Index: ELF/Config.h
===================================================================
--- ELF/Config.h
+++ ELF/Config.h
@@ -146,6 +146,7 @@
   bool Trace;
   bool Verbose;
   bool WarnCommon;
+  bool WarnOnce;
   bool WarnMissingEntry;
   bool ZCombreloc;
   bool ZExecstack;
Index: ELF/Driver.cpp
===================================================================
--- ELF/Driver.cpp
+++ ELF/Driver.cpp
@@ -681,6 +681,7 @@
   Config->UnresolvedSymbols = getUnresolvedSymbolPolicy(Args);
   Config->Verbose = Args.hasArg(OPT_verbose);
   Config->WarnCommon = Args.hasArg(OPT_warn_common);
+  Config->WarnOnce = Args.hasArg(OPT_warn_once);
   Config->ZCombreloc = !hasZOption(Args, "nocombreloc");
   Config->ZExecstack = hasZOption(Args, "execstack");
   Config->ZNocopyreloc = hasZOption(Args, "nocopyreloc");
Index: ELF/Options.td
===================================================================
--- ELF/Options.td
+++ ELF/Options.td
@@ -289,6 +289,9 @@
 def warn_common: F<"warn-common">,
   HelpText<"Warn about duplicate common symbols">;
 
+def warn_once: F<"warn-once">,
+  HelpText<"Show error or warning for each undefined symbol only once">;
+
 def warn_unresolved_symbols: F<"warn-unresolved-symbols">,
   HelpText<"Report unresolved symbols as warnings">;
 
Index: ELF/Relocations.cpp
===================================================================
--- ELF/Relocations.cpp
+++ ELF/Relocations.cpp
@@ -675,6 +675,7 @@
 template <class ELFT>
 static void reportUndefined(SymbolBody &Sym, InputSectionBase &S,
                             uint64_t Offset) {
+  assert(Sym.isUndefined());
   if (Config->UnresolvedSymbols == UnresolvedPolicy::IgnoreAll)
     return;
 
@@ -683,6 +684,11 @@
   if (Config->UnresolvedSymbols == UnresolvedPolicy::Ignore && CanBeExternal)
     return;
 
+  Undefined *U = cast<Undefined>(&Sym);
+  if (U->Reported && Config->WarnOnce)
+      return;
+  U->Reported = true;
+
   std::string Msg =
       "undefined symbol: " + toString(Sym) + "\n>>> referenced by ";
 
Index: ELF/Symbols.h
===================================================================
--- ELF/Symbols.h
+++ ELF/Symbols.h
@@ -206,6 +206,9 @@
   static bool classof(const SymbolBody *S) {
     return S->kind() == UndefinedKind;
   }
+
+  // Used for error reporting. True if symbol was reported.
+  unsigned Reported : 1;
 };
 
 class SharedSymbol : public Defined {
Index: ELF/Symbols.cpp
===================================================================
--- ELF/Symbols.cpp
+++ ELF/Symbols.cpp
@@ -290,7 +290,8 @@
 
 Undefined::Undefined(StringRefZ Name, bool IsLocal, uint8_t StOther,
                      uint8_t Type, InputFile *File)
-    : SymbolBody(SymbolBody::UndefinedKind, Name, IsLocal, StOther, Type) {
+    : SymbolBody(SymbolBody::UndefinedKind, Name, IsLocal, StOther, Type),
+      Reported(false) {
   this->File = File;
 }
 
Index: test/ELF/warn-once.s
===================================================================
--- test/ELF/warn-once.s
+++ test/ELF/warn-once.s
@@ -0,0 +1,17 @@
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t.o
+# RUN: not ld.lld %t.o -o %t1 2>&1 | FileCheck -check-prefix=ERR1 %s
+# ERR1: error: undefined symbol: foo
+# ERR1: error: undefined symbol: foo
+# ERR1: error: undefined symbol: boo
+# ERR1: error: undefined symbol: boo
+
+# RUN: not ld.lld --warn-once %t.o -o %t1 2>&1 | FileCheck -check-prefix=ERR2 %s
+# ERR2: error: undefined symbol: foo
+# ERR2-NOT: foo
+# ERR2: error: undefined symbol: boo
+# ERR2-NOT: boo
+
+callq foo@PLT
+callq foo@PLT
+callq boo@PLT
+callq boo@PLT