diff --git a/llvm/tools/LLVMBuild.txt b/llvm/tools/LLVMBuild.txt
--- a/llvm/tools/LLVMBuild.txt
+++ b/llvm/tools/LLVMBuild.txt
@@ -32,6 +32,7 @@
  llvm-dwarfdump
  llvm-dwp
  llvm-elfabi
+ llvm-ifs
  llvm-exegesis
  llvm-extract
  llvm-jitlistener
diff --git a/llvm/tools/llvm-ifs/CMakeLists.txt b/llvm/tools/llvm-ifs/CMakeLists.txt
new file mode 100644
--- /dev/null
+++ b/llvm/tools/llvm-ifs/CMakeLists.txt
@@ -0,0 +1,10 @@
+set(LLVM_LINK_COMPONENTS
+  Object
+  Support
+  TextAPI
+  ObjectYAML
+  )
+
+add_llvm_tool(llvm-ifs
+  llvm-ifs.cpp
+  )
diff --git a/llvm/tools/llvm-ifs/LLVMBuild.txt b/llvm/tools/llvm-ifs/LLVMBuild.txt
new file mode 100644
--- /dev/null
+++ b/llvm/tools/llvm-ifs/LLVMBuild.txt
@@ -0,0 +1,21 @@
+;===- ./tools/llvm-ifs/LLVMBuild.txt ---------------------------*- Conf -*--===;
+;
+; Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+; See https://llvm.org/LICENSE.txt for license information.
+; SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+;
+;===------------------------------------------------------------------------===;
+;
+; This is an LLVMBuild description file for the components in this subdirectory.
+;
+; For more information on the LLVMBuild system, please see:
+;
+;   http://llvm.org/docs/LLVMBuild.html
+;
+;===------------------------------------------------------------------------===;
+
+[component_0]
+type = Tool
+name = llvm-ifs
+parent = Tools
+required_libraries = Object Support TextAPI
diff --git a/llvm/tools/llvm-ifs/llvm-ifs.cpp b/llvm/tools/llvm-ifs/llvm-ifs.cpp
new file mode 100644
--- /dev/null
+++ b/llvm/tools/llvm-ifs/llvm-ifs.cpp
@@ -0,0 +1,429 @@
+//===- llvm-ifs.cpp -------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===-----------------------------------------------------------------------===/
+
+#include "llvm/ADT/StringRef.h"
+#include "llvm/ADT/StringSwitch.h"
+#include "llvm/ADT/Triple.h"
+#include "llvm/ObjectYAML/yaml2obj.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Errc.h"
+#include "llvm/Support/Error.h"
+#include "llvm/Support/FileOutputBuffer.h"
+#include "llvm/Support/MemoryBuffer.h"
+#include "llvm/Support/Path.h"
+#include "llvm/Support/WithColor.h"
+#include "llvm/Support/YAMLTraits.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/TextAPI/ELF/ELFStub.h"
+#include "llvm/TextAPI/MachO/InterfaceFile.h"
+#include "llvm/TextAPI/MachO/TextAPIReader.h"
+#include "llvm/TextAPI/MachO/TextAPIWriter.h"
+#include <string>
+
+using namespace llvm;
+using namespace llvm::yaml;
+using namespace llvm::elfabi;
+using namespace llvm::MachO;
+
+namespace {
+const VersionTuple IFSVersionCurrent(1, 0);
+};
+
+static cl::opt<std::string> Action("a", cl::desc("<llvm-ifs action>"),
+                                   cl::value_desc("write-ifs | write-bin"),
+                                   cl::init("write-ifs"));
+
+static cl::opt<std::string> ForceFormat("f", cl::desc("<force object format>"),
+                                        cl::value_desc("ELF | TBD"),
+                                        cl::init(""));
+
+static cl::list<std::string> InputFilenames(cl::Positional,
+                                            cl::desc("<input ifs files>"),
+                                            cl::ZeroOrMore);
+
+static cl::opt<std::string> OutputFilename("o", cl::desc("<output file>"),
+                                           cl::value_desc("path"));
+
+/// YAML traits for ELFSymbolType.
+template <> struct ScalarEnumerationTraits<ELFSymbolType> {
+  static void enumeration(IO &IO, ELFSymbolType &SymbolType) {
+    IO.enumCase(SymbolType, "NoType", ELFSymbolType::NoType);
+    IO.enumCase(SymbolType, "Func", ELFSymbolType::Func);
+    IO.enumCase(SymbolType, "Object", ELFSymbolType::Object);
+    IO.enumCase(SymbolType, "TLS", ELFSymbolType::TLS);
+    IO.enumCase(SymbolType, "Unknown", ELFSymbolType::Unknown);
+    // Treat other symbol types as noise, and map to Unknown.
+    if (!IO.outputting() && IO.matchEnumFallback())
+      SymbolType = ELFSymbolType::Unknown;
+  }
+};
+
+template <> struct ScalarTraits<VersionTuple> {
+  static void output(const VersionTuple &Value, void *,
+                     llvm::raw_ostream &Out) {
+    Out << Value.getAsString();
+  }
+
+  static StringRef input(StringRef Scalar, void *, VersionTuple &Value) {
+    if (Value.tryParse(Scalar))
+      return StringRef("Can't parse version: invalid version format.");
+
+    if (Value > IFSVersionCurrent)
+      return StringRef("Unsupported IFS version.");
+
+    // Returning empty StringRef indicates successful parse.
+    return StringRef();
+  }
+
+  // Don't place quotation marks around version value.
+  static QuotingType mustQuote(StringRef) { return QuotingType::None; }
+};
+
+/// YAML traits for ELFSymbol.
+template <> struct MappingTraits<ELFSymbol> {
+  static void mapping(IO &IO, ELFSymbol &Symbol) {
+    IO.mapRequired("Type", Symbol.Type);
+    // The need for symbol size depends on the symbol type.
+    if (Symbol.Type == ELFSymbolType::NoType)
+      IO.mapOptional("Size", Symbol.Size, (uint64_t)0);
+    else if (Symbol.Type == ELFSymbolType::Func)
+      Symbol.Size = 0;
+    else
+      IO.mapRequired("Size", Symbol.Size);
+    IO.mapOptional("Undefined", Symbol.Undefined, false);
+    IO.mapOptional("Weak", Symbol.Weak, false);
+    IO.mapOptional("Warning", Symbol.Warning);
+  }
+
+  // Compacts symbol information into a single line.
+  static const bool flow = true;
+};
+
+/// YAML traits for set of ELFSymbols.
+template <> struct CustomMappingTraits<std::set<ELFSymbol>> {
+  static void inputOne(IO &IO, StringRef Key, std::set<ELFSymbol> &Set) {
+    std::string Name = Key.str();
+    ELFSymbol Sym(Name);
+    IO.mapRequired(Name.c_str(), Sym);
+    Set.insert(Sym);
+  }
+
+  static void output(IO &IO, std::set<ELFSymbol> &Set) {
+    for (auto &Sym : Set)
+      IO.mapRequired(Sym.Name.c_str(), const_cast<ELFSymbol &>(Sym));
+  }
+};
+
+// A cumulative representation of ELF stubs.
+// Both textual and binary stubs will read into and write from this object.
+class IFSStub {
+  // TODO: Add support for symbol versioning.
+public:
+  VersionTuple IfsVersion;
+  std::string Triple;
+  std::string ObjectFileFormat;
+  Optional<std::string> SOName;
+  std::vector<std::string> NeededLibs;
+  std::set<ELFSymbol> Symbols;
+
+  IFSStub() = default;
+  IFSStub(const IFSStub &Stub)
+      : IfsVersion(Stub.IfsVersion), Triple(Stub.Triple),
+        ObjectFileFormat(Stub.ObjectFileFormat), SOName(Stub.SOName),
+        NeededLibs(Stub.NeededLibs), Symbols(Stub.Symbols) {}
+  IFSStub(IFSStub &&Stub)
+      : IfsVersion(std::move(Stub.IfsVersion)), Triple(std::move(Stub.Triple)),
+        ObjectFileFormat(std::move(Stub.ObjectFileFormat)),
+        SOName(std::move(Stub.SOName)), NeededLibs(std::move(Stub.NeededLibs)),
+        Symbols(std::move(Stub.Symbols)) {}
+};
+
+/// YAML traits for IFSStub objects.
+template <> struct MappingTraits<IFSStub> {
+  static void mapping(IO &IO, IFSStub &Stub) {
+    if (!IO.mapTag("!experimental-ifs-v1", true))
+      IO.setError("Not a .ifs YAML file.");
+    IO.mapRequired("IfsVersion", Stub.IfsVersion);
+    IO.mapOptional("Triple", Stub.Triple);
+    IO.mapOptional("ObjectFileFormat", Stub.ObjectFileFormat);
+    IO.mapOptional("SOName", Stub.SOName);
+    IO.mapOptional("NeededLibs", Stub.NeededLibs);
+    IO.mapRequired("Symbols", Stub.Symbols);
+  }
+};
+
+static Expected<std::unique_ptr<IFSStub>> readInputFile(StringRef FilePath) {
+  // Read in file.
+  ErrorOr<std::unique_ptr<MemoryBuffer>> BufOrError =
+      MemoryBuffer::getFileOrSTDIN(FilePath);
+  if (!BufOrError)
+    return createStringError(BufOrError.getError(), "Could not open `%s`",
+                             FilePath.data());
+
+  std::unique_ptr<MemoryBuffer> FileReadBuffer = std::move(*BufOrError);
+  yaml::Input YamlIn(FileReadBuffer->getBuffer());
+  std::unique_ptr<IFSStub> Stub(new IFSStub());
+  YamlIn >> *Stub;
+
+  if (std::error_code Err = YamlIn.error())
+    return createStringError(Err, "Failed reading Interface Stub File.");
+
+  return std::move(Stub);
+}
+
+int writeTbdStub(const llvm::Triple &T, const std::set<ELFSymbol> &Symbols,
+                 const StringRef Format, raw_ostream &Out) {
+  auto ArchOrError =
+      [](const llvm::Triple &T) -> llvm::Expected<llvm::MachO::Architecture> {
+    switch (T.getArch()) {
+    default:
+      return createStringError(errc::not_supported, "Invalid Architecture.");
+    case llvm::Triple::ArchType::x86:
+      return AK_i386;
+    case llvm::Triple::ArchType::x86_64:
+      return AK_x86_64;
+    case llvm::Triple::ArchType::arm:
+      return AK_armv7;
+    case llvm::Triple::ArchType::aarch64:
+      return AK_arm64;
+    }
+  }(T);
+
+  if (!ArchOrError)
+    return -1;
+
+  Architecture Arch = ArchOrError.get();
+
+  InterfaceFile File;
+  File.setFileType(FileType::TBD_V3);
+  File.setArchitectures(Arch);
+  File.setPlatform(PlatformKind::macOS);
+
+  for (const auto &Symbol : Symbols) {
+    auto Name = Symbol.Name;
+    auto Kind = SymbolKind::GlobalSymbol;
+    switch (Symbol.Type) {
+    default:
+    case llvm::elfabi::ELFSymbolType::NoType:
+      Kind = SymbolKind::GlobalSymbol;
+      break;
+    case llvm::elfabi::ELFSymbolType::Object:
+      Kind = SymbolKind::GlobalSymbol;
+      break;
+    case llvm::elfabi::ELFSymbolType::Func:
+      Kind = SymbolKind::GlobalSymbol;
+      break;
+    }
+    if (Symbol.Weak)
+      File.addSymbol(Kind, Name, Arch, SymbolFlags::WeakDefined);
+    else
+      File.addSymbol(Kind, Name, Arch);
+  }
+
+  SmallString<4096> Buffer;
+  raw_svector_ostream OS(Buffer);
+  if (Error Result = TextAPIWriter::writeToStream(OS, File))
+    return -1;
+  Out << OS.str();
+  return 0;
+}
+
+int writeElfStub(const llvm::Triple &T, const std::set<ELFSymbol> &Symbols,
+                 const StringRef Format, raw_ostream &Out) {
+  SmallString<0> Storage;
+  Storage.clear();
+  raw_svector_ostream OS(Storage);
+
+  OS << "--- !ELF\n";
+  OS << "FileHeader:\n";
+  OS << "  Class:           ELFCLASS";
+  OS << (T.isArch64Bit() ? "64" : "32");
+  OS << "\n";
+  OS << "  Data:            ELFDATA2";
+  OS << (T.isLittleEndian() ? "LSB" : "MSB");
+  OS << "\n";
+  OS << "  Type:            ET_DYN\n";
+  OS << "  Machine:         "
+     << llvm::StringSwitch<llvm::StringRef>(T.getArchName())
+            .Case("x86_64", "EM_X86_64")
+            .Case("i386", "EM_386")
+            .Case("i686", "EM_386")
+            .Case("aarch64", "EM_AARCH64")
+            .Case("amdgcn", "EM_AMDGPU")
+            .Case("r600", "EM_AMDGPU")
+            .Case("arm", "EM_ARM")
+            .Case("thumb", "EM_ARM")
+            .Case("avr", "EM_AVR")
+            .Case("mips", "EM_MIPS")
+            .Case("mipsel", "EM_MIPS")
+            .Case("mips64", "EM_MIPS")
+            .Case("mips64el", "EM_MIPS")
+            .Case("msp430", "EM_MSP430")
+            .Case("ppc", "EM_PPC")
+            .Case("ppc64", "EM_PPC64")
+            .Case("ppc64le", "EM_PPC64")
+            .Case("x86", T.isOSIAMCU() ? "EM_IAMCU" : "EM_386")
+            .Case("x86_64", "EM_X86_64")
+            .Default("EM_NONE")
+     << "\nSymbols:\n";
+  for (const auto &Symbol : Symbols) {
+    OS << "  - Name:            " << Symbol.Name << "\n"
+       << "    Type:            STT_";
+    switch (Symbol.Type) {
+    default:
+    case llvm::elfabi::ELFSymbolType::NoType:
+      OS << "NOTYPE";
+      break;
+    case llvm::elfabi::ELFSymbolType::Object:
+      OS << "OBJECT";
+      break;
+    case llvm::elfabi::ELFSymbolType::Func:
+      OS << "FUNC";
+      break;
+    }
+    OS << "\n    Binding:         STB_" << (Symbol.Weak ? "WEAK" : "GLOBAL")
+       << "\n";
+  }
+  OS << "...\n";
+
+  yaml::Input YIn(OS.str());
+  Error E = convertYAML(YIn, Out);
+  return !E ? -1 : 0;
+}
+
+int writeIfso(const IFSStub &Stub, bool IsWriteIfs, raw_ostream &Out) {
+  if (IsWriteIfs) {
+    yaml::Output YamlOut(Out, NULL, /*WrapColumn =*/0);
+    YamlOut << const_cast<IFSStub &>(Stub);
+    return 0;
+  }
+
+  std::string ObjectFileFormat =
+      ForceFormat.empty() ? Stub.ObjectFileFormat : ForceFormat;
+
+  if (ObjectFileFormat == "ELF")
+    return writeElfStub(llvm::Triple(Stub.Triple), Stub.Symbols,
+                        Stub.ObjectFileFormat, Out);
+  if (ObjectFileFormat == "TBD")
+    return writeTbdStub(llvm::Triple(Stub.Triple), Stub.Symbols,
+                        Stub.ObjectFileFormat, Out);
+
+  WithColor::error()
+      << "Invalid ObjectFileFormat: Only ELF and TBD are supported.\n";
+  return -1;
+}
+
+// New Interface Stubs Yaml Format:
+// --- !experimental-ifs-v1
+// IfsVersion:      1.0
+// Triple:          <llvm triple>
+// ObjectFileFormat: <ELF | others not yet supported>
+// Symbols:
+//   _ZSymbolName: { Type: <type> }
+// ...
+
+int main(int argc, char *argv[]) {
+  // Parse arguments.
+  cl::ParseCommandLineOptions(argc, argv);
+
+  if (InputFilenames.empty())
+    InputFilenames.push_back("-");
+
+  IFSStub Stub;
+  std::map<std::string, ELFSymbol> SymbolMap;
+
+  for (const std::string &InputFilePath : InputFilenames) {
+    Expected<std::unique_ptr<IFSStub>> StubOrErr = readInputFile(InputFilePath);
+    if (!StubOrErr) {
+      WithColor::error() << StubOrErr.takeError() << "\n";
+      return -1;
+    }
+    std::unique_ptr<IFSStub> TargetStub = std::move(StubOrErr.get());
+
+    if (Stub.Triple.empty()) {
+      Stub.IfsVersion = TargetStub->IfsVersion;
+      Stub.Triple = TargetStub->Triple;
+      Stub.ObjectFileFormat = TargetStub->ObjectFileFormat;
+      Stub.SOName = TargetStub->SOName;
+      Stub.NeededLibs = TargetStub->NeededLibs;
+    } else {
+      if (Stub.IfsVersion != TargetStub->IfsVersion) {
+        WithColor::error() << "Interface Stub: IfsVersion Mismatch.\n";
+        return -1;
+      }
+      if (Stub.Triple != TargetStub->Triple) {
+        WithColor::error() << "Interface Stub: Triple Mismatch.\n";
+        return -1;
+      }
+      if (Stub.ObjectFileFormat != TargetStub->ObjectFileFormat) {
+        WithColor::error() << "Interface Stub: ObjectFileFormat Mismatch.\n";
+        return -1;
+      }
+      if (Stub.SOName != TargetStub->SOName) {
+        WithColor::error() << "Interface Stub: SOName Mismatch.\n";
+        return -1;
+      }
+      if (Stub.NeededLibs != TargetStub->NeededLibs) {
+        WithColor::error() << "Interface Stub: NeededLibs Mismatch.\n";
+        return -1;
+      }
+    }
+
+    for (auto Symbol : TargetStub->Symbols) {
+      auto SI = SymbolMap.find(Symbol.Name);
+      if (SI == SymbolMap.end()) {
+        SymbolMap.insert(
+            std::pair<std::string, ELFSymbol>(Symbol.Name, Symbol));
+        continue;
+      }
+
+      // Check conflicts:
+      // Symbol.Name
+      if (Symbol.Size != SI->second.Size) {
+        WithColor::error() << "Interface Stub: Size Mismatch for" +
+                                  Symbol.Name + ".\n";
+        return -1;
+      }
+      if (Symbol.Type != SI->second.Type) {
+        WithColor::error() << "Interface Stub: Type Mismatch for" +
+                                  Symbol.Name + ".\n";
+        return -1;
+      }
+      if (Symbol.Undefined != SI->second.Undefined) {
+        WithColor::error() << "Interface Stub: Undefined Mismatch for" +
+                                  Symbol.Name + ".\n";
+        return -1;
+      }
+      if (Symbol.Warning != SI->second.Warning) {
+        WithColor::error() << "Interface Stub: Warning Mismatch for" +
+                                  Symbol.Name + ".\n";
+        return -1;
+      }
+      if (Symbol.Weak != SI->second.Weak) {
+        WithColor::error() << "Interface Stub: Weak Mismatch for" +
+                                  Symbol.Name + ".\n";
+        return -1;
+      }
+    }
+  }
+
+  for (auto &Entry : SymbolMap)
+    Stub.Symbols.insert(Entry.second);
+
+  std::error_code SysErr;
+
+  // Open file for writing.
+  raw_fd_ostream Out(OutputFilename, SysErr);
+  if (SysErr) {
+    WithColor::error() << "Couldn't open " << OutputFilename
+                       << " for writing.\n";
+    return -1;
+  }
+
+  return writeIfso(Stub, (Action == "write-ifs"), Out);
+}