Correctly handle different crate types disagreeing if the allocator shim is exported

Previously it would attempt to export the allocator shim even linking
for a crate type which pulls in the allocator shim from a dylib rather
than locally defining it.

Author: bjorn3

compiler/rustc_codegen_ssa/src/back/linker.rs

@@ -11,8 +11,9 @@ use rustc_metadata::{
 };
 use rustc_middle::bug;
 use rustc_middle::middle::dependency_format::Linkage;
-use rustc_middle::middle::exported_symbols;
-use rustc_middle::middle::exported_symbols::{ExportedSymbol, SymbolExportInfo, SymbolExportKind};
+use rustc_middle::middle::exported_symbols::{
+    self, ExportedSymbol, SymbolExportInfo, SymbolExportKind, SymbolExportLevel,
+};
 use rustc_middle::ty::TyCtxt;
 use rustc_session::Session;
 use rustc_session::config::{self, CrateType, DebugInfo, LinkerPluginLto, Lto, OptLevel, Strip};
@@ -22,6 +23,8 @@ use tracing::{debug, warn};
 
 use super::command::Command;
 use super::symbol_export;
+use crate::back::symbol_export::allocator_shim_symbols;
+use crate::base::needs_allocator_shim_for_linking;
 use crate::errors;
 
 #[cfg(test)]
@@ -1838,6 +1841,14 @@ fn exported_symbols_for_non_proc_macro(
         }
     });
 
+    // Mark allocator shim symbols as exported only if they were generated.
+    if export_threshold == SymbolExportLevel::Rust
+        && needs_allocator_shim_for_linking(tcx.dependency_formats(()), crate_type)
+        && tcx.allocator_kind(()).is_some()
+    {
+        symbols.extend(allocator_shim_symbols(tcx));
+    }
+
     symbols
 }
 

compiler/rustc_codegen_ssa/src/back/lto.rs

@@ -8,8 +8,9 @@ use rustc_middle::ty::TyCtxt;
 use rustc_session::config::{CrateType, Lto};
 use tracing::info;
 
-use crate::back::symbol_export::{self, symbol_name_for_instance_in_crate};
+use crate::back::symbol_export::{self, allocator_shim_symbols, symbol_name_for_instance_in_crate};
 use crate::back::write::CodegenContext;
+use crate::base::allocator_kind_for_codegen;
 use crate::errors::{DynamicLinkingWithLTO, LtoDisallowed, LtoDylib, LtoProcMacro};
 use crate::traits::*;
 
@@ -115,6 +116,11 @@ pub(super) fn exported_symbols_for_lto(
         }
     }
 
+    // Mark allocator shim symbols as exported only if they were generated.
+    if export_threshold == SymbolExportLevel::Rust && allocator_kind_for_codegen(tcx).is_some() {
+        symbols_below_threshold.extend(allocator_shim_symbols(tcx).map(|(name, _kind)| name));
+    }
+
     symbols_below_threshold
 }
 

compiler/rustc_codegen_ssa/src/back/symbol_export.rs

@@ -18,7 +18,7 @@ use rustc_symbol_mangling::mangle_internal_symbol;
 use rustc_target::spec::{SanitizerSet, TlsModel};
 use tracing::debug;
 
-use crate::base::allocator_kind_for_codegen;
+use crate::back::symbol_export;
 
 fn threshold(tcx: TyCtxt<'_>) -> SymbolExportLevel {
     crates_export_threshold(tcx.crate_types())
@@ -217,31 +217,6 @@ fn exported_non_generic_symbols_provider_local<'tcx>(
         ));
     }
 
-    // Mark allocator shim symbols as exported only if they were generated.
-    if allocator_kind_for_codegen(tcx).is_some() {
-        for symbol_name in ALLOCATOR_METHODS
-            .iter()
-            .map(|method| mangle_internal_symbol(tcx, global_fn_name(method.name).as_str()))
-            .chain([
-                mangle_internal_symbol(tcx, "__rust_alloc_error_handler"),
-                mangle_internal_symbol(tcx, OomStrategy::SYMBOL),
-                mangle_internal_symbol(tcx, NO_ALLOC_SHIM_IS_UNSTABLE),
-            ])
-        {
-            let exported_symbol = ExportedSymbol::NoDefId(SymbolName::new(tcx, &symbol_name));
-
-            symbols.push((
-                exported_symbol,
-                SymbolExportInfo {
-                    level: SymbolExportLevel::Rust,
-                    kind: SymbolExportKind::Text,
-                    used: false,
-                    rustc_std_internal_symbol: true,
-                },
-            ));
-        }
-    }
-
     if tcx.sess.instrument_coverage() || tcx.sess.opts.cg.profile_generate.enabled() {
         // These are weak symbols that point to the profile version and the
         // profile name, which need to be treated as exported so LTO doesn't nix
@@ -563,6 +538,31 @@ pub(crate) fn provide(providers: &mut Providers) {
         upstream_monomorphizations_for_provider;
 }
 
+pub(crate) fn allocator_shim_symbols(
+    tcx: TyCtxt<'_>,
+) -> impl Iterator<Item = (String, SymbolExportKind)> {
+    ALLOCATOR_METHODS
+        .iter()
+        .map(move |method| mangle_internal_symbol(tcx, global_fn_name(method.name).as_str()))
+        .chain([
+            mangle_internal_symbol(tcx, "__rust_alloc_error_handler"),
+            mangle_internal_symbol(tcx, OomStrategy::SYMBOL),
+            mangle_internal_symbol(tcx, NO_ALLOC_SHIM_IS_UNSTABLE),
+        ])
+        .map(move |symbol_name| {
+            let exported_symbol = ExportedSymbol::NoDefId(SymbolName::new(tcx, &symbol_name));
+
+            (
+                symbol_export::exporting_symbol_name_for_instance_in_crate(
+                    tcx,
+                    exported_symbol,
+                    LOCAL_CRATE,
+                ),
+                SymbolExportKind::Text,
+            )
+        })
+}
+
 fn symbol_export_level(tcx: TyCtxt<'_>, sym_def_id: DefId) -> SymbolExportLevel {
     // We export anything that's not mangled at the "C" layer as it probably has
     // to do with ABI concerns. We do not, however, apply such treatment to