4 files changed, 39 insertions, 4 deletions
diff --git a/llvm/tools/llvm-objcopy/ObjcopyOpts.td b/llvm/tools/llvm-objcopy/ObjcopyOpts.td
index 9d1fb19c40c..e7c7541a32c 100644
--- a/llvm/tools/llvm-objcopy/ObjcopyOpts.td
+++ b/llvm/tools/llvm-objcopy/ObjcopyOpts.td
@@ -90,3 +90,5 @@ def K : JoinedOrSeparate<["-"], "K">,
         Alias<keep_symbol>;
 def only_keep_debug : Flag<["-", "--"], "only-keep-debug">,
                           HelpText<"Currently ignored. Only for compaitability with GNU objcopy.">;
+def strip_unneeded : Flag<["-", "--"], "strip-unneeded">,
+                      HelpText<"Remove all symbols not needed by relocations">;
diff --git a/llvm/tools/llvm-objcopy/Object.cpp b/llvm/tools/llvm-objcopy/Object.cpp
index efb3207aa8d..bd728270fb7 100644
--- a/llvm/tools/llvm-objcopy/Object.cpp
+++ b/llvm/tools/llvm-objcopy/Object.cpp
@@ -185,6 +185,7 @@ void SymbolTableSection::addSymbol(StringRef Name, uint8_t Bind, uint8_t Type,
   Sym.Visibility = Visibility;
   Sym.Size = Sz;
   Sym.Index = Symbols.size();
+  Sym.ReferenceCount = 0;
   Symbols.emplace_back(llvm::make_unique<Symbol>(Sym));
   Size += this->EntrySize;
 }
@@ -255,6 +256,11 @@ const Symbol *SymbolTableSection::getSymbolByIndex(uint32_t Index) const {
   return Symbols[Index].get();
 }
 
+Symbol *SymbolTableSection::getSymbolByIndex(uint32_t Index) {
+  return const_cast<Symbol *>(
+      static_cast<const SymbolTableSection *>(this)->getSymbolByIndex(Index));
+}
+
 template <class ELFT>
 void ELFSectionWriter<ELFT>::visit(const SymbolTableSection &Sec) {
   uint8_t *Buf = Out.getBufferStart();
@@ -344,6 +350,12 @@ void RelocationSection::accept(SectionVisitor &Visitor) const {
   Visitor.visit(*this);
 }
 
+RelocationSection::~RelocationSection() {
+  for (auto &Rel : Relocations) {
+    --Rel.RelocSymbol->ReferenceCount;
+  }
+}
+
 void RelocationSection::removeSymbols(
     function_ref<bool(const Symbol &)> ToRemove) {
   for (const Relocation &Reloc : Relocations)
@@ -647,7 +659,9 @@ void initRelocations(RelocationSection *Relocs, SymbolTableSection *SymbolTable,
     ToAdd.Offset = Rel.r_offset;
     getAddend(ToAdd.Addend, Rel);
     ToAdd.Type = Rel.getType(false);
-    ToAdd.RelocSymbol = SymbolTable->getSymbolByIndex(Rel.getSymbol(false));
+    Symbol *Sym = SymbolTable->getSymbolByIndex(Rel.getSymbol(false));
+    ++Sym->ReferenceCount;
+    ToAdd.RelocSymbol = Sym;
     Relocs->addRelocation(ToAdd);
   }
 }
diff --git a/llvm/tools/llvm-objcopy/Object.h b/llvm/tools/llvm-objcopy/Object.h
index ac384c1fdfe..74ef5a7ebcc 100644
--- a/llvm/tools/llvm-objcopy/Object.h
+++ b/llvm/tools/llvm-objcopy/Object.h
@@ -344,6 +344,7 @@ struct Symbol {
   uint8_t Type;
   uint64_t Value;
   uint8_t Visibility;
+  uint32_t ReferenceCount;
 
   uint16_t getShndx() const;
 };
@@ -367,6 +368,7 @@ public:
   void addSymbolNames();
   const SectionBase *getStrTab() const { return SymbolNames; }
   const Symbol *getSymbolByIndex(uint32_t Index) const;
+  Symbol *getSymbolByIndex(uint32_t Index);
   void updateSymbols(function_ref<void(Symbol &)> Callable);
 
   void removeSectionReferences(const SectionBase *Sec) override;
@@ -381,7 +383,7 @@ public:
 };
 
 struct Relocation {
-  const Symbol *RelocSymbol = nullptr;
+  Symbol *RelocSymbol = nullptr;
   uint64_t Offset;
   uint64_t Addend;
   uint32_t Type;
@@ -432,6 +434,7 @@ class RelocationSection
   std::vector<Relocation> Relocations;
 
 public:
+  ~RelocationSection();
   void addRelocation(Relocation Rel) { Relocations.push_back(Rel); }
   void accept(SectionVisitor &Visitor) const override;
   void removeSymbols(function_ref<bool(const Symbol &)> ToRemove) override;
@@ -449,7 +452,7 @@ public:
 class GroupSection : public SectionBase {
   MAKE_SEC_WRITER_FRIEND
   const SymbolTableSection *SymTab = nullptr;
-  const Symbol *Sym = nullptr;
+  Symbol *Sym = nullptr;
   ELF::Elf32_Word FlagWord;
   SmallVector<SectionBase *, 3> GroupMembers;
 
@@ -459,9 +462,16 @@ public:
   ArrayRef<uint8_t> Contents;
 
   explicit GroupSection(ArrayRef<uint8_t> Data) : Contents(Data) {}
+  ~GroupSection() {
+    if (Sym)
+      --Sym->ReferenceCount;
+  }
 
   void setSymTab(const SymbolTableSection *SymTabSec) { SymTab = SymTabSec; }
-  void setSymbol(const Symbol *S) { Sym = S; }
+  void setSymbol(Symbol *S) {
+    Sym = S;
+    ++Sym->ReferenceCount;
+  }
   void setFlagWord(ELF::Elf32_Word W) { FlagWord = W; }
   void addMember(SectionBase *Sec) { GroupMembers.push_back(Sec); }
 
diff --git a/llvm/tools/llvm-objcopy/llvm-objcopy.cpp b/llvm/tools/llvm-objcopy/llvm-objcopy.cpp
index 99cc1039f7d..36b1b64e35d 100644
--- a/llvm/tools/llvm-objcopy/llvm-objcopy.cpp
+++ b/llvm/tools/llvm-objcopy/llvm-objcopy.cpp
@@ -156,6 +156,7 @@ struct CopyConfig {
   bool StripSections = false;
   bool StripNonAlloc = false;
   bool StripDWO = false;
+  bool StripUnneeded = false;
   bool ExtractDWO = false;
   bool LocalizeHidden = false;
   bool Weaken = false;
@@ -389,6 +390,13 @@ void HandleArgs(const CopyConfig &Config, Object &Obj, const Reader &Reader,
         return true;
       }
 
+      // TODO: We might handle the 'null symbol' in a different way
+      // by probably handling it the same way as we handle 'null section' ?
+      if (Config.StripUnneeded && !Sym.ReferenceCount && Sym.Index != 0 &&
+          (Sym.Binding == STB_LOCAL || Sym.getShndx() == SHN_UNDEF) &&
+          Sym.Type != STT_FILE && Sym.Type != STT_SECTION)
+        return true;
+
       return false;
     });
   }
@@ -479,6 +487,7 @@ CopyConfig ParseObjcopyOptions(ArrayRef<const char *> ArgsArr) {
   Config.StripDWO = InputArgs.hasArg(OBJCOPY_strip_dwo);
   Config.StripSections = InputArgs.hasArg(OBJCOPY_strip_sections);
   Config.StripNonAlloc = InputArgs.hasArg(OBJCOPY_strip_non_alloc);
+  Config.StripUnneeded = InputArgs.hasArg(OBJCOPY_strip_unneeded);
   Config.ExtractDWO = InputArgs.hasArg(OBJCOPY_extract_dwo);
   Config.LocalizeHidden = InputArgs.hasArg(OBJCOPY_localize_hidden);
   Config.Weaken = InputArgs.hasArg(OBJCOPY_weaken);