Rename a variable and add a comment.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@358049 91177308-0d34-0410-b5e6-96231b3b80d8

ELF/InputFiles.cpp

@@ -279,7 +279,7 @@ ObjFile<ELFT>::ObjFile(MemoryBufferRef M, StringRef ArchiveName)
 template <class ELFT>
 uint32_t ObjFile<ELFT>::getSectionIndex(const Elf_Sym &Sym) const {
   return CHECK(
-      this->getObj().getSectionIndex(&Sym, getELFSyms<ELFT>(), SymtabSHNDX),
+      this->getObj().getSectionIndex(&Sym, getELFSyms<ELFT>(), ShndxTable),
       this);
 }
 
@@ -479,7 +479,7 @@ void ObjFile<ELFT>::initializeSections(
       this->initSymtab<ELFT>(ObjSections, &Sec);
       break;
     case SHT_SYMTAB_SHNDX:
-      SymtabSHNDX = CHECK(Obj.getSHNDXTable(Sec, ObjSections), this);
+      ShndxTable = CHECK(Obj.getSHNDXTable(Sec, ObjSections), this);
       break;
     case SHT_STRTAB:
     case SHT_NULL:

ELF/InputFiles.h

@@ -253,7 +253,19 @@ template <class ELFT> class ObjFile : public ELFFileBase {
   bool shouldMerge(const Elf_Shdr &Sec);
   Symbol *createSymbol(const Elf_Sym *Sym);
 
-  ArrayRef<Elf_Word> SymtabSHNDX;
+  // Each ELF symbol contains a section index which the symbol belongs to.
+  // However, because the number of bits dedicated for that is limited, a
+  // symbol can directly point to a section only when the section index is
+  // equal to or smaller than 65280.
+  //
+  // If an object file contains more than 65280 sections, the file must
+  // contain .symtab_shndxr section. The section contains an array of
+  // 32-bit integers whose size is the same as the number of symbols.
+  // Nth symbol's section index is in the Nth entry of .symtab_shndxr.
+  //
+  // The following variable contains the contents of .symtab_shndxr.
+  // If the section does not exist (which is common), the array is empty.
+  ArrayRef<Elf_Word> ShndxTable;
 
   // .shstrtab contents.
   StringRef SectionStringTable;