Index: ELF/Driver.cpp
===================================================================
--- ELF/Driver.cpp
+++ ELF/Driver.cpp
@@ -496,9 +496,7 @@
   if (HasError)
     return; // There were duplicate symbols or incompatible files
 
-  for (StringRef S : Config->Undefined)
-    Symtab.addUndefinedOpt(S);
-
+  Symtab.scanUndefinedFlags();
   Symtab.scanShlibUndefined();
   Symtab.scanDynamicList();
   Symtab.scanVersionScript();
Index: ELF/SymbolTable.h
===================================================================
--- ELF/SymbolTable.h
+++ ELF/SymbolTable.h
@@ -59,6 +59,7 @@
   DefinedRegular<ELFT> *addIgnored(StringRef Name,
                                    uint8_t Visibility = llvm::ELF::STV_HIDDEN);
 
+  void scanUndefinedFlags();
   void scanShlibUndefined();
   void scanDynamicList();
   void scanVersionScript();
Index: ELF/SymbolTable.cpp
===================================================================
--- ELF/SymbolTable.cpp
+++ ELF/SymbolTable.cpp
@@ -151,17 +151,7 @@
 template <class ELFT>
 SymbolBody *SymbolTable<ELFT>::addUndefined(StringRef Name) {
   auto *Sym = new (Alloc)
-      UndefinedElf<ELFT>(Name, STB_GLOBAL, STV_DEFAULT, /*Type*/ 0, false);
-  resolve(Sym);
-  return Sym;
-}
-
-// Add an undefined symbol. Unlike addUndefined, that symbol
-// doesn't have to be resolved, thus "opt" (optional).
-template <class ELFT>
-SymbolBody *SymbolTable<ELFT>::addUndefinedOpt(StringRef Name) {
-  auto *Sym = new (Alloc)
-      UndefinedElf<ELFT>(Name, STB_GLOBAL, STV_HIDDEN, /*Type*/ 0, true);
+      UndefinedElf<ELFT>(Name, STB_GLOBAL, STV_DEFAULT, /*Type*/ 0);
   resolve(Sym);
   return Sym;
 }
@@ -368,6 +358,16 @@
     addFile(std::move(File));
 }
 
+// Process undefined (-u) flags by loading lazy symbols named by those flags.
+template <class ELFT>
+void SymbolTable<ELFT>::scanUndefinedFlags() {
+  for (StringRef S : Config->Undefined)
+    if (SymbolBody *Sym = find(S))
+      if (auto *L = dyn_cast<Lazy>(Sym))
+        if (std::unique_ptr<InputFile> File = L->getFile())
+          addFile(std::move(File));
+}
+
 // This function takes care of the case in which shared libraries depend on
 // the user program (not the other way, which is usual). Shared libraries
 // may have undefined symbols, expecting that the user program provides
Index: ELF/Symbols.h
===================================================================
--- ELF/Symbols.h
+++ ELF/Symbols.h
@@ -177,8 +177,6 @@
   // symbol or if the symbol should point to its plt entry.
   unsigned NeedsCopyOrPltAddr : 1;
 
-  unsigned CanKeepUndefined : 1;
-
   // The following fields have the same meaning as the ELF symbol attributes.
   uint8_t Type;    // symbol type
   uint8_t Binding; // symbol binding
@@ -325,10 +323,7 @@
 public:
   UndefinedElf(StringRef N, const Elf_Sym &Sym);
   UndefinedElf(const Elf_Sym &Sym);
-  UndefinedElf(StringRef Name, uint8_t Binding, uint8_t StOther, uint8_t Type,
-               bool CanKeepUndefined);
-
-  bool canKeepUndefined() const { return CanKeepUndefined; }
+  UndefinedElf(StringRef Name, uint8_t Binding, uint8_t StOther, uint8_t Type);
 
   uintX_t Size;
 
Index: ELF/Symbols.cpp
===================================================================
--- ELF/Symbols.cpp
+++ ELF/Symbols.cpp
@@ -104,7 +104,6 @@
 }
 
 void SymbolBody::init() {
-  CanKeepUndefined = false;
   NeedsCopyOrPltAddr = false;
   CanOmitFromDynSym = false;
 }
@@ -245,11 +244,8 @@
 
 template <typename ELFT>
 UndefinedElf<ELFT>::UndefinedElf(StringRef Name, uint8_t Binding,
-                                 uint8_t StOther, uint8_t Type,
-                                 bool CanKeepUndefined)
-    : SymbolBody(SymbolBody::UndefinedElfKind, Name, Binding, StOther, Type) {
-  this->CanKeepUndefined = CanKeepUndefined;
-}
+                                 uint8_t StOther, uint8_t Type)
+    : SymbolBody(SymbolBody::UndefinedElfKind, Name, Binding, StOther, Type) {}
 
 template <typename ELFT>
 UndefinedElf<ELFT>::UndefinedElf(const Elf_Sym &Sym)
Index: ELF/Writer.cpp
===================================================================
--- ELF/Writer.cpp
+++ ELF/Writer.cpp
@@ -1343,11 +1343,8 @@
       if (auto *SS = dyn_cast<SharedSymbol<ELFT>>(Body))
         SS->File->IsUsed = true;
 
-    if (Body->isUndefined() && !S->isWeak()) {
-      auto *U = dyn_cast<UndefinedElf<ELFT>>(Body);
-      if (!U || !U->canKeepUndefined())
-        reportUndefined<ELFT>(Symtab, Body);
-    }
+    if (Body->isUndefined() && !S->isWeak())
+      reportUndefined<ELFT>(Symtab, Body);
 
     if (auto *C = dyn_cast<DefinedCommon>(Body))
       CommonSymbols.push_back(C);
Index: test/ELF/undefined-opt.s
===================================================================
--- test/ELF/undefined-opt.s
+++ test/ELF/undefined-opt.s
@@ -51,5 +51,16 @@
 # UNK-UNDEFINED-SO-NOT:     Name: unknown
 # UNK-UNDEFINED-SO: ]
 
+# Added undefined symbols should appear in the dynamic table if necessary.
+# RUN: ld.lld -shared -o %t5 %t.o -u export
+# RUN: llvm-readobj --dyn-symbols %t5 | \
+# RUN:     FileCheck --check-prefix=EXPORT-SO %s
+# EXPORT-SO: DynamicSymbols [
+# EXPORT-SO:   Name: export
+# EXPORT-SO: ]
+
 .globl _start;
 _start:
+
+.globl export
+export: