From 964d3af793eeebbe4aa1289ffdffeca6e3d56664 Mon Sep 17 00:00:00 2001
From: bjorn3 <17426603+bjorn3@users.noreply.github.com>
Date: Wed, 29 Oct 2025 12:58:55 +0000
Subject: [PATCH 1/2] Move a special case for rust_eh_personality from
 reachable_non_generics to cg_llvm

This is a workaround for an LLVM bug, so put it in cg_llvm.
---
 compiler/rustc_codegen_llvm/src/back/lto.rs          | 3 +++
 compiler/rustc_codegen_ssa/src/back/symbol_export.rs | 7 +------
 2 files changed, 4 insertions(+), 6 deletions(-)

diff --git a/compiler/rustc_codegen_llvm/src/back/lto.rs b/compiler/rustc_codegen_llvm/src/back/lto.rs
index 5ac3a87c158e6..02b50fa8a6971 100644
--- a/compiler/rustc_codegen_llvm/src/back/lto.rs
+++ b/compiler/rustc_codegen_llvm/src/back/lto.rs
@@ -77,6 +77,9 @@ fn prepare_lto(
     // should have default visibility.
     symbols_below_threshold.push(c"__llvm_profile_counter_bias".to_owned());
 
+    // LTO seems to discard this otherwise under certain circumstances.
+    symbols_below_threshold.push(c"rust_eh_personality".to_owned());
+
     // If we're performing LTO for the entire crate graph, then for each of our
     // upstream dependencies, find the corresponding rlib and load the bitcode
     // from the archive.
diff --git a/compiler/rustc_codegen_ssa/src/back/symbol_export.rs b/compiler/rustc_codegen_ssa/src/back/symbol_export.rs
index 5bc18e2d7f8bb..8a1f20826a946 100644
--- a/compiler/rustc_codegen_ssa/src/back/symbol_export.rs
+++ b/compiler/rustc_codegen_ssa/src/back/symbol_export.rs
@@ -104,10 +104,6 @@ fn reachable_non_generics_provider(tcx: TyCtxt<'_>, _: LocalCrate) -> DefIdMap<S
             if tcx.cross_crate_inlinable(def_id) { None } else { Some(def_id) }
         })
         .map(|def_id| {
-            // We won't link right if this symbol is stripped during LTO.
-            let name = tcx.symbol_name(Instance::mono(tcx, def_id.to_def_id())).name;
-            let used = name == "rust_eh_personality";
-
             let export_level = if special_runtime_crate {
                 SymbolExportLevel::Rust
             } else {
@@ -131,8 +127,7 @@ fn reachable_non_generics_provider(tcx: TyCtxt<'_>, _: LocalCrate) -> DefIdMap<S
                     SymbolExportKind::Text
                 },
                 used: codegen_attrs.flags.contains(CodegenFnAttrFlags::USED_COMPILER)
-                    || codegen_attrs.flags.contains(CodegenFnAttrFlags::USED_LINKER)
-                    || used,
+                    || codegen_attrs.flags.contains(CodegenFnAttrFlags::USED_LINKER),
                 rustc_std_internal_symbol: codegen_attrs
                     .flags
                     .contains(CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL),

From e8d88c0581396142c245929dc7e5f5ca3c643c82 Mon Sep 17 00:00:00 2001
From: bjorn3 <17426603+bjorn3@users.noreply.github.com>
Date: Wed, 29 Oct 2025 13:06:24 +0000
Subject: [PATCH 2/2] Remove special case for the panic runtime from
 reachable_non_generics

The panic runtime uses #[rustc_std_internal_symbol] which has the same
effect as this special case with respect to symbol visibility.
---
 .../rustc_codegen_ssa/src/back/symbol_export.rs | 17 +++++++----------
 1 file changed, 7 insertions(+), 10 deletions(-)

diff --git a/compiler/rustc_codegen_ssa/src/back/symbol_export.rs b/compiler/rustc_codegen_ssa/src/back/symbol_export.rs
index 8a1f20826a946..d9ba5017a422d 100644
--- a/compiler/rustc_codegen_ssa/src/back/symbol_export.rs
+++ b/compiler/rustc_codegen_ssa/src/back/symbol_export.rs
@@ -51,15 +51,7 @@ fn reachable_non_generics_provider(tcx: TyCtxt<'_>, _: LocalCrate) -> DefIdMap<S
         return Default::default();
     }
 
-    // Check to see if this crate is a "special runtime crate". These
-    // crates, implementation details of the standard library, typically
-    // have a bunch of `pub extern` and `#[no_mangle]` functions as the
-    // ABI between them. We don't want their symbols to have a `C`
-    // export level, however, as they're just implementation details.
-    // Down below we'll hardwire all of the symbols to the `Rust` export
-    // level instead.
-    let special_runtime_crate =
-        tcx.is_panic_runtime(LOCAL_CRATE) || tcx.is_compiler_builtins(LOCAL_CRATE);
+    let is_compiler_builtins = tcx.is_compiler_builtins(LOCAL_CRATE);
 
     let mut reachable_non_generics: DefIdMap<_> = tcx
         .reachable_set(())
@@ -104,7 +96,12 @@ fn reachable_non_generics_provider(tcx: TyCtxt<'_>, _: LocalCrate) -> DefIdMap<S
             if tcx.cross_crate_inlinable(def_id) { None } else { Some(def_id) }
         })
         .map(|def_id| {
-            let export_level = if special_runtime_crate {
+            let export_level = if is_compiler_builtins {
+                // We don't want to export compiler-builtins symbols from any
+                // dylibs, even rust dylibs. Unlike all other crates it gets
+                // duplicated in every linker invocation and it may otherwise
+                // unintentionally override definitions of these symbols by
+                // libgcc or compiler-rt for C code.
                 SymbolExportLevel::Rust
             } else {
                 symbol_export_level(tcx, def_id.to_def_id())