alloc.rs - source
Description: Source of the Rust file `library/alloc/src/alloc.rs`.

#
alloc/
alloc.rs

    1//! Memory allocation APIs
    2
    3#![stable(feature = "alloc_module", since = "1.28.0")]
    4
    5#[stable(feature = "alloc_module", since = "1.28.0")]
    6#[doc(inline)]
    7pub use core::alloc::*;
    8use core::ptr::{self, NonNull};
    9use core::{cmp, hint};
    10
    11unsafe extern "Rust" {
    12    // These are the magic symbols to call the global allocator. rustc generates
    13    // them to call the global allocator if there is a `#[global_allocator]` attribute
    14    // (the code expanding that attribute macro generates those functions), or to call
    15    // the default implementations in std (`__rdl_alloc` etc. in `library/std/src/alloc.rs`)
    16    // otherwise.
    17    #[rustc_allocator]
    18    #[rustc_nounwind]
    19    #[rustc_std_internal_symbol]
    20    #[rustc_allocator_zeroed_variant = "__rust_alloc_zeroed"]
    21    fn __rust_alloc(size: usize, align: usize) -> *mut u8;
    22    #[rustc_deallocator]
    23    #[rustc_nounwind]
    24    #[rustc_std_internal_symbol]
    25    fn __rust_dealloc(ptr: *mut u8, size: usize, align: usize);
    26    #[rustc_reallocator]
    27    #[rustc_nounwind]
    28    #[rustc_std_internal_symbol]
    29    fn __rust_realloc(ptr: *mut u8, old_size: usize, align: usize, new_size: usize) -> *mut u8;
    30    #[rustc_allocator_zeroed]
    31    #[rustc_nounwind]
    32    #[rustc_std_internal_symbol]
    33    fn __rust_alloc_zeroed(size: usize, align: usize) -> *mut u8;
    34
    35    #[rustc_nounwind]
    36    #[rustc_std_internal_symbol]
    37    fn __rust_no_alloc_shim_is_unstable_v2();
    38}
    39
    40/// The global memory allocator.
    41///
    42/// This type implements the [`Allocator`] trait by forwarding calls
    43/// to the allocator registered with the `#[global_allocator]` attribute
    44/// if there is one, or the `std` crate’s default.
    45///
    46/// Note: while this type is unstable, the functionality it provides can be
    47/// accessed through the [free functions in `alloc`](self#functions).
    48#[unstable(feature = "allocator_api", issue = "32838")]
    49#[derive(Copy, Clone, Default, Debug)]
    50// the compiler needs to know when a Box uses the global allocator vs a custom one
    51#[lang = "global_alloc_ty"]
    52pub struct Global;
    53
    54/// Allocates memory with the global allocator.
    55///
    56/// This function forwards calls to the [`GlobalAlloc::alloc`] method
    57/// of the allocator registered with the `#[global_allocator]` attribute
    58/// if there is one, or the `std` crate’s default.
    59///
    60/// This function is expected to be deprecated in favor of the `allocate` method
    61/// of the [`Global`] type when it and the [`Allocator`] trait become stable.
    62///
    63/// # Safety
    64///
    65/// See [`GlobalAlloc::alloc`].
    66///
    67/// # Examples
    68///
    69/// ```
    70/// use std::alloc::{alloc, dealloc, handle_alloc_error, Layout};
    71///
    72/// unsafe {
    73///     let layout = Layout::new::<u16>();
    74///     let ptr = alloc(layout);
    75///     if ptr.is_null() {
    76///         handle_alloc_error(layout);
    77///     }
    78///
    79///     *(ptr as *mut u16) = 42;
    80///     assert_eq!(*(ptr as *mut u16), 42);
    81///
    82///     dealloc(ptr, layout);
    83/// }
    84/// ```
    85#[stable(feature = "global_alloc", since = "1.28.0")]
    86#[must_use = "losing the pointer will leak memory"]
    87#[inline]
    88#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
    89pub unsafe fn alloc(layout: Layout) -> *mut u8 {
    90    unsafe {
    91        // Make sure we don't accidentally allow omitting the allocator shim in
    92        // stable code until it is actually stabilized.
    93        __rust_no_alloc_shim_is_unstable_v2();
    94
    95        __rust_alloc(layout.size(), layout.align())
    96    }
    97}
    98
    99/// Deallocates memory with the global allocator.
    100///
    101/// This function forwards calls to the [`GlobalAlloc::dealloc`] method
    102/// of the allocator registered with the `#[global_allocator]` attribute
    103/// if there is one, or the `std` crate’s default.
    104///
    105/// This function is expected to be deprecated in favor of the `deallocate` method
    106/// of the [`Global`] type when it and the [`Allocator`] trait become stable.
    107///
    108/// # Safety
    109///
    110/// See [`GlobalAlloc::dealloc`].
    111#[stable(feature = "global_alloc", since = "1.28.0")]
    112#[inline]
    113#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
    114pub unsafe fn dealloc(ptr: *mut u8, layout: Layout) {
    115    unsafe { __rust_dealloc(ptr, layout.size(), layout.align()) }
    116}
    117
    118/// Reallocates memory with the global allocator.
    119///
    120/// This function forwards calls to the [`GlobalAlloc::realloc`] method
    121/// of the allocator registered with the `#[global_allocator]` attribute
    122/// if there is one, or the `std` crate’s default.
    123///
    124/// This function is expected to be deprecated in favor of the `grow` and `shrink` methods
    125/// of the [`Global`] type when it and the [`Allocator`] trait become stable.
    126///
    127/// # Safety
    128///
    129/// See [`GlobalAlloc::realloc`].
    130#[stable(feature = "global_alloc", since = "1.28.0")]
    131#[must_use = "losing the pointer will leak memory"]
    132#[inline]
    133#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
    134pub unsafe fn realloc(ptr: *mut u8, layout: Layout, new_size: usize) -> *mut u8 {
    135    unsafe { __rust_realloc(ptr, layout.size(), layout.align(), new_size) }
    136}
    137
    138/// Allocates zero-initialized memory with the global allocator.
    139///
    140/// This function forwards calls to the [`GlobalAlloc::alloc_zeroed`] method
    141/// of the allocator registered with the `#[global_allocator]` attribute
    142/// if there is one, or the `std` crate’s default.
    143///
    144/// This function is expected to be deprecated in favor of the `allocate_zeroed` method
    145/// of the [`Global`] type when it and the [`Allocator`] trait become stable.
    146///
    147/// # Safety
    148///
    149/// See [`GlobalAlloc::alloc_zeroed`].
    150///
    151/// # Examples
    152///
    153/// ```
    154/// use std::alloc::{alloc_zeroed, dealloc, handle_alloc_error, Layout};
    155///
    156/// unsafe {
    157///     let layout = Layout::new::<u16>();
    158///     let ptr = alloc_zeroed(layout);
    159///     if ptr.is_null() {
    160///         handle_alloc_error(layout);
    161///     }
    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]
    171#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
    172pub unsafe fn alloc_zeroed(layout: Layout) -> *mut u8 {
    173    unsafe {
    174        // Make sure we don't accidentally allow omitting the allocator shim in
    175        // stable code until it is actually stabilized.
    176        __rust_no_alloc_shim_is_unstable_v2();
    177
    178        __rust_alloc_zeroed(layout.size(), layout.align())
    179    }
    180}
    181
    182impl Global {
    183    #[inline]
    184    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
    185    fn alloc_impl_runtime(layout: Layout, zeroed: bool) -> Result<NonNull<[u8]>, AllocError> {
    186        match layout.size() {
    187            0 => Ok(NonNull::slice_from_raw_parts(layout.dangling(), 0)),
    188            // SAFETY: `layout` is non-zero in size,
    189            size => unsafe {
    190                let raw_ptr = if zeroed { alloc_zeroed(layout) } else { alloc(layout) };
    191                let ptr = NonNull::new(raw_ptr).ok_or(AllocError)?;
    192                Ok(NonNull::slice_from_raw_parts(ptr, size))
    193            },
    194        }
    195    }
    196
    197    #[inline]
    198    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
    199    fn deallocate_impl_runtime(ptr: NonNull<u8>, layout: Layout) {
    200        if layout.size() != 0 {
    201            // SAFETY:
    202            // * We have checked that `layout` is non-zero in size.
    203            // * The caller is obligated to provide a layout that "fits", and in this case,
    204            //   "fit" always means a layout that is equal to the original, because our
    205            //   `allocate()`, `grow()`, and `shrink()` implementations never returns a larger
    206            //   allocation than requested.
    207            // * Other conditions must be upheld by the caller, as per `Allocator::deallocate()`'s
    208            //   safety documentation.
    209            unsafe { dealloc(ptr.as_ptr(), layout) }
    210        }
    211    }
    212
    213    // SAFETY: Same as `Allocator::grow`
    214    #[inline]
    215    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
    216    fn grow_impl_runtime(
    217        &self,
    218        ptr: NonNull<u8>,
    219        old_layout: Layout,
    220        new_layout: Layout,
    221        zeroed: bool,
    222    ) -> Result<NonNull<[u8]>, AllocError> {
    223        debug_assert!(
    224            new_layout.size() >= old_layout.size(),
    225            "`new_layout.size()` must be greater than or equal to `old_layout.size()`"
    226        );
    227
    228        match old_layout.size() {
    229            0 => self.alloc_impl(new_layout, zeroed),
    230
    231            // SAFETY: `new_size` is non-zero as `old_size` is greater than or equal to `new_size`
    232            // as required by safety conditions. Other conditions must be upheld by the caller
    233            old_size if old_layout.align() == new_layout.align() => unsafe {
    234                let new_size = new_layout.size();
    235
    236                // `realloc` probably checks for `new_size >= old_layout.size()` or something similar.
    237                hint::assert_unchecked(new_size >= old_layout.size());
    238
    239                let raw_ptr = realloc(ptr.as_ptr(), old_layout, new_size);
    240                let ptr = NonNull::new(raw_ptr).ok_or(AllocError)?;
    241                if zeroed {
    242                    raw_ptr.add(old_size).write_bytes(0, new_size - old_size);
    243                }
    244                Ok(NonNull::slice_from_raw_parts(ptr, new_size))
    245            },
    246
    247            // SAFETY: because `new_layout.size()` must be greater than or equal to `old_size`,
    248            // both the old and new memory allocation are valid for reads and writes for `old_size`
    249            // bytes. Also, because the old allocation wasn't yet deallocated, it cannot overlap
    250            // `new_ptr`. Thus, the call to `copy_nonoverlapping` is safe. The safety contract
    251            // for `dealloc` must be upheld by the caller.
    252            old_size => unsafe {
    253                let new_ptr = self.alloc_impl(new_layout, zeroed)?;
    254                ptr::copy_nonoverlapping(ptr.as_ptr(), new_ptr.as_mut_ptr(), old_size);
    255                self.deallocate(ptr, old_layout);
    256                Ok(new_ptr)
    257            },
    258        }
    259    }
    260
    261    // SAFETY: Same as `Allocator::grow`
    262    #[inline]
    263    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
    264    fn shrink_impl_runtime(
    265        &self,
    266        ptr: NonNull<u8>,
    267        old_layout: Layout,
    268        new_layout: Layout,
    269        _zeroed: bool,
    270    ) -> Result<NonNull<[u8]>, AllocError> {
    271        debug_assert!(
    272            new_layout.size() <= old_layout.size(),
    273            "`new_layout.size()` must be smaller than or equal to `old_layout.size()`"
    274        );
    275
    276        match new_layout.size() {
    277            // SAFETY: conditions must be upheld by the caller
    278            0 => unsafe {
    279                self.deallocate(ptr, old_layout);
    280                Ok(NonNull::slice_from_raw_parts(new_layout.dangling(), 0))
    281            },
    282
    283            // SAFETY: `new_size` is non-zero. Other conditions must be upheld by the caller
    284            new_size if old_layout.align() == new_layout.align() => unsafe {
    285                // `realloc` probably checks for `new_size <= old_layout.size()` or something similar.
    286                hint::assert_unchecked(new_size <= old_layout.size());
    287
    288                let raw_ptr = realloc(ptr.as_ptr(), old_layout, new_size);
    289                let ptr = NonNull::new(raw_ptr).ok_or(AllocError)?;
    290                Ok(NonNull::slice_from_raw_parts(ptr, new_size))
    291            },
    292
    293            // SAFETY: because `new_size` must be smaller than or equal to `old_layout.size()`,
    294            // both the old and new memory allocation are valid for reads and writes for `new_size`
    295            // bytes. Also, because the old allocation wasn't yet deallocated, it cannot overlap
    296            // `new_ptr`. Thus, the call to `copy_nonoverlapping` is safe. The safety contract
    297            // for `dealloc` must be upheld by the caller.
    298            new_size => unsafe {
    299                let new_ptr = self.allocate(new_layout)?;
    300                ptr::copy_nonoverlapping(ptr.as_ptr(), new_ptr.as_mut_ptr(), new_size);
    301                self.deallocate(ptr, old_layout);
    302                Ok(new_ptr)
    303            },
    304        }
    305    }
    306
    307    // SAFETY: Same as `Allocator::allocate`
    308    #[inline]
    309    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
    310    #[rustc_const_unstable(feature = "const_heap", issue = "79597")]
    311    const fn alloc_impl(&self, layout: Layout, zeroed: bool) -> Result<NonNull<[u8]>, AllocError> {
    312        core::intrinsics::const_eval_select(
    313            (layout, zeroed),
    314            Global::alloc_impl_const,
    315            Global::alloc_impl_runtime,
    316        )
    317    }
    318
    319    // SAFETY: Same as `Allocator::deallocate`
    320    #[inline]
    321    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
    322    #[rustc_const_unstable(feature = "const_heap", issue = "79597")]
    323    const unsafe fn deallocate_impl(&self, ptr: NonNull<u8>, layout: Layout) {
    324        core::intrinsics::const_eval_select(
    325            (ptr, layout),
    326            Global::deallocate_impl_const,
    327            Global::deallocate_impl_runtime,
    328        )
    329    }
    330
    331    // SAFETY: Same as `Allocator::grow`
    332    #[inline]
    333    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
    334    #[rustc_const_unstable(feature = "const_heap", issue = "79597")]
    335    const unsafe fn grow_impl(
    336        &self,
    337        ptr: NonNull<u8>,
    338        old_layout: Layout,
    339        new_layout: Layout,
    340        zeroed: bool,
    341    ) -> Result<NonNull<[u8]>, AllocError> {
    342        core::intrinsics::const_eval_select(
    343            (self, ptr, old_layout, new_layout, zeroed),
    344            Global::grow_shrink_impl_const,
    345            Global::grow_impl_runtime,
    346        )
    347    }
    348
    349    // SAFETY: Same as `Allocator::shrink`
    350    #[inline]
    351    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
    352    #[rustc_const_unstable(feature = "const_heap", issue = "79597")]
    353    const unsafe fn shrink_impl(
    354        &self,
    355        ptr: NonNull<u8>,
    356        old_layout: Layout,
    357        new_layout: Layout,
    358    ) -> Result<NonNull<[u8]>, AllocError> {
    359        core::intrinsics::const_eval_select(
    360            (self, ptr, old_layout, new_layout, false),
    361            Global::grow_shrink_impl_const,
    362            Global::shrink_impl_runtime,
    363        )
    364    }
    365
    366    #[inline]
    367    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
    368    #[rustc_const_unstable(feature = "const_heap", issue = "79597")]
    369    const fn alloc_impl_const(layout: Layout, zeroed: bool) -> Result<NonNull<[u8]>, AllocError> {
    370        match layout.size() {
    371            0 => Ok(NonNull::slice_from_raw_parts(layout.dangling(), 0)),
    372            // SAFETY: `layout` is non-zero in size,
    373            size => unsafe {
    374                let raw_ptr = core::intrinsics::const_allocate(layout.size(), layout.align());
    375                let ptr = NonNull::new(raw_ptr).ok_or(AllocError)?;
    376                if zeroed {
    377                    // SAFETY: the pointer returned by `const_allocate` is valid to write to.
    378                    ptr.write_bytes(0, size);
    379                }
    380                Ok(NonNull::slice_from_raw_parts(ptr, size))
    381            },
    382        }
    383    }
    384
    385    #[inline]
    386    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
    387    #[rustc_const_unstable(feature = "const_heap", issue = "79597")]
    388    const fn deallocate_impl_const(ptr: NonNull<u8>, layout: Layout) {
    389        if layout.size() != 0 {
    390            // SAFETY: We checked for nonzero size; other preconditions must be upheld by caller.
    391            unsafe {
    392                core::intrinsics::const_deallocate(ptr.as_ptr(), layout.size(), layout.align());
    393            }
    394        }
    395    }
    396
    397    #[inline]
    398    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
    399    #[rustc_const_unstable(feature = "const_heap", issue = "79597")]
    400    const fn grow_shrink_impl_const(
    401        &self,
    402        ptr: NonNull<u8>,
    403        old_layout: Layout,
    404        new_layout: Layout,
    405        zeroed: bool,
    406    ) -> Result<NonNull<[u8]>, AllocError> {
    407        let new_ptr = self.alloc_impl(new_layout, zeroed)?;
    408        // SAFETY: both pointers are valid and this operations is in bounds.
    409        unsafe {
    410            ptr::copy_nonoverlapping(
    411                ptr.as_ptr(),
    412                new_ptr.as_mut_ptr(),
    413                cmp::min(old_layout.size(), new_layout.size()),
    414            );
    415        }
    416        unsafe {
    417            self.deallocate_impl(ptr, old_layout);
    418        }
    419        Ok(new_ptr)
    420    }
    421}
    422
    423#[unstable(feature = "allocator_api", issue = "32838")]
    424#[rustc_const_unstable(feature = "const_heap", issue = "79597")]
    425unsafe impl const Allocator for Global {
    426    #[inline]
    427    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
    428    fn allocate(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
    429        self.alloc_impl(layout, false)
    430    }
    431
    432    #[inline]
    433    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
    434    fn allocate_zeroed(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
    435        self.alloc_impl(layout, true)
    436    }
    437
    438    #[inline]
    439    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
    440    unsafe fn deallocate(&self, ptr: NonNull<u8>, layout: Layout) {
    441        // SAFETY: all conditions must be upheld by the caller
    442        unsafe { self.deallocate_impl(ptr, layout) }
    443    }
    444
    445    #[inline]
    446    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
    447    unsafe fn grow(
    448        &self,
    449        ptr: NonNull<u8>,
    450        old_layout: Layout,
    451        new_layout: Layout,
    452    ) -> Result<NonNull<[u8]>, AllocError> {
    453        // SAFETY: all conditions must be upheld by the caller
    454        unsafe { self.grow_impl(ptr, old_layout, new_layout, false) }
    455    }
    456
    457    #[inline]
    458    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
    459    unsafe fn grow_zeroed(
    460        &self,
    461        ptr: NonNull<u8>,
    462        old_layout: Layout,
    463        new_layout: Layout,
    464    ) -> Result<NonNull<[u8]>, AllocError> {
    465        // SAFETY: all conditions must be upheld by the caller
    466        unsafe { self.grow_impl(ptr, old_layout, new_layout, true) }
    467    }
    468
    469    #[inline]
    470    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
    471    unsafe fn shrink(
    472        &self,
    473        ptr: NonNull<u8>,
    474        old_layout: Layout,
    475        new_layout: Layout,
    476    ) -> Result<NonNull<[u8]>, AllocError> {
    477        // SAFETY: all conditions must be upheld by the caller
    478        unsafe { self.shrink_impl(ptr, old_layout, new_layout) }
    479    }
    480}
    481
    482/// The allocator for `Box`.
    483#[cfg(not(no_global_oom_handling))]
    484#[lang = "exchange_malloc"]
    485#[inline]
    486#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
    487unsafe fn exchange_malloc(size: usize, align: usize) -> *mut u8 {
    488    let layout = unsafe { Layout::from_size_align_unchecked(size, align) };
    489    match Global.allocate(layout) {
    490        Ok(ptr) => ptr.as_mut_ptr(),
    491        Err(_) => handle_alloc_error(layout),
    492    }
    493}
    494
    495// # Allocation error handler
    496
    497#[cfg(not(no_global_oom_handling))]
    498unsafe extern "Rust" {
    499    // This is the magic symbol to call the global alloc error handler. rustc generates
    500    // it to call `__rg_oom` if there is a `#[alloc_error_handler]`, or to call the
    501    // default implementations below (`__rdl_alloc_error_handler`) otherwise.
    502    #[rustc_std_internal_symbol]
    503    fn __rust_alloc_error_handler(size: usize, align: usize) -> !;
    504}
    505
    506/// Signals a memory allocation error.
    507///
    508/// Callers of memory allocation APIs wishing to cease execution
    509/// in response to an allocation error are encouraged to call this function,
    510/// rather than directly invoking [`panic!`] or similar.
    511///
    512/// This function is guaranteed to diverge (not return normally with a value), but depending on
    513/// global configuration, it may either panic (resulting in unwinding or aborting as per
    514/// configuration for all panics), or abort the process (with no unwinding).
    515///
    516/// The default behavior is:
    517///
    518///  * If the binary links against `std` (typically the case), then
    519///   print a message to standard error and abort the process.
    520///   This behavior can be replaced with [`set_alloc_error_hook`] and [`take_alloc_error_hook`].
    521///   Future versions of Rust may panic by default instead.
    522///
    523/// * If the binary does not link against `std` (all of its crates are marked
    524///   [`#![no_std]`][no_std]), then call [`panic!`] with a message.
    525///   [The panic handler] applies as to any panic.
    526///
    527/// [`set_alloc_error_hook`]: ../../std/alloc/fn.set_alloc_error_hook.html
    528/// [`take_alloc_error_hook`]: ../../std/alloc/fn.take_alloc_error_hook.html
    529/// [The panic handler]: https://doc.rust-lang.org/reference/runtime.html#the-panic_handler-attribute
    530/// [no_std]: https://doc.rust-lang.org/reference/names/preludes.html#the-no_std-attribute
    531#[stable(feature = "global_alloc", since = "1.28.0")]
    532#[rustc_const_unstable(feature = "const_alloc_error", issue = "92523")]
    533#[cfg(not(no_global_oom_handling))]
    534#[cold]
    535#[optimize(size)]
    536pub const fn handle_alloc_error(layout: Layout) -> ! {
    537    const fn ct_error(_: Layout) -> ! {
    538        panic!("allocation failed");
    539    }
    540
    541    #[inline]
    542    fn rt_error(layout: Layout) -> ! {
    543        unsafe {
    544            __rust_alloc_error_handler(layout.size(), layout.align());
    545        }
    546    }
    547
    548    #[cfg(not(panic = "immediate-abort"))]
    549    {
    550        core::intrinsics::const_eval_select((layout,), ct_error, rt_error)
    551    }
    552
    553    #[cfg(panic = "immediate-abort")]
    554    ct_error(layout)
    555}
    556
    557#[cfg(not(no_global_oom_handling))]
    558#[doc(hidden)]
    559#[allow(unused_attributes)]
    560#[unstable(feature = "alloc_internals", issue = "none")]
    561pub mod __alloc_error_handler {
    562    // called via generated `__rust_alloc_error_handler` if there is no
    563    // `#[alloc_error_handler]`.
    564    #[rustc_std_internal_symbol]
    565    pub unsafe fn __rdl_alloc_error_handler(size: usize, _align: usize) -> ! {
    566        core::panicking::panic_nounwind_fmt(
    567            format_args!("memory allocation of {size} bytes failed"),
    568            /* force_no_backtrace */ false,
    569        )
    570    }
    571}