[WIP] Use protected visibility for all rust symbols

TODO: This produces linker errors with ld.bfd, but works with ld.gold and ld.lld

Author: bjorn3

compiler/rustc_codegen_gcc/src/allocator.rs

@@ -57,6 +57,9 @@ pub(crate) unsafe fn codegen(tcx: TyCtxt<'_>, mods: &mut GccContext, _module_nam
             if tcx.sess.target.options.default_hidden_visibility {
                 #[cfg(feature="master")]
                 func.add_attribute(FnAttribute::Visibility(gccjit::Visibility::Hidden));
+            } else {
+                #[cfg(feature="master")]
+                func.add_attribute(FnAttribute::Visibility(gccjit::Visibility::Protected));
             }
             if tcx.sess.must_emit_unwind_tables() {
                 // TODO(antoyo): emit unwind tables.
@@ -101,6 +104,9 @@ pub(crate) unsafe fn codegen(tcx: TyCtxt<'_>, mods: &mut GccContext, _module_nam
     if tcx.sess.target.default_hidden_visibility {
         #[cfg(feature="master")]
         func.add_attribute(FnAttribute::Visibility(gccjit::Visibility::Hidden));
+    } else {
+        #[cfg(feature="master")]
+        func.add_attribute(FnAttribute::Visibility(gccjit::Visibility::Protected));
     }
 
     let callee = alloc_error_handler_name(alloc_error_handler_kind);

compiler/rustc_codegen_llvm/src/allocator.rs

@@ -66,6 +66,8 @@ pub(crate) unsafe fn codegen(
 
             if tcx.sess.target.default_hidden_visibility {
                 llvm::LLVMRustSetVisibility(llfn, llvm::Visibility::Hidden);
+            } else {
+                llvm::LLVMRustSetVisibility(llfn, llvm::Visibility::Protected);
             }
             if tcx.sess.must_emit_unwind_tables() {
                 let uwtable = attributes::uwtable_attr(llcx);
@@ -117,6 +119,8 @@ pub(crate) unsafe fn codegen(
 
     if tcx.sess.target.default_hidden_visibility {
         llvm::LLVMRustSetVisibility(llfn, llvm::Visibility::Hidden);
+    } else {
+        llvm::LLVMRustSetVisibility(llfn, llvm::Visibility::Protected);
     }
     if tcx.sess.must_emit_unwind_tables() {
         let uwtable = attributes::uwtable_attr(llcx);
@@ -156,6 +160,8 @@ pub(crate) unsafe fn codegen(
     let ll_g = llvm::LLVMRustGetOrInsertGlobal(llmod, name.as_ptr().cast(), name.len(), i8);
     if tcx.sess.target.default_hidden_visibility {
         llvm::LLVMRustSetVisibility(ll_g, llvm::Visibility::Hidden);
+    } else {
+        llvm::LLVMRustSetVisibility(ll_g, llvm::Visibility::Protected);
     }
     let val = tcx.sess.opts.unstable_opts.oom.should_panic();
     let llval = llvm::LLVMConstInt(i8, val as u64, False);
@@ -165,6 +171,8 @@ pub(crate) unsafe fn codegen(
     let ll_g = llvm::LLVMRustGetOrInsertGlobal(llmod, name.as_ptr().cast(), name.len(), i8);
     if tcx.sess.target.default_hidden_visibility {
         llvm::LLVMRustSetVisibility(ll_g, llvm::Visibility::Hidden);
+    } else {
+        llvm::LLVMRustSetVisibility(ll_g, llvm::Visibility::Protected);
     }
     let llval = llvm::LLVMConstInt(i8, 0, False);
     llvm::LLVMSetInitializer(ll_g, llval);

compiler/rustc_monomorphize/src/partitioning.rs

@@ -884,26 +884,37 @@ fn mono_item_visibility<'tcx>(
 }
 
 fn default_visibility(tcx: TyCtxt<'_>, id: DefId, is_generic: bool) -> Visibility {
-    if !tcx.sess.target.default_hidden_visibility {
-        return Visibility::Default;
-    }
+    let export_level = if is_generic {
+        // Generic functions never have export-level C.
+        SymbolExportLevel::Rust
+    } else if !id.is_local() {
+        // Things with export level C don't get instantiated in
+        // downstream crates.
+        SymbolExportLevel::Rust
+    } else {
+        match tcx.reachable_non_generics(id.krate).get(&id) {
+            Some(SymbolExportInfo { level: SymbolExportLevel::C, .. }) => SymbolExportLevel::C,
+            _ => SymbolExportLevel::Rust,
+        }
+    };
 
-    // Generic functions never have export-level C.
-    if is_generic {
-        return Visibility::Hidden;
-    }
+    match export_level {
+        // C-export level items remain at `Default` to allow C code to
+        // access and interpose them.
+        SymbolExportLevel::C => Visibility::Default,
 
-    // Things with export level C don't get instantiated in
-    // downstream crates.
-    if !id.is_local() {
-        return Visibility::Hidden;
-    }
-
-    // C-export level items remain at `Default`, all other internal
-    // items become `Hidden`.
-    match tcx.reachable_non_generics(id.krate).get(&id) {
-        Some(SymbolExportInfo { level: SymbolExportLevel::C, .. }) => Visibility::Default,
-        _ => Visibility::Hidden,
+        // All other items become `Hidden` or `Protected` depending on
+        // `default_hidden_visibility`.
+        SymbolExportLevel::Rust => {
+            if tcx.sess.target.default_hidden_visibility {
+                Visibility::Hidden
+            } else {
+                // Items with mangled symbols don't have a predictable name,
+                // so no dylib that doesn't depend on compiler internals can
+                // do interposition on rust items.
+                Visibility::Protected
+            }
+        }
     }
 }