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>
@@ -64,6 +65,7 @@
   std::vector<llvm::StringRef> SearchPaths;
   std::vector<llvm::StringRef> Undefined;
   std::vector<llvm::StringRef> VersionScriptGlobals;
+  llvm::StringSet<> TraceSymbol;
   std::vector<uint8_t> BuildIdVector;
   bool AllowMultipleDefinition;
   bool AsNeeded = false;
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) {
Index: ELF/InputFiles.h
===================================================================
--- ELF/InputFiles.h
+++ ELF/InputFiles.h
@@ -51,6 +51,9 @@
   StringRef getName() const { return MB.getBufferIdentifier(); }
   MemoryBufferRef MB;
 
+  void traceDefined(StringRef &Name);
+  void traceUndefined(StringRef &Name);
+
   // Filename of .a which contained this file. If this file was
   // not in an archive file, it is the empty string. We use this
   // string for creating error messages.
Index: ELF/InputFiles.cpp
===================================================================
--- ELF/InputFiles.cpp
+++ ELF/InputFiles.cpp
@@ -313,6 +313,34 @@
   return new (IAlloc.Allocate()) InputSection<ELFT>(this, &Sec);
 }
 
+// Print the module names which define the notified
+// symbols provided through -y or --trace-symbol option.
+void InputFile::traceDefined(StringRef &Name) {
+  if (Config->TraceSymbol.count(Name)) {
+    std::string Msg;
+    if (!ArchiveName.empty())
+      Msg += ArchiveName.str() + "(" + this->getName().str() + ")";
+    else
+      Msg += this->getName().str();
+    Msg += ": definition of " + Name.str();
+    llvm::outs() << Msg << "\n";
+  }
+}
+
+// Print the module names which reference the notified
+// symbols provided through -y or --trace-symbol option.
+void InputFile::traceUndefined(StringRef &Name) {
+  if (Config->TraceSymbol.count(Name)) {
+    std::string Msg;
+    if (!ArchiveName.empty())
+      Msg += ArchiveName.str() + "(" + this->getName().str() + ")";
+    else
+      Msg += this->getName().str();
+    Msg += ": reference to " + Name.str();
+    llvm::outs() << Msg << "\n";
+  }
+}
+
 template <class ELFT> void elf::ObjectFile<ELFT>::initializeSymbols() {
   this->initStringTable();
   Elf_Sym_Range Syms = this->getElfSymbols(false);
@@ -350,11 +378,13 @@
 
   switch (Sym->st_shndx) {
   case SHN_UNDEF:
+    InputFile::traceUndefined(Name);
     return elf::Symtab<ELFT>::X
         ->addUndefined(Name, Binding, Sym->st_other, Sym->getType(),
                        /*CanOmitFromDynSym*/ false, this)
         ->body();
   case SHN_COMMON:
+    InputFile::traceDefined(Name);
     return elf::Symtab<ELFT>::X
         ->addCommon(Name, Sym->st_size, Sym->st_value, Binding, Sym->st_other,
                     Sym->getType(), this)
@@ -525,9 +555,12 @@
 
     StringRef Name = check(Sym.getName(this->StringTable));
     if (Sym.isUndefined()) {
+      InputFile::traceUndefined(Name);
       Undefs.push_back(Name);
       continue;
     }
+    else if (Sym.isDefined())
+      InputFile::traceDefined(Name);
 
     if (Versym) {
       // Ignore local symbols and non-default versions.
Index: ELF/Options.td
===================================================================
--- ELF/Options.td
+++ ELF/Options.td
@@ -122,6 +122,9 @@
 def z : JoinedOrSeparate<["-"], "z">, MetaVarName<"<option>">,
   HelpText<"Linker option extensions">;
 
+def trace_symbol : Joined<["--", "-"], "trace-symbol=">,
+  HelpText<"Trace references to symbols">;
+
 // Aliases
 def alias_Bdynamic_call_shared: Flag<["-"], "call_shared">, Alias<Bdynamic>;
 def alias_Bdynamic_dy: Flag<["-"], "dy">, Alias<Bdynamic>;
@@ -154,6 +157,7 @@
 def alias_trace : Flag<["-"], "t">, Alias<trace>;
 def alias_undefined_u : JoinedOrSeparate<["-"], "u">, Alias<undefined>;
 def alias_wrap_wrap : Joined<["--", "-"], "wrap=">, Alias<wrap>;
+def alias_trace_symbol_y : JoinedOrSeparate<["-"], "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.cpp
===================================================================
--- ELF/SymbolTable.cpp
+++ ELF/SymbolTable.cpp
@@ -345,6 +345,8 @@
              /*CanOmitFromDynSym*/ false, /*IsUsedInRegularObj*/ true,
              Section ? Section->getFile() : nullptr);
   int Cmp = compareDefinedNonCommon(S, WasInserted, Sym.getBinding());
+  if (Cmp >= 0)
+    cast<InputFile>(Section->getFile())->traceDefined(Name);
   if (Cmp > 0)
     replaceBody<DefinedRegular<ELFT>>(S, Name, Sym, Section);
   else if (Cmp == 0)
Index: test/ELF/Inputs/trace-symbols-foo-global.s
===================================================================
--- test/ELF/Inputs/trace-symbols-foo-global.s
+++ test/ELF/Inputs/trace-symbols-foo-global.s
@@ -0,0 +1,5 @@
+.text
+.globl	foo
+.type	foo, @function
+foo:
+nop
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 +1,6 @@
+.comm	common,4,4
+.text
+.weak	foo
+.type	foo, @function
+foo:
+nop
Index: test/ELF/Inputs/trace-symbols-main.s
===================================================================
--- test/ELF/Inputs/trace-symbols-main.s
+++ test/ELF/Inputs/trace-symbols-main.s
@@ -0,0 +1,10 @@
+.hidden hsymbol 
+.text
+.globl	_start
+.type	_start, @function
+_start:
+
+.globl	main
+.type	main, @function
+main:
+call foo
Index: test/ELF/trace-symbols.s
===================================================================
--- test/ELF/trace-symbols.s
+++ test/ELF/trace-symbols.s
@@ -0,0 +1,58 @@
+# Test -y symbol and -trace-symbol=symbol
+
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux \
+# RUN: %p/Inputs/trace-symbols-main.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-global.s -o %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
+# RUN: ld.lld -y foo -trace-symbol=common -trace-symbol=hsymbol \ 
+# RUN: %t %t1 %t2 -o %t3 2>&1 | FileCheck -check-prefix=OBJECTDCOMMON %s
+# RUN: ld.lld -y foo -trace-symbol=common -trace-symbol=hsymbol \
+# RUN: %t %t1 %t2 -o %t3 2>&1 | FileCheck -check-prefix=OBJECTD1FOO %s
+# 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 %t %t2 %t1 -o %t4 2>&1 | not FileCheck \
+# RUN: -check-prefix=OBJECTD1FOO %s
+
+# RUN: ld.lld -shared %t1 -o %t1.so
+# RUN: ld.lld -y foo -y common %t %t1.so %t2 -o %t5 2>&1 | \
+# RUN: FileCheck -check-prefix=SHLIBDCOMMON %s
+# RUN: ld.lld -y foo -y common %t %t1.so %t2 -o %t5 2>&1 | \
+# RUN: FileCheck -check-prefix=SHLIBD1FOO %s
+# RUN: ld.lld -y foo -y common %t %t1.so %t2 -o %t5 2>&1 | \
+# RUN: FileCheck -check-prefix=OBJECTD2FOO %s
+# RUN: ld.lld -shared %t2 -o %t2.so
+# RUN: ld.lld -y foo -y common %t %t1.so %t2.so -o %t5 2>&1 | \
+# RUN: FileCheck -check-prefix=SHLIBD1FOO %s
+# RUN: ld.lld -y foo -y common %t %t2.so %t1.so -o %t5 2>&1 | \
+# RUN: FileCheck -check-prefix=SHLIBD2FOO %s
+
+# RUN: ar -r %t1.a %t1 
+# RUN: ld.lld -y foo -y common %t %t2 %t1.a -o %t6 2>&1 | \
+# RUN: FileCheck -check-prefix=OBJECTD2FOO %s
+# RUN: ld.lld -y foo -y common %t %t2 %t1.a -o %t6 2>&1 | \
+# RUN: not FileCheck -check-prefix=ARCHIVEDCOMMON %s
+# RUN: ar -r %t2.a %t2 
+# RUN: ld.lld -y foo %t %t1.a %t2.so -o %t8 | \
+# RUN: FileCheck -check-prefix=ARCHIVEDFOO %s
+# RUN: ld.lld -y foo %t %t1.a %t2.so -o %t8 | \
+# RUN: FileCheck -check-prefix=SHLIBD2FOO %s
+# RUN: ld.lld -y foo %t %t1.so %t2.a -o %t8 | \
+# RUN: FileCheck -check-prefix=SHLIBD1FOO %s
+
+# OBJECTRFOO: trace-symbols.s.tmp: reference to foo
+# OBJECTD1FOO: trace-symbols.s.tmp1: definition of foo
+# OBJECTD2FOO: trace-symbols.s.tmp2: definition of foo
+# OBJECTDCOMMON: trace-symbols.s.tmp1: definition of common
+# SHLIBD1FOO: trace-symbols.s.tmp1.so: definition of foo
+# SHLIBD2FOO: trace-symbols.s.tmp2.so: definition of foo
+# SHLIBDCOMMON: trace-symbols.s.tmp1.so: definition of common
+# ARCHIVEDFOO: trace-symbols.s.tmp1.a(trace-symbols.s.tmp1): definition of foo
+# ARCHIVEDCOMMON: trace-symbols.s.tmp1.a(trace-symbols.s.tmp1): definition of \
+# common