[Object] Teach Object and llvm-objdump about ".hidden"

[davide]

Summary

Discovered while trying to improve ELF visibility support in lld.

[• rafael]

LGTM

llvm/trunk/include/llvm/Object/ELFObjectFile.h

uint32_t ELFObjectFile<ELFT>::getSymbolFlags(DataRefImpl Symb) const {
 
   if (ESym->getType() == ELF::STT_COMMON ||
       EF.getSymbolTableIndex(ESym) == ELF::SHN_COMMON)
     Result |= SymbolRef::SF_Common;
 
   if (isExportedToOtherDSO(ESym))
     Result |= SymbolRef::SF_Exported;
 
+  if (ESym->getVisibility() == ELF::STV_HIDDEN)
+    Result |= SymbolRef::SF_Hidden;
+
   return Result;
 }
 
 template <class ELFT>
 std::error_code
 ELFObjectFile<ELFT>::getSymbolSection(DataRefImpl Symb,
                                       section_iterator &Res) const {
   const Elf_Sym *ESym = getSymbol(Symb);

llvm/trunk/include/llvm/Object/SymbolicFile.h

enum Flags : unsigned {
     SF_Weak = 1U << 2,           // Weak symbol
     SF_Absolute = 1U << 3,       // Absolute symbol
     SF_Common = 1U << 4,         // Symbol has common linkage
     SF_Indirect = 1U << 5,       // Symbol is an alias to another symbol
     SF_Exported = 1U << 6,       // Symbol is visible to other DSOs
     SF_FormatSpecific = 1U << 7, // Specific to the object file format
                                  // (e.g. section symbols)
     SF_Thumb = 1U << 8,          // Thumb symbol in a 32-bit ARM binary
+    SF_Hidden = 1U << 9,         // Symbol has hidden visibility
   };
 
   BasicSymbolRef() : OwningObject(nullptr) { }
   BasicSymbolRef(DataRefImpl SymbolP, const SymbolicFile *Owner);
 
   bool operator==(const BasicSymbolRef &Other) const;
   bool operator<(const BasicSymbolRef &Other) const;
 

llvm/trunk/test/Object/objdump-symbol-table.test

 macho-i386: SYMBOL TABLE:
 macho-i386: 00000000 g     F __TEXT,__text  00000024 _main
 macho-i386: 00000000         *UND*  00000000 _SomeOtherFunction
 macho-i386: 00000000         *UND*  00000000 _puts
 
 ELF-shared: shared-object-test.elf-i386:     file format
 ELF-shared: SYMBOL TABLE:
 ELF-shared: 00000200 l     F .text 00000003 local_func
+ELF-shared: 000012b8 l       *ABS* 00000000 .hidden _GLOBAL_OFFSET_TABLE_
+ELF-shared: 00001248 l       *ABS* 00000000 .hidden _DYNAMIC
 ELF-shared: 000012c4 g       .data 00000004 defined_sym
 ELF-shared: 000001f0 g     F .text 00000003 global_func

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

if (error(Symbol.getSize(Size)))
       continue;
     if (error(Symbol.getSection(Section)))
       continue;
 
     bool Global = Flags & SymbolRef::SF_Global;
     bool Weak = Flags & SymbolRef::SF_Weak;
     bool Absolute = Flags & SymbolRef::SF_Absolute;
     bool Common = Flags & SymbolRef::SF_Common;
+    bool Hidden = Flags & SymbolRef::SF_Hidden;
 
     if (Common) {
       uint32_t Alignment;
       if (error(Symbol.getAlignment(Alignment)))
         Alignment = 0;
       Address = Size;
       Size = Alignment;
     }
if (Absolute) {
         outs() << SegmentName << ",";
       }
       StringRef SectionName;
       if (error(Section->getName(SectionName)))
         SectionName = "";
       outs() << SectionName;
     }
     outs() << '\t'
-           << format("%08" PRIx64 " ", Size)
-           << Name
+           << format("%08" PRIx64 " ", Size);
+    if (Hidden) {
+      outs() << ".hidden ";
+    }
+    outs() << Name
            << '\n';
   }
 }
 
 static void PrintUnwindInfo(const ObjectFile *o) {
   outs() << "Unwind info:\n\n";
 
   if (const COFFObjectFile *coff = dyn_cast<COFFObjectFile>(o)) {