Index: ELF/Config.h
===================================================================
--- ELF/Config.h
+++ ELF/Config.h
@@ -180,6 +180,7 @@
   bool WarnCommon;
   bool WarnIfuncTextrel;
   bool WarnMissingEntry;
+  bool WarnOnce = false;
   bool WarnSymbolOrdering;
   bool WriteAddends;
   bool ZCombreloc;
Index: ELF/Driver.cpp
===================================================================
--- ELF/Driver.cpp
+++ ELF/Driver.cpp
@@ -1107,6 +1107,9 @@
         Files.back()->JustSymbols = true;
       }
       break;
+    case OPT_warn_once:
+      Config->WarnOnce = true;
+      break;
     case OPT_start_group:
       if (InputFile::IsInGroup)
         error("nested --start-group");
Index: ELF/Options.td
===================================================================
--- ELF/Options.td
+++ ELF/Options.td
@@ -372,6 +372,8 @@
 
 def warn_unresolved_symbols: F<"warn-unresolved-symbols">,
   HelpText<"Report unresolved symbols as warnings">;
+def warn_once: F<"warn-once">,
+  HelpText<"Warn only once per undefined symbol">;
 
 defm whole_archive: B<"whole-archive",
     "Force load of all members in a static library",
@@ -505,7 +507,6 @@
 def: F<"sort-common">;
 def: F<"stats">;
 def: F<"warn-execstack">;
-def: F<"warn-once">;
 def: F<"warn-shared-textrel">;
 def: F<"EB">;
 def: F<"EL">;
Index: ELF/Relocations.cpp
===================================================================
--- ELF/Relocations.cpp
+++ ELF/Relocations.cpp
@@ -655,6 +655,12 @@
   if (Config->UnresolvedSymbols == UnresolvedPolicy::Ignore && CanBeExternal)
     return false;
 
+  if (Config->WarnOnce) {
+    if (Sym.IsWarned)
+      return false;
+    Sym.IsWarned = true;
+  }
+
   std::string Msg =
       "undefined symbol: " + toString(Sym) + "\n>>> referenced by ";
 
Index: ELF/Symbols.h
===================================================================
--- ELF/Symbols.h
+++ ELF/Symbols.h
@@ -184,7 +184,7 @@
         Type(Type), StOther(StOther), SymbolKind(K), NeedsPltAddr(false),
         IsInIplt(false), IsInIgot(false), IsPreemptible(false),
         Used(!Config->GcSections), NeedsTocRestore(false),
-        ScriptDefined(false) {}
+        ScriptDefined(false), IsWarned(false) {}
 
 public:
   // True the symbol should point to its PLT entry.
@@ -210,6 +210,9 @@
   // True if this symbol is defined by a linker script.
   unsigned ScriptDefined : 1;
 
+  // True if this symbol is already reported as undefined
+  unsigned IsWarned : 1;
+
   bool isSection() const { return Type == llvm::ELF::STT_SECTION; }
   bool isTls() const { return Type == llvm::ELF::STT_TLS; }
   bool isFunc() const { return Type == llvm::ELF::STT_FUNC; }
Index: test/ELF/warn-once.s
===================================================================
--- test/ELF/warn-once.s
+++ test/ELF/warn-once.s
@@ -0,0 +1,18 @@
+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %s -o %t.o
+# RUN: not ld.lld -warn-once %t.o -o %t.exe 2>&1 | FileCheck %s
+
+# CHECK: error: undefined symbol: foo
+# CHECK-NEXT: >>> referenced by warn-once.s
+# CHECK-NEXT:                   {{.*}}:(.text+0x1)
+# CHECK-EMPTY:
+# CHECK-NOT: error: undefined symbol: foo
+# CHECK-NOT: >>> referenced by warn-once.s
+# CHECK-NOT:                   {{.*}}:(.text+0x6)
+
+.file "warn-once.s"
+
+  .globl _start
+_start:
+  call foo
+  call foo;
\ No newline at end of file