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      1 //===-- llvm-objdump.cpp - Object file dumping utility for llvm -----------===//
      2 //
      3 //                     The LLVM Compiler Infrastructure
      4 //
      5 // This file is distributed under the University of Illinois Open Source
      6 // License. See LICENSE.TXT for details.
      7 //
      8 //===----------------------------------------------------------------------===//
      9 //
     10 // This program is a utility that works like binutils "objdump", that is, it
     11 // dumps out a plethora of information about an object file depending on the
     12 // flags.
     13 //
     14 //===----------------------------------------------------------------------===//
     15 
     16 #include "llvm-objdump.h"
     17 #include "MCFunction.h"
     18 #include "llvm/Object/Archive.h"
     19 #include "llvm/Object/COFF.h"
     20 #include "llvm/Object/ObjectFile.h"
     21 #include "llvm/ADT/OwningPtr.h"
     22 #include "llvm/ADT/StringExtras.h"
     23 #include "llvm/ADT/Triple.h"
     24 #include "llvm/ADT/STLExtras.h"
     25 #include "llvm/MC/MCAsmInfo.h"
     26 #include "llvm/MC/MCDisassembler.h"
     27 #include "llvm/MC/MCInst.h"
     28 #include "llvm/MC/MCInstPrinter.h"
     29 #include "llvm/MC/MCSubtargetInfo.h"
     30 #include "llvm/Support/Casting.h"
     31 #include "llvm/Support/CommandLine.h"
     32 #include "llvm/Support/Debug.h"
     33 #include "llvm/Support/FileSystem.h"
     34 #include "llvm/Support/Format.h"
     35 #include "llvm/Support/GraphWriter.h"
     36 #include "llvm/Support/Host.h"
     37 #include "llvm/Support/ManagedStatic.h"
     38 #include "llvm/Support/MemoryBuffer.h"
     39 #include "llvm/Support/MemoryObject.h"
     40 #include "llvm/Support/PrettyStackTrace.h"
     41 #include "llvm/Support/Signals.h"
     42 #include "llvm/Support/SourceMgr.h"
     43 #include "llvm/Support/TargetRegistry.h"
     44 #include "llvm/Support/TargetSelect.h"
     45 #include "llvm/Support/raw_ostream.h"
     46 #include "llvm/Support/system_error.h"
     47 #include <algorithm>
     48 #include <cstring>
     49 using namespace llvm;
     50 using namespace object;
     51 
     52 static cl::list<std::string>
     53 InputFilenames(cl::Positional, cl::desc("<input object files>"),cl::ZeroOrMore);
     54 
     55 static cl::opt<bool>
     56 Disassemble("disassemble",
     57   cl::desc("Display assembler mnemonics for the machine instructions"));
     58 static cl::alias
     59 Disassembled("d", cl::desc("Alias for --disassemble"),
     60              cl::aliasopt(Disassemble));
     61 
     62 static cl::opt<bool>
     63 Relocations("r", cl::desc("Display the relocation entries in the file"));
     64 
     65 static cl::opt<bool>
     66 SectionContents("s", cl::desc("Display the content of each section"));
     67 
     68 static cl::opt<bool>
     69 SymbolTable("t", cl::desc("Display the symbol table"));
     70 
     71 static cl::opt<bool>
     72 MachO("macho", cl::desc("Use MachO specific object file parser"));
     73 static cl::alias
     74 MachOm("m", cl::desc("Alias for --macho"), cl::aliasopt(MachO));
     75 
     76 cl::opt<std::string>
     77 llvm::TripleName("triple", cl::desc("Target triple to disassemble for, "
     78                                     "see -version for available targets"));
     79 
     80 cl::opt<std::string>
     81 llvm::ArchName("arch", cl::desc("Target arch to disassemble for, "
     82                                 "see -version for available targets"));
     83 
     84 static cl::opt<bool>
     85 SectionHeaders("section-headers", cl::desc("Display summaries of the headers "
     86                                            "for each section."));
     87 static cl::alias
     88 SectionHeadersShort("headers", cl::desc("Alias for --section-headers"),
     89                     cl::aliasopt(SectionHeaders));
     90 static cl::alias
     91 SectionHeadersShorter("h", cl::desc("Alias for --section-headers"),
     92                       cl::aliasopt(SectionHeaders));
     93 
     94 static StringRef ToolName;
     95 
     96 static bool error(error_code ec) {
     97   if (!ec) return false;
     98 
     99   outs() << ToolName << ": error reading file: " << ec.message() << ".\n";
    100   outs().flush();
    101   return true;
    102 }
    103 
    104 static const Target *GetTarget(const ObjectFile *Obj = NULL) {
    105   // Figure out the target triple.
    106   llvm::Triple TT("unknown-unknown-unknown");
    107   if (TripleName.empty()) {
    108     if (Obj)
    109       TT.setArch(Triple::ArchType(Obj->getArch()));
    110   } else
    111     TT.setTriple(Triple::normalize(TripleName));
    112 
    113   if (!ArchName.empty())
    114     TT.setArchName(ArchName);
    115 
    116   TripleName = TT.str();
    117 
    118   // Get the target specific parser.
    119   std::string Error;
    120   const Target *TheTarget = TargetRegistry::lookupTarget(TripleName, Error);
    121   if (TheTarget)
    122     return TheTarget;
    123 
    124   errs() << ToolName << ": error: unable to get target for '" << TripleName
    125          << "', see --version and --triple.\n";
    126   return 0;
    127 }
    128 
    129 void llvm::DumpBytes(StringRef bytes) {
    130   static const char hex_rep[] = "0123456789abcdef";
    131   // FIXME: The real way to do this is to figure out the longest instruction
    132   //        and align to that size before printing. I'll fix this when I get
    133   //        around to outputting relocations.
    134   // 15 is the longest x86 instruction
    135   // 3 is for the hex rep of a byte + a space.
    136   // 1 is for the null terminator.
    137   enum { OutputSize = (15 * 3) + 1 };
    138   char output[OutputSize];
    139 
    140   assert(bytes.size() <= 15
    141     && "DumpBytes only supports instructions of up to 15 bytes");
    142   memset(output, ' ', sizeof(output));
    143   unsigned index = 0;
    144   for (StringRef::iterator i = bytes.begin(),
    145                            e = bytes.end(); i != e; ++i) {
    146     output[index] = hex_rep[(*i & 0xF0) >> 4];
    147     output[index + 1] = hex_rep[*i & 0xF];
    148     index += 3;
    149   }
    150 
    151   output[sizeof(output) - 1] = 0;
    152   outs() << output;
    153 }
    154 
    155 static bool RelocAddressLess(RelocationRef a, RelocationRef b) {
    156   uint64_t a_addr, b_addr;
    157   if (error(a.getAddress(a_addr))) return false;
    158   if (error(b.getAddress(b_addr))) return false;
    159   return a_addr < b_addr;
    160 }
    161 
    162 static void DisassembleObject(const ObjectFile *Obj, bool InlineRelocs) {
    163   const Target *TheTarget = GetTarget(Obj);
    164   if (!TheTarget) {
    165     // GetTarget prints out stuff.
    166     return;
    167   }
    168 
    169   error_code ec;
    170   for (section_iterator i = Obj->begin_sections(),
    171                         e = Obj->end_sections();
    172                         i != e; i.increment(ec)) {
    173     if (error(ec)) break;
    174     bool text;
    175     if (error(i->isText(text))) break;
    176     if (!text) continue;
    177 
    178     uint64_t SectionAddr;
    179     if (error(i->getAddress(SectionAddr))) break;
    180 
    181     // Make a list of all the symbols in this section.
    182     std::vector<std::pair<uint64_t, StringRef> > Symbols;
    183     for (symbol_iterator si = Obj->begin_symbols(),
    184                          se = Obj->end_symbols();
    185                          si != se; si.increment(ec)) {
    186       bool contains;
    187       if (!error(i->containsSymbol(*si, contains)) && contains) {
    188         uint64_t Address;
    189         if (error(si->getOffset(Address))) break;
    190         StringRef Name;
    191         if (error(si->getName(Name))) break;
    192         Symbols.push_back(std::make_pair(Address, Name));
    193       }
    194     }
    195 
    196     // Sort the symbols by address, just in case they didn't come in that way.
    197     array_pod_sort(Symbols.begin(), Symbols.end());
    198 
    199     // Make a list of all the relocations for this section.
    200     std::vector<RelocationRef> Rels;
    201     if (InlineRelocs) {
    202       for (relocation_iterator ri = i->begin_relocations(),
    203                                re = i->end_relocations();
    204                               ri != re; ri.increment(ec)) {
    205         if (error(ec)) break;
    206         Rels.push_back(*ri);
    207       }
    208     }
    209 
    210     // Sort relocations by address.
    211     std::sort(Rels.begin(), Rels.end(), RelocAddressLess);
    212 
    213     StringRef name;
    214     if (error(i->getName(name))) break;
    215     outs() << "Disassembly of section " << name << ':';
    216 
    217     // If the section has no symbols just insert a dummy one and disassemble
    218     // the whole section.
    219     if (Symbols.empty())
    220       Symbols.push_back(std::make_pair(0, name));
    221 
    222     // Set up disassembler.
    223     OwningPtr<const MCAsmInfo> AsmInfo(TheTarget->createMCAsmInfo(TripleName));
    224 
    225     if (!AsmInfo) {
    226       errs() << "error: no assembly info for target " << TripleName << "\n";
    227       return;
    228     }
    229 
    230     OwningPtr<const MCSubtargetInfo> STI(
    231       TheTarget->createMCSubtargetInfo(TripleName, "", ""));
    232 
    233     if (!STI) {
    234       errs() << "error: no subtarget info for target " << TripleName << "\n";
    235       return;
    236     }
    237 
    238     OwningPtr<const MCDisassembler> DisAsm(
    239       TheTarget->createMCDisassembler(*STI));
    240     if (!DisAsm) {
    241       errs() << "error: no disassembler for target " << TripleName << "\n";
    242       return;
    243     }
    244 
    245     int AsmPrinterVariant = AsmInfo->getAssemblerDialect();
    246     OwningPtr<MCInstPrinter> IP(TheTarget->createMCInstPrinter(
    247                                 AsmPrinterVariant, *AsmInfo, *STI));
    248     if (!IP) {
    249       errs() << "error: no instruction printer for target " << TripleName
    250              << '\n';
    251       return;
    252     }
    253 
    254     StringRef Bytes;
    255     if (error(i->getContents(Bytes))) break;
    256     StringRefMemoryObject memoryObject(Bytes);
    257     uint64_t Size;
    258     uint64_t Index;
    259     uint64_t SectSize;
    260     if (error(i->getSize(SectSize))) break;
    261 
    262     std::vector<RelocationRef>::const_iterator rel_cur = Rels.begin();
    263     std::vector<RelocationRef>::const_iterator rel_end = Rels.end();
    264     // Disassemble symbol by symbol.
    265     for (unsigned si = 0, se = Symbols.size(); si != se; ++si) {
    266       uint64_t Start = Symbols[si].first;
    267       uint64_t End;
    268       // The end is either the size of the section or the beginning of the next
    269       // symbol.
    270       if (si == se - 1)
    271         End = SectSize;
    272       // Make sure this symbol takes up space.
    273       else if (Symbols[si + 1].first != Start)
    274         End = Symbols[si + 1].first - 1;
    275       else
    276         // This symbol has the same address as the next symbol. Skip it.
    277         continue;
    278 
    279       outs() << '\n' << Symbols[si].second << ":\n";
    280 
    281 #ifndef NDEBUG
    282         raw_ostream &DebugOut = DebugFlag ? dbgs() : nulls();
    283 #else
    284         raw_ostream &DebugOut = nulls();
    285 #endif
    286 
    287       for (Index = Start; Index < End; Index += Size) {
    288         MCInst Inst;
    289 
    290         if (DisAsm->getInstruction(Inst, Size, memoryObject, Index,
    291                                    DebugOut, nulls())) {
    292           outs() << format("%8x:\t", SectionAddr + Index);
    293           DumpBytes(StringRef(Bytes.data() + Index, Size));
    294           IP->printInst(&Inst, outs(), "");
    295           outs() << "\n";
    296         } else {
    297           errs() << ToolName << ": warning: invalid instruction encoding\n";
    298           if (Size == 0)
    299             Size = 1; // skip illegible bytes
    300         }
    301 
    302         // Print relocation for instruction.
    303         while (rel_cur != rel_end) {
    304           uint64_t addr;
    305           SmallString<16> name;
    306           SmallString<32> val;
    307           if (error(rel_cur->getAddress(addr))) goto skip_print_rel;
    308           // Stop when rel_cur's address is past the current instruction.
    309           if (addr > Index + Size) break;
    310           if (error(rel_cur->getTypeName(name))) goto skip_print_rel;
    311           if (error(rel_cur->getValueString(val))) goto skip_print_rel;
    312 
    313           outs() << format("\t\t\t%8x: ", SectionAddr + addr) << name << "\t"
    314                  << val << "\n";
    315 
    316         skip_print_rel:
    317           ++rel_cur;
    318         }
    319       }
    320     }
    321   }
    322 }
    323 
    324 static void PrintRelocations(const ObjectFile *o) {
    325   error_code ec;
    326   for (section_iterator si = o->begin_sections(), se = o->end_sections();
    327                                                   si != se; si.increment(ec)){
    328     if (error(ec)) return;
    329     if (si->begin_relocations() == si->end_relocations())
    330       continue;
    331     StringRef secname;
    332     if (error(si->getName(secname))) continue;
    333     outs() << "RELOCATION RECORDS FOR [" << secname << "]:\n";
    334     for (relocation_iterator ri = si->begin_relocations(),
    335                              re = si->end_relocations();
    336                              ri != re; ri.increment(ec)) {
    337       if (error(ec)) return;
    338 
    339       uint64_t address;
    340       SmallString<32> relocname;
    341       SmallString<32> valuestr;
    342       if (error(ri->getTypeName(relocname))) continue;
    343       if (error(ri->getAddress(address))) continue;
    344       if (error(ri->getValueString(valuestr))) continue;
    345       outs() << address << " " << relocname << " " << valuestr << "\n";
    346     }
    347     outs() << "\n";
    348   }
    349 }
    350 
    351 static void PrintSectionHeaders(const ObjectFile *o) {
    352   outs() << "Sections:\n"
    353             "Idx Name          Size      Address          Type\n";
    354   error_code ec;
    355   unsigned i = 0;
    356   for (section_iterator si = o->begin_sections(), se = o->end_sections();
    357                                                   si != se; si.increment(ec)) {
    358     if (error(ec)) return;
    359     StringRef Name;
    360     if (error(si->getName(Name))) return;
    361     uint64_t Address;
    362     if (error(si->getAddress(Address))) return;
    363     uint64_t Size;
    364     if (error(si->getSize(Size))) return;
    365     bool Text, Data, BSS;
    366     if (error(si->isText(Text))) return;
    367     if (error(si->isData(Data))) return;
    368     if (error(si->isBSS(BSS))) return;
    369     std::string Type = (std::string(Text ? "TEXT " : "") +
    370                         (Data ? "DATA " : "") + (BSS ? "BSS" : ""));
    371     outs() << format("%3d %-13s %09"PRIx64" %017"PRIx64" %s\n", i, Name.str().c_str(), Size,
    372                      Address, Type.c_str());
    373     ++i;
    374   }
    375 }
    376 
    377 static void PrintSectionContents(const ObjectFile *o) {
    378   error_code ec;
    379   for (section_iterator si = o->begin_sections(),
    380                         se = o->end_sections();
    381                         si != se; si.increment(ec)) {
    382     if (error(ec)) return;
    383     StringRef Name;
    384     StringRef Contents;
    385     uint64_t BaseAddr;
    386     if (error(si->getName(Name))) continue;
    387     if (error(si->getContents(Contents))) continue;
    388     if (error(si->getAddress(BaseAddr))) continue;
    389 
    390     outs() << "Contents of section " << Name << ":\n";
    391 
    392     // Dump out the content as hex and printable ascii characters.
    393     for (std::size_t addr = 0, end = Contents.size(); addr < end; addr += 16) {
    394       outs() << format(" %04x ", BaseAddr + addr);
    395       // Dump line of hex.
    396       for (std::size_t i = 0; i < 16; ++i) {
    397         if (i != 0 && i % 4 == 0)
    398           outs() << ' ';
    399         if (addr + i < end)
    400           outs() << hexdigit((Contents[addr + i] >> 4) & 0xF, true)
    401                  << hexdigit(Contents[addr + i] & 0xF, true);
    402         else
    403           outs() << "  ";
    404       }
    405       // Print ascii.
    406       outs() << "  ";
    407       for (std::size_t i = 0; i < 16 && addr + i < end; ++i) {
    408         if (std::isprint(Contents[addr + i] & 0xFF))
    409           outs() << Contents[addr + i];
    410         else
    411           outs() << ".";
    412       }
    413       outs() << "\n";
    414     }
    415   }
    416 }
    417 
    418 static void PrintCOFFSymbolTable(const COFFObjectFile *coff) {
    419   const coff_file_header *header;
    420   if (error(coff->getHeader(header))) return;
    421   int aux_count = 0;
    422   const coff_symbol *symbol = 0;
    423   for (int i = 0, e = header->NumberOfSymbols; i != e; ++i) {
    424     if (aux_count--) {
    425       // Figure out which type of aux this is.
    426       if (symbol->StorageClass == COFF::IMAGE_SYM_CLASS_STATIC
    427           && symbol->Value == 0) { // Section definition.
    428         const coff_aux_section_definition *asd;
    429         if (error(coff->getAuxSymbol<coff_aux_section_definition>(i, asd)))
    430           return;
    431         outs() << "AUX "
    432                << format("scnlen 0x%x nreloc %d nlnno %d checksum 0x%x "
    433                          , unsigned(asd->Length)
    434                          , unsigned(asd->NumberOfRelocations)
    435                          , unsigned(asd->NumberOfLinenumbers)
    436                          , unsigned(asd->CheckSum))
    437                << format("assoc %d comdat %d\n"
    438                          , unsigned(asd->Number)
    439                          , unsigned(asd->Selection));
    440       } else {
    441         outs() << "AUX Unknown\n";
    442       }
    443     } else {
    444       StringRef name;
    445       if (error(coff->getSymbol(i, symbol))) return;
    446       if (error(coff->getSymbolName(symbol, name))) return;
    447       outs() << "[" << format("%2d", i) << "]"
    448              << "(sec " << format("%2d", int(symbol->SectionNumber)) << ")"
    449              << "(fl 0x00)" // Flag bits, which COFF doesn't have.
    450              << "(ty " << format("%3x", unsigned(symbol->Type)) << ")"
    451              << "(scl " << format("%3x", unsigned(symbol->StorageClass)) << ") "
    452              << "(nx " << unsigned(symbol->NumberOfAuxSymbols) << ") "
    453              << "0x" << format("%08x", unsigned(symbol->Value)) << " "
    454              << name << "\n";
    455       aux_count = symbol->NumberOfAuxSymbols;
    456     }
    457   }
    458 }
    459 
    460 static void PrintSymbolTable(const ObjectFile *o) {
    461   outs() << "SYMBOL TABLE:\n";
    462 
    463   if (const COFFObjectFile *coff = dyn_cast<const COFFObjectFile>(o))
    464     PrintCOFFSymbolTable(coff);
    465   else {
    466     error_code ec;
    467     for (symbol_iterator si = o->begin_symbols(),
    468                          se = o->end_symbols(); si != se; si.increment(ec)) {
    469       if (error(ec)) return;
    470       StringRef Name;
    471       uint64_t Offset;
    472       bool Global;
    473       SymbolRef::Type Type;
    474       bool Weak;
    475       bool Absolute;
    476       uint64_t Size;
    477       section_iterator Section = o->end_sections();
    478       if (error(si->getName(Name))) continue;
    479       if (error(si->getOffset(Offset))) continue;
    480       if (error(si->isGlobal(Global))) continue;
    481       if (error(si->getType(Type))) continue;
    482       if (error(si->isWeak(Weak))) continue;
    483       if (error(si->isAbsolute(Absolute))) continue;
    484       if (error(si->getSize(Size))) continue;
    485       if (error(si->getSection(Section))) continue;
    486 
    487       if (Offset == UnknownAddressOrSize)
    488         Offset = 0;
    489       char GlobLoc = ' ';
    490       if (Type != SymbolRef::ST_External)
    491         GlobLoc = Global ? 'g' : 'l';
    492       char Debug = (Type == SymbolRef::ST_Debug || Type == SymbolRef::ST_File)
    493                    ? 'd' : ' ';
    494       char FileFunc = ' ';
    495       if (Type == SymbolRef::ST_File)
    496         FileFunc = 'f';
    497       else if (Type == SymbolRef::ST_Function)
    498         FileFunc = 'F';
    499 
    500       outs() << format("%08x", Offset) << " "
    501              << GlobLoc // Local -> 'l', Global -> 'g', Neither -> ' '
    502              << (Weak ? 'w' : ' ') // Weak?
    503              << ' ' // Constructor. Not supported yet.
    504              << ' ' // Warning. Not supported yet.
    505              << ' ' // Indirect reference to another symbol.
    506              << Debug // Debugging (d) or dynamic (D) symbol.
    507              << FileFunc // Name of function (F), file (f) or object (O).
    508              << ' ';
    509       if (Absolute)
    510         outs() << "*ABS*";
    511       else if (Section == o->end_sections())
    512         outs() << "*UND*";
    513       else {
    514         StringRef SectionName;
    515         if (error(Section->getName(SectionName)))
    516           SectionName = "";
    517         outs() << SectionName;
    518       }
    519       outs() << '\t'
    520              << format("%08x ", Size)
    521              << Name
    522              << '\n';
    523     }
    524   }
    525 }
    526 
    527 static void DumpObject(const ObjectFile *o) {
    528   outs() << '\n';
    529   outs() << o->getFileName()
    530          << ":\tfile format " << o->getFileFormatName() << "\n\n";
    531 
    532   if (Disassemble)
    533     DisassembleObject(o, Relocations);
    534   if (Relocations && !Disassemble)
    535     PrintRelocations(o);
    536   if (SectionHeaders)
    537     PrintSectionHeaders(o);
    538   if (SectionContents)
    539     PrintSectionContents(o);
    540   if (SymbolTable)
    541     PrintSymbolTable(o);
    542 }
    543 
    544 /// @brief Dump each object file in \a a;
    545 static void DumpArchive(const Archive *a) {
    546   for (Archive::child_iterator i = a->begin_children(),
    547                                e = a->end_children(); i != e; ++i) {
    548     OwningPtr<Binary> child;
    549     if (error_code ec = i->getAsBinary(child)) {
    550       errs() << ToolName << ": '" << a->getFileName() << "': " << ec.message()
    551              << ".\n";
    552       continue;
    553     }
    554     if (ObjectFile *o = dyn_cast<ObjectFile>(child.get()))
    555       DumpObject(o);
    556     else
    557       errs() << ToolName << ": '" << a->getFileName() << "': "
    558               << "Unrecognized file type.\n";
    559   }
    560 }
    561 
    562 /// @brief Open file and figure out how to dump it.
    563 static void DumpInput(StringRef file) {
    564   // If file isn't stdin, check that it exists.
    565   if (file != "-" && !sys::fs::exists(file)) {
    566     errs() << ToolName << ": '" << file << "': " << "No such file\n";
    567     return;
    568   }
    569 
    570   if (MachO && Disassemble) {
    571     DisassembleInputMachO(file);
    572     return;
    573   }
    574 
    575   // Attempt to open the binary.
    576   OwningPtr<Binary> binary;
    577   if (error_code ec = createBinary(file, binary)) {
    578     errs() << ToolName << ": '" << file << "': " << ec.message() << ".\n";
    579     return;
    580   }
    581 
    582   if (Archive *a = dyn_cast<Archive>(binary.get())) {
    583     DumpArchive(a);
    584   } else if (ObjectFile *o = dyn_cast<ObjectFile>(binary.get())) {
    585     DumpObject(o);
    586   } else {
    587     errs() << ToolName << ": '" << file << "': " << "Unrecognized file type.\n";
    588   }
    589 }
    590 
    591 int main(int argc, char **argv) {
    592   // Print a stack trace if we signal out.
    593   sys::PrintStackTraceOnErrorSignal();
    594   PrettyStackTraceProgram X(argc, argv);
    595   llvm_shutdown_obj Y;  // Call llvm_shutdown() on exit.
    596 
    597   // Initialize targets and assembly printers/parsers.
    598   llvm::InitializeAllTargetInfos();
    599   llvm::InitializeAllTargetMCs();
    600   llvm::InitializeAllAsmParsers();
    601   llvm::InitializeAllDisassemblers();
    602 
    603   cl::ParseCommandLineOptions(argc, argv, "llvm object file dumper\n");
    604   TripleName = Triple::normalize(TripleName);
    605 
    606   ToolName = argv[0];
    607 
    608   // Defaults to a.out if no filenames specified.
    609   if (InputFilenames.size() == 0)
    610     InputFilenames.push_back("a.out");
    611 
    612   if (!Disassemble
    613       && !Relocations
    614       && !SectionHeaders
    615       && !SectionContents
    616       && !SymbolTable) {
    617     cl::PrintHelpMessage();
    618     return 2;
    619   }
    620 
    621   std::for_each(InputFilenames.begin(), InputFilenames.end(),
    622                 DumpInput);
    623 
    624   return 0;
    625 }
    626