Index: test/tools/llvm-objcopy/ELF/only-section-strip-undefined.test
===================================================================
--- /dev/null
+++ test/tools/llvm-objcopy/ELF/only-section-strip-undefined.test
@@ -0,0 +1,61 @@
+## Here we want to check that llvm-objcopy removes an undefined symbol
+## if all references to it have been stripped.
+
+# RUN: yaml2obj --docnum=1 %s -o %t.o
+# RUN: llvm-objcopy -j .other.section %t.o %t2.o
+# RUN: llvm-readobj --symbols %t2.o | FileCheck %s --implicit-check-not=bar
+
+# RUN: llvm-objcopy -j .text -j .rela.text1 %t.o %t2.o
+# RUN: llvm-readobj --symbols %t2.o | FileCheck %s --check-prefix=BAR
+
+# BAR: bar
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS64
+  Data:    ELFDATA2LSB
+  Type:    ET_REL
+  Machine: EM_X86_64
+Sections:
+  - Name:         .text
+    Type:         SHT_PROGBITS
+    Flags:        [ SHF_ALLOC, SHF_EXECINSTR ]
+  - Name:         .rela.text1
+    Type:         SHT_RELA
+    Relocations:
+      - Offset:   0x0000000000000001
+        Symbol:   bar
+        Type:     R_X86_64_32
+  - Name:         .rela.text2
+    Type:         SHT_RELA
+    Relocations:
+      - Offset:   0x0000000000000001
+        Symbol:   bar
+        Type:     R_X86_64_32
+  - Name:         .other.section
+    Type:         SHT_PROGBITS
+Symbols:
+  - Name:    bar
+    Binding: STB_GLOBAL
+...
+
+## Check we remove unreferenced undefined symbols, even if
+## they weren't previously referenced. This follows GNU.
+
+# RUN: yaml2obj --docnum=2 %s -o %t.o
+# RUN: llvm-objcopy -j .keep_me %t.o %t2.o
+# RUN: llvm-readobj --symbols %t2.o | FileCheck %s --implicit-check-not=bar
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS64
+  Data:    ELFDATA2LSB
+  Type:    ET_REL
+  Machine: EM_X86_64
+Sections:
+  - Name:         .keep_me
+    Type:         SHT_PROGBITS
+Symbols:
+  - Name:    bar
+    Binding: STB_GLOBAL
+...
Index: tools/llvm-objcopy/ELF/ELFObjcopy.cpp
===================================================================
--- tools/llvm-objcopy/ELF/ELFObjcopy.cpp
+++ tools/llvm-objcopy/ELF/ELFObjcopy.cpp
@@ -387,7 +387,8 @@
   // The purpose of this loop is to mark symbols referenced by sections
   // (like GroupSection or RelocationSection). This way, we know which
   // symbols are still 'needed' and which are not.
-  if (Config.StripUnneeded || !Config.UnneededSymbolsToRemove.empty()) {
+  if (Config.StripUnneeded || !Config.UnneededSymbolsToRemove.empty() ||
+      !Config.OnlySection.empty()) {
     for (auto &Section : Obj.sections())
       Section.markSymbols();
   }
@@ -415,6 +416,12 @@
         isUnneededSymbol(Sym))
       return true;
 
+    // We want to remove the undefined symbols if the source of reference,
+    // like relocation section was stripped.
+    if (!Config.OnlySection.empty() && !Sym.Referenced &&
+        Sym.getShndx() == SHN_UNDEF)
+      return true;
+
     return false;
   };