commit 46201fb7bc31ed90409440878ccbe567efd33cd8
author Paul Semel <semelpaul@gmail.com> Fri Jun 01 16:19:46 2018 +0000
committer Paul Semel <semelpaul@gmail.com> Fri Jun 01 16:19:46 2018 +0000
tree cb0ead3bb6726309d2af8700d78e060e2dbb697a
parent bc68385dad322f80a5b064db2f4e0fd3f9c21781

[llvm-objcopy] Fix null symbol handling

This fixes the bug where strip-all option was
leading to a malformed outputted ELF file.

Differential Revision: https://reviews.llvm.org/D47414

llvm-svn: 333772

llvm/tools/llvm-objcopy/Object.cpp

diff --git a/llvm/tools/llvm-objcopy/Object.cpp b/llvm/tools/llvm-objcopy/Object.cpp
index 6b656c6..606e032 100644
--- a/llvm/tools/llvm-objcopy/Object.cpp
+++ b/llvm/tools/llvm-objcopy/Object.cpp
@@ -200,8 +200,8 @@
 }
 
 void SymbolTableSection::updateSymbols(function_ref<void(Symbol &)> Callable) {
-  for (auto &Sym : Symbols)
-    Callable(*Sym);
+  std::for_each(std::begin(Symbols) + 1, std::end(Symbols),
+                [Callable](SymPtr &Sym) { Callable(*Sym); });
   std::stable_partition(
       std::begin(Symbols), std::end(Symbols),
       [](const SymPtr &Sym) { return Sym->Binding == STB_LOCAL; });
@@ -211,7 +211,7 @@
 void SymbolTableSection::removeSymbols(
     function_ref<bool(const Symbol &)> ToRemove) {
   Symbols.erase(
-      std::remove_if(std::begin(Symbols), std::end(Symbols),
+      std::remove_if(std::begin(Symbols) + 1, std::end(Symbols),
                      [ToRemove](const SymPtr &Sym) { return ToRemove(*Sym); }),
       std::end(Symbols));
   Size = Symbols.size() * EntrySize;

llvm/tools/llvm-objcopy/Object.h

diff --git a/llvm/tools/llvm-objcopy/Object.h b/llvm/tools/llvm-objcopy/Object.h
index d005f0d..c7939b4 100644
--- a/llvm/tools/llvm-objcopy/Object.h
+++ b/llvm/tools/llvm-objcopy/Object.h
@@ -367,7 +367,8 @@
                  SectionBase *DefinedIn, uint64_t Value, uint8_t Visibility,
                  uint16_t Shndx, uint64_t Sz);
   void addSymbolNames();
-  bool empty() const { return Symbols.empty(); }
+  // An 'empty' symbol table still contains a null symbol.
+  bool empty() const { return Symbols.size() == 1; }
   const SectionBase *getStrTab() const { return SymbolNames; }
   const Symbol *getSymbolByIndex(uint32_t Index) const;
   Symbol *getSymbolByIndex(uint32_t Index);

llvm/tools/llvm-objcopy/llvm-objcopy.cpp

diff --git a/llvm/tools/llvm-objcopy/llvm-objcopy.cpp b/llvm/tools/llvm-objcopy/llvm-objcopy.cpp
index bbd21d5..0563af9 100644
--- a/llvm/tools/llvm-objcopy/llvm-objcopy.cpp
+++ b/llvm/tools/llvm-objcopy/llvm-objcopy.cpp
@@ -292,9 +292,7 @@
         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.Referenced && Sym.Index != 0 &&
+      if (Config.StripUnneeded && !Sym.Referenced &&
           (Sym.Binding == STB_LOCAL || Sym.getShndx() == SHN_UNDEF) &&
           Sym.Type != STT_FILE && Sym.Type != STT_SECTION)
         return true;