Move OOM handling to liballoc and remove the oom lang item

This removes the need for `no_std` programs to define that lang item themselves:

Fixes #51540

Author: SimonSapin

src/liballoc/alloc.rs

@@ -15,6 +15,8 @@
 use core::intrinsics::{min_align_of_val, size_of_val};
 use core::ptr::{NonNull, Unique};
 use core::usize;
+#[cfg(target_has_atomic = "ptr")] use core::{mem, ptr};
+#[cfg(target_has_atomic = "ptr")] use core::sync::atomic::{AtomicPtr, Ordering};
 
 #[stable(feature = "alloc_module", since = "1.28.0")]
 #[doc(inline)]
@@ -191,12 +193,89 @@ pub(crate) unsafe fn box_free<T: ?Sized>(ptr: Unique<T>) {
 #[stable(feature = "global_alloc", since = "1.28.0")]
 #[rustc_allocator_nounwind]
 pub fn handle_alloc_error(layout: Layout) -> ! {
-    #[allow(improper_ctypes)]
-    extern "Rust" {
-        #[lang = "oom"]
-        fn oom_impl(layout: Layout) -> !;
+    #[cfg(target_has_atomic = "ptr")]
+    {
+        let hook = HOOK.load(Ordering::SeqCst);
+        let hook: fn(Layout) = if hook.is_null() {
+            default_alloc_error_hook
+        } else {
+            unsafe { mem::transmute(hook) }
+        };
+        hook(layout);
+    }
+    #[cfg(not(target_has_atomic = "ptr"))]
+    {
+        default_alloc_error_hook(layout)
+    }
+
+    unsafe {
+        #[cfg(not(stage0))]
+        {
+            #[allow(improper_ctypes)]
+            extern "Rust" {
+                // This function is generated by the compiler
+                // and calls __rust_abort_internal in src/libstd/alloc.rs
+                // if the `std` crate is linked.
+                fn __rust_maybe_abort_internal();
+            }
+            __rust_maybe_abort_internal();
+        }
+        // The above does nothing and returns when `std` is not linked.
+        // In that case we abort "naively" here:
+        ::core::intrinsics::abort()
+    }
+}
+
+fn default_alloc_error_hook(layout: Layout) {
+    #[cfg(stage0)]
+    let _ = layout;
+    #[cfg(not(stage0))]
+    unsafe {
+        #[allow(improper_ctypes)]
+        extern "Rust" {
+            // This function is generated by the compiler
+            // and calls __rust_default_alloc_error_hook in src/libstd/alloc.rs
+            // if the `std` crate is linked.
+            fn __rust_maybe_default_alloc_error_hook(size: usize, align: usize);
+        }
+        __rust_maybe_default_alloc_error_hook(layout.size(), layout.align())
+    }
+}
+
+#[cfg(target_has_atomic = "ptr")]
+static HOOK: AtomicPtr<()> = AtomicPtr::new(ptr::null_mut());
+
+/// Registers a custom allocation error hook, replacing any that was previously registered.
+///
+/// The allocation error hook is invoked when an infallible memory allocation fails, before
+/// the runtime aborts. The default hook prints a message to standard error,
+/// but this behavior can be customized with the [`set_alloc_error_hook`] and
+/// [`take_alloc_error_hook`] functions.
+///
+/// The hook is provided with a `Layout` struct which contains information
+/// about the allocation that failed.
+///
+/// The allocation error hook is a global resource.
+#[unstable(feature = "alloc_error_hook", issue = "51245")]
+#[cfg(target_has_atomic = "ptr")]
+pub fn set_alloc_error_hook(hook: fn(Layout)) {
+    HOOK.store(hook as *mut (), Ordering::SeqCst);
+}
+
+/// Unregisters the current allocation error hook, returning it.
+///
+/// *See also the function [`set_alloc_error_hook`].*
+///
+/// If no custom hook is registered, the default hook will be returned.
+#[unstable(feature = "alloc_error_hook", issue = "51245")]
+#[cfg(target_has_atomic = "ptr")]
+pub fn take_alloc_error_hook() -> fn(Layout) {
+    let hook = HOOK.swap(ptr::null_mut(), Ordering::SeqCst);
+    if hook.is_null() {
+        default_alloc_error_hook
+    } else {
+        unsafe { mem::transmute(hook) }
     }
-    unsafe { oom_impl(layout) }
 }
 
 #[cfg(test)]

src/librustc/middle/lang_items.rs

@@ -307,7 +307,6 @@ language_item_table! {
     ExchangeMallocFnLangItem,        "exchange_malloc",         exchange_malloc_fn;
     BoxFreeFnLangItem,               "box_free",                box_free_fn;
     DropInPlaceFnLangItem,           "drop_in_place",           drop_in_place_fn;
-    OomLangItem,                     "oom",                     oom;
 
     StartFnLangItem,                 "start",                   start_fn;
 

src/librustc/middle/weak_lang_items.rs

@@ -151,5 +151,4 @@ weak_lang_items! {
     panic_impl,         PanicImplLangItem,          rust_begin_unwind;
     eh_personality,     EhPersonalityLangItem,      rust_eh_personality;
     eh_unwind_resume,   EhUnwindResumeLangItem,     rust_eh_unwind_resume;
-    oom,                OomLangItem,                rust_oom;
 }

src/libstd/alloc.rs

@@ -74,10 +74,6 @@
 
 #![stable(feature = "alloc_module", since = "1.28.0")]
 
-use core::sync::atomic::{AtomicPtr, Ordering};
-use core::{mem, ptr};
-use sys_common::util::dumb_print;
-
 #[stable(feature = "alloc_module", since = "1.28.0")]
 #[doc(inline)]
 pub use alloc_crate::alloc::*;
@@ -86,64 +82,14 @@ pub use alloc_crate::alloc::*;
 #[doc(inline)]
 pub use alloc_system::System;
 
-static HOOK: AtomicPtr<()> = AtomicPtr::new(ptr::null_mut());
-
-/// Registers a custom allocation error hook, replacing any that was previously registered.
-///
-/// The allocation error hook is invoked when an infallible memory allocation fails, before
-/// the runtime aborts. The default hook prints a message to standard error,
-/// but this behavior can be customized with the [`set_alloc_error_hook`] and
-/// [`take_alloc_error_hook`] functions.
-///
-/// The hook is provided with a `Layout` struct which contains information
-/// about the allocation that failed.
-///
-/// The allocation error hook is a global resource.
-#[unstable(feature = "alloc_error_hook", issue = "51245")]
-pub fn set_alloc_error_hook(hook: fn(Layout)) {
-    HOOK.store(hook as *mut (), Ordering::SeqCst);
-}
-
-/// Unregisters the current allocation error hook, returning it.
-///
-/// *See also the function [`set_alloc_error_hook`].*
-///
-/// If no custom hook is registered, the default hook will be returned.
-#[unstable(feature = "alloc_error_hook", issue = "51245")]
-pub fn take_alloc_error_hook() -> fn(Layout) {
-    let hook = HOOK.swap(ptr::null_mut(), Ordering::SeqCst);
-    if hook.is_null() {
-        default_alloc_error_hook
-    } else {
-        unsafe { mem::transmute(hook) }
-    }
-}
-
-fn default_alloc_error_hook(layout: Layout) {
-    dumb_print(format_args!("memory allocation of {} bytes failed", layout.size()));
-}
-
-#[cfg(not(test))]
-#[doc(hidden)]
-#[lang = "oom"]
-#[unstable(feature = "alloc_internals", issue = "0")]
-pub extern fn rust_oom(layout: Layout) -> ! {
-    let hook = HOOK.load(Ordering::SeqCst);
-    let hook: fn(Layout) = if hook.is_null() {
-        default_alloc_error_hook
-    } else {
-        unsafe { mem::transmute(hook) }
-    };
-    hook(layout);
-    unsafe { ::sys::abort_internal(); }
-}
-
 #[cfg(not(test))]
 #[doc(hidden)]
 #[allow(unused_attributes)]
 #[unstable(feature = "alloc_internals", issue = "0")]
 pub mod __default_lib_allocator {
     use super::{System, Layout, GlobalAlloc};
+    use sys_common::util::dumb_print;
+
     // for symbol names src/librustc/middle/allocator.rs
     // for signatures src/librustc_allocator/lib.rs
 
@@ -181,4 +127,16 @@ pub mod __default_lib_allocator {
         let layout = Layout::from_size_align_unchecked(size, align);
         System.alloc_zeroed(layout)
     }
+
+    #[no_mangle]
+    #[rustc_std_internal_symbol]
+    pub extern fn __rust_default_alloc_error_hook(size: usize, _align: usize) {
+        dumb_print(format_args!("memory allocation of {} bytes failed", size));
+    }
+
+    #[no_mangle]
+    #[rustc_std_internal_symbol]
+    pub unsafe extern fn __rust_abort_internal() {
+        ::sys::abort_internal()
+    }
 }

src/test/ui/missing-allocator.rs

@@ -20,7 +20,4 @@ fn panic(_: &core::panic::PanicInfo) -> ! {
     loop {}
 }
 
-#[lang = "oom"]
-fn oom() {}
-
 extern crate alloc;