Index: llvm/test/tools/llvm-objcopy/COFF/add-section.test
===================================================================
--- llvm/test/tools/llvm-objcopy/COFF/add-section.test
+++ llvm/test/tools/llvm-objcopy/COFF/add-section.test
@@ -32,6 +32,38 @@
 # CHECK-ADD-EMPTY-NAME-NEXT:  0000: {{.+}}|DEADBEEF{{.+}}|
 # CHECK-ADD-EMPTY-NAME-NEXT: )
 
+## Test that llvm-objcopy can add a section to an object with extended
+## relocations.
+# RUN: %python %p/../Inputs/ungzip.py %p/Inputs/x86_64-xrelocs.obj.gz > %t.in.xrelocs.obj
+# RUN: llvm-objcopy --add-section=.test.section=%t.sec %t.in.xrelocs.obj %t1.xrelocs.obj
+# RUN: llvm-readobj --file-headers --sections --section-data %t1.xrelocs.obj | FileCheck %s --check-prefixes=CHECK-EXTENDED-RELOCS
+
+# CHECK-EXTENDED-RELOCS:      SectionCount: 5
+# CHECK-EXTENDED-RELOCS:      Name: .data
+# CHECK-EXTENDED-RELOCS-NEXT: VirtualSize:
+# CHECK-EXTENDED-RELOCS-NEXT: VirtualAddress:
+# CHECK-EXTENDED-RELOCS-NEXT: RawDataSize:
+# CHECK-EXTENDED-RELOCS-NEXT: PointerToRawData:
+# CHECK-EXTENDED-RELOCS-NEXT: PointerToRelocations:
+# CHECK-EXTENDED-RELOCS-NEXT: PointerToLineNumbers:
+# CHECK-EXTENDED-RELOCS-NEXT: RelocationCount: 65535
+# CHECK-EXTENDED-RELOCS-NEXT: LineNumberCount: 0
+# CHECK-EXTENDED-RELOCS-NEXT: Characteristics [
+# CHECK-EXTENDED-RELOCS-NEXT:   IMAGE_SCN_ALIGN_16BYTES
+# CHECK-EXTENDED-RELOCS-NEXT:   IMAGE_SCN_CNT_INITIALIZED_DATA
+# CHECK-EXTENDED-RELOCS-NEXT:   IMAGE_SCN_LNK_NRELOC_OVFL
+# CHECK-EXTENDED-RELOCS-NEXT:   IMAGE_SCN_MEM_READ
+# CHECK-EXTENDED-RELOCS-NEXT:   IMAGE_SCN_MEM_WRITE
+# CHECK-EXTENDED-RELOCS-NEXT: ]
+# CHECK-EXTENDED-RELOCS:      Name: .test.section
+# CHECK-EXTENDED-RELOCS:      Characteristics [
+# CHECK-EXTENDED-RELOCS-NEXT:   IMAGE_SCN_ALIGN_1BYTES
+# CHECK-EXTENDED-RELOCS-NEXT:   IMAGE_SCN_CNT_INITIALIZED_DATA
+# CHECK-EXTENDED-RELOCS-NEXT: ]
+# CHECK-EXTENDED-RELOCS:      SectionData (
+# CHECK-EXTENDED-RELOCS-NEXT:  0000: {{.+}}|DEADBEEF{{.+}}|
+# CHECK-EXTENDED-RELOCS-NEXT: )
+
 ## Test that llvm-objcopy produces an error if the file with section contents
 ## to be added does not exist.
 # RUN: not llvm-objcopy --add-section=.another.section=%t2 %t %t3 2>&1 | FileCheck -DFILE1=%t -DFILE2=%t2 %s --check-prefixes=ERR1
Index: llvm/tools/llvm-objcopy/COFF/Reader.cpp
===================================================================
--- llvm/tools/llvm-objcopy/COFF/Reader.cpp
+++ llvm/tools/llvm-objcopy/COFF/Reader.cpp
@@ -63,6 +63,7 @@
     Sections.push_back(Section());
     Section &S = Sections.back();
     S.Header = *Sec;
+    S.Header.Characteristics &= ~COFF::IMAGE_SCN_LNK_NRELOC_OVFL;
     ArrayRef<uint8_t> Contents;
     if (Error E = COFFObj.getSectionContents(Sec, Contents))
       return E;
@@ -74,9 +75,6 @@
       S.Name = *NameOrErr;
     else
       return NameOrErr.takeError();
-    if (Sec->hasExtendedRelocations())
-      return createStringError(object_error::parse_failed,
-                               "extended relocations not supported yet");
   }
   Obj.addSections(Sections);
   return Error::success();
Index: llvm/tools/llvm-objcopy/COFF/Writer.cpp
===================================================================
--- llvm/tools/llvm-objcopy/COFF/Writer.cpp
+++ llvm/tools/llvm-objcopy/COFF/Writer.cpp
@@ -97,9 +97,16 @@
       S.Header.PointerToRawData = FileSize;
     FileSize += S.Header.SizeOfRawData; // For executables, this is already
                                         // aligned to FileAlignment.
-    S.Header.NumberOfRelocations = S.Relocs.size();
-    S.Header.PointerToRelocations =
-        S.Header.NumberOfRelocations > 0 ? FileSize : 0;
+    if (S.Relocs.size() >= 0xffff) {
+      S.Header.Characteristics |= COFF::IMAGE_SCN_LNK_NRELOC_OVFL;
+      S.Header.NumberOfRelocations = 0xffff;
+      S.Header.PointerToRelocations = FileSize;
+      FileSize += sizeof(coff_relocation);
+    } else {
+      S.Header.NumberOfRelocations = S.Relocs.size();
+      S.Header.PointerToRelocations = S.Relocs.size() ? FileSize : 0;
+    }
+
     FileSize += S.Relocs.size() * sizeof(coff_relocation);
     FileSize = alignTo(FileSize, FileAlignment);
 
@@ -307,6 +314,15 @@
              S.Header.SizeOfRawData - Contents.size());
 
     Ptr += S.Header.SizeOfRawData;
+
+    if (S.Relocs.size() >= 0xffff) {
+      object::coff_relocation R;
+      R.VirtualAddress = S.Relocs.size() + 1;
+      R.SymbolTableIndex = 0;
+      R.Type = 0;
+      memcpy(Ptr, &R, sizeof(R));
+      Ptr += sizeof(R);
+    }
     for (const auto &R : S.Relocs) {
       memcpy(Ptr, &R.Reloc, sizeof(R.Reloc));
       Ptr += sizeof(R.Reloc);