src/liballoc/alloc.rs

   1 //! Memory allocation APIs
   2
   3 #![stable(feature = "alloc_module", since = "1.28.0")]
   4
   5 use core::intrinsics::{self, min_align_of_val, size_of_val};
   6 use core::ptr::{NonNull, Unique};
   7
   8 #[stable(feature = "alloc_module", since = "1.28.0")]
   9 #[doc(inline)]
  10 pub use core::alloc::*;
  11
  12 #[cfg(test)]
  13 mod tests;
  14
  15 extern "Rust" {
  16     // These are the magic symbols to call the global allocator.  rustc generates
  17     // them from the `#[global_allocator]` attribute if there is one, or uses the
  18     // default implementations in libstd (`__rdl_alloc` etc in `src/libstd/alloc.rs`)
  19     // otherwise.
  20     #[rustc_allocator]
  21     #[rustc_allocator_nounwind]
  22     fn __rust_alloc(size: usize, align: usize) -> *mut u8;
  23     #[rustc_allocator_nounwind]
  24     fn __rust_dealloc(ptr: *mut u8, size: usize, align: usize);
  25     #[rustc_allocator_nounwind]
  26     fn __rust_realloc(ptr: *mut u8, old_size: usize, align: usize, new_size: usize) -> *mut u8;
  27     #[rustc_allocator_nounwind]
  28     fn __rust_alloc_zeroed(size: usize, align: usize) -> *mut u8;
  29 }
  30
  31 /// The global memory allocator.
  32 ///
  33 /// This type implements the [`AllocRef`] trait by forwarding calls
  34 /// to the allocator registered with the `#[global_allocator]` attribute
  35 /// if there is one, or the `std` crate’s default.
  36 ///
  37 /// Note: while this type is unstable, the functionality it provides can be
  38 /// accessed through the [free functions in `alloc`](index.html#functions).
  39 ///
  40 /// [`AllocRef`]: trait.AllocRef.html
  41 #[unstable(feature = "allocator_api", issue = "32838")]
  42 #[derive(Copy, Clone, Default, Debug)]
  43 pub struct Global;
  44
  45 /// Allocate memory with the global allocator.
  46 ///
  47 /// This function forwards calls to the [`GlobalAlloc::alloc`] method
  48 /// of the allocator registered with the `#[global_allocator]` attribute
  49 /// if there is one, or the `std` crate’s default.
  50 ///
  51 /// This function is expected to be deprecated in favor of the `alloc` method
  52 /// of the [`Global`] type when it and the [`AllocRef`] trait become stable.
  53 ///
  54 /// # Safety
  55 ///
  56 /// See [`GlobalAlloc::alloc`].
  57 ///
  58 /// [`Global`]: struct.Global.html
  59 /// [`AllocRef`]: trait.AllocRef.html
  60 /// [`GlobalAlloc::alloc`]: trait.GlobalAlloc.html#tymethod.alloc
  61 ///
  62 /// # Examples
  63 ///
  64 /// ```
  65 /// use std::alloc::{alloc, dealloc, Layout};
  66 ///
  67 /// unsafe {
  68 ///     let layout = Layout::new::<u16>();
  69 ///     let ptr = alloc(layout);
  70 ///
  71 ///     *(ptr as *mut u16) = 42;
  72 ///     assert_eq!(*(ptr as *mut u16), 42);
  73 ///
  74 ///     dealloc(ptr, layout);
  75 /// }
  76 /// ```
  77 #[stable(feature = "global_alloc", since = "1.28.0")]
  78 #[inline]
  79 pub unsafe fn alloc(layout: Layout) -> *mut u8 {
  80     __rust_alloc(layout.size(), layout.align())
  81 }
  82
  83 /// Deallocate memory with the global allocator.
  84 ///
  85 /// This function forwards calls to the [`GlobalAlloc::dealloc`] method
  86 /// of the allocator registered with the `#[global_allocator]` attribute
  87 /// if there is one, or the `std` crate’s default.
  88 ///
  89 /// This function is expected to be deprecated in favor of the `dealloc` method
  90 /// of the [`Global`] type when it and the [`AllocRef`] trait become stable.
  91 ///
  92 /// # Safety
  93 ///
  94 /// See [`GlobalAlloc::dealloc`].
  95 ///
  96 /// [`Global`]: struct.Global.html
  97 /// [`AllocRef`]: trait.AllocRef.html
  98 /// [`GlobalAlloc::dealloc`]: trait.GlobalAlloc.html#tymethod.dealloc
  99 #[stable(feature = "global_alloc", since = "1.28.0")]
 100 #[inline]
 101 pub unsafe fn dealloc(ptr: *mut u8, layout: Layout) {
 102     __rust_dealloc(ptr, layout.size(), layout.align())
 103 }
 104
 105 /// Reallocate memory with the global allocator.
 106 ///
 107 /// This function forwards calls to the [`GlobalAlloc::realloc`] method
 108 /// of the allocator registered with the `#[global_allocator]` attribute
 109 /// if there is one, or the `std` crate’s default.
 110 ///
 111 /// This function is expected to be deprecated in favor of the `realloc` method
 112 /// of the [`Global`] type when it and the [`AllocRef`] trait become stable.
 113 ///
 114 /// # Safety
 115 ///
 116 /// See [`GlobalAlloc::realloc`].
 117 ///
 118 /// [`Global`]: struct.Global.html
 119 /// [`AllocRef`]: trait.AllocRef.html
 120 /// [`GlobalAlloc::realloc`]: trait.GlobalAlloc.html#method.realloc
 121 #[stable(feature = "global_alloc", since = "1.28.0")]
 122 #[inline]
 123 pub unsafe fn realloc(ptr: *mut u8, layout: Layout, new_size: usize) -> *mut u8 {
 124     __rust_realloc(ptr, layout.size(), layout.align(), new_size)
 125 }
 126
 127 /// Allocate zero-initialized memory with the global allocator.
 128 ///
 129 /// This function forwards calls to the [`GlobalAlloc::alloc_zeroed`] method
 130 /// of the allocator registered with the `#[global_allocator]` attribute
 131 /// if there is one, or the `std` crate’s default.
 132 ///
 133 /// This function is expected to be deprecated in favor of the `alloc_zeroed` method
 134 /// of the [`Global`] type when it and the [`AllocRef`] trait become stable.
 135 ///
 136 /// # Safety
 137 ///
 138 /// See [`GlobalAlloc::alloc_zeroed`].
 139 ///
 140 /// [`Global`]: struct.Global.html
 141 /// [`AllocRef`]: trait.AllocRef.html
 142 /// [`GlobalAlloc::alloc_zeroed`]: trait.GlobalAlloc.html#method.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 #[inline]
 160 pub unsafe fn alloc_zeroed(layout: Layout) -> *mut u8 {
 161     __rust_alloc_zeroed(layout.size(), layout.align())
 162 }
 163
 164 #[unstable(feature = "allocator_api", issue = "32838")]
 165 unsafe impl AllocRef for Global {
 166     #[inline]
 167     fn alloc(&mut self, layout: Layout, init: AllocInit) -> Result<MemoryBlock, AllocErr> {
 168         unsafe {
 169             let size = layout.size();
 170             if size == 0 {
 171                 Ok(MemoryBlock { ptr: layout.dangling(), size: 0 })
 172             } else {
 173                 let raw_ptr = match init {
 174                     AllocInit::Uninitialized => alloc(layout),
 175                     AllocInit::Zeroed => alloc_zeroed(layout),
 176                 };
 177                 let ptr = NonNull::new(raw_ptr).ok_or(AllocErr)?;
 178                 Ok(MemoryBlock { ptr, size })
 179             }
 180         }
 181     }
 182
 183     #[inline]
 184     unsafe fn dealloc(&mut self, ptr: NonNull<u8>, layout: Layout) {
 185         if layout.size() != 0 {
 186             dealloc(ptr.as_ptr(), layout)
 187         }
 188     }
 189
 190     #[inline]
 191     unsafe fn grow(
 192         &mut self,
 193         ptr: NonNull<u8>,
 194         layout: Layout,
 195         new_size: usize,
 196         placement: ReallocPlacement,
 197         init: AllocInit,
 198     ) -> Result<MemoryBlock, AllocErr> {
 199         let size = layout.size();
 200         debug_assert!(
 201             new_size >= size,
 202             "`new_size` must be greater than or equal to `memory.size()`"
 203         );
 204
 205         if size == new_size {
 206             return Ok(MemoryBlock { ptr, size });
 207         }
 208
 209         match placement {
 210             ReallocPlacement::InPlace => Err(AllocErr),
 211             ReallocPlacement::MayMove if layout.size() == 0 => {
 212                 let new_layout = Layout::from_size_align_unchecked(new_size, layout.align());
 213                 self.alloc(new_layout, init)
 214             }
 215             ReallocPlacement::MayMove => {
 216                 // `realloc` probably checks for `new_size > size` or something similar.
 217                 intrinsics::assume(new_size > size);
 218                 let ptr = realloc(ptr.as_ptr(), layout, new_size);
 219                 let memory =
 220                     MemoryBlock { ptr: NonNull::new(ptr).ok_or(AllocErr)?, size: new_size };
 221                 init.init_offset(memory, size);
 222                 Ok(memory)
 223             }
 224         }
 225     }
 226
 227     #[inline]
 228     unsafe fn shrink(
 229         &mut self,
 230         ptr: NonNull<u8>,
 231         layout: Layout,
 232         new_size: usize,
 233         placement: ReallocPlacement,
 234     ) -> Result<MemoryBlock, AllocErr> {
 235         let size = layout.size();
 236         debug_assert!(
 237             new_size <= size,
 238             "`new_size` must be smaller than or equal to `memory.size()`"
 239         );
 240
 241         if size == new_size {
 242             return Ok(MemoryBlock { ptr, size });
 243         }
 244
 245         match placement {
 246             ReallocPlacement::InPlace => Err(AllocErr),
 247             ReallocPlacement::MayMove if new_size == 0 => {
 248                 self.dealloc(ptr, layout);
 249                 Ok(MemoryBlock { ptr: layout.dangling(), size: 0 })
 250             }
 251             ReallocPlacement::MayMove => {
 252                 // `realloc` probably checks for `new_size < size` or something similar.
 253                 intrinsics::assume(new_size < size);
 254                 let ptr = realloc(ptr.as_ptr(), layout, new_size);
 255                 Ok(MemoryBlock { ptr: NonNull::new(ptr).ok_or(AllocErr)?, size: new_size })
 256             }
 257         }
 258     }
 259 }
 260
 261 /// The allocator for unique pointers.
 262 // This function must not unwind. If it does, MIR codegen will fail.
 263 #[cfg(not(test))]
 264 #[lang = "exchange_malloc"]
 265 #[inline]
 266 unsafe fn exchange_malloc(size: usize, align: usize) -> *mut u8 {
 267     let layout = Layout::from_size_align_unchecked(size, align);
 268     match Global.alloc(layout, AllocInit::Uninitialized) {
 269         Ok(memory) => memory.ptr.as_ptr(),
 270         Err(_) => handle_alloc_error(layout),
 271     }
 272 }
 273
 274 #[cfg_attr(not(test), lang = "box_free")]
 275 #[inline]
 276 // This signature has to be the same as `Box`, otherwise an ICE will happen.
 277 // When an additional parameter to `Box` is added (like `A: AllocRef`), this has to be added here as
 278 // well.
 279 // For example if `Box` is changed to  `struct Box<T: ?Sized, A: AllocRef>(Unique<T>, A)`,
 280 // this function has to be changed to `fn box_free<T: ?Sized, A: AllocRef>(Unique<T>, A)` as well.
 281 pub(crate) unsafe fn box_free<T: ?Sized>(ptr: Unique<T>) {
 282     let size = size_of_val(ptr.as_ref());
 283     let align = min_align_of_val(ptr.as_ref());
 284     let layout = Layout::from_size_align_unchecked(size, align);
 285     Global.dealloc(ptr.cast().into(), layout)
 286 }
 287
 288 /// Abort on memory allocation error or failure.
 289 ///
 290 /// Callers of memory allocation APIs wishing to abort computation
 291 /// in response to an allocation error are encouraged to call this function,
 292 /// rather than directly invoking `panic!` or similar.
 293 ///
 294 /// The default behavior of this function is to print a message to standard error
 295 /// and abort the process.
 296 /// It can be replaced with [`set_alloc_error_hook`] and [`take_alloc_error_hook`].
 297 ///
 298 /// [`set_alloc_error_hook`]: ../../std/alloc/fn.set_alloc_error_hook.html
 299 /// [`take_alloc_error_hook`]: ../../std/alloc/fn.take_alloc_error_hook.html
 300 #[stable(feature = "global_alloc", since = "1.28.0")]
 301 #[rustc_allocator_nounwind]
 302 pub fn handle_alloc_error(layout: Layout) -> ! {
 303     extern "Rust" {
 304         #[lang = "oom"]
 305         fn oom_impl(layout: Layout) -> !;
 306     }
 307     unsafe { oom_impl(layout) }
 308 }