Index: ELF/Config.h
===================================================================
--- ELF/Config.h
+++ ELF/Config.h
@@ -12,6 +12,7 @@
 
 #include "llvm/ADT/MapVector.h"
 #include "llvm/ADT/StringRef.h"
+#include "llvm/ADT/StringSet.h"
 #include "llvm/Support/ELF.h"
 
 #include <vector>
@@ -59,6 +60,7 @@
   llvm::StringRef OutputFile;
   llvm::StringRef SoName;
   llvm::StringRef Sysroot;
+  llvm::StringSet<> TraceSymbol;
   std::string RPath;
   std::vector<Version> SymbolVersions;
   std::vector<llvm::StringRef> DynamicList;
Index: ELF/Driver.cpp
===================================================================
--- ELF/Driver.cpp
+++ ELF/Driver.cpp
@@ -417,6 +417,9 @@
     if (Optional<MemoryBufferRef> Buffer = readFile(Arg->getValue()))
       parseVersionScript(*Buffer);
   }
+
+  for (auto *Arg : Args.filtered(OPT_trace_symbol))
+    Config->TraceSymbol.insert(Arg->getValue());
 }
 
 void LinkerDriver::createFiles(opt::InputArgList &Args) {
@@ -499,6 +502,7 @@
   Symtab.scanShlibUndefined();
   Symtab.scanDynamicList();
   Symtab.scanVersionScript();
+  Symtab.traceDefined();
 
   Symtab.addCombinedLtoObject();
   if (HasError)
Index: ELF/InputFiles.h
===================================================================
--- ELF/InputFiles.h
+++ ELF/InputFiles.h
@@ -140,6 +140,8 @@
 
   const Elf_Shdr *getSymbolTable() const { return this->Symtab; };
 
+  void traceUndefined(StringRef Name);
+
   // Get MIPS GP0 value defined by this file. This value represents the gp value
   // used to create the relocatable object and required to support
   // R_MIPS_GPREL16 / R_MIPS_GPREL32 relocations.
Index: ELF/InputFiles.cpp
===================================================================
--- ELF/InputFiles.cpp
+++ ELF/InputFiles.cpp
@@ -313,6 +313,14 @@
   return new (IAlloc.Allocate()) InputSection<ELFT>(this, &Sec);
 }
 
+// Print the module names which reference the notified
+// symbols provided through -y or --trace-symbol option.
+template <class ELFT> 
+void elf::ObjectFile<ELFT>::traceUndefined(StringRef Name) {
+  if (!Config->TraceSymbol.empty() && Config->TraceSymbol.count(Name))
+    outs() << getFilename(this) << ": reference to " << Name << "\n";
+}
+
 template <class ELFT> void elf::ObjectFile<ELFT>::initializeSymbols() {
   this->initStringTable();
   Elf_Sym_Range Syms = this->getElfSymbols(false);
@@ -350,6 +358,7 @@
 
   switch (Sym->st_shndx) {
   case SHN_UNDEF:
+    traceUndefined(Name);
     return elf::Symtab<ELFT>::X
         ->addUndefined(Name, Binding, Sym->st_other, Sym->getType(),
                        /*CanOmitFromDynSym*/ false, this)
Index: ELF/Options.td
===================================================================
--- ELF/Options.td
+++ ELF/Options.td
@@ -164,6 +164,8 @@
 def z: JS<"z">, MetaVarName<"<option>">,
   HelpText<"Linker option extensions">;
 
+def trace_symbol : J<"trace-symbol=">, HelpText<"Trace references to symbols">;
+
 // Aliases
 def alias_Bdynamic_call_shared: F<"call_shared">, Alias<Bdynamic>;
 def alias_Bdynamic_dy: F<"dy">, Alias<Bdynamic>;
@@ -196,6 +198,7 @@
 def alias_trace: F<"t">, Alias<trace>;
 def alias_undefined_u: JoinedOrSeparate<["-"], "u">, Alias<undefined>;
 def alias_wrap_wrap: J<"wrap=">, Alias<wrap>;
+def alias_trace_symbol_y : JS<"y">, Alias<trace_symbol>;
 
 // Our symbol resolution algorithm handles symbols in archive files differently
 // than traditional linkers, so we don't need --start-group and --end-group.
Index: ELF/SymbolTable.h
===================================================================
--- ELF/SymbolTable.h
+++ ELF/SymbolTable.h
@@ -84,6 +84,7 @@
   void scanVersionScript();
   SymbolBody *find(StringRef Name);
   void wrap(StringRef Name);
+  void traceDefined();
 
 private:
   std::pair<Symbol *, bool> insert(StringRef Name);
Index: ELF/SymbolTable.cpp
===================================================================
--- ELF/SymbolTable.cpp
+++ ELF/SymbolTable.cpp
@@ -541,6 +541,18 @@
   }
 }
 
+// Print the module names which define the notified
+// symbols provided through -y or --trace-symbol option.
+template <class ELFT> void SymbolTable<ELFT>::traceDefined() {
+  for (const auto &symbol : Config->TraceSymbol) {
+    if (SymbolBody *B = find(symbol.getKey()))
+      if (B->isDefined() || B->isCommon())
+        if (InputFile *File = B->getSourceFile<ELFT>())
+          outs() << getFilename(File) << ": definition of " 
+                 << B->getName() << "\n";
+  }
+}
+
 template class elf::SymbolTable<ELF32LE>;
 template class elf::SymbolTable<ELF32BE>;
 template class elf::SymbolTable<ELF64LE>;
Index: test/ELF/Inputs/trace-symbols-foo-strong.s
===================================================================
--- test/ELF/Inputs/trace-symbols-foo-strong.s
+++ test/ELF/Inputs/trace-symbols-foo-strong.s
@@ -0,0 +1,14 @@
+.text
+.globl	foo
+.type	foo, @function
+foo:
+nop
+
+.globl	bar
+.type	bar, @function
+bar:
+nop
+
+.global func2
+.type   func2, @function
+func2:
Index: test/ELF/Inputs/trace-symbols-foo-weak.s
===================================================================
--- test/ELF/Inputs/trace-symbols-foo-weak.s
+++ test/ELF/Inputs/trace-symbols-foo-weak.s
@@ -0,0 +1,12 @@
+.comm	common,4,4
+.text
+.weak	foo
+.type	foo, @function
+foo:
+callq bar@PLT
+
+.globl  func1
+.type   func1, @function
+func1:
+call func2@PLT
+
Index: test/ELF/trace-symbols.s
===================================================================
--- test/ELF/trace-symbols.s
+++ test/ELF/trace-symbols.s
@@ -0,0 +1,84 @@
+# Test -y symbol and -trace-symbol=symbol
+
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux  \
+# RUN: %p/Inputs/trace-symbols-foo-weak.s -o %t1
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux  \
+# RUN: %p/Inputs/trace-symbols-foo-strong.s -o %t2
+# RUN: ld.lld -shared %t1 -o %t1.so
+# RUN: ld.lld -shared %t2 -o %t2.so
+# RUN: ar -r %t1.a %t1
+# RUN: ar -r %t2.a %t2 
+
+# RUN: ld.lld -y foo -trace-symbol=common -trace-symbol=hsymbol  \
+# RUN: %t %t1 %t2 -o %t3 2>&1 | FileCheck -check-prefix=OBJECTRFOO %s
+# OBJECTRFOO: trace-symbols.s.tmp: reference to foo
+
+# RUN: ld.lld -y foo -trace-symbol=common -trace-symbol=hsymbol  \ 
+# RUN: %t %t1 %t2 -o %t3 2>&1 | not FileCheck -check-prefix=OBJECTDCOMMON %s
+# OBJECTDCOMMON: trace-symbols.s.tmp1: definition of common
+
+# RUN: ld.lld -y foo -trace-symbol=common -trace-symbol=hsymbol  \
+# RUN: %t %t1 %t2 -o %t3 2>&1 | not FileCheck -check-prefix=OBJECTD1FOO %s
+# RUN: ld.lld -y foo -y common %t %t2 %t1 -o %t3 2>&1 | not FileCheck  \
+# RUN: -check-prefix=OBJECTD1FOO %s
+# OBJECTD1FOO: trace-symbols.s.tmp1: definition of foo
+
+# RUN: ld.lld -y foo -trace-symbol=common -trace-symbol=hsymbol  \
+# RUN: %t %t1 %t2 -o %t3 2>&1 | FileCheck -check-prefix=OBJECTD2FOO %s
+# RUN: ld.lld -y foo -y common --trace-symbol=hsymbol  \
+# RUN: %t %t2 %t1 -o %t4 2>&1 | FileCheck -check-prefix=OBJECTD2FOO %s
+# RUN: ld.lld -y foo -y common %t %t1.so %t2 -o %t3 2>&1 |  \
+# RUN: FileCheck -check-prefix=OBJECTD2FOO %s
+# RUN: ld.lld -y foo -y common %t %t2 %t1.a -o %t3 2>&1 |  \
+# RUN: FileCheck -check-prefix=OBJECTD2FOO %s
+# OBJECTD2FOO: trace-symbols.s.tmp2: definition of foo
+
+# RUN: ld.lld -y foo -y common %t %t1.so %t2 -o %t3 2>&1 |  \
+# RUN: FileCheck -check-prefix=SHLIBDCOMMON %s
+# SHLIBDCOMMON: trace-symbols.s.tmp1.so: definition of common
+
+# RUN: ld.lld -y foo -y common %t %t1.so %t2 -o %t3 2>&1 |  \
+# RUN: not FileCheck -check-prefix=SHLIBD1FOO %s
+# RUN: ld.lld -y foo -y common %t %t1.so %t2.so -o %t3 2>&1 |  \
+# RUN: FileCheck -check-prefix=SHLIBD1FOO %s
+# RUN: ld.lld -y foo %t %t1.so %t2.a -o %t3 |  \
+# RUN: FileCheck -check-prefix=SHLIBD1FOO %s
+# SHLIBD1FOO: trace-symbols.s.tmp1.so: definition of foo
+
+# RUN: ld.lld -y foo -y common %t %t2.so %t1.so -o %t3 2>&1 |  \
+# RUN: FileCheck -check-prefix=SHLIBD2FOO %s
+# RUN: ld.lld -y foo %t %t1.a %t2.so -o %t3 |  \
+# RUN: not FileCheck -check-prefix=SHLIBD2FOO %s
+# SHLIBD2FOO: trace-symbols.s.tmp2.so: definition of foo
+
+# RUN: ld.lld -y foo -y common %t %t2 %t1.a -o %t3 2>&1 |  \
+# RUN: not FileCheck -check-prefix=ARCHIVEDCOMMON %s
+# ARCHIVEDCOMMON: trace-symbols.s.tmp1.a(trace-symbols.s.tmp1): definition of \
+# common
+
+# RUN: ld.lld -y foo %t %t1.a %t2.so -o %t3 |  \
+# RUN: FileCheck -check-prefix=ARCHIVED1FOO %s
+# ARCHIVED1FOO: trace-symbols.s.tmp1.a(trace-symbols.s.tmp1): definition of foo
+
+# RUN: ld.lld -y foo %t %t1.a %t2.a -o %t3 |  \
+# RUN: FileCheck -check-prefix=ARCHIVED2FOO %s
+# ARCHIVED2FOO: trace-symbols.s.tmp2.a(trace-symbols.s.tmp2): definition of foo
+
+# RUN: ld.lld -y bar %t %t1.so %t2.so -o %t3 |  \
+# RUN: FileCheck -check-prefix=SHLIBDBAR %s
+# SHLIBDBAR: trace-symbols.s.tmp2.so: definition of bar
+
+# RUN: ld.lld -y foo -y bar %t %t1.so %t2.so -o %t3 |  \
+# RUN: not FileCheck -check-prefix=SHLIBRBAR %s
+# SHLIBRBAR: trace-symbols.s.tmp1.so: reference to bar
+
+# RUN: ld.lld -y foo -y bar %t -u bar --start-lib %t1 %t2 --end-lib -o %t3 |  \
+# RUN: FileCheck -check-prefix=STARTLIB %s
+# STARTLIB: trace-symbols.s.tmp1: reference to bar 
+
+.hidden hsymbol 
+.globl	_start
+.type	_start, @function
+_start:
+call foo