Index: llvm/lib/MC/MCDwarf.cpp
===================================================================
--- llvm/lib/MC/MCDwarf.cpp
+++ llvm/lib/MC/MCDwarf.cpp
@@ -1612,14 +1612,24 @@
 
   MCSymbol *sectionEnd = context.createTempSymbol();
 
+  dwarf::DwarfFormat Format = IsEH ? dwarf::DWARF32 : context.getDwarfFormat();
+  unsigned UnitLengthBytes = dwarf::getUnitLengthFieldByteSize(Format);
+  unsigned OffsetSize = dwarf::getDwarfOffsetByteSize(Format);
+  bool IsDwarf64 = Format == dwarf::DWARF64;
+
+  if (IsDwarf64)
+    // DWARF64 mark
+    Streamer.emitInt32(dwarf::DW_LENGTH_DWARF64);
+
   // Length
-  const MCExpr *Length =
-      MakeStartMinusEndExpr(context, *sectionStart, *sectionEnd, 4);
-  emitAbsValue(Streamer, Length, 4);
+  const MCExpr *Length = MakeStartMinusEndExpr(context, *sectionStart,
+                                               *sectionEnd, UnitLengthBytes);
+  emitAbsValue(Streamer, Length, OffsetSize);
 
   // CIE ID
-  unsigned CIE_ID = IsEH ? 0 : -1;
-  Streamer.emitInt32(CIE_ID);
+  uint64_t CIE_ID =
+      IsEH ? 0 : (IsDwarf64 ? dwarf::DW64_CIE_ID : dwarf::DW_CIE_ID);
+  Streamer.emitIntValue(CIE_ID, OffsetSize);
 
   // Version
   uint8_t CIEVersion = getCIEVersion(IsEH, context.getDwarfVersion());
@@ -1729,9 +1739,16 @@
 
   CFAOffset = InitialCFAOffset;
 
+  dwarf::DwarfFormat Format = IsEH ? dwarf::DWARF32 : context.getDwarfFormat();
+  unsigned OffsetSize = dwarf::getDwarfOffsetByteSize(Format);
+
+  if (Format == dwarf::DWARF64)
+    // DWARF64 mark
+    Streamer.emitInt32(dwarf::DW_LENGTH_DWARF64);
+
   // Length
   const MCExpr *Length = MakeStartMinusEndExpr(context, *fdeStart, *fdeEnd, 0);
-  emitAbsValue(Streamer, Length, 4);
+  emitAbsValue(Streamer, Length, OffsetSize);
 
   Streamer.emitLabel(fdeStart);
 
@@ -1740,13 +1757,13 @@
   if (IsEH) {
     const MCExpr *offset =
         MakeStartMinusEndExpr(context, cieStart, *fdeStart, 0);
-    emitAbsValue(Streamer, offset, 4);
+    emitAbsValue(Streamer, offset, OffsetSize);
   } else if (!asmInfo->doesDwarfUseRelocationsAcrossSections()) {
     const MCExpr *offset =
         MakeStartMinusEndExpr(context, SectionStart, cieStart, 0);
-    emitAbsValue(Streamer, offset, 4);
+    emitAbsValue(Streamer, offset, OffsetSize);
   } else {
-    Streamer.emitSymbolValue(&cieStart, 4,
+    Streamer.emitSymbolValue(&cieStart, OffsetSize,
                              asmInfo->needsDwarfSectionOffsetDirective());
   }
 
Index: llvm/test/MC/ELF/gen-dwarf64.s
===================================================================
--- llvm/test/MC/ELF/gen-dwarf64.s
+++ llvm/test/MC/ELF/gen-dwarf64.s
@@ -10,6 +10,8 @@
 
 ## The references to other debug info sections are 64-bit, as required for DWARF64.
 # REL:       Relocations [
+# REL:         Section ({{[0-9]+}}) .rela.debug_frame {
+# REL-NEXT:      R_X86_64_64 .debug_frame 0x0
 # REL:         Section ({{[0-9]+}}) .rela.debug_info {
 # REL-NEXT:      R_X86_64_64 .debug_abbrev 0x0
 # REL-NEXT:      R_X86_64_64 .debug_line 0x0
@@ -40,6 +42,20 @@
 # DUMP-NEXT:      [0x0000000000000000, 0x0000000000000001) ".foo"
 # DUMP-NEXT:      [0x0000000000000000, 0x0000000000000001) ".bar")
 
+# DUMP:       .debug_frame contents:
+# DUMP:       00000000 {{([[:xdigit:]]{16})}} ffffffffffffffff CIE
+# DUMP-NEXT:    Format: DWARF64
+# DUMP:       {{([[:xdigit:]]{8})}} {{([[:xdigit:]]{16})}} 0000000000000000 FDE cie=00000000 pc=00000000...00000001
+# DUMP-NEXT:    Format: DWARF64
+
+## Even though the debug info sections are in the 64-bit format,
+## .eh_frame is still generated as 32-bit.
+# DUMP:       .eh_frame contents:
+# DUMP:       00000000 {{([[:xdigit:]]{8})}} 00000000 CIE
+# DUMP-NEXT:    Format: DWARF32
+# DUMP:       {{([[:xdigit:]]{8})}} {{([[:xdigit:]]{8})}} {{([[:xdigit:]]{8})}} FDE cie=00000000 pc=00000000...00000001
+# DUMP-NEXT:    Format: DWARF32
+
 # DUMP:       .debug_aranges contents:
 # DUMP-NEXT:  Address Range Header: 
 # DUMP-SAME:    format = DWARF64
@@ -76,10 +92,14 @@
 # DUMP5-NEXT: 0x0000001e: [DW_RLE_start_length]: 0x0000000000000000, 0x0000000000000001 => [0x0000000000000000, 0x0000000000000001)
 # DUMP5-NEXT: 0x00000028: [DW_RLE_end_of_list ]
 
+    .cfi_sections .eh_frame, .debug_frame
+
     .section .foo, "ax", @progbits
 foo:
     nop
 
     .section .bar, "ax", @progbits
 bar:
+    .cfi_startproc
     nop
+    .cfi_endproc