Add option '-fvisibility=<hidden|default>' able to hide symbols not marked as 'export' on non-Windows targets. Resolves #2431 (#2894)

driver/cl_options.cpp

@@ -81,6 +81,13 @@ static cl::opt<bool, true>
     createSharedLib("shared", cl::desc("Create shared library (DLL)"),
                     cl::ZeroOrMore, cl::location(global.params.dll));
 
+cl::opt<ubyte> defaultToHiddenVisibility(
+    "fvisibility", cl::ZeroOrMore,
+    cl::desc("Default visibility of symbols (not relevant for Windows)"),
+    clEnumValues(clEnumValN(0, "default", "Export all symbols"),
+                 clEnumValN(1, "hidden",
+                            "Only export symbols marked with 'export'")));
+
 static cl::opt<bool, true> verbose("v", cl::desc("Verbose"), cl::ZeroOrMore,
                                    cl::location(global.params.verbose));
 

driver/cl_options.h

@@ -77,6 +77,7 @@ extern cl::opt<std::string> mABI;
 extern FloatABI::Type floatABI;
 extern cl::opt<bool> linkonceTemplates;
 extern cl::opt<bool> disableLinkerStripDead;
+extern cl::opt<ubyte> defaultToHiddenVisibility;
 
 // Math options
 extern bool fFastMath;

gen/declarations.cpp

@@ -17,6 +17,7 @@
 #include "dmd/nspace.h"
 #include "dmd/root/rmem.h"
 #include "dmd/template.h"
+#include "driver/cl_options.h"
 #include "gen/classes.h"
 #include "gen/functions.h"
 #include "gen/irstate.h"
@@ -308,6 +309,11 @@ public:
           gvar->setDLLStorageClass(LLGlobalValue::DLLExportStorageClass);
         }
 
+        // Hide non-exported symbols
+        if (opts::defaultToHiddenVisibility && !decl->isExport()) {
+          gvar->setVisibility(LLGlobalValue::HiddenVisibility);
+        }
+
         // Also set up the debug info.
         irs->DBuilder.EmitGlobalVariable(gvar, decl);
       }

gen/functions.cpp

@@ -574,6 +574,13 @@ void DtoDeclareFunction(FuncDeclaration *fdecl) {
                                  : LLGlobalValue::DLLExportStorageClass);
   }
 
+  // Hide non-exported symbols
+  if (opts::defaultToHiddenVisibility &&
+             !fdecl->isImportedSymbol() &&
+             !fdecl->isExport()) {
+    func->setVisibility(LLGlobalValue::HiddenVisibility);
+  }
+
   IF_LOG Logger::cout() << "func = " << *func << std::endl;
 
   // add func to IRFunc

tests/codegen/export_marked_symbols1.d

@@ -0,0 +1,26 @@
+// Test that passing -fvisibility=hidden hides all unexported symbols
+
+// UNSUPPORTED: Windows
+
+// RUN: ldc2 %s -betterC -shared -fvisibility=hidden -of=lib%t.so
+// RUN: nm -g lib%t.so | FileCheck %s
+
+// CHECK: test__exportedFunDef
+// CHECK: test__exportedVarDef
+// CHECK-NOT: test__nonExportedFunDecl
+// CHECK-NOT: test__nonExportedFunDef
+// CHECK-NOT: test__nonExportedVarDecl
+// CHECK-NOT: test__nonExportedVarDef
+
+
+extern(C) export int test__exportedFunDef() { return 42; }
+extern(C) int test__nonExportedFunDef() { return 101; }
+
+extern(C) export int test__exportedFunDecl();
+extern(C) int test__nonExportedFunDecl();
+
+extern(C) export int test__exportedVarDef;
+extern(C) int test__nonExportedVarDef;
+
+extern(C) extern export int test__exportedVarDecl;
+extern(C) extern int test__nonExportedVarDecl;

tests/codegen/export_marked_symbols2.d

@@ -0,0 +1,26 @@
+// Test that compiling with -fvisibility=default exports all symbols on non-Windows targets
+
+// UNSUPPORTED: Windows
+
+// RUN: ldc2 %s -betterC -shared -fvisibility=default -of=lib%t.so
+// RUN: nm -g lib%t.so | FileCheck %s
+
+// CHECK: test__exportedFunDef
+// CHECK: test__exportedVarDef
+// CHECK-NOT: test__nonExportedFunDecl
+// CHECK: test__nonExportedFunDef
+// CHECK-NOT: test__nonExportedVarDecl
+// CHECK: test__nonExportedVarDef
+
+
+extern(C) export int test__exportedFunDef() { return 42; }
+extern(C) int test__nonExportedFunDef() { return 101; }
+
+extern(C) export int test__exportedFunDecl();
+extern(C) int test__nonExportedFunDecl();
+
+extern(C) export int test__exportedVarDef;
+extern(C) int test__nonExportedVarDef;
+
+extern(C) extern export int test__exportedVarDecl;
+extern(C) extern int test__nonExportedVarDecl;

tests/codegen/export_marked_symbols_thin_lto.d

@@ -0,0 +1,15 @@
+// Test that -fvisibility=hidden works with thin LTO
+
+// REQUIRES: LTO
+
+// RUN: ldc2 %S/inputs/export_marked_symbols_thin_lto_lib.d -c -fvisibility=hidden -flto=thin -of=%t1%obj
+// RUN: ldc2 %s -I%S/inputs -c -flto=thin -of=%t2%obj
+// RUN: ldc2 %t1%obj %t2%obj -flto=thin
+
+import export_marked_symbols_thin_lto_lib;
+
+void main()
+{
+    exportedFoo();
+    normalFoo();
+}

tests/codegen/inputs/export_marked_symbols_thin_lto_lib.d

@@ -0,0 +1,2 @@
+export void exportedFoo() {}
+void normalFoo() {} // hidden visibility