Index: llvm/trunk/lib/Target/AMDGPU/MCTargetDesc/AMDGPUAsmBackend.cpp
===================================================================
--- llvm/trunk/lib/Target/AMDGPU/MCTargetDesc/AMDGPUAsmBackend.cpp
+++ llvm/trunk/lib/Target/AMDGPU/MCTargetDesc/AMDGPUAsmBackend.cpp
@@ -127,11 +127,14 @@
 namespace {
 
 class ELFAMDGPUAsmBackend : public AMDGPUAsmBackend {
+  bool Is64Bit;
+
 public:
-  ELFAMDGPUAsmBackend(const Target &T) : AMDGPUAsmBackend(T) { }
+  ELFAMDGPUAsmBackend(const Target &T, bool Is64Bit) :
+      AMDGPUAsmBackend(T), Is64Bit(Is64Bit) { }
 
   MCObjectWriter *createObjectWriter(raw_pwrite_stream &OS) const override {
-    return createAMDGPUELFObjectWriter(OS);
+    return createAMDGPUELFObjectWriter(Is64Bit, OS);
   }
 };
 
@@ -140,5 +143,8 @@
 MCAsmBackend *llvm::createAMDGPUAsmBackend(const Target &T,
                                            const MCRegisterInfo &MRI,
                                            const Triple &TT, StringRef CPU) {
-  return new ELFAMDGPUAsmBackend(T);
+  Triple TargetTriple(TT);
+
+  // Use 64-bit ELF for amdgcn
+  return new ELFAMDGPUAsmBackend(T, TargetTriple.getArch() == Triple::amdgcn);
 }
Index: llvm/trunk/lib/Target/AMDGPU/MCTargetDesc/AMDGPUELFObjectWriter.cpp
===================================================================
--- llvm/trunk/lib/Target/AMDGPU/MCTargetDesc/AMDGPUELFObjectWriter.cpp
+++ llvm/trunk/lib/Target/AMDGPU/MCTargetDesc/AMDGPUELFObjectWriter.cpp
@@ -18,7 +18,7 @@
 
 class AMDGPUELFObjectWriter : public MCELFObjectTargetWriter {
 public:
-  AMDGPUELFObjectWriter();
+  AMDGPUELFObjectWriter(bool Is64Bit);
 protected:
   unsigned GetRelocType(const MCValue &Target, const MCFixup &Fixup,
                         bool IsPCRel) const override {
@@ -30,10 +30,10 @@
 
 } // End anonymous namespace
 
-AMDGPUELFObjectWriter::AMDGPUELFObjectWriter()
-  : MCELFObjectTargetWriter(false, 0, ELF::EM_AMDGPU, false) { }
+AMDGPUELFObjectWriter::AMDGPUELFObjectWriter(bool Is64Bit)
+  : MCELFObjectTargetWriter(Is64Bit, 0, ELF::EM_AMDGPU, false) { }
 
-MCObjectWriter *llvm::createAMDGPUELFObjectWriter(raw_pwrite_stream &OS) {
-  MCELFObjectTargetWriter *MOTW = new AMDGPUELFObjectWriter();
+MCObjectWriter *llvm::createAMDGPUELFObjectWriter(bool Is64Bit, raw_pwrite_stream &OS) {
+  MCELFObjectTargetWriter *MOTW = new AMDGPUELFObjectWriter(Is64Bit);
   return createELFObjectWriter(MOTW, OS, true);
 }
Index: llvm/trunk/lib/Target/AMDGPU/MCTargetDesc/AMDGPUMCTargetDesc.h
===================================================================
--- llvm/trunk/lib/Target/AMDGPU/MCTargetDesc/AMDGPUMCTargetDesc.h
+++ llvm/trunk/lib/Target/AMDGPU/MCTargetDesc/AMDGPUMCTargetDesc.h
@@ -46,7 +46,8 @@
 MCAsmBackend *createAMDGPUAsmBackend(const Target &T, const MCRegisterInfo &MRI,
                                      const Triple &TT, StringRef CPU);
 
-MCObjectWriter *createAMDGPUELFObjectWriter(raw_pwrite_stream &OS);
+MCObjectWriter *createAMDGPUELFObjectWriter(bool Is64Bit,
+                                            raw_pwrite_stream &OS);
 } // namespace llvm
 
 #define GET_REGINFO_ENUM
Index: llvm/trunk/test/CodeGen/AMDGPU/elf.ll
===================================================================
--- llvm/trunk/test/CodeGen/AMDGPU/elf.ll
+++ llvm/trunk/test/CodeGen/AMDGPU/elf.ll
@@ -8,7 +8,7 @@
 ; Test that we don't try to produce a COFF file on windows
 ; RUN: llc < %s -mtriple=amdgcn-pc-mingw -mcpu=SI -verify-machineinstrs -filetype=obj | llvm-readobj -s -symbols -file-headers - | FileCheck --check-prefix=ELF %s
 
-; ELF: Format: ELF32
+; ELF: Format: ELF64
 ; ELF: Machine: EM_AMDGPU (0xE0)
 ; ELF: Name: .AMDGPU.config
 ; ELF: Type: SHT_PROGBITS