[ELF2] Fix mixed-Endian handling in DynamicSection<ELFT>::writeTo

[hfinkel]

Summary

Using the "raw" Elf64_Dyn or Elf32_Dyn structures in DynamicSection<ELFT>::writeTo does not correctly handle mixed-Endian situations. Instead, use the corresponding llvm::object::* structures which have Endian-converting members (like the rest of the code).

This fixes all currently-failing elf2 tests when running on big-Endian PPC64/Linux.

[• rafael]

It should be possible to add a testcase with a big ending .o file that
is currently failing when running on a little endian machine, no?
LGTM wit that.

[hfinkel]

With a test case, r249150.

ELF/OutputSections.h

 
 template <class ELFT>
 class DynamicSection final : public OutputSectionBase<ELFT::Is64Bits> {
   typedef OutputSectionBase<ELFT::Is64Bits> Base;
   typedef typename Base::HeaderT HeaderT;
   typedef typename llvm::object::ELFFile<ELFT>::Elf_Rel Elf_Rel;
   typedef typename llvm::object::ELFFile<ELFT>::Elf_Rela Elf_Rela;
   typedef typename llvm::object::ELFFile<ELFT>::Elf_Sym Elf_Sym;
+  typedef typename llvm::object::ELFFile<ELFT>::Elf_Dyn Elf_Dyn;
 
 public:
   DynamicSection(SymbolTable &SymTab, HashTableSection<ELFT> &HashSec,
                  RelocationSection<ELFT> &RelaDynSec);
   void finalize() override;
   void writeTo(uint8_t *Buf) override;
 
 private:

ELF/OutputSections.cpp

template <class ELFT> void DynamicSection<ELFT>::finalize() {
   NumEntries += SharedFiles.size();
 
   ++NumEntries; // DT_NULL
 
   Header.sh_size = NumEntries * Header.sh_entsize;
 }
 
 template <class ELFT> void DynamicSection<ELFT>::writeTo(uint8_t *Buf) {
-  typedef typename std::conditional<ELFT::Is64Bits, Elf64_Dyn, Elf32_Dyn>::type
-      Elf_Dyn;
   auto *P = reinterpret_cast<Elf_Dyn *>(Buf);
 
   if (RelaDynSec.hasRelocs()) {
     bool IsRela = RelaDynSec.isRela();
     P->d_tag = IsRela ? DT_RELA : DT_REL;
     P->d_un.d_ptr = RelaDynSec.getVA();
     ++P;