cfg(all(not(no_global_oom_handling), not(test)))]
383#[cold]
384pub const fn handle_alloc_error(layout: Layout) -> ! {
385 const fn ct_error(_: Layout) -> ! {
386 panic!("allocation failed");
387 }
388
389 fn rt_error(layout: Layout) -> ! {
390 unsafe {
391 __rust_alloc_error_handler(layout.size(), layout.align());
392 }
393 }
394
395 unsafe { core::intrinsics::const_eval_select((layout,), ct_error, rt_error) }
396}
397
398// For alloc test `std::alloc::handle_alloc_error` can be used directly.
399#[cfg(all(not(no_global_oom_handling), test))]
400pub use std::alloc::handle_alloc_error;
401
402#[cfg(all(not(no_global_oom_handling), not(test)))]
403#[doc(hidden)]
404#[allow(unused_attributes)]
405#[unstable(feature = "alloc_internals", issue = "none")]
406pub mod __alloc_error_handler {
407 // called via generated `__rust_alloc_error_handler` if there is no
408 // `#[alloc_error_handler]`.
409 #[rustc_std_internal_symbol]
410 pub unsafe fn __rdl_oom(size: usize, _align: usize) -> ! {
411 extern "Rust" {
412 // This symbol is emitted by rustc next to __rust_alloc_error_handler.
413 // Its value depends on the -Zoom={panic,abort} compiler option.
414 static __rust_alloc_error_handler_should_panic: u8;
415 }
416
417 #[allow(unused_unsafe)]
418 if unsafe { __rust_alloc_error_handler_should_panic != 0 } {
419 panic!("memory allocation of {size} bytes failed")
420 } else {
421 core::panicking::panic_nounwind_fmt(format_args!(
422 "memory allocation of {size} bytes failed"
423 ))
424 }
425 }
426}
427
428/// Specialize clones into pre-allocated, uninitialized memory.
429/// Used by `Box::clone` and `Rc`/`Arc::make_mut`.
430pub(crate) trait WriteCloneIntoRaw: Sized {
431 unsafe fn write_clone_into_raw(&self, target: *mut Self);
432}
433
434impl<T: Clone> WriteCloneIntoRaw for T {
435 #[inline]
436 default unsafe fn write_clone_into_raw(&self, target: *mut Self) {
437 // Having allocated *first* may allow the optimizer to create
438 // the cloned value in-place, skipping the local and move.
439 unsafe { target.write(self.clone()) };
440 }
441}
442
443impl<T: Copy> WriteCloneIntoRaw for T {
444 #[inline]
445 unsafe fn write_clone_into_raw(&self, target: *mut Self) {
446 // We can always copy in-place, without ever involving a local value.
447 unsafe { target.copy_from_nonoverlapping(self, 1) };
448 }
449}