Index: lld/Common/Reproduce.cpp
===================================================================
--- lld/Common/Reproduce.cpp
+++ lld/Common/Reproduce.cpp
@@ -54,7 +54,12 @@
   std::string k = std::string(arg.getSpelling());
   if (arg.getNumValues() == 0)
     return k;
-  std::string v = quote(arg.getValue());
+  std::string v;
+  for (size_t i = 0; i < arg.getNumValues(); ++i) {
+    if (i > 0)
+      v.push_back(' ');
+    v+= quote(arg.getValue(i));
+  }
   if (arg.getOption().getRenderStyle() == opt::Option::RenderJoinedStyle)
     return k + v;
   return k + " " + v;
Index: lld/MachO/Driver.h
===================================================================
--- lld/MachO/Driver.h
+++ lld/MachO/Driver.h
@@ -35,6 +35,8 @@
 #undef OPTION
 };
 
+std::string createResponseFile(const llvm::opt::InputArgList &args);
+
 // Check for both libfoo.dylib and libfoo.tbd (in that order).
 llvm::Optional<std::string> resolveDylibPath(llvm::StringRef path);
 
Index: lld/MachO/Driver.cpp
===================================================================
--- lld/MachO/Driver.cpp
+++ lld/MachO/Driver.cpp
@@ -38,6 +38,7 @@
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/Path.h"
 #include "llvm/Support/TargetSelect.h"
+#include "llvm/Support/TarWriter.h"
 
 #include <algorithm>
 
@@ -548,6 +549,12 @@
   }
 }
 
+static const char *getReproduceOption(opt::InputArgList &args) {
+  if (auto *arg = args.getLastArg(OPT_reproduce))
+    return arg->getValue();
+  return getenv("LLD_REPRODUCE");
+}
+
 bool macho::link(llvm::ArrayRef<const char *> argsArr, bool canExitEarly,
                  raw_ostream &stdoutOS, raw_ostream &stderrOS) {
   lld::stdoutOS = &stdoutOS;
@@ -569,6 +576,20 @@
     return true;
   }
 
+  if (const char *path = getReproduceOption(args)) {
+    // Note that --reproduce is a debug option so you can ignore it
+    // if you are trying to understand the whole picture of the code.
+    Expected<std::unique_ptr<TarWriter>> errOrWriter =
+        TarWriter::create(path, path::stem(path));
+    if (errOrWriter) {
+      tar = std::move(*errOrWriter);
+      tar->append("response.txt", createResponseFile(args));
+      tar->append("version.txt", getLLDVersion() + "\n");
+    } else {
+      error("--reproduce: " + toString(errOrWriter.takeError()));
+    }
+  }
+
   config = make<Configuration>();
   symtab = make<SymbolTable>();
   target = createTargetInfo(args);
Index: lld/MachO/DriverUtils.cpp
===================================================================
--- lld/MachO/DriverUtils.cpp
+++ lld/MachO/DriverUtils.cpp
@@ -9,8 +9,10 @@
 #include "Driver.h"
 #include "InputFiles.h"
 
+#include "lld/Common/Args.h"
 #include "lld/Common/ErrorHandler.h"
 #include "lld/Common/Memory.h"
+#include "lld/Common/Reproduce.h"
 #include "llvm/Option/Arg.h"
 #include "llvm/Option/ArgList.h"
 #include "llvm/Option/Option.h"
@@ -92,6 +94,55 @@
   lld::outs() << "\n";
 }
 
+static std::string rewritePath(StringRef s) {
+  if (fs::exists(s))
+    return relativeToRoot(s);
+  return std::string(s);
+}
+
+// Reconstructs command line arguments so that so that you can re-run
+// the same command with the same inputs. This is for --reproduce.
+std::string macho::createResponseFile(const opt::InputArgList &args) {
+  SmallString<0> data;
+  raw_svector_ostream os(data);
+
+  // Copy the command line to the output while rewriting paths.
+  for (auto *arg : args) {
+    switch (arg->getOption().getID()) {
+    case OPT_reproduce:
+      break;
+    case OPT_INPUT:
+      os << quote(rewritePath(arg->getValue())) << "\n";
+      break;
+    case OPT_o:
+      os << "-o " << quote(sys::path::filename(arg->getValue())) << "\n";
+      break;
+    case OPT_filelist:
+      if (Optional<MemoryBufferRef> buffer = readFile(arg->getValue()))
+        for (StringRef path : args::getLines(*buffer))
+          os << quote(rewritePath(path)) << "\n";
+      break;
+    case OPT_force_load:
+    case OPT_rpath:
+    case OPT_syslibroot:
+    case OPT_F:
+    case OPT_L:
+    case OPT_order_file:
+      os << arg->getSpelling() << " " << quote(rewritePath(arg->getValue()))
+         << "\n";
+      break;
+    case OPT_sectcreate:
+      os << arg->getSpelling() << " " << quote(arg->getValue(0)) << " "
+         << quote(arg->getValue(1)) << " "
+         << quote(rewritePath(arg->getValue(2))) << "\n";
+      break;
+    default:
+      os << toString(*arg) << "\n";
+    }
+  }
+  return std::string(data.str());
+}
+
 Optional<std::string> macho::resolveDylibPath(StringRef path) {
   // TODO: if a tbd and dylib are both present, we should check to make sure
   // they are consistent.
Index: lld/MachO/InputFiles.h
===================================================================
--- lld/MachO/InputFiles.h
+++ lld/MachO/InputFiles.h
@@ -27,6 +27,7 @@
 namespace lto {
 class InputFile;
 } // namespace lto
+class TarWriter;
 } // namespace llvm
 
 namespace lld {
@@ -36,6 +37,10 @@
 class Symbol;
 struct Reloc;
 
+// If -reproduce option is given, all input files are written
+// to this tar archive.
+extern std::unique_ptr<llvm::TarWriter> tar;
+
 // If .subsections_via_symbols is set, each InputSection will be split along
 // symbol boundaries. The keys of a SubsectionMap represent the offsets of
 // each subsection from the start of the original pre-split InputSection.
Index: lld/MachO/InputFiles.cpp
===================================================================
--- lld/MachO/InputFiles.cpp
+++ lld/MachO/InputFiles.cpp
@@ -56,12 +56,14 @@
 
 #include "lld/Common/ErrorHandler.h"
 #include "lld/Common/Memory.h"
+#include "lld/Common/Reproduce.h"
 #include "llvm/ADT/iterator.h"
 #include "llvm/BinaryFormat/MachO.h"
 #include "llvm/LTO/LTO.h"
 #include "llvm/Support/Endian.h"
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/Path.h"
+#include "llvm/Support/TarWriter.h"
 
 using namespace llvm;
 using namespace llvm::MachO;
@@ -71,6 +73,7 @@
 using namespace lld::macho;
 
 std::vector<InputFile *> macho::inputFiles;
+std::unique_ptr<TarWriter> macho::tar;
 
 // Open a given file path and return it as a memory-mapped file.
 Optional<MemoryBufferRef> macho::readFile(StringRef path) {
@@ -88,8 +91,11 @@
   // If this is a regular non-fat file, return it.
   const char *buf = mbref.getBufferStart();
   auto *hdr = reinterpret_cast<const MachO::fat_header *>(buf);
-  if (read32be(&hdr->magic) != MachO::FAT_MAGIC)
+  if (read32be(&hdr->magic) != MachO::FAT_MAGIC) {
+    if (tar)
+      tar->append(relativeToRoot(path), mbref.getBuffer());
     return mbref;
+  }
 
   // Object files and archive files may be fat files, which contains
   // multiple real files for different CPU ISAs. Here, we search for a
@@ -112,6 +118,8 @@
     uint32_t size = read32be(&arch[i].size);
     if (offset + size > mbref.getBufferSize())
       error(path + ": slice extends beyond end of file");
+    if (tar)
+      tar->append(relativeToRoot(path), mbref.getBuffer());
     return MemoryBufferRef(StringRef(buf + offset, size), path.copy(bAlloc));
   }
 
Index: lld/MachO/Options.td
===================================================================
--- lld/MachO/Options.td
+++ lld/MachO/Options.td
@@ -14,6 +14,10 @@
 def color_diagnostics_eq: Joined<["--"], "color-diagnostics=">,
   HelpText<"Use colors in diagnostics (default: auto)">,
   MetaVarName<"[auto,always,never]">;
+def reproduce: Separate<["--"], "reproduce">;
+def reproduce_eq: Joined<["--"], "reproduce=">,
+    Alias<!cast<Separate>(reproduce)>,
+    HelpText<"Write tar file containing inputs and command to reproduce link">;
 
 
 // This is a complete Options.td compiled from Apple's ld(1) manpage
Index: lld/test/MachO/reproduce.s
===================================================================
--- /dev/null
+++ lld/test/MachO/reproduce.s
@@ -0,0 +1,37 @@
+# REQUIRES: x86
+
+# RUN: rm -rf %t.dir
+# RUN: mkdir -p %t.dir/build1
+# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-macos %s -o %t.dir/build1/foo.o
+# RUN: cd %t.dir
+# RUN: %lld -platform_version macos 10.10.0 11.0 build1/foo.o -o bar --reproduce repro1.tar
+# RUN: tar xOf repro1.tar repro1/%:t.dir/build1/foo.o > build1-foo.o
+# RUN: cmp build1/foo.o build1-foo.o
+
+# RUN: tar xf repro1.tar repro1/response.txt repro1/version.txt
+# RUN: FileCheck %s --check-prefix=RSP1 < repro1/response.txt
+# RSP1:      {{^}}-platform_version macos 10.10.0 11.0{{$}}
+# RSP1-NOT:  {{^}}repro1{{[/\\]}}
+# RSP1-NEXT: {{[/\\]}}foo.o
+# RSP1-NEXT: -o bar
+# RSP1-NOT:  --reproduce
+
+# RUN: FileCheck %s --check-prefix=VERSION < repro1/version.txt
+# VERSION: LLD
+
+# RUN: mkdir -p %t.dir/build2/a/b/c
+# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-macos %s -o %t.dir/build2/foo.o
+# RUN: cd %t.dir/build2/a/b/c
+# RUN: echo ./../../../foo.o > %t.dir/build2/filelist
+# RUN: env LLD_REPRODUCE=repro2.tar %lld -filelist %t.dir/build2/filelist -o /dev/null
+# RUN: tar xOf repro2.tar repro2/%:t.dir/build2/foo.o > build2-foo.o
+# RUN: cmp %t.dir/build2/foo.o build2-foo.o
+
+# RUN: tar xf repro2.tar repro2/response.txt repro2/version.txt
+# RUN: FileCheck %s --check-prefix=RSP2 < repro2/response.txt
+# RSP2-NOT:  {{^}}repro2{{[/\\]}}
+# RSP2: {{[/\\]}}foo.o
+
+.globl _main
+_main:
+  ret