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      1 //===-- lib/MC/MCObjectSymbolizer.cpp -------------------------------------===//
      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 #include "llvm/MC/MCObjectSymbolizer.h"
     11 #include "llvm/ADT/SmallString.h"
     12 #include "llvm/MC/MCContext.h"
     13 #include "llvm/MC/MCExpr.h"
     14 #include "llvm/MC/MCInst.h"
     15 #include "llvm/MC/MCRelocationInfo.h"
     16 #include "llvm/MC/MCSymbol.h"
     17 #include "llvm/Object/ELFObjectFile.h"
     18 #include "llvm/Object/MachO.h"
     19 #include "llvm/Support/raw_ostream.h"
     20 #include <algorithm>
     21 
     22 using namespace llvm;
     23 using namespace object;
     24 
     25 //===- MCMachObjectSymbolizer ---------------------------------------------===//
     26 
     27 namespace {
     28 class MCMachObjectSymbolizer : public MCObjectSymbolizer {
     29   const MachOObjectFile *MOOF;
     30   // __TEXT;__stubs support.
     31   uint64_t StubsStart;
     32   uint64_t StubsCount;
     33   uint64_t StubSize;
     34   uint64_t StubsIndSymIndex;
     35 
     36 public:
     37   MCMachObjectSymbolizer(MCContext &Ctx,
     38                          std::unique_ptr<MCRelocationInfo> RelInfo,
     39                          const MachOObjectFile *MOOF);
     40 
     41   StringRef findExternalFunctionAt(uint64_t Addr) override;
     42 
     43   void tryAddingPcLoadReferenceComment(raw_ostream &cStream, int64_t Value,
     44                                        uint64_t Address) override;
     45 };
     46 } // End unnamed namespace
     47 
     48 MCMachObjectSymbolizer::MCMachObjectSymbolizer(
     49     MCContext &Ctx, std::unique_ptr<MCRelocationInfo> RelInfo,
     50     const MachOObjectFile *MOOF)
     51   : MCObjectSymbolizer(Ctx, std::move(RelInfo), MOOF), MOOF(MOOF),
     52     StubsStart(0), StubsCount(0), StubSize(0), StubsIndSymIndex(0) {
     53 
     54   for (const SectionRef &Section : MOOF->sections()) {
     55     StringRef Name;
     56     Section.getName(Name);
     57     if (Name == "__stubs") {
     58       SectionRef StubsSec = Section;
     59       if (MOOF->is64Bit()) {
     60         MachO::section_64 S = MOOF->getSection64(StubsSec.getRawDataRefImpl());
     61         StubsIndSymIndex = S.reserved1;
     62         StubSize = S.reserved2;
     63       } else {
     64         MachO::section S = MOOF->getSection(StubsSec.getRawDataRefImpl());
     65         StubsIndSymIndex = S.reserved1;
     66         StubSize = S.reserved2;
     67       }
     68       assert(StubSize && "Mach-O stub entry size can't be zero!");
     69       StubsSec.getAddress(StubsStart);
     70       StubsSec.getSize(StubsCount);
     71       StubsCount /= StubSize;
     72     }
     73   }
     74 }
     75 
     76 StringRef MCMachObjectSymbolizer::findExternalFunctionAt(uint64_t Addr) {
     77   // FIXME: also, this can all be done at the very beginning, by iterating over
     78   // all stubs and creating the calls to outside functions. Is it worth it
     79   // though?
     80   if (!StubSize)
     81     return StringRef();
     82   uint64_t StubIdx = (Addr - StubsStart) / StubSize;
     83   if (StubIdx >= StubsCount)
     84     return StringRef();
     85 
     86   uint32_t SymtabIdx =
     87     MOOF->getIndirectSymbolTableEntry(MOOF->getDysymtabLoadCommand(), StubIdx);
     88 
     89   StringRef SymName;
     90   symbol_iterator SI = MOOF->symbol_begin();
     91   for (uint32_t i = 0; i != SymtabIdx; ++i)
     92     ++SI;
     93   SI->getName(SymName);
     94   assert(SI != MOOF->symbol_end() && "Stub wasn't found in the symbol table!");
     95   assert(SymName.front() == '_' && "Mach-O symbol doesn't start with '_'!");
     96   return SymName.substr(1);
     97 }
     98 
     99 void MCMachObjectSymbolizer::
    100 tryAddingPcLoadReferenceComment(raw_ostream &cStream, int64_t Value,
    101                                 uint64_t Address) {
    102   if (const RelocationRef *R = findRelocationAt(Address)) {
    103     const MCExpr *RelExpr = RelInfo->createExprForRelocation(*R);
    104     if (!RelExpr || RelExpr->EvaluateAsAbsolute(Value) == false)
    105       return;
    106   }
    107   uint64_t Addr = Value;
    108   if (const SectionRef *S = findSectionContaining(Addr)) {
    109     StringRef Name; S->getName(Name);
    110     uint64_t SAddr; S->getAddress(SAddr);
    111     if (Name == "__cstring") {
    112       StringRef Contents;
    113       S->getContents(Contents);
    114       Contents = Contents.substr(Addr - SAddr);
    115       cStream << " ## literal pool for: "
    116               << Contents.substr(0, Contents.find_first_of(0));
    117     }
    118   }
    119 }
    120 
    121 //===- MCObjectSymbolizer -------------------------------------------------===//
    122 
    123 MCObjectSymbolizer::MCObjectSymbolizer(
    124   MCContext &Ctx, std::unique_ptr<MCRelocationInfo> RelInfo,
    125   const ObjectFile *Obj)
    126   : MCSymbolizer(Ctx, std::move(RelInfo)), Obj(Obj), SortedSections(),
    127     AddrToReloc() {}
    128 
    129 bool MCObjectSymbolizer::
    130 tryAddingSymbolicOperand(MCInst &MI, raw_ostream &cStream,
    131                          int64_t Value, uint64_t Address, bool IsBranch,
    132                          uint64_t Offset, uint64_t InstSize) {
    133   if (IsBranch) {
    134     StringRef ExtFnName = findExternalFunctionAt((uint64_t)Value);
    135     if (!ExtFnName.empty()) {
    136       MCSymbol *Sym = Ctx.GetOrCreateSymbol(ExtFnName);
    137       const MCExpr *Expr = MCSymbolRefExpr::Create(Sym, Ctx);
    138       MI.addOperand(MCOperand::CreateExpr(Expr));
    139       return true;
    140     }
    141   }
    142 
    143   if (const RelocationRef *R = findRelocationAt(Address + Offset)) {
    144     if (const MCExpr *RelExpr = RelInfo->createExprForRelocation(*R)) {
    145       MI.addOperand(MCOperand::CreateExpr(RelExpr));
    146       return true;
    147     }
    148     // Only try to create a symbol+offset expression if there is no relocation.
    149     return false;
    150   }
    151 
    152   // Interpret Value as a branch target.
    153   if (IsBranch == false)
    154     return false;
    155   uint64_t UValue = Value;
    156   // FIXME: map instead of looping each time?
    157   for (const SymbolRef &Symbol : Obj->symbols()) {
    158     uint64_t SymAddr;
    159     Symbol.getAddress(SymAddr);
    160     uint64_t SymSize;
    161     Symbol.getSize(SymSize);
    162     StringRef SymName;
    163     Symbol.getName(SymName);
    164     SymbolRef::Type SymType;
    165     Symbol.getType(SymType);
    166     if (SymAddr == UnknownAddressOrSize || SymSize == UnknownAddressOrSize ||
    167         SymName.empty() || SymType != SymbolRef::ST_Function)
    168       continue;
    169 
    170     if ( SymAddr == UValue ||
    171         (SymAddr <= UValue && SymAddr + SymSize > UValue)) {
    172       MCSymbol *Sym = Ctx.GetOrCreateSymbol(SymName);
    173       const MCExpr *Expr = MCSymbolRefExpr::Create(Sym, Ctx);
    174       if (SymAddr != UValue) {
    175         const MCExpr *Off = MCConstantExpr::Create(UValue - SymAddr, Ctx);
    176         Expr = MCBinaryExpr::CreateAdd(Expr, Off, Ctx);
    177       }
    178       MI.addOperand(MCOperand::CreateExpr(Expr));
    179       return true;
    180     }
    181   }
    182   return false;
    183 }
    184 
    185 void MCObjectSymbolizer::
    186 tryAddingPcLoadReferenceComment(raw_ostream &cStream,
    187                                 int64_t Value, uint64_t Address) {
    188 }
    189 
    190 StringRef MCObjectSymbolizer::findExternalFunctionAt(uint64_t Addr) {
    191   return StringRef();
    192 }
    193 
    194 MCObjectSymbolizer *MCObjectSymbolizer::createObjectSymbolizer(
    195     MCContext &Ctx, std::unique_ptr<MCRelocationInfo> RelInfo,
    196     const ObjectFile *Obj) {
    197   if (const MachOObjectFile *MOOF = dyn_cast<MachOObjectFile>(Obj))
    198     return new MCMachObjectSymbolizer(Ctx, std::move(RelInfo), MOOF);
    199   return new MCObjectSymbolizer(Ctx, std::move(RelInfo), Obj);
    200 }
    201 
    202 // SortedSections implementation.
    203 
    204 static bool SectionStartsBefore(const SectionRef &S, uint64_t Addr) {
    205   uint64_t SAddr; S.getAddress(SAddr);
    206   return SAddr < Addr;
    207 }
    208 
    209 const SectionRef *MCObjectSymbolizer::findSectionContaining(uint64_t Addr) {
    210   if (SortedSections.empty())
    211     buildSectionList();
    212 
    213   SortedSectionList::iterator
    214     EndIt = SortedSections.end(),
    215     It = std::lower_bound(SortedSections.begin(), EndIt,
    216                           Addr, SectionStartsBefore);
    217   if (It == EndIt)
    218     return nullptr;
    219   uint64_t SAddr; It->getAddress(SAddr);
    220   uint64_t SSize; It->getSize(SSize);
    221   if (Addr >= SAddr + SSize)
    222     return nullptr;
    223   return &*It;
    224 }
    225 
    226 const RelocationRef *MCObjectSymbolizer::findRelocationAt(uint64_t Addr) {
    227   if (AddrToReloc.empty())
    228     buildRelocationByAddrMap();
    229 
    230   AddrToRelocMap::const_iterator RI = AddrToReloc.find(Addr);
    231   if (RI == AddrToReloc.end())
    232     return nullptr;
    233   return &RI->second;
    234 }
    235 
    236 void MCObjectSymbolizer::buildSectionList() {
    237   for (const SectionRef &Section : Obj->sections()) {
    238     bool RequiredForExec;
    239     Section.isRequiredForExecution(RequiredForExec);
    240     if (RequiredForExec == false)
    241       continue;
    242     uint64_t SAddr;
    243     Section.getAddress(SAddr);
    244     uint64_t SSize;
    245     Section.getSize(SSize);
    246     SortedSectionList::iterator It =
    247         std::lower_bound(SortedSections.begin(), SortedSections.end(), SAddr,
    248                          SectionStartsBefore);
    249     if (It != SortedSections.end()) {
    250       uint64_t FoundSAddr; It->getAddress(FoundSAddr);
    251       if (FoundSAddr < SAddr + SSize)
    252         llvm_unreachable("Inserting overlapping sections");
    253     }
    254     SortedSections.insert(It, Section);
    255   }
    256 }
    257 
    258 void MCObjectSymbolizer::buildRelocationByAddrMap() {
    259   for (const SectionRef &Section : Obj->sections()) {
    260     for (const RelocationRef &Reloc : Section.relocations()) {
    261       uint64_t Address;
    262       Reloc.getAddress(Address);
    263       // At a specific address, only keep the first relocation.
    264       if (AddrToReloc.find(Address) == AddrToReloc.end())
    265         AddrToReloc[Address] = Reloc;
    266     }
    267   }
    268 }
    269