lld/lib/ReaderWriter/MachO/MachONormalizedFileToAtoms.cpp

//===- lib/ReaderWriter/MachO/MachONormalizedFileToAtoms.cpp --------------===//
//
//                             The LLVM Linker
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//

///
/// \file Converts from in-memory normalized mach-o to in-memory Atoms.
///
///                  +------------+
///                  | normalized |
///                  +------------+
///                        |
///                        |
///                        v
///                    +-------+
///                    | Atoms |
///                    +-------+

#include "MachONormalizedFile.h"
#include "File.h"
#include "Atoms.h"

#include "lld/Core/LLVM.h"

#include "llvm/Support/MachO.h"

using namespace llvm::MachO;

namespace lld {
namespace mach_o {
namespace normalized {

static uint64_t nextSymbolAddress(const NormalizedFile &normalizedFile,
                                const Symbol &symbol) {
  uint64_t symbolAddr = symbol.value;
  uint8_t symbolSectionIndex = symbol.sect;
  const Section &section = normalizedFile.sections[symbolSectionIndex - 1];
  // If no symbol after this address, use end of section address.
  uint64_t closestAddr = section.address + section.content.size();
  for (const Symbol &s : normalizedFile.globalSymbols) {
    if (s.sect != symbolSectionIndex)
      continue;
    uint64_t sValue = s.value;
    if (sValue <= symbolAddr)
      continue;
    if (sValue < closestAddr)
      closestAddr = s.value;
  }
  for (const Symbol &s : normalizedFile.localSymbols) {
    if (s.sect != symbolSectionIndex)
      continue;
    uint64_t sValue = s.value;
    if (sValue <= symbolAddr)
      continue;
    if (sValue < closestAddr)
      closestAddr = s.value;
  }
  return closestAddr;
}

static Atom::Scope atomScope(uint8_t scope) {
  switch (scope) {
  case N_EXT:
    return Atom::scopeGlobal;
  case N_PEXT | N_EXT:
    return Atom::scopeLinkageUnit;
  case 0:
    return Atom::scopeTranslationUnit;
  }
  llvm_unreachable("unknown scope value!");
}

static void processSymbol(const NormalizedFile &normalizedFile, MachOFile &file,
                          const Symbol &sym, bool copyRefs) {
  // Mach-O symbol table does have size in it, so need to scan ahead
  // to find symbol with next highest address.
  const Section &section = normalizedFile.sections[sym.sect - 1];
  uint64_t offset = sym.value - section.address;
  uint64_t size = nextSymbolAddress(normalizedFile, sym) - sym.value;
  ArrayRef<uint8_t> atomContent = section.content.slice(offset, size);
  file.addDefinedAtom(sym.name, atomContent, atomScope(sym.scope), copyRefs);
}


static void processUndefindeSymbol(MachOFile &file, const Symbol &sym,
                                  bool copyRefs) {
  // Undefinded symbols with n_value!=0 are actually tentative definitions.
  if (sym.value == Hex64(0)) {
    file.addUndefinedAtom(sym.name, copyRefs);
  } else {
    file.addTentativeDefAtom(sym.name, atomScope(sym.scope), sym.value,
                              DefinedAtom::Alignment(sym.desc >> 8), copyRefs);
  }
}


static ErrorOr<std::unique_ptr<lld::File>>
normalizedObjectToAtoms(const NormalizedFile &normalizedFile, StringRef path,
                        bool copyRefs) {
  std::unique_ptr<MachOFile> file(new MachOFile(path));

  for (const Symbol &sym : normalizedFile.globalSymbols) {
    processSymbol(normalizedFile, *file, sym, copyRefs);
  }

  for (const Symbol &sym : normalizedFile.localSymbols) {
    processSymbol(normalizedFile, *file, sym, copyRefs);
  }

  for (auto &sym : normalizedFile.undefinedSymbols) {
    processUndefindeSymbol(*file, sym, copyRefs);
  }

  return std::unique_ptr<File>(std::move(file));
}

ErrorOr<std::unique_ptr<lld::File>>
normalizedToAtoms(const NormalizedFile &normalizedFile, StringRef path,
                  bool copyRefs) {
  switch (normalizedFile.fileType) {
  case MH_OBJECT:
    return normalizedObjectToAtoms(normalizedFile, path, copyRefs);
  default:
    llvm_unreachable("unhandled MachO file type!");
  }
}

} // namespace normalized
} // namespace mach_o
} // namespace lld