Rollup merge of #110782 - matthiaskrgr:revert_panic_oom, r=Amanieu

Revert panic oom

This temporarily reverts https://github.com/rust-lang/rust/pull/109507 until https://github.com/rust-lang/rust/issues/110771 is addressed

r? `@Amanieu`

compiler/rustc_builtin_macros/messages.ftl

@@ -4,6 +4,8 @@ builtin_macros_requires_cfg_pattern =
 
 builtin_macros_expected_one_cfg_pattern = expected 1 cfg-pattern
 
+builtin_macros_alloc_error_must_be_fn = alloc_error_handler must be a function
+
 builtin_macros_assert_requires_boolean = macro requires a boolean expression as an argument
     .label = boolean expression required
 

compiler/rustc_builtin_macros/src/alloc_error_handler.rs

@@ -0,0 +1,97 @@
+use crate::errors;
+use crate::util::check_builtin_macro_attribute;
+
+use rustc_ast::ptr::P;
+use rustc_ast::{self as ast, FnHeader, FnSig, Generics, StmtKind};
+use rustc_ast::{Fn, ItemKind, Stmt, TyKind, Unsafe};
+use rustc_expand::base::{Annotatable, ExtCtxt};
+use rustc_span::symbol::{kw, sym, Ident};
+use rustc_span::Span;
+use thin_vec::{thin_vec, ThinVec};
+
+pub fn expand(
+    ecx: &mut ExtCtxt<'_>,
+    _span: Span,
+    meta_item: &ast::MetaItem,
+    item: Annotatable,
+) -> Vec<Annotatable> {
+    check_builtin_macro_attribute(ecx, meta_item, sym::alloc_error_handler);
+
+    let orig_item = item.clone();
+
+    // Allow using `#[alloc_error_handler]` on an item statement
+    // FIXME - if we get deref patterns, use them to reduce duplication here
+    let (item, is_stmt, sig_span) =
+        if let Annotatable::Item(item) = &item
+            && let ItemKind::Fn(fn_kind) = &item.kind
+        {
+            (item, false, ecx.with_def_site_ctxt(fn_kind.sig.span))
+        } else if let Annotatable::Stmt(stmt) = &item
+            && let StmtKind::Item(item) = &stmt.kind
+            && let ItemKind::Fn(fn_kind) = &item.kind
+        {
+            (item, true, ecx.with_def_site_ctxt(fn_kind.sig.span))
+        } else {
+            ecx.sess.parse_sess.span_diagnostic.emit_err(errors::AllocErrorMustBeFn {span: item.span() });
+            return vec![orig_item];
+        };
+
+    // Generate a bunch of new items using the AllocFnFactory
+    let span = ecx.with_def_site_ctxt(item.span);
+
+    // Generate item statements for the allocator methods.
+    let stmts = thin_vec![generate_handler(ecx, item.ident, span, sig_span)];
+
+    // Generate anonymous constant serving as container for the allocator methods.
+    let const_ty = ecx.ty(sig_span, TyKind::Tup(ThinVec::new()));
+    let const_body = ecx.expr_block(ecx.block(span, stmts));
+    let const_item = ecx.item_const(span, Ident::new(kw::Underscore, span), const_ty, const_body);
+    let const_item = if is_stmt {
+        Annotatable::Stmt(P(ecx.stmt_item(span, const_item)))
+    } else {
+        Annotatable::Item(const_item)
+    };
+
+    // Return the original item and the new methods.
+    vec![orig_item, const_item]
+}
+
+// #[rustc_std_internal_symbol]
+// unsafe fn __rg_oom(size: usize, align: usize) -> ! {
+//     handler(core::alloc::Layout::from_size_align_unchecked(size, align))
+// }
+fn generate_handler(cx: &ExtCtxt<'_>, handler: Ident, span: Span, sig_span: Span) -> Stmt {
+    let usize = cx.path_ident(span, Ident::new(sym::usize, span));
+    let ty_usize = cx.ty_path(usize);
+    let size = Ident::from_str_and_span("size", span);
+    let align = Ident::from_str_and_span("align", span);
+
+    let layout_new = cx.std_path(&[sym::alloc, sym::Layout, sym::from_size_align_unchecked]);
+    let layout_new = cx.expr_path(cx.path(span, layout_new));
+    let layout = cx.expr_call(
+        span,
+        layout_new,
+        thin_vec![cx.expr_ident(span, size), cx.expr_ident(span, align)],
+    );
+
+    let call = cx.expr_call_ident(sig_span, handler, thin_vec![layout]);
+
+    let never = ast::FnRetTy::Ty(cx.ty(span, TyKind::Never));
+    let params = thin_vec![cx.param(span, size, ty_usize.clone()), cx.param(span, align, ty_usize)];
+    let decl = cx.fn_decl(params, never);
+    let header = FnHeader { unsafety: Unsafe::Yes(span), ..FnHeader::default() };
+    let sig = FnSig { decl, header, span: span };
+
+    let body = Some(cx.block_expr(call));
+    let kind = ItemKind::Fn(Box::new(Fn {
+        defaultness: ast::Defaultness::Final,
+        sig,
+        generics: Generics::default(),
+        body,
+    }));
+
+    let attrs = thin_vec![cx.attr_word(sym::rustc_std_internal_symbol, span)];
+
+    let item = cx.item(span, Ident::from_str_and_span("__rg_oom", span), attrs, kind);
+    cx.stmt_item(sig_span, item)
+}

compiler/rustc_builtin_macros/src/errors.rs

@@ -19,6 +19,13 @@ pub(crate) struct OneCfgPattern {
     pub(crate) span: Span,
 }
 
+#[derive(Diagnostic)]
+#[diag(builtin_macros_alloc_error_must_be_fn)]
+pub(crate) struct AllocErrorMustBeFn {
+    #[primary_span]
+    pub(crate) span: Span,
+}
+
 #[derive(Diagnostic)]
 #[diag(builtin_macros_assert_requires_boolean)]
 pub(crate) struct AssertRequiresBoolean {

compiler/rustc_builtin_macros/src/lib.rs

@@ -27,6 +27,7 @@ use rustc_expand::proc_macro::BangProcMacro;
 use rustc_fluent_macro::fluent_messages;
 use rustc_span::symbol::sym;
 
+mod alloc_error_handler;
 mod assert;
 mod cfg;
 mod cfg_accessible;
@@ -103,6 +104,7 @@ pub fn register_builtin_macros(resolver: &mut dyn ResolverExpand) {
     }
 
     register_attr! {
+        alloc_error_handler: alloc_error_handler::expand,
         bench: test::expand_bench,
         cfg_accessible: cfg_accessible::Expander,
         cfg_eval: cfg_eval::expand,

compiler/rustc_codegen_cranelift/example/alloc_example.rs

@@ -1,4 +1,4 @@
-#![feature(start, core_intrinsics)]
+#![feature(start, core_intrinsics, alloc_error_handler)]
 #![no_std]
 
 extern crate alloc;
@@ -22,6 +22,11 @@ fn panic_handler(_: &core::panic::PanicInfo) -> ! {
     core::intrinsics::abort();
 }
 
+#[alloc_error_handler]
+fn alloc_error_handler(_: alloc::alloc::Layout) -> ! {
+    core::intrinsics::abort();
+}
+
 #[start]
 fn main(_argc: isize, _argv: *const *const u8) -> isize {
     let world: Box<&str> = Box::new("Hello World!\0");

compiler/rustc_codegen_cranelift/src/allocator.rs

@@ -6,6 +6,7 @@ use crate::prelude::*;
 use rustc_ast::expand::allocator::{AllocatorKind, AllocatorTy, ALLOCATOR_METHODS};
 use rustc_codegen_ssa::base::allocator_kind_for_codegen;
 use rustc_session::config::OomStrategy;
+use rustc_span::symbol::sym;
 
 /// Returns whether an allocator shim was created
 pub(crate) fn codegen(
@@ -14,7 +15,13 @@ pub(crate) fn codegen(
     unwind_context: &mut UnwindContext,
 ) -> bool {
     let Some(kind) = allocator_kind_for_codegen(tcx) else { return false };
-    codegen_inner(module, unwind_context, kind, tcx.sess.opts.unstable_opts.oom);
+    codegen_inner(
+        module,
+        unwind_context,
+        kind,
+        tcx.alloc_error_handler_kind(()).unwrap(),
+        tcx.sess.opts.unstable_opts.oom,
+    );
     true
 }
 
@@ -22,6 +29,7 @@ fn codegen_inner(
     module: &mut impl Module,
     unwind_context: &mut UnwindContext,
     kind: AllocatorKind,
+    alloc_error_handler_kind: AllocatorKind,
     oom_strategy: OomStrategy,
 ) {
     let usize_ty = module.target_config().pointer_type();
@@ -63,6 +71,19 @@ fn codegen_inner(
         );
     }
 
+    let sig = Signature {
+        call_conv: module.target_config().default_call_conv,
+        params: vec![AbiParam::new(usize_ty), AbiParam::new(usize_ty)],
+        returns: vec![],
+    };
+    crate::common::create_wrapper_function(
+        module,
+        unwind_context,
+        sig,
+        "__rust_alloc_error_handler",
+        &alloc_error_handler_kind.fn_name(sym::oom),
+    );
+
     let data_id = module.declare_data(OomStrategy::SYMBOL, Linkage::Export, false, false).unwrap();
     let mut data_ctx = DataContext::new();
     data_ctx.set_align(1);

compiler/rustc_codegen_gcc/example/alloc_example.rs

@@ -1,4 +1,4 @@
-#![feature(start, core_intrinsics, lang_items)]
+#![feature(start, core_intrinsics, alloc_error_handler, lang_items)]
 #![no_std]
 
 extern crate alloc;
@@ -21,6 +21,11 @@ fn panic_handler(_: &core::panic::PanicInfo) -> ! {
     core::intrinsics::abort();
 }
 
+#[alloc_error_handler]
+fn alloc_error_handler(_: alloc::alloc::Layout) -> ! {
+    core::intrinsics::abort();
+}
+
 #[lang = "eh_personality"]
 fn eh_personality() -> ! {
     loop {}

compiler/rustc_codegen_gcc/src/allocator.rs

@@ -5,10 +5,11 @@ use rustc_ast::expand::allocator::{AllocatorKind, AllocatorTy, ALLOCATOR_METHODS
 use rustc_middle::bug;
 use rustc_middle::ty::TyCtxt;
 use rustc_session::config::OomStrategy;
+use rustc_span::symbol::sym;
 
 use crate::GccContext;
 
-pub(crate) unsafe fn codegen(tcx: TyCtxt<'_>, mods: &mut GccContext, _module_name: &str, kind: AllocatorKind) {
+pub(crate) unsafe fn codegen(tcx: TyCtxt<'_>, mods: &mut GccContext, _module_name: &str, kind: AllocatorKind, alloc_error_handler_kind: AllocatorKind) {
     let context = &mods.context;
     let usize =
         match tcx.sess.target.pointer_width {
@@ -86,6 +87,37 @@ pub(crate) unsafe fn codegen(tcx: TyCtxt<'_>, mods: &mut GccContext, _module_nam
         // as described in https://github.com/rust-lang/rust/commit/77a96ed5646f7c3ee8897693decc4626fe380643
     }
 
+    let types = [usize, usize];
+    let name = "__rust_alloc_error_handler".to_string();
+    let args: Vec<_> = types.iter().enumerate()
+        .map(|(index, typ)| context.new_parameter(None, *typ, &format!("param{}", index)))
+        .collect();
+    let func = context.new_function(None, FunctionType::Exported, void, &args, name, false);
+
+    if tcx.sess.target.default_hidden_visibility {
+        #[cfg(feature="master")]
+        func.add_attribute(FnAttribute::Visibility(gccjit::Visibility::Hidden));
+    }
+
+    let callee = alloc_error_handler_kind.fn_name(sym::oom);
+    let args: Vec<_> = types.iter().enumerate()
+        .map(|(index, typ)| context.new_parameter(None, *typ, &format!("param{}", index)))
+        .collect();
+    let callee = context.new_function(None, FunctionType::Extern, void, &args, callee, false);
+    #[cfg(feature="master")]
+    callee.add_attribute(FnAttribute::Visibility(gccjit::Visibility::Hidden));
+
+    let block = func.new_block("entry");
+
+    let args = args
+        .iter()
+        .enumerate()
+        .map(|(i, _)| func.get_param(i as i32).to_rvalue())
+        .collect::<Vec<_>>();
+    let _ret = context.new_call(None, callee, &args);
+    //llvm::LLVMSetTailCall(ret, True);
+    block.end_with_void_return(None);
+
     let name = OomStrategy::SYMBOL.to_string();
     let global = context.new_global(None, GlobalKind::Exported, i8, name);
     let value = tcx.sess.opts.unstable_opts.oom.should_panic();

compiler/rustc_codegen_gcc/src/lib.rs

@@ -163,11 +163,11 @@ impl CodegenBackend for GccCodegenBackend {
 }
 
 impl ExtraBackendMethods for GccCodegenBackend {
-    fn codegen_allocator<'tcx>(&self, tcx: TyCtxt<'tcx>, module_name: &str, kind: AllocatorKind) -> Self::Module {
+    fn codegen_allocator<'tcx>(&self, tcx: TyCtxt<'tcx>, module_name: &str, kind: AllocatorKind, alloc_error_handler_kind: AllocatorKind) -> Self::Module {
         let mut mods = GccContext {
             context: Context::default(),
         };
-        unsafe { allocator::codegen(tcx, &mut mods, module_name, kind); }
+        unsafe { allocator::codegen(tcx, &mut mods, module_name, kind, alloc_error_handler_kind); }
         mods
     }
 

compiler/rustc_codegen_llvm/src/allocator.rs

@@ -4,6 +4,7 @@ use rustc_ast::expand::allocator::{AllocatorKind, AllocatorTy, ALLOCATOR_METHODS
 use rustc_middle::bug;
 use rustc_middle::ty::TyCtxt;
 use rustc_session::config::{DebugInfo, OomStrategy};
+use rustc_span::symbol::sym;
 
 use crate::debuginfo;
 use crate::llvm::{self, False, True};
@@ -14,6 +15,7 @@ pub(crate) unsafe fn codegen(
     module_llvm: &mut ModuleLlvm,
     module_name: &str,
     kind: AllocatorKind,
+    alloc_error_handler_kind: AllocatorKind,
 ) {
     let llcx = &*module_llvm.llcx;
     let llmod = module_llvm.llmod();
@@ -98,6 +100,52 @@ pub(crate) unsafe fn codegen(
         llvm::LLVMDisposeBuilder(llbuilder);
     }
 
+    // rust alloc error handler
+    let args = [usize, usize]; // size, align
+
+    let ty = llvm::LLVMFunctionType(void, args.as_ptr(), args.len() as c_uint, False);
+    let name = "__rust_alloc_error_handler";
+    let llfn = llvm::LLVMRustGetOrInsertFunction(llmod, name.as_ptr().cast(), name.len(), ty);
+    // -> ! DIFlagNoReturn
+    let no_return = llvm::AttributeKind::NoReturn.create_attr(llcx);
+    attributes::apply_to_llfn(llfn, llvm::AttributePlace::Function, &[no_return]);
+
+    if tcx.sess.target.default_hidden_visibility {
+        llvm::LLVMRustSetVisibility(llfn, llvm::Visibility::Hidden);
+    }
+    if tcx.sess.must_emit_unwind_tables() {
+        let uwtable = attributes::uwtable_attr(llcx);
+        attributes::apply_to_llfn(llfn, llvm::AttributePlace::Function, &[uwtable]);
+    }
+
+    let callee = alloc_error_handler_kind.fn_name(sym::oom);
+    let callee = llvm::LLVMRustGetOrInsertFunction(llmod, callee.as_ptr().cast(), callee.len(), ty);
+    // -> ! DIFlagNoReturn
+    attributes::apply_to_llfn(callee, llvm::AttributePlace::Function, &[no_return]);
+    llvm::LLVMRustSetVisibility(callee, llvm::Visibility::Hidden);
+
+    let llbb = llvm::LLVMAppendBasicBlockInContext(llcx, llfn, "entry\0".as_ptr().cast());
+
+    let llbuilder = llvm::LLVMCreateBuilderInContext(llcx);
+    llvm::LLVMPositionBuilderAtEnd(llbuilder, llbb);
+    let args = args
+        .iter()
+        .enumerate()
+        .map(|(i, _)| llvm::LLVMGetParam(llfn, i as c_uint))
+        .collect::<Vec<_>>();
+    let ret = llvm::LLVMRustBuildCall(
+        llbuilder,
+        ty,
+        callee,
+        args.as_ptr(),
+        args.len() as c_uint,
+        [].as_ptr(),
+        0 as c_uint,
+    );
+    llvm::LLVMSetTailCall(ret, True);
+    llvm::LLVMBuildRetVoid(llbuilder);
+    llvm::LLVMDisposeBuilder(llbuilder);
+
     // __rust_alloc_error_handler_should_panic
     let name = OomStrategy::SYMBOL;
     let ll_g = llvm::LLVMRustGetOrInsertGlobal(llmod, name.as_ptr().cast(), name.len(), i8);

compiler/rustc_codegen_llvm/src/lib.rs

@@ -115,10 +115,11 @@ impl ExtraBackendMethods for LlvmCodegenBackend {
         tcx: TyCtxt<'tcx>,
         module_name: &str,
         kind: AllocatorKind,
+        alloc_error_handler_kind: AllocatorKind,
     ) -> ModuleLlvm {
         let mut module_llvm = ModuleLlvm::new_metadata(tcx, module_name);
         unsafe {
-            allocator::codegen(tcx, &mut module_llvm, module_name, kind);
+            allocator::codegen(tcx, &mut module_llvm, module_name, kind, alloc_error_handler_kind);
         }
         module_llvm
     }

compiler/rustc_codegen_ssa/src/back/symbol_export.rs

@@ -219,7 +219,7 @@ fn exported_symbols_provider_local(
         for symbol_name in ALLOCATOR_METHODS
             .iter()
             .map(|method| format!("__rust_{}", method.name))
-            .chain([OomStrategy::SYMBOL.to_string()])
+            .chain(["__rust_alloc_error_handler".to_string(), OomStrategy::SYMBOL.to_string()])
         {
             let exported_symbol = ExportedSymbol::NoDefId(SymbolName::new(tcx, &symbol_name));
 

compiler/rustc_codegen_ssa/src/base.rs

@@ -635,9 +635,16 @@ pub fn codegen_crate<B: ExtraBackendMethods>(
     if let Some(kind) = allocator_kind_for_codegen(tcx) {
         let llmod_id =
             cgu_name_builder.build_cgu_name(LOCAL_CRATE, &["crate"], Some("allocator")).to_string();
-        let module_llvm = tcx
-            .sess
-            .time("write_allocator_module", || backend.codegen_allocator(tcx, &llmod_id, kind));
+        let module_llvm = tcx.sess.time("write_allocator_module", || {
+            backend.codegen_allocator(
+                tcx,
+                &llmod_id,
+                kind,
+                // If allocator_kind is Some then alloc_error_handler_kind must
+                // also be Some.
+                tcx.alloc_error_handler_kind(()).unwrap(),
+            )
+        });
 
         ongoing_codegen.submit_pre_codegened_module_to_llvm(
             tcx,

compiler/rustc_codegen_ssa/src/traits/backend.rs

@@ -123,6 +123,7 @@ pub trait ExtraBackendMethods: CodegenBackend + WriteBackendMethods + Sized + Se
         tcx: TyCtxt<'tcx>,
         module_name: &str,
         kind: AllocatorKind,
+        alloc_error_handler_kind: AllocatorKind,
     ) -> Self::Module;
     /// This generates the codegen unit and returns it along with
     /// a `u64` giving an estimate of the unit's processing cost.

compiler/rustc_feature/src/active.rs

@@ -291,6 +291,8 @@ declare_features! (
     (active, abi_x86_interrupt, "1.17.0", Some(40180), None),
     /// Allows additional const parameter types, such as `&'static str` or user defined types
     (incomplete, adt_const_params, "1.56.0", Some(95174), None),
+    /// Allows defining an `#[alloc_error_handler]`.
+    (active, alloc_error_handler, "1.29.0", Some(51540), None),
     /// Allows trait methods with arbitrary self types.
     (active, arbitrary_self_types, "1.23.0", Some(44874), None),
     /// Allows using `const` operands in inline assembly.

compiler/rustc_feature/src/removed.rs

@@ -47,8 +47,6 @@ declare_features! (
 
     (removed, advanced_slice_patterns, "1.0.0", Some(62254), None,
      Some("merged into `#![feature(slice_patterns)]`")),
-    /// Allows defining an `#[alloc_error_handler]`.
-    (removed, alloc_error_handler, "CURRENT_RUSTC_VERSION", Some(51540), None, Some("now handled by panic handler")),
     (removed, allocator, "1.0.0", None, None, None),
     /// Allows a test to fail without failing the whole suite.
     (removed, allow_fail, "1.19.0", Some(46488), None, Some("removed due to no clear use cases")),

compiler/rustc_interface/src/tests.rs

@@ -777,7 +777,7 @@ fn test_unstable_options_tracking_hash() {
     tracked!(no_link, true);
     tracked!(no_profiler_runtime, true);
     tracked!(no_unique_section_names, true);
-    tracked!(oom, OomStrategy::Unwind);
+    tracked!(oom, OomStrategy::Panic);
     tracked!(osx_rpath_install_name, true);
     tracked!(packed_bundled_libs, true);
     tracked!(panic_abort_tests, true);

compiler/rustc_metadata/messages.ftl

@@ -155,9 +155,19 @@ metadata_no_multiple_global_alloc =
 metadata_prev_global_alloc =
     previous global allocator defined here
 
+metadata_no_multiple_alloc_error_handler =
+    cannot define multiple allocation error handlers
+    .label = cannot define a new allocation error handler
+
+metadata_prev_alloc_error_handler =
+    previous allocation error handler defined here
+
 metadata_conflicting_global_alloc =
     the `#[global_allocator]` in {$other_crate_name} conflicts with global allocator in: {$crate_name}
 
+metadata_conflicting_alloc_error_handler =
+    the `#[alloc_error_handler]` in {$other_crate_name} conflicts with allocation error handler in: {$crate_name}
+
 metadata_global_alloc_required =
     no global memory allocator found but one is required; link to std or add `#[global_allocator]` to a static item that implements the GlobalAlloc trait
 

compiler/rustc_metadata/src/creader.rs

@@ -38,8 +38,13 @@ pub struct CStore {
     /// This crate needs an allocator and either provides it itself, or finds it in a dependency.
     /// If the above is true, then this field denotes the kind of the found allocator.
     allocator_kind: Option<AllocatorKind>,
+    /// This crate needs an allocation error handler and either provides it itself, or finds it in a dependency.
+    /// If the above is true, then this field denotes the kind of the found allocator.
+    alloc_error_handler_kind: Option<AllocatorKind>,
     /// This crate has a `#[global_allocator]` item.
     has_global_allocator: bool,
+    /// This crate has a `#[alloc_error_handler]` item.
+    has_alloc_error_handler: bool,
 
     /// The interned [StableCrateId]s.
     pub(crate) stable_crate_ids: StableCrateIdMap,
@@ -216,10 +221,18 @@ impl CStore {
         self.allocator_kind
     }
 
+    pub(crate) fn alloc_error_handler_kind(&self) -> Option<AllocatorKind> {
+        self.alloc_error_handler_kind
+    }
+
     pub(crate) fn has_global_allocator(&self) -> bool {
         self.has_global_allocator
     }
 
+    pub(crate) fn has_alloc_error_handler(&self) -> bool {
+        self.has_alloc_error_handler
+    }
+
     pub fn report_unused_deps(&self, tcx: TyCtxt<'_>) {
         let json_unused_externs = tcx.sess.opts.json_unused_externs;
 
@@ -255,7 +268,9 @@ impl CStore {
             metas: IndexVec::from_iter(iter::once(None)),
             injected_panic_runtime: None,
             allocator_kind: None,
+            alloc_error_handler_kind: None,
             has_global_allocator: false,
+            has_alloc_error_handler: false,
             stable_crate_ids,
             unused_externs: Vec::new(),
         }
@@ -761,6 +776,14 @@ impl<'a, 'tcx> CrateLoader<'a, 'tcx> {
             }
             spans => !spans.is_empty(),
         };
+        self.cstore.has_alloc_error_handler = match &*alloc_error_handler_spans(krate) {
+            [span1, span2, ..] => {
+                self.sess
+                    .emit_err(errors::NoMultipleAllocErrorHandler { span2: *span2, span1: *span1 });
+                true
+            }
+            spans => !spans.is_empty(),
+        };
 
         // Check to see if we actually need an allocator. This desire comes
         // about through the `#![needs_allocator]` attribute and is typically
@@ -801,6 +824,21 @@ impl<'a, 'tcx> CrateLoader<'a, 'tcx> {
                 }
             }
         }
+        let mut alloc_error_handler =
+            self.cstore.has_alloc_error_handler.then(|| Symbol::intern("this crate"));
+        for (_, data) in self.cstore.iter_crate_data() {
+            if data.has_alloc_error_handler() {
+                match alloc_error_handler {
+                    Some(other_crate) => {
+                        self.sess.emit_err(errors::ConflictingAllocErrorHandler {
+                            crate_name: data.name(),
+                            other_crate_name: other_crate,
+                        });
+                    }
+                    None => alloc_error_handler = Some(data.name()),
+                }
+            }
+        }
 
         if global_allocator.is_some() {
             self.cstore.allocator_kind = Some(AllocatorKind::Global);
@@ -816,6 +854,14 @@ impl<'a, 'tcx> CrateLoader<'a, 'tcx> {
             }
             self.cstore.allocator_kind = Some(AllocatorKind::Default);
         }
+
+        if alloc_error_handler.is_some() {
+            self.cstore.alloc_error_handler_kind = Some(AllocatorKind::Global);
+        } else {
+            // The alloc crate provides a default allocation error handler if
+            // one isn't specified.
+            self.cstore.alloc_error_handler_kind = Some(AllocatorKind::Default);
+        }
     }
 
     fn inject_dependency_if(
@@ -991,6 +1037,28 @@ fn global_allocator_spans(krate: &ast::Crate) -> Vec<Span> {
     f.spans
 }
 
+fn alloc_error_handler_spans(krate: &ast::Crate) -> Vec<Span> {
+    struct Finder {
+        name: Symbol,
+        spans: Vec<Span>,
+    }
+    impl<'ast> visit::Visitor<'ast> for Finder {
+        fn visit_item(&mut self, item: &'ast ast::Item) {
+            if item.ident.name == self.name
+                && attr::contains_name(&item.attrs, sym::rustc_std_internal_symbol)
+            {
+                self.spans.push(item.span);
+            }
+            visit::walk_item(self, item)
+        }
+    }
+
+    let name = Symbol::intern(&AllocatorKind::Global.fn_name(sym::oom));
+    let mut f = Finder { name, spans: Vec::new() };
+    visit::walk_crate(&mut f, krate);
+    f.spans
+}
+
 // On Windows the compiler would sometimes intermittently fail to open the
 // proc-macro DLL with `Error::LoadLibraryExW`. It is suspected that something in the
 // system still holds a lock on the file, so we retry a few times before calling it

compiler/rustc_metadata/src/errors.rs

@@ -352,6 +352,16 @@ pub struct NoMultipleGlobalAlloc {
     pub span1: Span,
 }
 
+#[derive(Diagnostic)]
+#[diag(metadata_no_multiple_alloc_error_handler)]
+pub struct NoMultipleAllocErrorHandler {
+    #[primary_span]
+    #[label]
+    pub span2: Span,
+    #[label(metadata_prev_alloc_error_handler)]
+    pub span1: Span,
+}
+
 #[derive(Diagnostic)]
 #[diag(metadata_conflicting_global_alloc)]
 pub struct ConflictingGlobalAlloc {
@@ -359,6 +369,13 @@ pub struct ConflictingGlobalAlloc {
     pub other_crate_name: Symbol,
 }
 
+#[derive(Diagnostic)]
+#[diag(metadata_conflicting_alloc_error_handler)]
+pub struct ConflictingAllocErrorHandler {
+    pub crate_name: Symbol,
+    pub other_crate_name: Symbol,
+}
+
 #[derive(Diagnostic)]
 #[diag(metadata_global_alloc_required)]
 pub struct GlobalAllocRequired;

compiler/rustc_metadata/src/rmeta/decoder.rs

@@ -1683,6 +1683,10 @@ impl CrateMetadata {
         self.root.has_global_allocator
     }
 
+    pub(crate) fn has_alloc_error_handler(&self) -> bool {
+        self.root.has_alloc_error_handler
+    }
+
     pub(crate) fn has_default_lib_allocator(&self) -> bool {
         self.root.has_default_lib_allocator
     }

compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs

@@ -290,6 +290,7 @@ provide! { tcx, def_id, other, cdata,
     is_panic_runtime => { cdata.root.panic_runtime }
     is_compiler_builtins => { cdata.root.compiler_builtins }
     has_global_allocator => { cdata.root.has_global_allocator }
+    has_alloc_error_handler => { cdata.root.has_alloc_error_handler }
     has_panic_handler => { cdata.root.has_panic_handler }
     is_profiler_runtime => { cdata.root.profiler_runtime }
     required_panic_strategy => { cdata.root.required_panic_strategy }
@@ -378,6 +379,7 @@ pub(in crate::rmeta) fn provide(providers: &mut Providers) {
     // resolve! Does this work? Unsure! That's what the issue is about
     *providers = Providers {
         allocator_kind: |tcx, ()| CStore::from_tcx(tcx).allocator_kind(),
+        alloc_error_handler_kind: |tcx, ()| CStore::from_tcx(tcx).alloc_error_handler_kind(),
         is_private_dep: |_tcx, LocalCrate| false,
         native_library: |tcx, id| {
             tcx.native_libraries(id.krate)
@@ -494,6 +496,7 @@ pub(in crate::rmeta) fn provide(providers: &mut Providers) {
 
         dependency_formats: |tcx, ()| Lrc::new(crate::dependency_format::calculate(tcx)),
         has_global_allocator: |tcx, LocalCrate| CStore::from_tcx(tcx).has_global_allocator(),
+        has_alloc_error_handler: |tcx, LocalCrate| CStore::from_tcx(tcx).has_alloc_error_handler(),
         postorder_cnums: |tcx, ()| {
             tcx.arena
                 .alloc_slice(&CStore::from_tcx(tcx).crate_dependencies_in_postorder(LOCAL_CRATE))

compiler/rustc_metadata/src/rmeta/encoder.rs

@@ -676,6 +676,7 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
                 panic_in_drop_strategy: tcx.sess.opts.unstable_opts.panic_in_drop,
                 edition: tcx.sess.edition(),
                 has_global_allocator: tcx.has_global_allocator(LOCAL_CRATE),
+                has_alloc_error_handler: tcx.has_alloc_error_handler(LOCAL_CRATE),
                 has_panic_handler: tcx.has_panic_handler(LOCAL_CRATE),
                 has_default_lib_allocator: attr::contains_name(&attrs, sym::default_lib_allocator),
                 proc_macro_data,

compiler/rustc_metadata/src/rmeta/mod.rs

@@ -225,6 +225,7 @@ pub(crate) struct CrateRoot {
     panic_in_drop_strategy: PanicStrategy,
     edition: Edition,
     has_global_allocator: bool,
+    has_alloc_error_handler: bool,
     has_panic_handler: bool,
     has_default_lib_allocator: bool,
 

compiler/rustc_middle/src/query/mod.rs

@@ -1351,6 +1351,13 @@ rustc_queries! {
         desc { "checking if the crate has_global_allocator" }
         separate_provide_extern
     }
+    query has_alloc_error_handler(_: CrateNum) -> bool {
+        // This query depends on untracked global state in CStore
+        eval_always
+        fatal_cycle
+        desc { "checking if the crate has_alloc_error_handler" }
+        separate_provide_extern
+    }
     query has_panic_handler(_: CrateNum) -> bool {
         fatal_cycle
         desc { "checking if the crate has_panic_handler" }
@@ -1723,6 +1730,10 @@ rustc_queries! {
         eval_always
         desc { "getting the allocator kind for the current crate" }
     }
+    query alloc_error_handler_kind(_: ()) -> Option<AllocatorKind> {
+        eval_always
+        desc { "alloc error handler kind for the current crate" }
+    }
 
     query upvars_mentioned(def_id: DefId) -> Option<&'tcx FxIndexMap<hir::HirId, hir::Upvar>> {
         desc { |tcx| "collecting upvars mentioned in `{}`", tcx.def_path_str(def_id) }

compiler/rustc_session/src/config.rs

@@ -3048,9 +3048,9 @@ pub(crate) mod dep_tracking {
 #[derive(Clone, Copy, PartialEq, Hash, Debug, Encodable, Decodable, HashStable_Generic)]
 pub enum OomStrategy {
     /// Generate a panic that can be caught by `catch_unwind`.
-    Unwind,
+    Panic,
 
-    /// Calls the panic hook as normal but aborts instead of unwinding.
+    /// Abort the process immediately.
     Abort,
 }
 
@@ -3059,7 +3059,7 @@ impl OomStrategy {
 
     pub fn should_panic(self) -> u8 {
         match self {
-            OomStrategy::Unwind => 1,
+            OomStrategy::Panic => 1,
             OomStrategy::Abort => 0,
         }
     }

compiler/rustc_session/src/options.rs

@@ -662,7 +662,7 @@ mod parse {
 
     pub(crate) fn parse_oom_strategy(slot: &mut OomStrategy, v: Option<&str>) -> bool {
         match v {
-            Some("unwind") => *slot = OomStrategy::Unwind,
+            Some("panic") => *slot = OomStrategy::Panic,
             Some("abort") => *slot = OomStrategy::Abort,
             _ => return false,
         }

library/alloc/Cargo.toml

@@ -35,6 +35,3 @@ compiler-builtins-mem = ['compiler_builtins/mem']
 compiler-builtins-c = ["compiler_builtins/c"]
 compiler-builtins-no-asm = ["compiler_builtins/no-asm"]
 compiler-builtins-mangled-names = ["compiler_builtins/mangled-names"]
-
-# Make panics and failed asserts immediately abort without formatting any message
-panic_immediate_abort = ["core/panic_immediate_abort"]

library/alloc/src/alloc.rs

@@ -14,11 +14,6 @@ use core::ptr::{self, NonNull};
 #[doc(inline)]
 pub use core::alloc::*;
 
-#[cfg(not(no_global_oom_handling))]
-use core::any::Any;
-#[cfg(not(no_global_oom_handling))]
-use core::panic::BoxMeUp;
-
 #[cfg(test)]
 mod tests;
 
@@ -348,77 +343,14 @@ pub(crate) unsafe fn box_free<T: ?Sized, A: Allocator>(ptr: Unique<T>, alloc: A)
     }
 }
 
-/// Payload passed to the panic handler when `handle_alloc_error` is called.
-#[unstable(feature = "panic_oom_payload", issue = "none")]
-#[derive(Debug)]
-pub struct AllocErrorPanicPayload {
-    layout: Layout,
-}
-
-impl AllocErrorPanicPayload {
-    /// Internal function for the standard library to clone a payload.
-    #[unstable(feature = "std_internals", issue = "none")]
-    #[doc(hidden)]
-    pub fn internal_clone(&self) -> Self {
-        AllocErrorPanicPayload { layout: self.layout }
-    }
-
-    /// Returns the [`Layout`] of the allocation attempt that caused the error.
-    #[unstable(feature = "panic_oom_payload", issue = "none")]
-    pub fn layout(&self) -> Layout {
-        self.layout
-    }
-}
-
-#[unstable(feature = "std_internals", issue = "none")]
-#[cfg(not(no_global_oom_handling))]
-unsafe impl BoxMeUp for AllocErrorPanicPayload {
-    fn take_box(&mut self) -> *mut (dyn Any + Send) {
-        use crate::boxed::Box;
-        Box::into_raw(Box::new(self.internal_clone()))
-    }
-
-    fn get(&mut self) -> &(dyn Any + Send) {
-        self
-    }
-}
-
 // # Allocation error handler
 
-#[cfg(all(not(no_global_oom_handling), not(test)))]
-fn rust_oom(layout: Layout) -> ! {
-    if cfg!(feature = "panic_immediate_abort") {
-        core::intrinsics::abort()
-    }
-
-    extern "Rust" {
-        // NOTE This function never crosses the FFI boundary; it's a Rust-to-Rust call
-        // that gets resolved to the `#[panic_handler]` function.
-        #[lang = "panic_impl"]
-        fn panic_impl(pi: &core::panic::PanicInfo<'_>) -> !;
-
-        // This symbol is emitted by rustc .
-        // Its value depends on the -Zoom={unwind,abort} compiler option.
-        static __rust_alloc_error_handler_should_panic: u8;
-    }
-
-    // Hack to work around issues with the lifetime of Arguments.
-    match format_args!("memory allocation of {} bytes failed", layout.size()) {
-        fmt => {
-            // Create a PanicInfo with a custom payload for the panic handler.
-            let can_unwind = unsafe { __rust_alloc_error_handler_should_panic != 0 };
-            let mut pi = core::panic::PanicInfo::internal_constructor(
-                Some(&fmt),
-                core::panic::Location::caller(),
-                can_unwind,
-            );
-            let payload = AllocErrorPanicPayload { layout };
-            pi.set_payload(&payload);
-
-            // SAFETY: `panic_impl` is defined in safe Rust code and thus is safe to call.
-            unsafe { panic_impl(&pi) }
-        }
-    }
+#[cfg(not(no_global_oom_handling))]
+extern "Rust" {
+    // This is the magic symbol to call the global alloc error handler. rustc generates
+    // it to call `__rg_oom` if there is a `#[alloc_error_handler]`, or to call the
+    // default implementations below (`__rdl_oom`) otherwise.
+    fn __rust_alloc_error_handler(size: usize, align: usize) -> !;
 }
 
 /// Abort on memory allocation error or failure.
@@ -426,6 +358,13 @@ fn rust_oom(layout: Layout) -> ! {
 /// Callers of memory allocation APIs wishing to abort computation
 /// in response to an allocation error are encouraged to call this function,
 /// rather than directly invoking `panic!` or similar.
+///
+/// The default behavior of this function is to print a message to standard error
+/// and abort the process.
+/// It can be replaced with [`set_alloc_error_hook`] and [`take_alloc_error_hook`].
+///
+/// [`set_alloc_error_hook`]: ../../std/alloc/fn.set_alloc_error_hook.html
+/// [`take_alloc_error_hook`]: ../../std/alloc/fn.take_alloc_error_hook.html
 #[stable(feature = "global_alloc", since = "1.28.0")]
 #[rustc_const_unstable(feature = "const_alloc_error", issue = "92523")]
 #[cfg(all(not(no_global_oom_handling), not(test)))]
@@ -436,7 +375,9 @@ pub const fn handle_alloc_error(layout: Layout) -> ! {
     }
 
     fn rt_error(layout: Layout) -> ! {
-        rust_oom(layout);
+        unsafe {
+            __rust_alloc_error_handler(layout.size(), layout.align());
+        }
     }
 
     unsafe { core::intrinsics::const_eval_select((layout,), ct_error, rt_error) }
@@ -446,7 +387,6 @@ pub const fn handle_alloc_error(layout: Layout) -> ! {
 #[cfg(all(not(no_global_oom_handling), test))]
 pub use std::alloc::handle_alloc_error;
 
-#[cfg(bootstrap)]
 #[cfg(all(not(no_global_oom_handling), not(test)))]
 #[doc(hidden)]
 #[allow(unused_attributes)]
@@ -458,7 +398,7 @@ pub mod __alloc_error_handler {
     pub unsafe fn __rdl_oom(size: usize, _align: usize) -> ! {
         extern "Rust" {
             // This symbol is emitted by rustc next to __rust_alloc_error_handler.
-            // Its value depends on the -Zoom={unwind,abort} compiler option.
+            // Its value depends on the -Zoom={panic,abort} compiler option.
             static __rust_alloc_error_handler_should_panic: u8;
         }
 

library/alloc/src/lib.rs

@@ -135,7 +135,6 @@
 #![feature(maybe_uninit_slice)]
 #![feature(maybe_uninit_uninit_array)]
 #![feature(maybe_uninit_uninit_array_transpose)]
-#![feature(panic_internals)]
 #![feature(pattern)]
 #![feature(pointer_byte_offsets)]
 #![feature(provide_any)]

library/core/src/macros/mod.rs

@@ -1531,6 +1531,16 @@ pub(crate) mod builtin {
         /* compiler built-in */
     }
 
+    /// Attribute macro applied to a function to register it as a handler for allocation failure.
+    ///
+    /// See also [`std::alloc::handle_alloc_error`](../../../std/alloc/fn.handle_alloc_error.html).
+    #[unstable(feature = "alloc_error_handler", issue = "51540")]
+    #[allow_internal_unstable(rustc_attrs)]
+    #[rustc_builtin_macro]
+    pub macro alloc_error_handler($item:item) {
+        /* compiler built-in */
+    }
+
     /// Keeps the item it's applied to if the passed path is accessible, and removes it otherwise.
     #[unstable(
         feature = "cfg_accessible",

library/core/src/prelude/v1.rs

@@ -76,7 +76,9 @@ pub use crate::macros::builtin::{RustcDecodable, RustcEncodable};
 // Do not `doc(no_inline)` so that they become doc items on their own
 // (no public module for them to be re-exported from).
 #[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
-pub use crate::macros::builtin::{bench, derive, global_allocator, test, test_case};
+pub use crate::macros::builtin::{
+    alloc_error_handler, bench, derive, global_allocator, test, test_case,
+};
 
 #[unstable(feature = "derive_const", issue = "none")]
 pub use crate::macros::builtin::derive_const;

library/std/Cargo.toml

@@ -67,7 +67,7 @@ llvm-libunwind = ["unwind/llvm-libunwind"]
 system-llvm-libunwind = ["unwind/system-llvm-libunwind"]
 
 # Make panics and failed asserts immediately abort without formatting any message
-panic_immediate_abort = ["alloc/panic_immediate_abort"]
+panic_immediate_abort = ["core/panic_immediate_abort"]
 
 # Enable std_detect default features for stdarch/crates/std_detect:
 # https://github.com/rust-lang/stdarch/blob/master/crates/std_detect/Cargo.toml

library/std/src/alloc.rs

@@ -57,8 +57,9 @@
 #![stable(feature = "alloc_module", since = "1.28.0")]
 
 use core::intrinsics;
-use core::ptr;
 use core::ptr::NonNull;
+use core::sync::atomic::{AtomicPtr, Ordering};
+use core::{mem, ptr};
 
 #[stable(feature = "alloc_module", since = "1.28.0")]
 #[doc(inline)]
@@ -285,6 +286,76 @@ unsafe impl Allocator for 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.
+///
+/// # Examples
+///
+/// ```
+/// #![feature(alloc_error_hook)]
+///
+/// use std::alloc::{Layout, set_alloc_error_hook};
+///
+/// fn custom_alloc_error_hook(layout: Layout) {
+///    panic!("memory allocation of {} bytes failed", layout.size());
+/// }
+///
+/// set_alloc_error_hook(custom_alloc_error_hook);
+/// ```
+#[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) {
+    extern "Rust" {
+        // This symbol is emitted by rustc next to __rust_alloc_error_handler.
+        // Its value depends on the -Zoom={panic,abort} compiler option.
+        static __rust_alloc_error_handler_should_panic: u8;
+    }
+
+    #[allow(unused_unsafe)]
+    if unsafe { __rust_alloc_error_handler_should_panic != 0 } {
+        panic!("memory allocation of {} bytes failed", layout.size());
+    } else {
+        rtprintpanic!("memory allocation of {} bytes failed\n", layout.size());
+    }
+}
+
+#[cfg(not(test))]
+#[doc(hidden)]
+#[alloc_error_handler]
+#[unstable(feature = "alloc_internals", issue = "none")]
+pub 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);
+    crate::process::abort()
+}
+
 #[cfg(not(test))]
 #[doc(hidden)]
 #[allow(unused_attributes)]

library/std/src/lib.rs

@@ -236,6 +236,7 @@
 //
 // Language features:
 // tidy-alphabetical-start
+#![feature(alloc_error_handler)]
 #![feature(allocator_internals)]
 #![feature(allow_internal_unsafe)]
 #![feature(allow_internal_unstable)]
@@ -319,7 +320,6 @@
 #![feature(get_mut_unchecked)]
 #![feature(map_try_insert)]
 #![feature(new_uninit)]
-#![feature(panic_oom_payload)]
 #![feature(slice_concat_trait)]
 #![feature(thin_box)]
 #![feature(try_reserve_kind)]

library/std/src/panicking.rs

@@ -245,24 +245,19 @@ fn default_hook(info: &PanicInfo<'_>) {
 
     // The current implementation always returns `Some`.
     let location = info.location().unwrap();
+
+    let msg = match info.payload().downcast_ref::<&'static str>() {
+        Some(s) => *s,
+        None => match info.payload().downcast_ref::<String>() {
+            Some(s) => &s[..],
+            None => "Box<dyn Any>",
+        },
+    };
     let thread = thread_info::current_thread();
     let name = thread.as_ref().and_then(|t| t.name()).unwrap_or("<unnamed>");
 
     let write = |err: &mut dyn crate::io::Write| {
-        // Use the panic message directly if available, otherwise take it from
-        // the payload.
-        if let Some(msg) = info.message() {
-            let _ = writeln!(err, "thread '{name}' panicked at '{msg}', {location}");
-        } else {
-            let msg = if let Some(s) = info.payload().downcast_ref::<&'static str>() {
-                *s
-            } else if let Some(s) = info.payload().downcast_ref::<String>() {
-                &s[..]
-            } else {
-                "Box<dyn Any>"
-            };
-            let _ = writeln!(err, "thread '{name}' panicked at '{msg}', {location}");
-        }
+        let _ = writeln!(err, "thread '{name}' panicked at '{msg}', {location}");
 
         static FIRST_PANIC: AtomicBool = AtomicBool::new(true);
 
@@ -529,8 +524,6 @@ pub fn panicking() -> bool {
 #[cfg(not(test))]
 #[panic_handler]
 pub fn begin_panic_handler(info: &PanicInfo<'_>) -> ! {
-    use alloc::alloc::AllocErrorPanicPayload;
-
     struct PanicPayload<'a> {
         inner: &'a fmt::Arguments<'a>,
         string: Option<String>,
@@ -557,7 +550,8 @@ pub fn begin_panic_handler(info: &PanicInfo<'_>) -> ! {
     unsafe impl<'a> BoxMeUp for PanicPayload<'a> {
         fn take_box(&mut self) -> *mut (dyn Any + Send) {
             // We do two allocations here, unfortunately. But (a) they're required with the current
-            // scheme, and (b) OOM uses its own separate payload type which doesn't allocate.
+            // scheme, and (b) we don't handle panic + OOM properly anyway (see comment in
+            // begin_panic below).
             let contents = mem::take(self.fill());
             Box::into_raw(Box::new(contents))
         }
@@ -582,14 +576,7 @@ pub fn begin_panic_handler(info: &PanicInfo<'_>) -> ! {
     let loc = info.location().unwrap(); // The current implementation always returns Some
     let msg = info.message().unwrap(); // The current implementation always returns Some
     crate::sys_common::backtrace::__rust_end_short_backtrace(move || {
-        if let Some(payload) = info.payload().downcast_ref::<AllocErrorPanicPayload>() {
-            rust_panic_with_hook(
-                &mut payload.internal_clone(),
-                info.message(),
-                loc,
-                info.can_unwind(),
-            );
-        } else if let Some(msg) = msg.as_str() {
+        if let Some(msg) = msg.as_str() {
             rust_panic_with_hook(&mut StrPanicPayload(msg), info.message(), loc, info.can_unwind());
         } else {
             rust_panic_with_hook(
@@ -636,7 +623,11 @@ pub const fn begin_panic<M: Any + Send>(msg: M) -> ! {
 
     unsafe impl<A: Send + 'static> BoxMeUp for PanicPayload<A> {
         fn take_box(&mut self) -> *mut (dyn Any + Send) {
-            // Note that this should be the only allocation performed in this code path.
+            // Note that this should be the only allocation performed in this code path. Currently
+            // this means that panic!() on OOM will invoke this code path, but then again we're not
+            // really ready for panic on OOM anyway. If we do start doing this, then we should
+            // propagate this allocation to be performed in the parent of this thread instead of the
+            // thread that's panicking.
             let data = match self.inner.take() {
                 Some(a) => Box::new(a) as Box<dyn Any + Send>,
                 None => process::abort(),

library/std/src/prelude/v1.rs

@@ -60,7 +60,9 @@ pub use core::prelude::v1::{RustcDecodable, RustcEncodable};
 // Do not `doc(no_inline)` so that they become doc items on their own
 // (no public module for them to be re-exported from).
 #[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
-pub use core::prelude::v1::{bench, derive, global_allocator, test, test_case};
+pub use core::prelude::v1::{
+    alloc_error_handler, bench, derive, global_allocator, test, test_case,
+};
 
 #[unstable(feature = "derive_const", issue = "none")]
 pub use core::prelude::v1::derive_const;

src/tools/rust-analyzer/crates/hir-def/src/builtin_attr.rs

@@ -381,6 +381,10 @@ pub const INERT_ATTRIBUTES: &[BuiltinAttribute] = &[
 
     rustc_attr!(rustc_allocator, Normal, template!(Word), WarnFollowing, IMPL_DETAIL),
     rustc_attr!(rustc_nounwind, Normal, template!(Word), WarnFollowing, IMPL_DETAIL),
+    gated!(
+        alloc_error_handler, Normal, template!(Word), WarnFollowing,
+        experimental!(alloc_error_handler)
+    ),
     gated!(
         default_lib_allocator, Normal, template!(Word), WarnFollowing, allocator_internals,
         experimental!(default_lib_allocator),

tests/run-make/coverage-reports/expected_show_coverage.issue-84561.txt

@@ -136,10 +136,10 @@
   134|       |
   135|       |impl std::fmt::Debug for Foo {
   136|       |    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
-  137|      9|        write!(f, "try and succeed")?;
+  137|      7|        write!(f, "try and succeed")?;
                                                   ^0
-  138|      9|        Ok(())
-  139|      9|    }
+  138|      7|        Ok(())
+  139|      7|    }
   140|       |}
   141|       |
   142|       |static mut DEBUG_LEVEL_ENABLED: bool = false;

tests/run-make/issue-51671/Makefile

@@ -6,3 +6,4 @@ all:
 	$(RUSTC) --emit=obj app.rs
 	nm $(TMPDIR)/app.o | $(CGREP) rust_begin_unwind
 	nm $(TMPDIR)/app.o | $(CGREP) rust_eh_personality
+	nm $(TMPDIR)/app.o | $(CGREP) __rg_oom

tests/run-make/issue-51671/app.rs

@@ -1,5 +1,5 @@
 #![crate_type = "bin"]
-#![feature(lang_items)]
+#![feature(lang_items, alloc_error_handler)]
 #![no_main]
 #![no_std]
 
@@ -13,3 +13,8 @@ fn panic(_: &PanicInfo) -> ! {
 
 #[lang = "eh_personality"]
 fn eh() {}
+
+#[alloc_error_handler]
+fn oom(_: Layout) -> ! {
+    loop {}
+}

tests/run-make/issue-69368/Makefile

@@ -0,0 +1,19 @@
+# ignore-cross-compile
+include ../tools.mk
+
+# Test that previously triggered a linker failure with root cause
+# similar to one found in the issue #69368.
+#
+# The crate that provides oom lang item is missing some other lang
+# items. Necessary to prevent the use of start-group / end-group.
+#
+# The weak lang items are defined in a separate compilation units,
+# so that linker could omit them if not used.
+#
+# The crates that need those weak lang items are dependencies of
+# crates that provide them.
+
+all:
+	$(RUSTC) a.rs
+	$(RUSTC) b.rs
+	$(RUSTC) c.rs

tests/run-make/issue-69368/a.rs

@@ -0,0 +1,26 @@
+#![crate_type = "rlib"]
+#![feature(lang_items)]
+#![feature(panic_unwind)]
+#![no_std]
+
+extern crate panic_unwind;
+
+#[panic_handler]
+pub fn panic_handler(_: &core::panic::PanicInfo) -> ! {
+    loop {}
+}
+
+#[no_mangle]
+extern "C" fn __rust_drop_panic() -> ! {
+    loop {}
+}
+
+#[no_mangle]
+extern "C" fn __rust_foreign_exception() -> ! {
+    loop {}
+}
+
+#[lang = "eh_personality"]
+fn eh_personality() {
+    loop {}
+}

tests/run-make/issue-69368/b.rs

@@ -0,0 +1,8 @@
+#![crate_type = "rlib"]
+#![feature(alloc_error_handler)]
+#![no_std]
+
+#[alloc_error_handler]
+pub fn error_handler(_: core::alloc::Layout) -> ! {
+    panic!();
+}

tests/run-make/issue-69368/c.rs

@@ -0,0 +1,34 @@
+#![crate_type = "bin"]
+#![feature(start)]
+#![no_std]
+
+extern crate alloc;
+extern crate a;
+extern crate b;
+
+use alloc::vec::Vec;
+use core::alloc::*;
+
+struct Allocator;
+
+unsafe impl GlobalAlloc for Allocator {
+    unsafe fn alloc(&self, _: Layout) -> *mut u8 {
+        loop {}
+    }
+
+    unsafe fn dealloc(&self, _: *mut u8, _: Layout) {
+        loop {}
+    }
+}
+
+#[global_allocator]
+static ALLOCATOR: Allocator = Allocator;
+
+#[start]
+fn main(argc: isize, _argv: *const *const u8) -> isize {
+    let mut v = Vec::new();
+    for i in 0..argc {
+        v.push(i);
+    }
+    v.iter().sum()
+}

tests/run-make/wasm-symbols-not-exported/bar.rs

@@ -1,4 +1,4 @@
-#![feature(panic_handler)]
+#![feature(panic_handler, alloc_error_handler)]
 #![crate_type = "cdylib"]
 #![no_std]
 
@@ -24,6 +24,11 @@ pub extern fn foo(a: u32) -> u32 {
     a * 2
 }
 
+#[alloc_error_handler]
+fn a(_: core::alloc::Layout) -> ! {
+    loop {}
+}
+
 #[panic_handler]
 fn b(_: &core::panic::PanicInfo) -> ! {
     loop {}

tests/ui/alloc-error/alloc-error-handler-bad-signature-1.rs

@@ -0,0 +1,18 @@
+// compile-flags:-C panic=abort
+
+#![feature(alloc_error_handler)]
+#![no_std]
+#![no_main]
+
+use core::alloc::Layout;
+
+#[alloc_error_handler]
+fn oom(
+    info: &Layout, //~^ ERROR mismatched types
+) -> () //~^^ ERROR mismatched types
+{
+    loop {}
+}
+
+#[panic_handler]
+fn panic(_: &core::panic::PanicInfo) -> ! { loop {} }

tests/ui/alloc-error/alloc-error-handler-bad-signature-1.stderr

@@ -0,0 +1,44 @@
+error[E0308]: mismatched types
+  --> $DIR/alloc-error-handler-bad-signature-1.rs:10:1
+   |
+LL |    #[alloc_error_handler]
+   |    ---------------------- in this procedural macro expansion
+LL | // fn oom(
+LL | ||     info: &Layout,
+LL | || ) -> ()
+   | ||_______- arguments to this function are incorrect
+LL | |  {
+LL | |      loop {}
+LL | |  }
+   | |__^ expected `&Layout`, found `Layout`
+   |
+note: function defined here
+  --> $DIR/alloc-error-handler-bad-signature-1.rs:10:4
+   |
+LL | fn oom(
+   |    ^^^
+LL |     info: &Layout,
+   |     -------------
+   = note: this error originates in the attribute macro `alloc_error_handler` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0308]: mismatched types
+  --> $DIR/alloc-error-handler-bad-signature-1.rs:10:1
+   |
+LL |    #[alloc_error_handler]
+   |    ---------------------- in this procedural macro expansion
+LL | // fn oom(
+LL | ||     info: &Layout,
+LL | || ) -> ()
+   | ||_______^ expected `!`, found `()`
+LL | |  {
+LL | |      loop {}
+LL | |  }
+   | |__- expected `!` because of return type
+   |
+   = note:   expected type `!`
+           found unit type `()`
+   = note: this error originates in the attribute macro `alloc_error_handler` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0308`.

tests/ui/alloc-error/alloc-error-handler-bad-signature-2.rs

@@ -0,0 +1,17 @@
+// compile-flags:-C panic=abort
+
+#![feature(alloc_error_handler)]
+#![no_std]
+#![no_main]
+
+struct Layout;
+
+#[alloc_error_handler]
+fn oom(
+    info: Layout, //~^ ERROR mismatched types
+) { //~^^ ERROR mismatched types
+    loop {}
+}
+
+#[panic_handler]
+fn panic(_: &core::panic::PanicInfo) -> ! { loop {} }

tests/ui/alloc-error/alloc-error-handler-bad-signature-2.stderr

@@ -0,0 +1,50 @@
+error[E0308]: mismatched types
+  --> $DIR/alloc-error-handler-bad-signature-2.rs:10:1
+   |
+LL |    #[alloc_error_handler]
+   |    ---------------------- in this procedural macro expansion
+LL | // fn oom(
+LL | ||     info: Layout,
+LL | || ) {
+   | ||_- arguments to this function are incorrect
+LL | |      loop {}
+LL | |  }
+   | |__^ expected `Layout`, found `core::alloc::Layout`
+   |
+   = note: `core::alloc::Layout` and `Layout` have similar names, but are actually distinct types
+note: `core::alloc::Layout` is defined in crate `core`
+  --> $SRC_DIR/core/src/alloc/layout.rs:LL:COL
+note: `Layout` is defined in the current crate
+  --> $DIR/alloc-error-handler-bad-signature-2.rs:7:1
+   |
+LL | struct Layout;
+   | ^^^^^^^^^^^^^
+note: function defined here
+  --> $DIR/alloc-error-handler-bad-signature-2.rs:10:4
+   |
+LL | fn oom(
+   |    ^^^
+LL |     info: Layout,
+   |     ------------
+   = note: this error originates in the attribute macro `alloc_error_handler` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0308]: mismatched types
+  --> $DIR/alloc-error-handler-bad-signature-2.rs:10:1
+   |
+LL |    #[alloc_error_handler]
+   |    ---------------------- in this procedural macro expansion
+LL | // fn oom(
+LL | ||     info: Layout,
+LL | || ) {
+   | ||_^ expected `!`, found `()`
+LL | |      loop {}
+LL | |  }
+   | |__- expected `!` because of return type
+   |
+   = note:   expected type `!`
+           found unit type `()`
+   = note: this error originates in the attribute macro `alloc_error_handler` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0308`.

tests/ui/alloc-error/alloc-error-handler-bad-signature-3.rs

@@ -0,0 +1,15 @@
+// compile-flags:-C panic=abort
+
+#![feature(alloc_error_handler)]
+#![no_std]
+#![no_main]
+
+struct Layout;
+
+#[alloc_error_handler]
+fn oom() -> ! { //~ ERROR function takes 0 arguments but 1 argument was supplied
+    loop {}
+}
+
+#[panic_handler]
+fn panic(_: &core::panic::PanicInfo) -> ! { loop {} }

tests/ui/alloc-error/alloc-error-handler-bad-signature-3.stderr

@@ -0,0 +1,21 @@
+error[E0061]: this function takes 0 arguments but 1 argument was supplied
+  --> $DIR/alloc-error-handler-bad-signature-3.rs:10:1
+   |
+LL |   #[alloc_error_handler]
+   |   ---------------------- in this procedural macro expansion
+LL |   fn oom() -> ! {
+   |  _-^^^^^^^^^^^^
+LL | |     loop {}
+LL | | }
+   | |_- unexpected argument of type `core::alloc::Layout`
+   |
+note: function defined here
+  --> $DIR/alloc-error-handler-bad-signature-3.rs:10:4
+   |
+LL | fn oom() -> ! {
+   |    ^^^
+   = note: this error originates in the attribute macro `alloc_error_handler` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0061`.

tests/ui/alloc-error/default-alloc-error-hook.rs

@@ -2,7 +2,7 @@
 // ignore-emscripten no processes
 // ignore-sgx no processes
 
-use std::alloc::{handle_alloc_error, Layout};
+use std::alloc::{Layout, handle_alloc_error};
 use std::env;
 use std::process::Command;
 use std::str;
@@ -24,5 +24,5 @@ fn main() {
         .strip_suffix("qemu: uncaught target signal 6 (Aborted) - core dumped\n")
         .unwrap_or(stderr);
 
-    assert!(stderr.contains("memory allocation of 42 bytes failed"));
+    assert_eq!(stderr, "memory allocation of 42 bytes failed\n");
 }

tests/ui/allocator/no_std-alloc-error-handler-custom.rs

@@ -0,0 +1,84 @@
+// run-pass
+// ignore-android no libc
+// ignore-emscripten no libc
+// ignore-sgx no libc
+// ignore-wasm32 no libc
+// only-linux
+// compile-flags:-C panic=abort
+// aux-build:helper.rs
+
+#![feature(rustc_private, lang_items)]
+#![feature(alloc_error_handler)]
+#![no_std]
+#![no_main]
+
+extern crate alloc;
+extern crate libc;
+
+// ARM targets need these symbols
+#[no_mangle]
+pub fn __aeabi_unwind_cpp_pr0() {}
+
+#[no_mangle]
+pub fn __aeabi_unwind_cpp_pr1() {}
+
+use alloc::boxed::Box;
+use alloc::string::ToString;
+use core::alloc::{GlobalAlloc, Layout};
+use core::ptr::null_mut;
+
+extern crate helper;
+
+struct MyAllocator;
+
+#[alloc_error_handler]
+fn my_oom(layout: Layout) -> ! {
+    use alloc::fmt::write;
+    unsafe {
+        let size = layout.size();
+        let mut s = alloc::string::String::new();
+        write(&mut s, format_args!("My OOM: failed to allocate {} bytes!\n", size)).unwrap();
+        libc::write(libc::STDERR_FILENO, s.as_ptr() as *const _, s.len());
+        libc::exit(0)
+    }
+}
+
+unsafe impl GlobalAlloc for MyAllocator {
+    unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
+        if layout.size() < 4096 { libc::malloc(layout.size()) as _ } else { null_mut() }
+    }
+    unsafe fn dealloc(&self, _ptr: *mut u8, _layout: Layout) {}
+}
+
+#[global_allocator]
+static A: MyAllocator = MyAllocator;
+
+#[panic_handler]
+fn panic(panic_info: &core::panic::PanicInfo) -> ! {
+    unsafe {
+        let s = panic_info.to_string();
+        const PSTR: &str = "panic occurred: ";
+        const CR: &str = "\n";
+        libc::write(libc::STDERR_FILENO, PSTR.as_ptr() as *const _, PSTR.len());
+        libc::write(libc::STDERR_FILENO, s.as_ptr() as *const _, s.len());
+        libc::write(libc::STDERR_FILENO, CR.as_ptr() as *const _, CR.len());
+        libc::exit(1)
+    }
+}
+
+// Because we are compiling this code with `-C panic=abort`, this wouldn't normally be needed.
+// However, `core` and `alloc` are both compiled with `-C panic=unwind`, which means that functions
+// in these libraries will refer to `rust_eh_personality` if LLVM can not *prove* the contents won't
+// unwind. So, for this test case we will define the symbol.
+#[lang = "eh_personality"]
+extern "C" fn rust_eh_personality() {}
+
+#[derive(Default, Debug)]
+struct Page(#[allow(unused_tuple_struct_fields)] [[u64; 32]; 16]);
+
+#[no_mangle]
+fn main(_argc: i32, _argv: *const *const u8) -> isize {
+    let zero = Box::<Page>::new(Default::default());
+    helper::work_with(&zero);
+    1
+}

tests/ui/feature-gates/feature-gate-alloc-error-handler.rs

@@ -0,0 +1,16 @@
+// compile-flags:-C panic=abort
+
+#![no_std]
+#![no_main]
+
+use core::alloc::Layout;
+
+#[alloc_error_handler] //~ ERROR use of unstable library feature 'alloc_error_handler'
+fn oom(info: Layout) -> ! {
+    loop {}
+}
+
+#[panic_handler]
+fn panic(_: &core::panic::PanicInfo) -> ! {
+    loop {}
+}

tests/ui/feature-gates/feature-gate-alloc-error-handler.stderr

@@ -0,0 +1,12 @@
+error[E0658]: use of unstable library feature 'alloc_error_handler'
+  --> $DIR/feature-gate-alloc-error-handler.rs:8:3
+   |
+LL | #[alloc_error_handler]
+   |   ^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #51540 <https://github.com/rust-lang/rust/issues/51540> for more information
+   = help: add `#![feature(alloc_error_handler)]` to the crate attributes to enable
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0658`.

tests/ui/missing/missing-allocator.rs

@@ -3,10 +3,16 @@
 
 #![no_std]
 #![crate_type = "staticlib"]
+#![feature(alloc_error_handler)]
 
 #[panic_handler]
 fn panic(_: &core::panic::PanicInfo) -> ! {
     loop {}
 }
 
+#[alloc_error_handler]
+fn oom(_: core::alloc::Layout) -> ! {
+    loop {}
+}
+
 extern crate alloc;

tests/ui/oom_unwind.rs

@@ -1,4 +1,4 @@
-// compile-flags: -Z oom=unwind
+// compile-flags: -Z oom=panic
 // run-pass
 // no-prefer-dynamic
 // needs-unwind