Index: lib/Target/AArch64/MCTargetDesc/AArch64ELFStreamer.cpp
===================================================================
--- lib/Target/AArch64/MCTargetDesc/AArch64ELFStreamer.cpp
+++ lib/Target/AArch64/MCTargetDesc/AArch64ELFStreamer.cpp
@@ -102,6 +102,14 @@
     MCELFStreamer::ChangeSection(Section, Subsection);
   }
 
+  // Reset state between object emissions
+  void reset() override {
+    MappingSymbolCounter = 0;
+    MCELFStreamer::reset();
+    LastMappingSymbols.clear();
+    LastEMS = EMS_None;
+  }
+
   /// This function is the one used to emit instruction data into the ELF
   /// streamer. We override it to add the appropriate mapping symbol if
   /// necessary.
Index: lib/Target/ARM/MCTargetDesc/ARMELFStreamer.cpp
===================================================================
--- lib/Target/ARM/MCTargetDesc/ARMELFStreamer.cpp
+++ lib/Target/ARM/MCTargetDesc/ARMELFStreamer.cpp
@@ -1171,6 +1171,8 @@
   ATS.reset();
   MappingSymbolCounter = 0;
   MCELFStreamer::reset();
+  LastMappingSymbols.clear();
+  LastEMSInfo.reset();
   // MCELFStreamer clear's the assembler's e_flags. However, for
   // arm we manually set the ABI version on streamer creation, so
   // do the same here
Index: unittests/Target/ARM/CMakeLists.txt
===================================================================
--- /dev/null
+++ unittests/Target/ARM/CMakeLists.txt
@@ -0,0 +1,22 @@
+include_directories(
+  ${CMAKE_SOURCE_DIR}/lib/Target/ARM
+  ${CMAKE_BINARY_DIR}/lib/Target/ARM
+  )
+
+set(LLVM_LINK_COMPONENTS
+  ARMCodeGen
+  ARMDesc
+  ARMInfo
+  CodeGen
+  Core
+  MC
+  Object
+  Support
+  Target
+  )
+
+add_llvm_unittest(ARMTests
+  ELFStreamer.cpp
+  )
+
+target_link_libraries(ARMTests LLVMTestingSupport)
Index: unittests/Target/ARM/ELFStreamer.cpp
===================================================================
--- /dev/null
+++ unittests/Target/ARM/ELFStreamer.cpp
@@ -0,0 +1,102 @@
+#include "ARMSubtarget.h"
+#include "ARMTargetMachine.h"
+#include "llvm/MC/MCAsmBackend.h"
+#include "llvm/MC/MCAsmInfo.h"
+#include "llvm/MC/MCCodeEmitter.h"
+#include "llvm/MC/MCContext.h"
+#include "llvm/MC/MCObjectFileInfo.h"
+#include "llvm/MC/MCSectionELF.h"
+#include "llvm/MC/MCStreamer.h"
+#include "llvm/MC/MCTargetOptionsCommandFlags.h"
+#include "llvm/Object/ObjectFile.h"
+#include "llvm/Support/Error.h"
+#include "llvm/Support/TargetRegistry.h"
+#include "llvm/Support/TargetSelect.h"
+#include "llvm/Testing/Support/Error.h"
+
+#include "gtest/gtest.h"
+
+using namespace llvm;
+
+namespace {
+
+struct Generator {
+  std::unique_ptr<MCRegisterInfo> MRI;
+  std::unique_ptr<MCAsmInfo> MAI;
+  std::unique_ptr<MCObjectFileInfo> MOFI;
+  std::unique_ptr<MCContext> MC;
+  std::unique_ptr<MCInstrInfo> MII;
+  std::unique_ptr<MCSubtargetInfo> MSTI;
+  std::unique_ptr<MCStreamer> MS;
+
+  SmallString<4096> FileBytes;
+  std::unique_ptr<raw_svector_ostream> Stream;
+
+  Generator();
+};
+
+Generator::Generator() {
+  Triple TheTriple(Triple::normalize("arm--"));
+
+  LLVMInitializeARMTargetInfo();
+  LLVMInitializeARMTarget();
+  LLVMInitializeARMTargetMC();
+
+  std::string ErrorStr;
+  std::string TripleName;
+
+  // Get the target.
+  const Target *TheTarget =
+      TargetRegistry::lookupTarget(TripleName, TheTriple, ErrorStr);
+
+  TripleName = TheTriple.getTriple();
+
+  // Create all the MC Objects.
+  MRI.reset(TheTarget->createMCRegInfo(TripleName));
+  MAI.reset(TheTarget->createMCAsmInfo(*MRI, TripleName));
+  MOFI.reset(new MCObjectFileInfo);
+  MC.reset(new MCContext(MAI.get(), MRI.get(), MOFI.get()));
+  MOFI->InitMCObjectFileInfo(TheTriple, /*PIC*/ false, *MC);
+
+  MCTargetOptions Options;
+  auto MAB = TheTarget->createMCAsmBackend(*MRI, TripleName, "", Options);
+  MII.reset(TheTarget->createMCInstrInfo());
+  MSTI.reset(TheTarget->createMCSubtargetInfo(TripleName, "", ""));
+  auto MCE = TheTarget->createMCCodeEmitter(*MII, *MRI, *MC);
+
+  Stream = make_unique<raw_svector_ostream>(FileBytes);
+
+  MCTargetOptions MCOptions = InitMCTargetOptionsFromFlags();
+  MS.reset(TheTarget->createMCObjectStreamer(
+      TheTriple, *MC, std::unique_ptr<MCAsmBackend>(MAB), *Stream,
+      std::unique_ptr<MCCodeEmitter>(MCE), *MSTI, MCOptions.MCRelaxAll,
+      MCOptions.MCIncrementalLinkerCompatible, false));
+}
+
+} // anonymous namespace
+
+TEST(ELFStreamer, TestReset) {
+  Generator Gen;
+
+  // Test that the OutStreamer can be reused without crashing
+  // A C++ unittest is needed here since no LLVM tool currently does this (reset and reuse)
+  // > llvm-mc only supports one input file and hence only one streamer,
+  // > clang will create a new streamer for each object
+  for (int i = 0; i < 10; i++) {
+    // Switch section back and forth and emit some random data between resets
+    // to trigger section switching logic.
+    auto s1 = Gen.MC->getELFSection(".foo", 0 /*Type*/, 0 /*Flags*/);
+    auto s2 = Gen.MC->getELFSection(".bar", 0 /*Type*/, 0 /*Flags*/);
+    Gen.MS->SwitchSection( s1);
+    Gen.MS->EmitBytes("0");
+    Gen.MS->SwitchSection( s2);
+    Gen.MS->EmitBytes("0");
+    Gen.MS->SwitchSection( s1);
+    Gen.MS->EmitBytes("0");
+    Gen.MS->SwitchSection( s2);
+    Gen.MS->EmitBytes("0");
+    Gen.MS->Finish();
+    Gen.MS->reset();
+    // Not really sure what to test about the output here. Just to make sure no crash for now...
+  }
+}