[llvm-objcopy] Add --strip-unneeded option

This option removes symbols that are not needed by relocations.

Differential Revision: https://reviews.llvm.org/D46896

llvm-svn: 332915

1 files changed, 15 insertions, 1 deletions

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);
   }
 }