From 67b7b7f66b0c23e0d0aa4cd10578cc1511eedcb4 Mon Sep 17 00:00:00 2001
From: bjorn3 <17426603+bjorn3@users.noreply.github.com>
Date: Thu, 26 Jun 2025 13:44:01 +0000
Subject: [PATCH] Support #[alloc_error_handler] without the allocator shim

Currently it is possible to avoid linking the allocator shim when
__rust_no_alloc_shim_is_unstable_v2 is defined when linking rlibs
directly as some build systems need. However this requires liballoc to
be compiled with --cfg no_global_oom_handling, which places huge
restrictions on what functions you can call and makes it impossible to
use libstd. Or alternatively you have to define
__rust_alloc_error_handler and (when using libstd)
__rust_alloc_error_handler_should_panic
using #[rustc_std_internal_symbol]. With this commit you can either use
libstd and define __rust_alloc_error_handler_should_panic or not use
libstd and use #[alloc_error_handler] instead. Both options are still
unstable though.

Eventually the alloc_error_handler may either be removed entirely
(though the PR for that has been stale for years now) or we may start
using weak symbols for it instead. For the latter case this commit is a
prerequisite anyway.
---
 src/allocator.rs | 28 +++++++++++++++-------------
 1 file changed, 15 insertions(+), 13 deletions(-)

diff --git a/src/allocator.rs b/src/allocator.rs
index 04f1129d87c1..9533f870434a 100644
--- a/src/allocator.rs
+++ b/src/allocator.rs
@@ -3,8 +3,8 @@
 
 use cranelift_frontend::{FunctionBuilder, FunctionBuilderContext};
 use rustc_ast::expand::allocator::{
-    ALLOCATOR_METHODS, AllocatorKind, AllocatorTy, NO_ALLOC_SHIM_IS_UNSTABLE,
-    alloc_error_handler_name, default_fn_name, global_fn_name,
+    ALLOC_ERROR_HANDLER, ALLOCATOR_METHODS, AllocatorKind, AllocatorTy, NO_ALLOC_SHIM_IS_UNSTABLE,
+    default_fn_name, global_fn_name,
 };
 use rustc_codegen_ssa::base::allocator_kind_for_codegen;
 use rustc_session::config::OomStrategy;
@@ -72,17 +72,19 @@ 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,
-        sig,
-        &mangle_internal_symbol(tcx, "__rust_alloc_error_handler"),
-        &mangle_internal_symbol(tcx, alloc_error_handler_name(alloc_error_handler_kind)),
-    );
+    if alloc_error_handler_kind == AllocatorKind::Default {
+        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,
+            sig,
+            &mangle_internal_symbol(tcx, &global_fn_name(ALLOC_ERROR_HANDLER)),
+            &mangle_internal_symbol(tcx, &default_fn_name(ALLOC_ERROR_HANDLER)),
+        );
+    }
 
     {
         let sig = Signature {