//===--- AVR.cpp - AVR ToolChain Implementations ----------------*- C++ -*-===//

//

// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.

// See https://llvm.org/LICENSE.txt for license information.

// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception

//

//===----------------------------------------------------------------------===//

#include "AVR.h"

#include "CommonArgs.h"

#include "clang/Driver/Compilation.h"

#include "clang/Driver/DriverDiagnostic.h"

#include "clang/Driver/InputInfo.h"

#include "clang/Driver/Options.h"

#include "llvm/ADT/Optional.h"

#include "llvm/ADT/StringExtras.h"

#include "llvm/ADT/StringSwitch.h"

#include "llvm/MC/MCSubtargetInfo.h"

#include "llvm/MC/SubtargetFeature.h"

#include "llvm/Option/ArgList.h"

#include "llvm/Support/FileSystem.h"

using namespace clang::driver;

using namespace clang::driver::toolchains;

using namespace clang::driver::tools;

using namespace clang;

using namespace llvm::opt;

namespace {

constexpr struct {

  StringRef Name;

  StringRef SubPath;

  StringRef Family;

  unsigned DataAddr;

} MCUInfo[] = {

    {"at90s1200", "", "avr1", 0},

    {"attiny11", "", "avr1", 0},

    {"attiny12", "", "avr1", 0},

    {"attiny15", "", "avr1", 0},

    {"attiny28", "", "avr1", 0},

    {"at90s2313", "tiny-stack", "avr2", 0x800060},

    {"at90s2323", "tiny-stack", "avr2", 0x800060},

    {"at90s2333", "tiny-stack", "avr2", 0x800060},

    {"at90s2343", "tiny-stack", "avr2", 0x800060},

    {"at90s4433", "tiny-stack", "avr2", 0x800060},

    {"attiny22", "tiny-stack", "avr2", 0x800060},

    {"attiny26", "tiny-stack", "avr2", 0x800060},

    {"at90s4414", "", "avr2", 0x800060},

    {"at90s4434", "", "avr2", 0x800060},

    {"at90s8515", "", "avr2", 0x800060},

    {"at90c8534", "", "avr2", 0x800060},

    {"at90s8535", "", "avr2", 0x800060},

    {"attiny13", "avr25/tiny-stack", "avr25", 0x800060},

    {"attiny13a", "avr25/tiny-stack", "avr25", 0x800060},

    {"attiny2313", "avr25/tiny-stack", "avr25", 0x800060},

    {"attiny2313a", "avr25/tiny-stack", "avr25", 0x800060},

    {"attiny24", "avr25/tiny-stack", "avr25", 0x800060},

    {"attiny24a", "avr25/tiny-stack", "avr25", 0x800060},

    {"attiny25", "avr25/tiny-stack", "avr25", 0x800060},

    {"attiny261", "avr25/tiny-stack", "avr25", 0x800060},

    {"attiny261a", "avr25/tiny-stack", "avr25", 0x800060},

    {"at86rf401", "avr25", "avr25", 0x800060},

    {"ata5272", "avr25", "avr25", 0x800100},

    {"attiny4313", "avr25", "avr25", 0x800060},

    {"attiny44", "avr25", "avr25", 0x800060},

    {"attiny44a", "avr25", "avr25", 0x800060},

    {"attiny84", "avr25", "avr25", 0x800060},

    {"attiny84a", "avr25", "avr25", 0x800060},

    {"attiny45", "avr25", "avr25", 0x800060},

    {"attiny85", "avr25", "avr25", 0x800060},

    {"attiny441", "avr25", "avr25", 0x800100},

    {"attiny461", "avr25", "avr25", 0x800060},

    {"attiny461a", "avr25", "avr25", 0x800060},

    {"attiny841", "avr25", "avr25", 0x800100},

    {"attiny861", "avr25", "avr25", 0x800060},

    {"attiny861a", "avr25", "avr25", 0x800060},

    {"attiny87", "avr25", "avr25", 0x800100},

    {"attiny43u", "avr25", "avr25", 0x800060},

    {"attiny48", "avr25", "avr25", 0x800100},

    {"attiny88", "avr25", "avr25", 0x800100},

    {"attiny828", "avr25", "avr25", 0x800100},

    {"at43usb355", "avr3", "avr3", 0x800100},

    {"at76c711", "avr3", "avr3", 0x800060},

    {"atmega103", "avr31", "avr31", 0x800060},

    {"at43usb320", "avr31", "avr31", 0x800060},

    {"attiny167", "avr35", "avr35", 0x800100},

    {"at90usb82", "avr35", "avr35", 0x800100},

    {"at90usb162", "avr35", "avr35", 0x800100},

    {"ata5505", "avr35", "avr35", 0x800100},

    {"atmega8u2", "avr35", "avr35", 0x800100},

    {"atmega16u2", "avr35", "avr35", 0x800100},

    {"atmega32u2", "avr35", "avr35", 0x800100},

    {"attiny1634", "avr35", "avr35", 0x800100},

    {"atmega8", "avr4", "avr4", 0x800060},

    {"ata6289", "avr4", "avr4", 0x800100},

    {"atmega8a", "avr4", "avr4", 0x800060},

    {"ata6285", "avr4", "avr4", 0x800100},

    {"ata6286", "avr4", "avr4", 0x800100},

    {"atmega48", "avr4", "avr4", 0x800100},

    {"atmega48a", "avr4", "avr4", 0x800100},

    {"atmega48pa", "avr4", "avr4", 0x800100},

    {"atmega48pb", "avr4", "avr4", 0x800100},

    {"atmega48p", "avr4", "avr4", 0x800100},

    {"atmega88", "avr4", "avr4", 0x800100},

    {"atmega88a", "avr4", "avr4", 0x800100},

    {"atmega88p", "avr4", "avr4", 0x800100},

    {"atmega88pa", "avr4", "avr4", 0x800100},

    {"atmega88pb", "avr4", "avr4", 0x800100},

    {"atmega8515", "avr4", "avr4", 0x800060},

    {"atmega8535", "avr4", "avr4", 0x800060},

    {"atmega8hva", "avr4", "avr4", 0x800100},

    {"at90pwm1", "avr4", "avr4", 0x800100},

    {"at90pwm2", "avr4", "avr4", 0x800100},

    {"at90pwm2b", "avr4", "avr4", 0x800100},

    {"at90pwm3", "avr4", "avr4", 0x800100},

    {"at90pwm3b", "avr4", "avr4", 0x800100},

    {"at90pwm81", "avr4", "avr4", 0x800100},

    {"ata5790", "avr5", "avr5", 0x800100},

    {"ata5795", "avr5", "avr5", 0x800100},

    {"atmega16", "avr5", "avr5", 0x800060},

    {"atmega16a", "avr5", "avr5", 0x800060},

    {"atmega161", "avr5", "avr5", 0x800060},

    {"atmega162", "avr5", "avr5", 0x800100},

    {"atmega163", "avr5", "avr5", 0x800060},

    {"atmega164a", "avr5", "avr5", 0x800100},

    {"atmega164p", "avr5", "avr5", 0x800100},

    {"atmega164pa", "avr5", "avr5", 0x800100},

    {"atmega165", "avr5", "avr5", 0x800100},

    {"atmega165a", "avr5", "avr5", 0x800100},

    {"atmega165p", "avr5", "avr5", 0x800100},

    {"atmega165pa", "avr5", "avr5", 0x800100},

    {"atmega168", "avr5", "avr5", 0x800100},

    {"atmega168a", "avr5", "avr5", 0x800100},

    {"atmega168p", "avr5", "avr5", 0x800100},

    {"atmega168pa", "avr5", "avr5", 0x800100},

    {"atmega168pb", "avr5", "avr5", 0x800100},

    {"atmega169", "avr5", "avr5", 0x800100},

    {"atmega169a", "avr5", "avr5", 0x800100},

    {"atmega169p", "avr5", "avr5", 0x800100},

    {"atmega169pa", "avr5", "avr5", 0x800100},

    {"atmega32", "avr5", "avr5", 0x800060},

    {"atmega32a", "avr5", "avr5", 0x800060},

    {"atmega323", "avr5", "avr5", 0x800060},

    {"atmega324a", "avr5", "avr5", 0x800100},

    {"atmega324p", "avr5", "avr5", 0x800100},

    {"atmega324pa", "avr5", "avr5", 0x800100},

    {"atmega325", "avr5", "avr5", 0x800100},

    {"atmega325a", "avr5", "avr5", 0x800100},

    {"atmega325p", "avr5", "avr5", 0x800100},

    {"atmega325pa", "avr5", "avr5", 0x800100},

    {"atmega3250", "avr5", "avr5", 0x800100},

    {"atmega3250a", "avr5", "avr5", 0x800100},

    {"atmega3250p", "avr5", "avr5", 0x800100},

    {"atmega3250pa", "avr5", "avr5", 0x800100},

    {"atmega328", "avr5", "avr5", 0x800100},

    {"atmega328p", "avr5", "avr5", 0x800100},

    {"atmega329", "avr5", "avr5", 0x800100},

    {"atmega329a", "avr5", "avr5", 0x800100},

    {"atmega329p", "avr5", "avr5", 0x800100},

    {"atmega329pa", "avr5", "avr5", 0x800100},

    {"atmega3290", "avr5", "avr5", 0x800100},

    {"atmega3290a", "avr5", "avr5", 0x800100},

    {"atmega3290p", "avr5", "avr5", 0x800100},

    {"atmega3290pa", "avr5", "avr5", 0x800100},

    {"atmega406", "avr5", "avr5", 0x800100},

    {"atmega64", "avr5", "avr5", 0x800100},

    {"atmega64a", "avr5", "avr5", 0x800100},

    {"atmega640", "avr5", "avr5", 0x800200},

    {"atmega644", "avr5", "avr5", 0x800100},

    {"atmega644a", "avr5", "avr5", 0x800100},

    {"atmega644p", "avr5", "avr5", 0x800100},

    {"atmega644pa", "avr5", "avr5", 0x800100},

    {"atmega645", "avr5", "avr5", 0x800100},

    {"atmega645a", "avr5", "avr5", 0x800100},

    {"atmega645p", "avr5", "avr5", 0x800100},

    {"atmega649", "avr5", "avr5", 0x800100},

    {"atmega649a", "avr5", "avr5", 0x800100},

    {"atmega649p", "avr5", "avr5", 0x800100},

    {"atmega6450", "avr5", "avr5", 0x800100},

    {"atmega6450a", "avr5", "avr5", 0x800100},

    {"atmega6450p", "avr5", "avr5", 0x800100},

    {"atmega6490", "avr5", "avr5", 0x800100},

    {"atmega6490a", "avr5", "avr5", 0x800100},

    {"atmega6490p", "avr5", "avr5", 0x800100},

    {"atmega64rfr2", "avr5", "avr5", 0x800200},

    {"atmega644rfr2", "avr5", "avr5", 0x800200},

    {"atmega16hva", "avr5", "avr5", 0x800100},

    {"atmega16hva2", "avr5", "avr5", 0x800100},

    {"atmega16hvb", "avr5", "avr5", 0x800100},

    {"atmega16hvbrevb", "avr5", "avr5", 0x800100},

    {"atmega32hvb", "avr5", "avr5", 0x800100},

    {"atmega32hvbrevb", "avr5", "avr5", 0x800100},

    {"atmega64hve", "avr5", "avr5", 0x800100},

    {"at90can32", "avr5", "avr5", 0x800100},

    {"at90can64", "avr5", "avr5", 0x800100},

    {"at90pwm161", "avr5", "avr5", 0x800100},

    {"at90pwm216", "avr5", "avr5", 0x800100},

    {"at90pwm316", "avr5", "avr5", 0x800100},

    {"atmega32c1", "avr5", "avr5", 0x800100},

    {"atmega64c1", "avr5", "avr5", 0x800100},

    {"atmega16m1", "avr5", "avr5", 0x800100},

    {"atmega32m1", "avr5", "avr5", 0x800100},

    {"atmega64m1", "avr5", "avr5", 0x800100},

    {"atmega16u4", "avr5", "avr5", 0x800100},

    {"atmega32u4", "avr5", "avr5", 0x800100},

    {"atmega32u6", "avr5", "avr5", 0x800100},

    {"at90usb646", "avr5", "avr5", 0x800100},

    {"at90usb647", "avr5", "avr5", 0x800100},

    {"at90scr100", "avr5", "avr5", 0x800100},

    {"at94k", "avr5", "avr5", 0x800060},

    {"m3000", "avr5", "avr5", 0x800060},

    {"atmega128", "avr51", "avr51", 0x800100},

    {"atmega128a", "avr51", "avr51", 0x800100},

    {"atmega1280", "avr51", "avr51", 0x800200},

    {"atmega1281", "avr51", "avr51", 0x800200},

    {"atmega1284", "avr51", "avr51", 0x800100},

    {"atmega1284p", "avr51", "avr51", 0x800100},

    {"atmega128rfa1", "avr51", "avr51", 0x800200},

    {"atmega128rfr2", "avr51", "avr51", 0x800200},

    {"atmega1284rfr2", "avr51", "avr51", 0x800200},

    {"at90can128", "avr51", "avr51", 0x800200},

    {"at90usb1286", "avr51", "avr51", 0x800200},

    {"at90usb1287", "avr51", "avr51", 0x800200},

    {"atmega2560", "avr6", "avr6", 0x800200},

    {"atmega2561", "avr6", "avr6", 0x800200},

    {"atmega256rfr2", "avr6", "avr6", 0x800200},

    {"atmega2564rfr2", "avr6", "avr6", 0x800200},

    {"attiny4", "avrtiny", "avrtiny", 0x800040},

    {"attiny5", "avrtiny", "avrtiny", 0x800040},

    {"attiny9", "avrtiny", "avrtiny", 0x800040},

    {"attiny10", "avrtiny", "avrtiny", 0x800040},

    {"attiny20", "avrtiny", "avrtiny", 0x800040},

    {"attiny40", "avrtiny", "avrtiny", 0x800040},

    {"atxmega16a4", "avrxmega2", "avrxmega2", 0x802000},

    {"atxmega16a4u", "avrxmega2", "avrxmega2", 0x802000},

    {"atxmega16c4", "avrxmega2", "avrxmega2", 0x802000},

    {"atxmega16d4", "avrxmega2", "avrxmega2", 0x802000},

    {"atxmega32a4", "avrxmega2", "avrxmega2", 0x802000},

    {"atxmega32a4u", "avrxmega2", "avrxmega2", 0x802000},

    {"atxmega32c4", "avrxmega2", "avrxmega2", 0x802000},

    {"atxmega32d4", "avrxmega2", "avrxmega2", 0x802000},

    {"atxmega32e5", "avrxmega2", "avrxmega2", 0x802000},

    {"atxmega16e5", "avrxmega2", "avrxmega2", 0x802000},

    {"atxmega8e5", "avrxmega2", "avrxmega2", 0x802000},

    {"atxmega64a3u", "avrxmega4", "avrxmega4", 0x802000},

    {"atxmega64a4u", "avrxmega4", "avrxmega4", 0x802000},

    {"atxmega64b1", "avrxmega4", "avrxmega4", 0x802000},

    {"atxmega64b3", "avrxmega4", "avrxmega4", 0x802000},

    {"atxmega64c3", "avrxmega4", "avrxmega4", 0x802000},

    {"atxmega64d3", "avrxmega4", "avrxmega4", 0x802000},

    {"atxmega64d4", "avrxmega4", "avrxmega4", 0x802000},

    {"atxmega64a1", "avrxmega5", "avrxmega5", 0x802000},

    {"atxmega64a1u", "avrxmega5", "avrxmega5", 0x802000},

    {"atxmega128a3", "avrxmega6", "avrxmega6", 0x802000},

    {"atxmega128a3u", "avrxmega6", "avrxmega6", 0x802000},

    {"atxmega128b1", "avrxmega6", "avrxmega6", 0x802000},

    {"atxmega128b3", "avrxmega6", "avrxmega6", 0x802000},

    {"atxmega128c3", "avrxmega6", "avrxmega6", 0x802000},

    {"atxmega128d3", "avrxmega6", "avrxmega6", 0x802000},

    {"atxmega128d4", "avrxmega6", "avrxmega6", 0x802000},

    {"atxmega192a3", "avrxmega6", "avrxmega6", 0x802000},

    {"atxmega192a3u", "avrxmega6", "avrxmega6", 0x802000},

    {"atxmega192c3", "avrxmega6", "avrxmega6", 0x802000},

    {"atxmega192d3", "avrxmega6", "avrxmega6", 0x802000},

    {"atxmega256a3", "avrxmega6", "avrxmega6", 0x802000},

    {"atxmega256a3u", "avrxmega6", "avrxmega6", 0x802000},

    {"atxmega256a3b", "avrxmega6", "avrxmega6", 0x802000},

    {"atxmega256a3bu", "avrxmega6", "avrxmega6", 0x802000},

    {"atxmega256c3", "avrxmega6", "avrxmega6", 0x802000},

    {"atxmega256d3", "avrxmega6", "avrxmega6", 0x802000},

    {"atxmega384c3", "avrxmega6", "avrxmega6", 0x802000},

    {"atxmega384d3", "avrxmega6", "avrxmega6", 0x802000},

    {"atxmega128a1", "avrxmega7", "avrxmega7", 0x802000},

    {"atxmega128a1u", "avrxmega7", "avrxmega7", 0x802000},

    {"atxmega128a4u", "avrxmega7", "avrxmega7", 0x802000},

};

std::string GetMCUSubPath(StringRef MCUName) {

  for (const auto &MCU : MCUInfo)

    if (MCU.Name == MCUName)

      return std::string(MCU.SubPath);

  return "";

}

llvm::Optional<StringRef> GetMCUFamilyName(StringRef MCUName) {

  for (const auto &MCU : MCUInfo)

    if (MCU.Name == MCUName)

      return Optional<StringRef>(MCU.Family);

  return Optional<StringRef>();

}

llvm::Optional<unsigned> GetMCUSectionAddressData(StringRef MCUName) {

  for (const auto &MCU : MCUInfo)

    if (MCU.Name == MCUName && 
MCU.DataAddr > 038
)

      return Optional<unsigned>(MCU.DataAddr);

  return Optional<unsigned>();

}

const StringRef PossibleAVRLibcLocations[] = {

    "/avr",

    "/usr/avr",

    "/usr/lib/avr",

};

} // end anonymous namespace

/// AVR Toolchain

AVRToolChain::AVRToolChain(const Driver &D, const llvm::Triple &Triple,

                           const ArgList &Args)

    : Generic_ELF(D, Triple, Args), LinkStdlib(false) {

  GCCInstallation.init(Triple, Args);

  // Only add default libraries if the user hasn't explicitly opted out.

  if (!Args.hasArg(options::OPT_nostdlib) &&

      
!Args.hasArg(options::OPT_nodefaultlibs)47
 &&

      
!Args.hasArg(options::OPT_c /* does not apply when not linking */)46
) {

    std::string CPU = getCPUName(D, Args, Triple);

    if (CPU.empty()) {

      // We cannot link any standard libraries without an MCU specified.

      D.Diag(diag::warn_drv_avr_mcu_not_specified);

    } else {

      Optional<StringRef> FamilyName = GetMCUFamilyName(CPU);

      Optional<std::string> AVRLibcRoot = findAVRLibcInstallation();

      if (!FamilyName.hasValue()) {

        // We do not have an entry for this CPU in the family

        // mapping table yet.

        D.Diag(diag::warn_drv_avr_family_linking_stdlibs_not_implemented)

            << CPU;

      } else if (!GCCInstallation.isValid()) {

        // No avr-gcc found and so no runtime linked.

        D.Diag(diag::warn_drv_avr_gcc_not_found);

      } else 
if (15
!AVRLibcRoot.hasValue()15
) {

        // No avr-libc found and so no runtime linked.

        D.Diag(diag::warn_drv_avr_libc_not_found);

      } else { // We have enough information to link stdlibs

        std::string GCCRoot(GCCInstallation.getInstallPath());

        std::string GCCParentPath(GCCInstallation.getParentLibPath());

        std::string LibcRoot = AVRLibcRoot.getValue();

        std::string SubPath = GetMCUSubPath(CPU);

        getProgramPaths().push_back(GCCParentPath + "/../bin");

        getFilePaths().push_back(LibcRoot + std::string("/lib/") + SubPath);

        getFilePaths().push_back(GCCRoot + std::string("/") + SubPath);

        LinkStdlib = true;

      }

    }

    if (!LinkStdlib)

      D.Diag(diag::warn_drv_avr_stdlib_not_linked);

  }

}

void AVRToolChain::AddClangSystemIncludeArgs(const ArgList &DriverArgs,

                                             ArgStringList &CC1Args) const {

  if (DriverArgs.hasArg(options::OPT_nostdinc) ||

      
DriverArgs.hasArg(options::OPT_nostdlibinc)47
)

    return;

  // Omit if there is no avr-libc installed.

  Optional<std::string> AVRLibcRoot = findAVRLibcInstallation();

  if (!AVRLibcRoot.hasValue())

    return;

  // Add 'avr-libc/include' to clang system include paths if applicable.

  std::string AVRInc = AVRLibcRoot.getValue() + "/include";

  if (llvm::sys::fs::is_directory(AVRInc))

    addSystemInclude(DriverArgs, CC1Args, AVRInc);

}

void AVRToolChain::addClangTargetOptions(

    const llvm::opt::ArgList &DriverArgs, llvm::opt::ArgStringList &CC1Args,

    Action::OffloadKind DeviceOffloadKind) const {

  // By default, use `.ctors` (not `.init_array`), as required by libgcc, which

  // runs constructors/destructors on AVR.

  if (!DriverArgs.hasFlag(options::OPT_fuse_init_array,

                          options::OPT_fno_use_init_array, false))

    CC1Args.push_back("-fno-use-init-array");

}

Tool *AVRToolChain::buildLinker() const {

  return new tools::AVR::Linker(getTriple(), *this, LinkStdlib);

}

void AVR::Linker::ConstructJob(Compilation &C, const JobAction &JA,

                               const InputInfo &Output,

                               const InputInfoList &Inputs, const ArgList &Args,

                               const char *LinkingOutput) const {

  const Driver &D = getToolChain().getDriver();

  // Compute information about the target AVR.

  std::string CPU = getCPUName(D, Args, getToolChain().getTriple());

  llvm::Optional<StringRef> FamilyName = GetMCUFamilyName(CPU);

  llvm::Optional<unsigned> SectionAddressData = GetMCUSectionAddressData(CPU);

  std::string Linker = getToolChain().GetProgramPath(getShortName());

  ArgStringList CmdArgs;

  AddLinkerInputs(getToolChain(), Inputs, Args, CmdArgs, JA);

  CmdArgs.push_back("-o");

  CmdArgs.push_back(Output.getFilename());

  // Enable garbage collection of unused sections.

  CmdArgs.push_back("--gc-sections");

  // Add library search paths before we specify libraries.

  Args.AddAllArgs(CmdArgs, options::OPT_L);

  getToolChain().AddFilePathLibArgs(Args, CmdArgs);

  if (SectionAddressData.hasValue()) {

    std::string DataSectionArg = std::string("-Tdata=0x") +

                                 llvm::utohexstr(SectionAddressData.getValue());

    CmdArgs.push_back(Args.MakeArgString(DataSectionArg));

  } else {

    // We do not have an entry for this CPU in the address mapping table yet.

    D.Diag(diag::warn_drv_avr_linker_section_addresses_not_implemented) << CPU;

  }

  // If the family name is known, we can link with the device-specific libgcc.

  // Without it, libgcc will simply not be linked. This matches avr-gcc

  // behavior.

  if (LinkStdlib) {

    assert(!CPU.empty() && "CPU name must be known in order to link stdlibs");

    CmdArgs.push_back("--start-group");

    // Add the object file for the CRT.

    std::string CrtFileName = std::string("-l:crt") + CPU + std::string(".o");

    CmdArgs.push_back(Args.MakeArgString(CrtFileName));

    CmdArgs.push_back("-lgcc");

    CmdArgs.push_back("-lm");

    CmdArgs.push_back("-lc");

    // Add the link library specific to the MCU.

    CmdArgs.push_back(Args.MakeArgString(std::string("-l") + CPU));

    CmdArgs.push_back("--end-group");

    // Specify the family name as the emulation mode to use.

    // This is almost always required because otherwise avr-ld

    // will assume 'avr2' and warn about the program being larger

    // than the bare minimum supports.

    CmdArgs.push_back(Args.MakeArgString(std::string("-m") + *FamilyName));

  }

  C.addCommand(std::make_unique<Command>(

      JA, *this, ResponseFileSupport::AtFileCurCP(), Args.MakeArgString(Linker),

      CmdArgs, Inputs, Output));

}

llvm::Optional<std::string> AVRToolChain::findAVRLibcInstallation() const {

  // Search avr-libc installation according to avr-gcc installation.

  std::string GCCParent(GCCInstallation.getParentLibPath());

  std::string Path(GCCParent + "/avr");

  if (llvm::sys::fs::is_directory(Path))

    return Path;

  Path = GCCParent + "/../avr";

  if (llvm::sys::fs::is_directory(Path))

    return Path;

  // Search avr-libc installation from possible locations, and return the first

  // one that exists, if there is no avr-gcc installed.

  
for (StringRef PossiblePath : PossibleAVRLibcLocations)52
 {

    std::string Path = getDriver().SysRoot + PossiblePath.str();

    if (llvm::sys::fs::is_directory(Path))

      return Path;

  }

  return llvm::None;

}