[JITLink][MachO] Treat linker private symbols as hidden rather than private.

Linker-private symbols should be resolvable across object file boundaries.

Author: lhames

llvm/lib/ExecutionEngine/JITLink/MachOLinkGraphBuilder.cpp

@@ -64,9 +64,7 @@ Linkage MachOLinkGraphBuilder::getLinkage(uint16_t Desc) {
 }
 
 Scope MachOLinkGraphBuilder::getScope(StringRef Name, uint8_t Type) {
-  if (Name.startswith("l"))
-    return Scope::Local;
-  if (Type & MachO::N_PEXT)
+  if (Name.startswith("l") || (Type & MachO::N_PEXT))
     return Scope::Hidden;
   if (Type & MachO::N_EXT)
     return Scope::Default;

llvm/lib/ExecutionEngine/Orc/Mangling.cpp

@@ -89,14 +89,25 @@ getObjectSymbolInfo(ExecutionSession &ES, MemoryBufferRef ObjBuffer) {
   if (!Obj)
     return Obj.takeError();
 
+  bool IsMachO = isa<object::MachOObjectFile>(Obj->get());
+
   SymbolFlagsMap SymbolFlags;
   for (auto &Sym : (*Obj)->symbols()) {
     // Skip symbols not defined in this object file.
     if (Sym.getFlags() & object::BasicSymbolRef::SF_Undefined)
       continue;
 
-    // Skip symbols that are not global.
-    if (!(Sym.getFlags() & object::BasicSymbolRef::SF_Global))
+    // Get the symbol name.
+    auto Name = Sym.getName();
+    if (!Name)
+      return Name.takeError();
+
+    bool IsLinkerPrivate = IsMachO && Name->startswith("l");
+
+    // Skip symbols that are not global. Treat linker private symbols as global
+    // hidden.
+    if (!(Sym.getFlags() & object::BasicSymbolRef::SF_Global) &&
+        !IsLinkerPrivate)
       continue;
 
     // Skip symbols that have type SF_File.
@@ -106,9 +117,6 @@ getObjectSymbolInfo(ExecutionSession &ES, MemoryBufferRef ObjBuffer) {
     } else
       return SymType.takeError();
 
-    auto Name = Sym.getName();
-    if (!Name)
-      return Name.takeError();
     auto InternedName = ES.intern(*Name);
     auto SymFlags = JITSymbolFlags::fromObjectSymbol(Sym);
     if (!SymFlags)
@@ -118,9 +126,10 @@ getObjectSymbolInfo(ExecutionSession &ES, MemoryBufferRef ObjBuffer) {
 
   SymbolStringPtr InitSymbol;
 
-  if (auto *MachOObj = dyn_cast<object::MachOObjectFile>(Obj->get())) {
-    for (auto &Sec : MachOObj->sections()) {
-      auto SecType = MachOObj->getSectionType(Sec);
+  if (IsMachO) {
+    auto &MachOObj = cast<object::MachOObjectFile>(*Obj->get());
+    for (auto &Sec : MachOObj.sections()) {
+      auto SecType = MachOObj.getSectionType(Sec);
       if ((SecType & MachO::SECTION_TYPE) == MachO::S_MOD_INIT_FUNC_POINTERS) {
         std::string InitSymString;
         raw_string_ostream(InitSymString)

llvm/test/ExecutionEngine/JITLink/X86/Inputs/MachO_linker_private_def.s

@@ -0,0 +1,10 @@
+# Supplies a linker private definition, "l_foo".
+
+	.section	__TEXT,__text,regular,pure_instructions
+	.macosx_version_min 10, 14
+	.p2align	4, 0x90
+l_foo:
+	xorl	%eax, %eax
+	retq
+
+.subsections_via_symbols

llvm/test/ExecutionEngine/JITLink/X86/MachO_linker_private_symbols.s

@@ -0,0 +1,19 @@
+# RUN: rm -rf %t && mkdir -p %t
+# RUN: llvm-mc -triple=x86_64-apple-macosx10.9 -filetype=obj \
+# RUN:   -o %t/MachO_linker_private_def.o %S/Inputs/MachO_linker_private_def.s
+# RUN: llvm-mc -triple=x86_64-apple-macosx10.9 -filetype=obj \
+# RUN:   -o %t/MachO_linker_private_symbols.o %s
+# RUN: llvm-jitlink -noexec %t/MachO_linker_private_def.o \
+# RUN: %t/MachO_linker_private_symbols.o
+#
+# Check that we can resolve linker-private symbol definitions across object
+# boundaries.
+
+	.section	__TEXT,__text,regular,pure_instructions
+	.macosx_version_min 10, 14
+	.globl	_main
+	.p2align	4, 0x90
+_main:
+	jmp	l_foo
+
+.subsections_via_symbols