[Sema] Provide -fvisibility-global-new-delete-hidden option

When the global new and delete operators aren't declared, Clang
provides and implicit declaration, but this declaration currently
always uses the default visibility. This is a problem when the
C++ library itself is being built with non-default visibility because
the implicit declaration will force the new and delete operators to
have the default visibility unlike the rest of the library.

The existing workaround is to use assembly to enforce the visiblity:
https://fuchsia.googlesource.com/zircon/+/master/system/ulib/zxcpp/new.cpp#108
but that solution is not always available, e.g. in the case of of
libFuzzer which is using an internal version of libc++ that's also built
with -fvisibility=hidden where the existing behavior is causing issues.

This change introduces a new option -fvisibility-global-new-delete-hidden
which makes the implicit declaration of the global new and delete
operators hidden.

Differential Revision: https://reviews.llvm.org/D53787

llvm-svn: 348234

clang/include/clang/Basic/LangOptions.def

@@ -227,7 +227,8 @@ BENIGN_LANGOPT(DumpRecordLayouts , 1, 0, "dumping the layout of IRgen'd records"
 BENIGN_LANGOPT(DumpRecordLayoutsSimple , 1, 0, "dumping the layout of IRgen'd records in a simple form")
 BENIGN_LANGOPT(DumpVTableLayouts , 1, 0, "dumping the layouts of emitted vtables")
 LANGOPT(NoConstantCFStrings , 1, 0, "no constant CoreFoundation strings")
-BENIGN_LANGOPT(InlineVisibilityHidden , 1, 0, "hidden default visibility for inline C++ methods")
+BENIGN_LANGOPT(InlineVisibilityHidden , 1, 0, "hidden visibility for inline C++ methods")
+LANGOPT(GlobalAllocationFunctionVisibilityHidden , 1, 0, "hidden visibility for global operator new and delete declaration")
 BENIGN_LANGOPT(ParseUnknownAnytype, 1, 0, "__unknown_anytype")
 BENIGN_LANGOPT(DebuggerSupport , 1, 0, "debugger support")
 BENIGN_LANGOPT(DebuggerCastResultToId, 1, 0, "for 'po' in the debugger, cast the result to id if it is of unknown type")

clang/include/clang/Driver/Options.td

@@ -1734,6 +1734,8 @@ def fvisibility_inlines_hidden : Flag<["-"], "fvisibility-inlines-hidden">, Grou
 def fvisibility_ms_compat : Flag<["-"], "fvisibility-ms-compat">, Group<f_Group>,
   HelpText<"Give global types 'default' visibility and global functions and "
            "variables 'hidden' visibility by default">;
+def fvisibility_global_new_delete_hidden : Flag<["-"], "fvisibility-global-new-delete-hidden">, Group<f_Group>,
+  HelpText<"Give global C++ operator new and delete declarations hidden visibility">, Flags<[CC1Option]>;
 def fwhole_program_vtables : Flag<["-"], "fwhole-program-vtables">, Group<f_Group>,
   Flags<[CoreOption, CC1Option]>,
   HelpText<"Enables whole-program vtable optimization. Requires -flto">;

clang/lib/Driver/ToolChains/Clang.cpp

@@ -4329,6 +4329,7 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
   }
 
   Args.AddLastArg(CmdArgs, options::OPT_fvisibility_inlines_hidden);
+  Args.AddLastArg(CmdArgs, options::OPT_fvisibility_global_new_delete_hidden);
 
   Args.AddLastArg(CmdArgs, options::OPT_ftlsmodel_EQ);
 

clang/lib/Frontend/CompilerInvocation.cpp

@@ -2487,6 +2487,9 @@ static void ParseLangArgs(LangOptions &Opts, ArgList &Args, InputKind IK,
   if (Args.hasArg(OPT_fvisibility_inlines_hidden))
     Opts.InlineVisibilityHidden = 1;
 
+  if (Args.hasArg(OPT_fvisibility_global_new_delete_hidden))
+    Opts.GlobalAllocationFunctionVisibilityHidden = 1;
+
   if (Args.hasArg(OPT_ftrapv)) {
     Opts.setSignedOverflowBehavior(LangOptions::SOB_Trapping);
     // Set the handler, if one is specified.

clang/lib/Sema/SemaExprCXX.cpp

@@ -2816,9 +2816,10 @@ void Sema::DeclareGlobalAllocationFunction(DeclarationName Name,
     // Global allocation functions should always be visible.
     Alloc->setVisibleDespiteOwningModule();
 
-    // Implicit sized deallocation functions always have default visibility.
-    Alloc->addAttr(
-        VisibilityAttr::CreateImplicit(Context, VisibilityAttr::Default));
+    Alloc->addAttr(VisibilityAttr::CreateImplicit(
+        Context, LangOpts.GlobalAllocationFunctionVisibilityHidden
+                     ? VisibilityAttr::Hidden
+                     : VisibilityAttr::Default));
 
     llvm::SmallVector<ParmVarDecl *, 3> ParamDecls;
     for (QualType T : Params) {