[Object] object::ELFObjectFile::symbol_begin(): skip symbol index 0

For clients iterating the symbol table, none expects to handle index 0
(STN_UNDEF). Skip it to improve consistency with other binary formats.
Clients that need STN_UNDEF (e.g. lld) can use
getSectionContentsAsArray(). A test will be added in D62148.

Reviewed By: mtrent

Differential Revision: https://reviews.llvm.org/D62296

llvm-svn: 361506

llvm/include/llvm/Object/ELFObjectFile.h

@@ -982,7 +982,9 @@ ELFObjectFile<ELFT>::ELFObjectFile(ELFObjectFile<ELFT> &&Other)
 
 template <class ELFT>
 basic_symbol_iterator ELFObjectFile<ELFT>::symbol_begin() const {
-  DataRefImpl Sym = toDRI(DotSymtabSec, 0);
+  DataRefImpl Sym =
+      toDRI(DotSymtabSec,
+            DotSymtabSec && DotSymtabSec->sh_size >= sizeof(Elf_Sym) ? 1 : 0);
   return basic_symbol_iterator(SymbolRef(Sym, this));
 }
 

llvm/tools/llvm-objdump/llvm-objdump.cpp

@@ -1643,11 +1643,6 @@ void printSymbolTable(const ObjectFile *O, StringRef ArchiveName,
 
   const StringRef FileName = O->getFileName();
   for (auto I = O->symbol_begin(), E = O->symbol_end(); I != E; ++I) {
-    // Skip printing the special zero symbol when dumping an ELF file.
-    // This makes the output consistent with the GNU objdump.
-    if (I == O->symbol_begin() && isa<ELFObjectFileBase>(O))
-      continue;
-
     const SymbolRef &Symbol = *I;
     uint64_t Address = unwrapOrError(Symbol.getAddress(), ArchiveName, FileName,
                                      ArchitectureName);