Loading...
Note: File does not exist in v5.9.
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;
9
10#[cfg(not(test))]
11use core::ptr::{self, NonNull};
12
13#[stable(feature = "alloc_module", since = "1.28.0")]
14#[doc(inline)]
15pub use core::alloc::*;
16
17#[cfg(test)]
18mod tests;
19
20extern "Rust" {
21 // These are the magic symbols to call the global allocator. rustc generates
22 // them to call `__rg_alloc` etc. if there is a `#[global_allocator]` attribute
23 // (the code expanding that attribute macro generates those functions), or to call
24 // the default implementations in std (`__rdl_alloc` etc. in `library/std/src/alloc.rs`)
25 // otherwise.
26 // The rustc fork of LLVM 14 and earlier also special-cases these function names to be able to optimize them
27 // like `malloc`, `realloc`, and `free`, respectively.
28 #[rustc_allocator]
29 #[rustc_nounwind]
30 fn __rust_alloc(size: usize, align: usize) -> *mut u8;
31 #[rustc_deallocator]
32 #[rustc_nounwind]
33 fn __rust_dealloc(ptr: *mut u8, size: usize, align: usize);
34 #[rustc_reallocator]
35 #[rustc_nounwind]
36 fn __rust_realloc(ptr: *mut u8, old_size: usize, align: usize, new_size: usize) -> *mut u8;
37 #[rustc_allocator_zeroed]
38 #[rustc_nounwind]
39 fn __rust_alloc_zeroed(size: usize, align: usize) -> *mut u8;
40
41 static __rust_no_alloc_shim_is_unstable: u8;
42}
43
44/// The global memory allocator.
45///
46/// This type implements the [`Allocator`] trait by forwarding calls
47/// to the allocator registered with the `#[global_allocator]` attribute
48/// if there is one, or the `std` crate’s default.
49///
50/// Note: while this type is unstable, the functionality it provides can be
51/// accessed through the [free functions in `alloc`](self#functions).
52#[unstable(feature = "allocator_api", issue = "32838")]
53#[derive(Copy, Clone, Default, Debug)]
54#[cfg(not(test))]
55pub struct Global;
56
57#[cfg(test)]
58pub use std::alloc::Global;
59
60/// Allocate memory with the global allocator.
61///
62/// This function forwards calls to the [`GlobalAlloc::alloc`] method
63/// of the allocator registered with the `#[global_allocator]` attribute
64/// if there is one, or the `std` crate’s default.
65///
66/// This function is expected to be deprecated in favor of the `alloc` method
67/// of the [`Global`] type when it and the [`Allocator`] trait become stable.
68///
69/// # Safety
70///
71/// See [`GlobalAlloc::alloc`].
72///
73/// # Examples
74///
75/// ```
76/// use std::alloc::{alloc, dealloc, handle_alloc_error, Layout};
77///
78/// unsafe {
79/// let layout = Layout::new::<u16>();
80/// let ptr = alloc(layout);
81/// if ptr.is_null() {
82/// handle_alloc_error(layout);
83/// }
84///
85/// *(ptr as *mut u16) = 42;
86/// assert_eq!(*(ptr as *mut u16), 42);
87///
88/// dealloc(ptr, layout);
89/// }
90/// ```
91#[stable(feature = "global_alloc", since = "1.28.0")]
92#[must_use = "losing the pointer will leak memory"]
93#[inline]
94pub unsafe fn alloc(layout: Layout) -> *mut u8 {
95 unsafe {
96 // Make sure we don't accidentally allow omitting the allocator shim in
97 // stable code until it is actually stabilized.
98 core::ptr::read_volatile(&__rust_no_alloc_shim_is_unstable);
99
100 __rust_alloc(layout.size(), layout.align())
101 }
102}
103
104/// Deallocate memory with the global allocator.
105///
106/// This function forwards calls to the [`GlobalAlloc::dealloc`] method
107/// of the allocator registered with the `#[global_allocator]` attribute
108/// if there is one, or the `std` crate’s default.
109///
110/// This function is expected to be deprecated in favor of the `dealloc` method
111/// of the [`Global`] type when it and the [`Allocator`] trait become stable.
112///
113/// # Safety
114///
115/// See [`GlobalAlloc::dealloc`].
116#[stable(feature = "global_alloc", since = "1.28.0")]
117#[inline]
118pub unsafe fn dealloc(ptr: *mut u8, layout: Layout) {
119 unsafe { __rust_dealloc(ptr, layout.size(), layout.align()) }
120}
121
122/// Reallocate memory with the global allocator.
123///
124/// This function forwards calls to the [`GlobalAlloc::realloc`] method
125/// of the allocator registered with the `#[global_allocator]` attribute
126/// if there is one, or the `std` crate’s default.
127///
128/// This function is expected to be deprecated in favor of the `realloc` method
129/// of the [`Global`] type when it and the [`Allocator`] trait become stable.
130///
131/// # Safety
132///
133/// See [`GlobalAlloc::realloc`].
134#[stable(feature = "global_alloc", since = "1.28.0")]
135#[must_use = "losing the pointer will leak memory"]
136#[inline]
137pub unsafe fn realloc(ptr: *mut u8, layout: Layout, new_size: usize) -> *mut u8 {
138 unsafe { __rust_realloc(ptr, layout.size(), layout.align(), new_size) }
139}
140
141/// Allocate zero-initialized memory with the global allocator.
142///
143/// This function forwards calls to the [`GlobalAlloc::alloc_zeroed`] method
144/// of the allocator registered with the `#[global_allocator]` attribute
145/// if there is one, or the `std` crate’s default.
146///
147/// This function is expected to be deprecated in favor of the `alloc_zeroed` method
148/// of the [`Global`] type when it and the [`Allocator`] trait become stable.
149///
150/// # Safety
151///
152/// See [`GlobalAlloc::alloc_zeroed`].
153///
154/// # Examples
155///
156/// ```
157/// use std::alloc::{alloc_zeroed, dealloc, Layout};
158///
159/// unsafe {
160/// let layout = Layout::new::<u16>();
161/// let ptr = alloc_zeroed(layout);
162///
163/// assert_eq!(*(ptr as *mut u16), 0);
164///
165/// dealloc(ptr, layout);
166/// }
167/// ```
168#[stable(feature = "global_alloc", since = "1.28.0")]
169#[must_use = "losing the pointer will leak memory"]
170#[inline]
171pub unsafe fn alloc_zeroed(layout: Layout) -> *mut u8 {
172 unsafe { __rust_alloc_zeroed(layout.size(), layout.align()) }
173}
174
175#[cfg(not(test))]
176impl Global {
177 #[inline]
178 fn alloc_impl(&self, layout: Layout, zeroed: bool) -> Result<NonNull<[u8]>, AllocError> {
179 match layout.size() {
180 0 => Ok(NonNull::slice_from_raw_parts(layout.dangling(), 0)),
181 // SAFETY: `layout` is non-zero in size,
182 size => unsafe {
183 let raw_ptr = if zeroed { alloc_zeroed(layout) } else { alloc(layout) };
184 let ptr = NonNull::new(raw_ptr).ok_or(AllocError)?;
185 Ok(NonNull::slice_from_raw_parts(ptr, size))
186 },
187 }
188 }
189
190 // SAFETY: Same as `Allocator::grow`
191 #[inline]
192 unsafe fn grow_impl(
193 &self,
194 ptr: NonNull<u8>,
195 old_layout: Layout,
196 new_layout: Layout,
197 zeroed: bool,
198 ) -> Result<NonNull<[u8]>, AllocError> {
199 debug_assert!(
200 new_layout.size() >= old_layout.size(),
201 "`new_layout.size()` must be greater than or equal to `old_layout.size()`"
202 );
203
204 match old_layout.size() {
205 0 => self.alloc_impl(new_layout, zeroed),
206
207 // SAFETY: `new_size` is non-zero as `old_size` is greater than or equal to `new_size`
208 // as required by safety conditions. Other conditions must be upheld by the caller
209 old_size if old_layout.align() == new_layout.align() => unsafe {
210 let new_size = new_layout.size();
211
212 // `realloc` probably checks for `new_size >= old_layout.size()` or something similar.
213 intrinsics::assume(new_size >= old_layout.size());
214
215 let raw_ptr = realloc(ptr.as_ptr(), old_layout, new_size);
216 let ptr = NonNull::new(raw_ptr).ok_or(AllocError)?;
217 if zeroed {
218 raw_ptr.add(old_size).write_bytes(0, new_size - old_size);
219 }
220 Ok(NonNull::slice_from_raw_parts(ptr, new_size))
221 },
222
223 // SAFETY: because `new_layout.size()` must be greater than or equal to `old_size`,
224 // both the old and new memory allocation are valid for reads and writes for `old_size`
225 // bytes. Also, because the old allocation wasn't yet deallocated, it cannot overlap
226 // `new_ptr`. Thus, the call to `copy_nonoverlapping` is safe. The safety contract
227 // for `dealloc` must be upheld by the caller.
228 old_size => unsafe {
229 let new_ptr = self.alloc_impl(new_layout, zeroed)?;
230 ptr::copy_nonoverlapping(ptr.as_ptr(), new_ptr.as_mut_ptr(), old_size);
231 self.deallocate(ptr, old_layout);
232 Ok(new_ptr)
233 },
234 }
235 }
236}
237
238#[unstable(feature = "allocator_api", issue = "32838")]
239#[cfg(not(test))]
240unsafe impl Allocator for Global {
241 #[inline]
242 fn allocate(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
243 self.alloc_impl(layout, false)
244 }
245
246 #[inline]
247 fn allocate_zeroed(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
248 self.alloc_impl(layout, true)
249 }
250
251 #[inline]
252 unsafe fn deallocate(&self, ptr: NonNull<u8>, layout: Layout) {
253 if layout.size() != 0 {
254 // SAFETY: `layout` is non-zero in size,
255 // other conditions must be upheld by the caller
256 unsafe { dealloc(ptr.as_ptr(), layout) }
257 }
258 }
259
260 #[inline]
261 unsafe fn grow(
262 &self,
263 ptr: NonNull<u8>,
264 old_layout: Layout,
265 new_layout: Layout,
266 ) -> Result<NonNull<[u8]>, AllocError> {
267 // SAFETY: all conditions must be upheld by the caller
268 unsafe { self.grow_impl(ptr, old_layout, new_layout, false) }
269 }
270
271 #[inline]
272 unsafe fn grow_zeroed(
273 &self,
274 ptr: NonNull<u8>,
275 old_layout: Layout,
276 new_layout: Layout,
277 ) -> Result<NonNull<[u8]>, AllocError> {
278 // SAFETY: all conditions must be upheld by the caller
279 unsafe { self.grow_impl(ptr, old_layout, new_layout, true) }
280 }
281
282 #[inline]
283 unsafe fn shrink(
284 &self,
285 ptr: NonNull<u8>,
286 old_layout: Layout,
287 new_layout: Layout,
288 ) -> Result<NonNull<[u8]>, AllocError> {
289 debug_assert!(
290 new_layout.size() <= old_layout.size(),
291 "`new_layout.size()` must be smaller than or equal to `old_layout.size()`"
292 );
293
294 match new_layout.size() {
295 // SAFETY: conditions must be upheld by the caller
296 0 => unsafe {
297 self.deallocate(ptr, old_layout);
298 Ok(NonNull::slice_from_raw_parts(new_layout.dangling(), 0))
299 },
300
301 // SAFETY: `new_size` is non-zero. Other conditions must be upheld by the caller
302 new_size if old_layout.align() == new_layout.align() => unsafe {
303 // `realloc` probably checks for `new_size <= old_layout.size()` or something similar.
304 intrinsics::assume(new_size <= old_layout.size());
305
306 let raw_ptr = realloc(ptr.as_ptr(), old_layout, new_size);
307 let ptr = NonNull::new(raw_ptr).ok_or(AllocError)?;
308 Ok(NonNull::slice_from_raw_parts(ptr, new_size))
309 },
310
311 // SAFETY: because `new_size` must be smaller than or equal to `old_layout.size()`,
312 // both the old and new memory allocation are valid for reads and writes for `new_size`
313 // bytes. Also, because the old allocation wasn't yet deallocated, it cannot overlap
314 // `new_ptr`. Thus, the call to `copy_nonoverlapping` is safe. The safety contract
315 // for `dealloc` must be upheld by the caller.
316 new_size => unsafe {
317 let new_ptr = self.allocate(new_layout)?;
318 ptr::copy_nonoverlapping(ptr.as_ptr(), new_ptr.as_mut_ptr(), new_size);
319 self.deallocate(ptr, old_layout);
320 Ok(new_ptr)
321 },
322 }
323 }
324}
325
326/// The allocator for unique pointers.
327#[cfg(all(not(no_global_oom_handling), not(test)))]
328#[lang = "exchange_malloc"]
329#[inline]
330unsafe fn exchange_malloc(size: usize, align: usize) -> *mut u8 {
331 let layout = unsafe { Layout::from_size_align_unchecked(size, align) };
332 match Global.allocate(layout) {
333 Ok(ptr) => ptr.as_mut_ptr(),
334 Err(_) => handle_alloc_error(layout),
335 }
336}
337
338// # Allocation error handler
339
340#[cfg(not(no_global_oom_handling))]
341extern "Rust" {
342 // This is the magic symbol to call the global alloc error handler. rustc generates
343 // it to call `__rg_oom` if there is a `#[alloc_error_handler]`, or to call the
344 // default implementations below (`__rdl_oom`) otherwise.
345 fn __rust_alloc_error_handler(size: usize, align: usize) -> !;
346}
347
348/// Signal a memory allocation error.
349///
350/// Callers of memory allocation APIs wishing to cease execution
351/// in response to an allocation error are encouraged to call this function,
352/// rather than directly invoking [`panic!`] or similar.
353///
354/// This function is guaranteed to diverge (not return normally with a value), but depending on
355/// global configuration, it may either panic (resulting in unwinding or aborting as per
356/// configuration for all panics), or abort the process (with no unwinding).
357///
358/// The default behavior is:
359///
360/// * If the binary links against `std` (typically the case), then
361/// print a message to standard error and abort the process.
362/// This behavior can be replaced with [`set_alloc_error_hook`] and [`take_alloc_error_hook`].
363/// Future versions of Rust may panic by default instead.
364///
365/// * If the binary does not link against `std` (all of its crates are marked
366/// [`#![no_std]`][no_std]), then call [`panic!`] with a message.
367/// [The panic handler] applies as to any panic.
368///
369/// [`set_alloc_error_hook`]: ../../std/alloc/fn.set_alloc_error_hook.html
370/// [`take_alloc_error_hook`]: ../../std/alloc/fn.take_alloc_error_hook.html
371/// [The panic handler]: https://doc.rust-lang.org/reference/runtime.html#the-panic_handler-attribute
372/// [no_std]: https://doc.rust-lang.org/reference/names/preludes.html#the-no_std-attribute
373#[stable(feature = "global_alloc", since = "1.28.0")]
374#[rustc_const_unstable(feature = "const_alloc_error", issue = "92523")]
375#[cfg(all(not(no_global_oom_handling), not(test)))]
376#[cold]
377pub const fn handle_alloc_error(layout: Layout) -> ! {
378 const fn ct_error(_: Layout) -> ! {
379 panic!("allocation failed");
380 }
381
382 fn rt_error(layout: Layout) -> ! {
383 unsafe {
384 __rust_alloc_error_handler(layout.size(), layout.align());
385 }
386 }
387
388 unsafe { core::intrinsics::const_eval_select((layout,), ct_error, rt_error) }
389}
390
391// For alloc test `std::alloc::handle_alloc_error` can be used directly.
392#[cfg(all(not(no_global_oom_handling), test))]
393pub use std::alloc::handle_alloc_error;
394
395#[cfg(all(not(no_global_oom_handling), not(test)))]
396#[doc(hidden)]
397#[allow(unused_attributes)]
398#[unstable(feature = "alloc_internals", issue = "none")]
399pub mod __alloc_error_handler {
400 // called via generated `__rust_alloc_error_handler` if there is no
401 // `#[alloc_error_handler]`.
402 #[rustc_std_internal_symbol]
403 pub unsafe fn __rdl_oom(size: usize, _align: usize) -> ! {
404 extern "Rust" {
405 // This symbol is emitted by rustc next to __rust_alloc_error_handler.
406 // Its value depends on the -Zoom={panic,abort} compiler option.
407 static __rust_alloc_error_handler_should_panic: u8;
408 }
409
410 if unsafe { __rust_alloc_error_handler_should_panic != 0 } {
411 panic!("memory allocation of {size} bytes failed")
412 } else {
413 core::panicking::panic_nounwind_fmt(
414 format_args!("memory allocation of {size} bytes failed"),
415 /* force_no_backtrace */ false,
416 )
417 }
418 }
419}
420
421/// Specialize clones into pre-allocated, uninitialized memory.
422/// Used by `Box::clone` and `Rc`/`Arc::make_mut`.
423pub(crate) trait WriteCloneIntoRaw: Sized {
424 unsafe fn write_clone_into_raw(&self, target: *mut Self);
425}
426
427impl<T: Clone> WriteCloneIntoRaw for T {
428 #[inline]
429 default unsafe fn write_clone_into_raw(&self, target: *mut Self) {
430 // Having allocated *first* may allow the optimizer to create
431 // the cloned value in-place, skipping the local and move.
432 unsafe { target.write(self.clone()) };
433 }
434}
435
436impl<T: Copy> WriteCloneIntoRaw for T {
437 #[inline]
438 unsafe fn write_clone_into_raw(&self, target: *mut Self) {
439 // We can always copy in-place, without ever involving a local value.
440 unsafe { target.copy_from_nonoverlapping(self, 1) };
441 }
442}