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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
19use core::marker::Destruct;
20
21#[cfg(test)]
22mod tests;
23
24extern "Rust" {
25 // These are the magic symbols to call the global allocator. rustc generates
26 // them to call `__rg_alloc` etc. if there is a `#[global_allocator]` attribute
27 // (the code expanding that attribute macro generates those functions), or to call
28 // the default implementations in libstd (`__rdl_alloc` etc. in `library/std/src/alloc.rs`)
29 // otherwise.
30 // The rustc fork of LLVM also special-cases these function names to be able to optimize them
31 // like `malloc`, `realloc`, and `free`, respectively.
32 #[rustc_allocator]
33 #[rustc_allocator_nounwind]
34 fn __rust_alloc(size: usize, align: usize) -> *mut u8;
35 #[rustc_allocator_nounwind]
36 fn __rust_dealloc(ptr: *mut u8, size: usize, align: usize);
37 #[rustc_allocator_nounwind]
38 fn __rust_realloc(ptr: *mut u8, old_size: usize, align: usize, new_size: usize) -> *mut u8;
39 #[rustc_allocator_nounwind]
40 fn __rust_alloc_zeroed(size: usize, align: usize) -> *mut u8;
41}
42
43/// The global memory allocator.
44///
45/// This type implements the [`Allocator`] trait by forwarding calls
46/// to the allocator registered with the `#[global_allocator]` attribute
47/// if there is one, or the `std` crate’s default.
48///
49/// Note: while this type is unstable, the functionality it provides can be
50/// accessed through the [free functions in `alloc`](self#functions).
51#[unstable(feature = "allocator_api", issue = "32838")]
52#[derive(Copy, Clone, Default, Debug)]
53#[cfg(not(test))]
54pub struct Global;
55
56#[cfg(test)]
57pub use std::alloc::Global;
58
59/// Allocate memory with the global allocator.
60///
61/// This function forwards calls to the [`GlobalAlloc::alloc`] method
62/// of the allocator registered with the `#[global_allocator]` attribute
63/// if there is one, or the `std` crate’s default.
64///
65/// This function is expected to be deprecated in favor of the `alloc` method
66/// of the [`Global`] type when it and the [`Allocator`] trait become stable.
67///
68/// # Safety
69///
70/// See [`GlobalAlloc::alloc`].
71///
72/// # Examples
73///
74/// ```
75/// use std::alloc::{alloc, dealloc, Layout};
76///
77/// unsafe {
78/// let layout = Layout::new::<u16>();
79/// let ptr = alloc(layout);
80///
81/// *(ptr as *mut u16) = 42;
82/// assert_eq!(*(ptr as *mut u16), 42);
83///
84/// dealloc(ptr, layout);
85/// }
86/// ```
87#[stable(feature = "global_alloc", since = "1.28.0")]
88#[must_use = "losing the pointer will leak memory"]
89#[inline]
90pub unsafe fn alloc(layout: Layout) -> *mut u8 {
91 unsafe { __rust_alloc(layout.size(), layout.align()) }
92}
93
94/// Deallocate memory with the global allocator.
95///
96/// This function forwards calls to the [`GlobalAlloc::dealloc`] method
97/// of the allocator registered with the `#[global_allocator]` attribute
98/// if there is one, or the `std` crate’s default.
99///
100/// This function is expected to be deprecated in favor of the `dealloc` method
101/// of the [`Global`] type when it and the [`Allocator`] trait become stable.
102///
103/// # Safety
104///
105/// See [`GlobalAlloc::dealloc`].
106#[stable(feature = "global_alloc", since = "1.28.0")]
107#[inline]
108pub unsafe fn dealloc(ptr: *mut u8, layout: Layout) {
109 unsafe { __rust_dealloc(ptr, layout.size(), layout.align()) }
110}
111
112/// Reallocate memory with the global allocator.
113///
114/// This function forwards calls to the [`GlobalAlloc::realloc`] method
115/// of the allocator registered with the `#[global_allocator]` attribute
116/// if there is one, or the `std` crate’s default.
117///
118/// This function is expected to be deprecated in favor of the `realloc` method
119/// of the [`Global`] type when it and the [`Allocator`] trait become stable.
120///
121/// # Safety
122///
123/// See [`GlobalAlloc::realloc`].
124#[stable(feature = "global_alloc", since = "1.28.0")]
125#[must_use = "losing the pointer will leak memory"]
126#[inline]
127pub unsafe fn realloc(ptr: *mut u8, layout: Layout, new_size: usize) -> *mut u8 {
128 unsafe { __rust_realloc(ptr, layout.size(), layout.align(), new_size) }
129}
130
131/// Allocate zero-initialized memory with the global allocator.
132///
133/// This function forwards calls to the [`GlobalAlloc::alloc_zeroed`] method
134/// of the allocator registered with the `#[global_allocator]` attribute
135/// if there is one, or the `std` crate’s default.
136///
137/// This function is expected to be deprecated in favor of the `alloc_zeroed` method
138/// of the [`Global`] type when it and the [`Allocator`] trait become stable.
139///
140/// # Safety
141///
142/// See [`GlobalAlloc::alloc_zeroed`].
143///
144/// # Examples
145///
146/// ```
147/// use std::alloc::{alloc_zeroed, dealloc, Layout};
148///
149/// unsafe {
150/// let layout = Layout::new::<u16>();
151/// let ptr = alloc_zeroed(layout);
152///
153/// assert_eq!(*(ptr as *mut u16), 0);
154///
155/// dealloc(ptr, layout);
156/// }
157/// ```
158#[stable(feature = "global_alloc", since = "1.28.0")]
159#[must_use = "losing the pointer will leak memory"]
160#[inline]
161pub unsafe fn alloc_zeroed(layout: Layout) -> *mut u8 {
162 unsafe { __rust_alloc_zeroed(layout.size(), layout.align()) }
163}
164
165#[cfg(not(test))]
166impl Global {
167 #[inline]
168 fn alloc_impl(&self, layout: Layout, zeroed: bool) -> Result<NonNull<[u8]>, AllocError> {
169 match layout.size() {
170 0 => Ok(NonNull::slice_from_raw_parts(layout.dangling(), 0)),
171 // SAFETY: `layout` is non-zero in size,
172 size => unsafe {
173 let raw_ptr = if zeroed { alloc_zeroed(layout) } else { alloc(layout) };
174 let ptr = NonNull::new(raw_ptr).ok_or(AllocError)?;
175 Ok(NonNull::slice_from_raw_parts(ptr, size))
176 },
177 }
178 }
179
180 // SAFETY: Same as `Allocator::grow`
181 #[inline]
182 unsafe fn grow_impl(
183 &self,
184 ptr: NonNull<u8>,
185 old_layout: Layout,
186 new_layout: Layout,
187 zeroed: bool,
188 ) -> Result<NonNull<[u8]>, AllocError> {
189 debug_assert!(
190 new_layout.size() >= old_layout.size(),
191 "`new_layout.size()` must be greater than or equal to `old_layout.size()`"
192 );
193
194 match old_layout.size() {
195 0 => self.alloc_impl(new_layout, zeroed),
196
197 // SAFETY: `new_size` is non-zero as `old_size` is greater than or equal to `new_size`
198 // as required by safety conditions. Other conditions must be upheld by the caller
199 old_size if old_layout.align() == new_layout.align() => unsafe {
200 let new_size = new_layout.size();
201
202 // `realloc` probably checks for `new_size >= old_layout.size()` or something similar.
203 intrinsics::assume(new_size >= old_layout.size());
204
205 let raw_ptr = realloc(ptr.as_ptr(), old_layout, new_size);
206 let ptr = NonNull::new(raw_ptr).ok_or(AllocError)?;
207 if zeroed {
208 raw_ptr.add(old_size).write_bytes(0, new_size - old_size);
209 }
210 Ok(NonNull::slice_from_raw_parts(ptr, new_size))
211 },
212
213 // SAFETY: because `new_layout.size()` must be greater than or equal to `old_size`,
214 // both the old and new memory allocation are valid for reads and writes for `old_size`
215 // bytes. Also, because the old allocation wasn't yet deallocated, it cannot overlap
216 // `new_ptr`. Thus, the call to `copy_nonoverlapping` is safe. The safety contract
217 // for `dealloc` must be upheld by the caller.
218 old_size => unsafe {
219 let new_ptr = self.alloc_impl(new_layout, zeroed)?;
220 ptr::copy_nonoverlapping(ptr.as_ptr(), new_ptr.as_mut_ptr(), old_size);
221 self.deallocate(ptr, old_layout);
222 Ok(new_ptr)
223 },
224 }
225 }
226}
227
228#[unstable(feature = "allocator_api", issue = "32838")]
229#[cfg(not(test))]
230unsafe impl Allocator for Global {
231 #[inline]
232 fn allocate(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
233 self.alloc_impl(layout, false)
234 }
235
236 #[inline]
237 fn allocate_zeroed(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
238 self.alloc_impl(layout, true)
239 }
240
241 #[inline]
242 unsafe fn deallocate(&self, ptr: NonNull<u8>, layout: Layout) {
243 if layout.size() != 0 {
244 // SAFETY: `layout` is non-zero in size,
245 // other conditions must be upheld by the caller
246 unsafe { dealloc(ptr.as_ptr(), layout) }
247 }
248 }
249
250 #[inline]
251 unsafe fn grow(
252 &self,
253 ptr: NonNull<u8>,
254 old_layout: Layout,
255 new_layout: Layout,
256 ) -> Result<NonNull<[u8]>, AllocError> {
257 // SAFETY: all conditions must be upheld by the caller
258 unsafe { self.grow_impl(ptr, old_layout, new_layout, false) }
259 }
260
261 #[inline]
262 unsafe fn grow_zeroed(
263 &self,
264 ptr: NonNull<u8>,
265 old_layout: Layout,
266 new_layout: Layout,
267 ) -> Result<NonNull<[u8]>, AllocError> {
268 // SAFETY: all conditions must be upheld by the caller
269 unsafe { self.grow_impl(ptr, old_layout, new_layout, true) }
270 }
271
272 #[inline]
273 unsafe fn shrink(
274 &self,
275 ptr: NonNull<u8>,
276 old_layout: Layout,
277 new_layout: Layout,
278 ) -> Result<NonNull<[u8]>, AllocError> {
279 debug_assert!(
280 new_layout.size() <= old_layout.size(),
281 "`new_layout.size()` must be smaller than or equal to `old_layout.size()`"
282 );
283
284 match new_layout.size() {
285 // SAFETY: conditions must be upheld by the caller
286 0 => unsafe {
287 self.deallocate(ptr, old_layout);
288 Ok(NonNull::slice_from_raw_parts(new_layout.dangling(), 0))
289 },
290
291 // SAFETY: `new_size` is non-zero. Other conditions must be upheld by the caller
292 new_size if old_layout.align() == new_layout.align() => unsafe {
293 // `realloc` probably checks for `new_size <= old_layout.size()` or something similar.
294 intrinsics::assume(new_size <= old_layout.size());
295
296 let raw_ptr = realloc(ptr.as_ptr(), old_layout, new_size);
297 let ptr = NonNull::new(raw_ptr).ok_or(AllocError)?;
298 Ok(NonNull::slice_from_raw_parts(ptr, new_size))
299 },
300
301 // SAFETY: because `new_size` must be smaller than or equal to `old_layout.size()`,
302 // both the old and new memory allocation are valid for reads and writes for `new_size`
303 // bytes. Also, because the old allocation wasn't yet deallocated, it cannot overlap
304 // `new_ptr`. Thus, the call to `copy_nonoverlapping` is safe. The safety contract
305 // for `dealloc` must be upheld by the caller.
306 new_size => unsafe {
307 let new_ptr = self.allocate(new_layout)?;
308 ptr::copy_nonoverlapping(ptr.as_ptr(), new_ptr.as_mut_ptr(), new_size);
309 self.deallocate(ptr, old_layout);
310 Ok(new_ptr)
311 },
312 }
313 }
314}
315
316/// The allocator for unique pointers.
317#[cfg(all(not(no_global_oom_handling), not(test)))]
318#[lang = "exchange_malloc"]
319#[inline]
320unsafe fn exchange_malloc(size: usize, align: usize) -> *mut u8 {
321 let layout = unsafe { Layout::from_size_align_unchecked(size, align) };
322 match Global.allocate(layout) {
323 Ok(ptr) => ptr.as_mut_ptr(),
324 Err(_) => handle_alloc_error(layout),
325 }
326}
327
328#[cfg_attr(not(test), lang = "box_free")]
329#[inline]
330#[rustc_const_unstable(feature = "const_box", issue = "92521")]
331// This signature has to be the same as `Box`, otherwise an ICE will happen.
332// When an additional parameter to `Box` is added (like `A: Allocator`), this has to be added here as
333// well.
334// For example if `Box` is changed to `struct Box<T: ?Sized, A: Allocator>(Unique<T>, A)`,
335// this function has to be changed to `fn box_free<T: ?Sized, A: Allocator>(Unique<T>, A)` as well.
336pub(crate) const unsafe fn box_free<T: ?Sized, A: ~const Allocator + ~const Destruct>(
337 ptr: Unique<T>,
338 alloc: A,
339) {
340 unsafe {
341 let size = size_of_val(ptr.as_ref());
342 let align = min_align_of_val(ptr.as_ref());
343 let layout = Layout::from_size_align_unchecked(size, align);
344 alloc.deallocate(From::from(ptr.cast()), layout)
345 }
346}
347
348// # Allocation error handler
349
350#[cfg(not(no_global_oom_handling))]
351extern "Rust" {
352 // This is the magic symbol to call the global alloc error handler. rustc generates
353 // it to call `__rg_oom` if there is a `#[alloc_error_handler]`, or to call the
354 // default implementations below (`__rdl_oom`) otherwise.
355 fn __rust_alloc_error_handler(size: usize, align: usize) -> !;
356}
357
358/// Abort on memory allocation error or failure.
359///
360/// Callers of memory allocation APIs wishing to abort computation
361/// in response to an allocation error are encouraged to call this function,
362/// rather than directly invoking `panic!` or similar.
363///
364/// The default behavior of this function is to print a message to standard error
365/// and abort the process.
366/// It can be replaced with [`set_alloc_error_hook`] and [`take_alloc_error_hook`].
367///
368/// [`set_alloc_error_hook`]: ../../std/alloc/fn.set_alloc_error_hook.html
369/// [`take_alloc_error_hook`]: ../../std/alloc/fn.take_alloc_error_hook.html
370#[stable(feature = "global_alloc", since = "1.28.0")]
371#[rustc_const_unstable(feature = "const_alloc_error", issue = "92523")]
372#[cfg(all(not(no_global_oom_handling), not(test)))]
373#[cold]
374pub const fn handle_alloc_error(layout: Layout) -> ! {
375 const fn ct_error(_: Layout) -> ! {
376 panic!("allocation failed");
377 }
378
379 fn rt_error(layout: Layout) -> ! {
380 unsafe {
381 __rust_alloc_error_handler(layout.size(), layout.align());
382 }
383 }
384
385 unsafe { core::intrinsics::const_eval_select((layout,), ct_error, rt_error) }
386}
387
388// For alloc test `std::alloc::handle_alloc_error` can be used directly.
389#[cfg(all(not(no_global_oom_handling), test))]
390pub use std::alloc::handle_alloc_error;
391
392#[cfg(all(not(no_global_oom_handling), not(test)))]
393#[doc(hidden)]
394#[allow(unused_attributes)]
395#[unstable(feature = "alloc_internals", issue = "none")]
396pub mod __alloc_error_handler {
397 use crate::alloc::Layout;
398
399 // called via generated `__rust_alloc_error_handler`
400
401 // if there is no `#[alloc_error_handler]`
402 #[rustc_std_internal_symbol]
403 pub unsafe extern "C-unwind" fn __rdl_oom(size: usize, _align: usize) -> ! {
404 panic!("memory allocation of {size} bytes failed")
405 }
406
407 // if there is an `#[alloc_error_handler]`
408 #[rustc_std_internal_symbol]
409 pub unsafe extern "C-unwind" fn __rg_oom(size: usize, align: usize) -> ! {
410 let layout = unsafe { Layout::from_size_align_unchecked(size, align) };
411 extern "Rust" {
412 #[lang = "oom"]
413 fn oom_impl(layout: Layout) -> !;
414 }
415 unsafe { oom_impl(layout) }
416 }
417}
418
419/// Specialize clones into pre-allocated, uninitialized memory.
420/// Used by `Box::clone` and `Rc`/`Arc::make_mut`.
421pub(crate) trait WriteCloneIntoRaw: Sized {
422 unsafe fn write_clone_into_raw(&self, target: *mut Self);
423}
424
425impl<T: Clone> WriteCloneIntoRaw for T {
426 #[inline]
427 default unsafe fn write_clone_into_raw(&self, target: *mut Self) {
428 // Having allocated *first* may allow the optimizer to create
429 // the cloned value in-place, skipping the local and move.
430 unsafe { target.write(self.clone()) };
431 }
432}
433
434impl<T: Copy> WriteCloneIntoRaw for T {
435 #[inline]
436 unsafe fn write_clone_into_raw(&self, target: *mut Self) {
437 // We can always copy in-place, without ever involving a local value.
438 unsafe { target.copy_from_nonoverlapping(self, 1) };
439 }
440}