lib/ExecutionEngine/RuntimeDyld/RuntimeDyldMachO.cpp

//===-- RuntimeDyldMachO.cpp - Run-time dynamic linker for MC-JIT -*- C++ -*-=//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// Implementation of the MC-JIT runtime dynamic linker.
//
//===----------------------------------------------------------------------===//

#define DEBUG_TYPE "dyld"
#include "llvm/ADT/OwningPtr.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/ADT/STLExtras.h"
#include "RuntimeDyldMachO.h"
using namespace llvm;
using namespace llvm::object;

namespace llvm {

void RuntimeDyldMachO::resolveRelocation(uint8_t *LocalAddress,
                                         uint64_t FinalAddress,
                                         uint64_t Value,
                                         uint32_t Type,
                                         int64_t Addend) {
  bool isPCRel = (Type >> 24) & 1;
  unsigned MachoType = (Type >> 28) & 0xf;
  unsigned Size = 1 << ((Type >> 25) & 3);

  DEBUG(dbgs() << "resolveRelocation LocalAddress: " << format("%p", LocalAddress)
        << " FinalAddress: " << format("%p", FinalAddress)
        << " Value: " << format("%p", Value)
        << " Addend: " << Addend
        << " isPCRel: " << isPCRel
        << " MachoType: " << MachoType
        << " Size: " << Size
        << "\n");

  // This just dispatches to the proper target specific routine.
  switch (Arch) {
  default: llvm_unreachable("Unsupported CPU type!");
  case Triple::x86_64: // Fall through.
  case Triple::x86:
    resolveX86_64Relocation(LocalAddress,
                            FinalAddress,
                            (uintptr_t)Value,
                            isPCRel,
                            MachoType,
                            Size,
                            Addend);
    break;
  case Triple::arm:    // Fall through.
  case Triple::thumb:
    resolveARMRelocation(LocalAddress,
                         FinalAddress,
                         (uintptr_t)Value,
                         isPCRel,
                         MachoType,
                         Size,
                         Addend);
    break;
  }
}

bool RuntimeDyldMachO::
resolveX86_64Relocation(uint8_t *LocalAddress,
                        uint64_t FinalAddress,
                        uint64_t Value,
                        bool isPCRel,
                        unsigned Type,
                        unsigned Size,
                        int64_t Addend) {
  // If the relocation is PC-relative, the value to be encoded is the
  // pointer difference.
  if (isPCRel)
    // FIXME: It seems this value needs to be adjusted by 4 for an effective PC
    // address. Is that expected? Only for branches, perhaps?
    Value -= FinalAddress + 4;

  switch(Type) {
  default:
    llvm_unreachable("Invalid relocation type!");
  case macho::RIT_X86_64_Signed1:
  case macho::RIT_X86_64_Signed2:
  case macho::RIT_X86_64_Signed4:
  case macho::RIT_X86_64_Signed:
  case macho::RIT_X86_64_Unsigned:
  case macho::RIT_X86_64_Branch: {
    Value += Addend;
    // Mask in the target value a byte at a time (we don't have an alignment
    // guarantee for the target address, so this is safest).
    uint8_t *p = (uint8_t*)LocalAddress;
    for (unsigned i = 0; i < Size; ++i) {
      *p++ = (uint8_t)Value;
      Value >>= 8;
    }
    return false;
  }
  case macho::RIT_X86_64_GOTLoad:
  case macho::RIT_X86_64_GOT:
  case macho::RIT_X86_64_Subtractor:
  case macho::RIT_X86_64_TLV:
    return Error("Relocation type not implemented yet!");
  }
}

bool RuntimeDyldMachO::
resolveARMRelocation(uint8_t *LocalAddress,
                     uint64_t FinalAddress,
                     uint64_t Value,
                     bool isPCRel,
                     unsigned Type,
                     unsigned Size,
                     int64_t Addend) {
  // If the relocation is PC-relative, the value to be encoded is the
  // pointer difference.
  if (isPCRel) {
    Value -= FinalAddress;
    // ARM PCRel relocations have an effective-PC offset of two instructions
    // (four bytes in Thumb mode, 8 bytes in ARM mode).
    // FIXME: For now, assume ARM mode.
    Value -= 8;
  }

  switch(Type) {
  default:
    llvm_unreachable("Invalid relocation type!");
  case macho::RIT_Vanilla: {
    // Mask in the target value a byte at a time (we don't have an alignment
    // guarantee for the target address, so this is safest).
    uint8_t *p = (uint8_t*)LocalAddress;
    for (unsigned i = 0; i < Size; ++i) {
      *p++ = (uint8_t)Value;
      Value >>= 8;
    }
    break;
  }
  case macho::RIT_ARM_Branch24Bit: {
    // Mask the value into the target address. We know instructions are
    // 32-bit aligned, so we can do it all at once.
    uint32_t *p = (uint32_t*)LocalAddress;
    // The low two bits of the value are not encoded.
    Value >>= 2;
    // Mask the value to 24 bits.
    Value &= 0xffffff;
    // FIXME: If the destination is a Thumb function (and the instruction
    // is a non-predicated BL instruction), we need to change it to a BLX
    // instruction instead.

    // Insert the value into the instruction.
    *p = (*p & ~0xffffff) | Value;
    break;
  }
  case macho::RIT_ARM_ThumbBranch22Bit:
  case macho::RIT_ARM_ThumbBranch32Bit:
  case macho::RIT_ARM_Half:
  case macho::RIT_ARM_HalfDifference:
  case macho::RIT_Pair:
  case macho::RIT_Difference:
  case macho::RIT_ARM_LocalDifference:
  case macho::RIT_ARM_PreboundLazyPointer:
    return Error("Relocation type not implemented yet!");
  }
  return false;
}

void RuntimeDyldMachO::
processRelocationRef(const ObjRelocationInfo &Rel, const ObjectFile &Obj,
                     ObjSectionToIDMap &ObjSectionToID,
                     LocalSymbolMap &Symbols, StubMap &Stubs) {

  uint32_t RelType = (uint32_t) (Rel.Type & 0xffffffffL);
  RelocationValueRef Value;
  SectionEntry &Section = Sections[Rel.SectionID];
  uint8_t *Target = Section.Address + Rel.Offset;

  bool isExtern = (RelType >> 27) & 1;
  if (isExtern) {
    StringRef TargetName;
    const SymbolRef &Symbol = Rel.Symbol;
    Symbol.getName(TargetName);
    // First look the symbol in object file symbols.
    LocalSymbolMap::iterator it = Symbols.find(TargetName.data());
    if (it != Symbols.end()) {
      Value.SectionID = it->second.first;
      Value.Addend = it->second.second;
    } else {
      // Second look the symbol in global symbol table.
      StringMap<SymbolLoc>::iterator itS = SymbolTable.find(TargetName.data());
      if (itS != SymbolTable.end()) {
        Value.SectionID = itS->second.first;
        Value.Addend = itS->second.second;
      } else
        Value.SymbolName = TargetName.data();
    }
  } else {
    error_code err;
    uint8_t sIdx = static_cast<uint8_t>(RelType & 0xFF);
    section_iterator sIt = Obj.begin_sections(),
                     sItEnd = Obj.end_sections();
    for (uint8_t i = 1; i < sIdx; i++) {
      error_code err;
      sIt.increment(err);
      if (sIt == sItEnd)
        break;
    }
    assert(sIt != sItEnd && "No section containing relocation!");
    Value.SectionID = findOrEmitSection(*sIt, true, ObjSectionToID);
    Value.Addend = *(const intptr_t *)Target;
    if (Value.Addend) {
      // The MachO addend is offset from the current section, we need set it
      // as offset from destination section
      Value.Addend += Section.ObjAddress - Sections[Value.SectionID].ObjAddress;
    }
  }

  if (Arch == Triple::arm && RelType == macho::RIT_ARM_Branch24Bit) {
    // This is an ARM branch relocation, need to use a stub function.

    //  Look up for existing stub.
    StubMap::const_iterator stubIt = Stubs.find(Value);
    if (stubIt != Stubs.end())
      resolveRelocation(Target, (uint64_t)Target,
                        (uint64_t)Section.Address + stubIt->second,
                        RelType, 0);
    else {
      // Create a new stub function.
      Stubs[Value] = Section.StubOffset;
      uint8_t *StubTargetAddr = createStubFunction(Section.Address +
                                                   Section.StubOffset);
      AddRelocation(Value, Rel.SectionID, StubTargetAddr - Section.Address,
                    macho::RIT_Vanilla);
      resolveRelocation(Target, (uint64_t)Target,
                        (uint64_t)Section.Address + Section.StubOffset,
                        RelType, 0);
      Section.StubOffset += getMaxStubSize();
    }
  } else
    AddRelocation(Value, Rel.SectionID, Rel.Offset, RelType);
}


bool RuntimeDyldMachO::isCompatibleFormat(const MemoryBuffer *InputBuffer) const {
  StringRef Magic = InputBuffer->getBuffer().slice(0, 4);
  if (Magic == "\xFE\xED\xFA\xCE") return true;
  if (Magic == "\xCE\xFA\xED\xFE") return true;
  if (Magic == "\xFE\xED\xFA\xCF") return true;
  if (Magic == "\xCF\xFA\xED\xFE") return true;
  return false;
}

} // end namespace llvm