[ARC] Add SystemV ABI

[clayborg]

Looks good.

[tatyana-krasnukha]

Added a list of registers with correct dwarf numbers

[clayborg]

source/Plugins/ABI/SysV-arc/ABISysV_arc.cpp

43 ↗

(On Diff #182323)

add "namespace {" around all of this

52 ↗

(On Diff #182323)

Don't end this namespace here? It starts up again on line 70. I would move the #define statements above the dwarf namespace

[tatyana-krasnukha]

Addressed the comment

[tatyana-krasnukha]

Updated according to D55718

[tatyana-krasnukha]

Updated file headers to reflect the new license;
Updated according to the last revision of D55718.

[tatyana-krasnukha]

Rebased on the current trunk.

Updated according to the last revision of D55718.

lldb/source/API/SystemInitializerFull.cpp

 #include "lldb/Initialization/SystemInitializerCommon.h"
 #include "lldb/Interpreter/CommandInterpreter.h"
 #include "lldb/Symbol/ClangASTContext.h"
 #include "lldb/Utility/Timer.h"
 
 #include "Plugins/ABI/MacOSX-arm/ABIMacOSX_arm.h"
 #include "Plugins/ABI/MacOSX-arm64/ABIMacOSX_arm64.h"
 #include "Plugins/ABI/MacOSX-i386/ABIMacOSX_i386.h"
+#include "Plugins/ABI/SysV-arc/ABISysV_arc.h"
 #include "Plugins/ABI/SysV-arm/ABISysV_arm.h"
 #include "Plugins/ABI/SysV-arm64/ABISysV_arm64.h"
 #include "Plugins/ABI/SysV-hexagon/ABISysV_hexagon.h"
 #include "Plugins/ABI/SysV-i386/ABISysV_i386.h"
 #include "Plugins/ABI/SysV-mips/ABISysV_mips.h"
 #include "Plugins/ABI/SysV-mips64/ABISysV_mips64.h"
 #include "Plugins/ABI/SysV-ppc/ABISysV_ppc.h"
 #include "Plugins/ABI/SysV-ppc64/ABISysV_ppc64.h"

 SystemInitializerFull::~SystemInitializerFull() {}
 
 #define LLDB_PROCESS_AArch64(op)                                               \
   ABIMacOSX_arm64::op();                                                       \
   ABISysV_arm64::op();
 #define LLDB_PROCESS_ARM(op)                                                   \
   ABIMacOSX_arm::op();                                                         \
   ABISysV_arm::op();
+#define LLDB_PROCESS_ARC(op)                                                   \
+  ABISysV_arc::op();
 #define LLDB_PROCESS_Hexagon(op) ABISysV_hexagon::op();
 #define LLDB_PROCESS_Mips(op)                                                  \
   ABISysV_mips::op();                                                          \
   ABISysV_mips64::op();
 #define LLDB_PROCESS_PowerPC(op)                                               \
   ABISysV_ppc::op();                                                          \
   ABISysV_ppc64::op();
 #define LLDB_PROCESS_SystemZ(op) ABISysV_s390x::op();
 #define LLDB_PROCESS_X86(op)                                                   \
   ABIMacOSX_i386::op();                                                        \
   ABISysV_i386::op();                                                          \
   ABISysV_x86_64::op();                                                        \
   ABIWindows_x86_64::op();
 
 #define LLDB_PROCESS_AMDGPU(op)
-#define LLDB_PROCESS_ARC(op)
 #define LLDB_PROCESS_AVR(op)
 #define LLDB_PROCESS_BPF(op)
 #define LLDB_PROCESS_Lanai(op)
 #define LLDB_PROCESS_MSP430(op)
 #define LLDB_PROCESS_NVPTX(op)
 #define LLDB_PROCESS_RISCV(op)
 #define LLDB_PROCESS_Sparc(op)
 #define LLDB_PROCESS_WebAssembly(op)

lldb/source/Plugins/ABI/CMakeLists.txt

 if ("AArch64" IN_LIST LLVM_TARGETS_TO_BUILD)
   add_subdirectory(MacOSX-arm64)
   add_subdirectory(SysV-arm64)
 endif()
 if ("ARM" IN_LIST LLVM_TARGETS_TO_BUILD)
   add_subdirectory(MacOSX-arm)
   add_subdirectory(SysV-arm)
 endif()
+if ("ARC" IN_LIST LLVM_TARGETS_TO_BUILD)
+  add_subdirectory(SysV-arc)
+endif()
 if ("Hexagon" IN_LIST LLVM_TARGETS_TO_BUILD)
   add_subdirectory(SysV-hexagon)
 endif()
 if ("Mips" IN_LIST LLVM_TARGETS_TO_BUILD)
   add_subdirectory(SysV-mips)
   add_subdirectory(SysV-mips64)
 endif()
 if ("PowerPC" IN_LIST LLVM_TARGETS_TO_BUILD)

lldb/source/Plugins/ABI/SysV-arc/ABISysV_arc.h

+//===-- ArchitectureArc.h ---------------------------------------*- 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef liblldb_ABISysV_arc_h_
+#define liblldb_ABISysV_arc_h_
+
+// Other libraries and framework includes
+#include <llvm/ADT/Optional.h>
+
+// Project includes
+#include "lldb/Target/ABI.h"
+#include "lldb/lldb-private.h"
+
+class ABISysV_arc : public lldb_private::ABI {
+public:
+  ~ABISysV_arc() override = default;
+
+  size_t GetRedZoneSize() const override;
+
+  bool PrepareTrivialCall(lldb_private::Thread &thread, lldb::addr_t sp,
+                          lldb::addr_t functionAddress,
+                          lldb::addr_t returnAddress,
+                          llvm::ArrayRef<lldb::addr_t> args) const override;
+
+  // Special thread plan for GDB style non-jit function calls.
+  bool
+  PrepareTrivialCall(lldb_private::Thread &thread, lldb::addr_t sp,
+                     lldb::addr_t functionAddress, lldb::addr_t returnAddress,
+                     llvm::Type &prototype,
+                     llvm::ArrayRef<ABI::CallArgument> args) const override;
+
+  bool GetArgumentValues(lldb_private::Thread &thread,
+                         lldb_private::ValueList &values) const override;
+
+  lldb_private::Status
+  SetReturnValueObject(lldb::StackFrameSP &frame_sp,
+                       lldb::ValueObjectSP &new_value) override;
+
+  lldb::ValueObjectSP
+  GetReturnValueObjectImpl(lldb_private::Thread &thread,
+                           lldb_private::CompilerType &type) const override;
+
+  // Specialized to work with llvm IR types.
+  lldb::ValueObjectSP GetReturnValueObjectImpl(lldb_private::Thread &thread,
+                                               llvm::Type &type) const override;
+
+  bool
+  CreateFunctionEntryUnwindPlan(lldb_private::UnwindPlan &unwind_plan) override;
+
+  bool CreateDefaultUnwindPlan(lldb_private::UnwindPlan &unwind_plan) override;
+
+  bool RegisterIsVolatile(const lldb_private::RegisterInfo *reg_info) override;
+
+  bool CallFrameAddressIsValid(lldb::addr_t cfa) override {
+    // Stack call frame address must be 4 byte aligned.
+    return (cfa & 0x3ull) == 0;
+  }
+
+  bool CodeAddressIsValid(lldb::addr_t pc) override {
+    // Code addresse must be 2 byte aligned.
+    return (pc & 1ull) == 0;
+  }
+
+  const lldb_private::RegisterInfo *
+  GetRegisterInfoArray(uint32_t &count) override;
+
+  //------------------------------------------------------------------
+  // Static Functions
+  //------------------------------------------------------------------
+
+  static void Initialize();
+
+  static void Terminate();
+
+  static lldb::ABISP CreateInstance(lldb::ProcessSP process_sp,
+                                    const lldb_private::ArchSpec &arch);
+
+  static lldb_private::ConstString GetPluginNameStatic();
+
+  //------------------------------------------------------------------
+  // PluginInterface protocol
+  //------------------------------------------------------------------
+
+  lldb_private::ConstString GetPluginName() override;
+
+  uint32_t GetPluginVersion() override;
+
+private:
+  lldb::ValueObjectSP
+  GetReturnValueObjectSimple(lldb_private::Thread &thread,
+                             lldb_private::CompilerType &ast_type) const;
+
+  bool IsRegisterFileReduced(lldb_private::RegisterContext &reg_ctx) const;
+
+  using lldb_private::ABI::ABI; // Call CreateInstance instead.
+
+  using RegisterFileFlag = llvm::Optional<bool>;
+  mutable RegisterFileFlag m_is_reg_file_reduced;
+};
+
+#endif // liblldb_ABISysV_arc_h_

lldb/source/Plugins/ABI/SysV-arc/ABISysV_arc.cpp

+//===-- ABISysV_arc.cpp ---------------------------------------*- 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 "ABISysV_arc.h"
+
+// C Includes
+// C++ Includes
+#include <array>
+#include <limits>
+#include <type_traits>
+
+// Other libraries and framework includes
+#include "llvm/ADT/Triple.h"
+#include "llvm/IR/DerivedTypes.h"
+#include "llvm/Support/MathExtras.h"
+
+#include "lldb/Core/Module.h"
+#include "lldb/Core/PluginManager.h"
+#include "lldb/Core/Value.h"
+#include "lldb/Core/ValueObjectConstResult.h"
+#include "lldb/Core/ValueObjectMemory.h"
+#include "lldb/Core/ValueObjectRegister.h"
+#include "lldb/Symbol/UnwindPlan.h"
+#include "lldb/Target/Process.h"
+#include "lldb/Target/RegisterContext.h"
+#include "lldb/Target/StackFrame.h"
+#include "lldb/Target/Target.h"
+#include "lldb/Target/Thread.h"
+#include "lldb/Utility/ConstString.h"
+#include "lldb/Utility/RegisterValue.h"
+#include "lldb/Utility/Status.h"
+
+#define DEFINE_REG_NAME(reg_num)      ConstString(#reg_num).GetCString()
+#define DEFINE_REG_NAME_STR(reg_name) ConstString(reg_name).GetCString()
+
+// The ABI is not a source of such information as size, offset, encoding, etc.
+// of a register. Just provides correct dwarf and eh_frame numbers.
+
+#define DEFINE_GENERIC_REGISTER_STUB(dwarf_num, str_name, generic_num)        \
+  {                                                                           \
+    DEFINE_REG_NAME(dwarf_num), DEFINE_REG_NAME_STR(str_name),                \
+    0, 0, eEncodingInvalid, eFormatDefault,                                   \
+    { dwarf_num, dwarf_num, generic_num, LLDB_INVALID_REGNUM, dwarf_num },    \
+    nullptr, nullptr, nullptr, 0                                              \
+  }
+
+#define DEFINE_REGISTER_STUB(dwarf_num, str_name) \
+  DEFINE_GENERIC_REGISTER_STUB(dwarf_num, str_name, LLDB_INVALID_REGNUM)
+
+using namespace lldb;
+using namespace lldb_private;
+
+namespace {
+namespace dwarf {
+enum regnums {
+  r0, r1, r2, r3, r4, r5, r6, r7, r8, r9, r10, r11, r12, r13, r14, r15, r16,
+  r17, r18, r19, r20, r21, r22, r23, r24, r25, r26,
+  r27, fp = r27, r28, sp = r28, r29, r30, r31, blink = r31,
+  r32, r33, r34, r35, r36, r37, r38, r39, r40, r41, r42, r43, r44, r45, r46,
+  r47, r48, r49, r50, r51, r52, r53, r54, r55, r56, r57, r58, r59, r60,
+  /*reserved,*/ /*limm indicator,*/ r63 = 63, pc = 70, status32 = 74
+};
+
+static const std::array<RegisterInfo, 64> g_register_infos = { {
+    DEFINE_GENERIC_REGISTER_STUB(r0, nullptr, LLDB_REGNUM_GENERIC_ARG1),
+    DEFINE_GENERIC_REGISTER_STUB(r1, nullptr, LLDB_REGNUM_GENERIC_ARG2),
+    DEFINE_GENERIC_REGISTER_STUB(r2, nullptr, LLDB_REGNUM_GENERIC_ARG3),
+    DEFINE_GENERIC_REGISTER_STUB(r3, nullptr, LLDB_REGNUM_GENERIC_ARG4),
+    DEFINE_GENERIC_REGISTER_STUB(r4, nullptr, LLDB_REGNUM_GENERIC_ARG5),
+    DEFINE_GENERIC_REGISTER_STUB(r5, nullptr, LLDB_REGNUM_GENERIC_ARG6),
+    DEFINE_GENERIC_REGISTER_STUB(r6, nullptr, LLDB_REGNUM_GENERIC_ARG7),
+    DEFINE_GENERIC_REGISTER_STUB(r7, nullptr, LLDB_REGNUM_GENERIC_ARG8),
+    DEFINE_REGISTER_STUB(r8, nullptr),
+    DEFINE_REGISTER_STUB(r9, nullptr),
+    DEFINE_REGISTER_STUB(r10, nullptr),
+    DEFINE_REGISTER_STUB(r11, nullptr),
+    DEFINE_REGISTER_STUB(r12, nullptr),
+    DEFINE_REGISTER_STUB(r13, nullptr),
+    DEFINE_REGISTER_STUB(r14, nullptr),
+    DEFINE_REGISTER_STUB(r15, nullptr),
+    DEFINE_REGISTER_STUB(r16, nullptr),
+    DEFINE_REGISTER_STUB(r17, nullptr),
+    DEFINE_REGISTER_STUB(r18, nullptr),
+    DEFINE_REGISTER_STUB(r19, nullptr),
+    DEFINE_REGISTER_STUB(r20, nullptr),
+    DEFINE_REGISTER_STUB(r21, nullptr),
+    DEFINE_REGISTER_STUB(r22, nullptr),
+    DEFINE_REGISTER_STUB(r23, nullptr),
+    DEFINE_REGISTER_STUB(r24, nullptr),
+    DEFINE_REGISTER_STUB(r25, nullptr),
+    DEFINE_REGISTER_STUB(r26, "gp"),
+    DEFINE_GENERIC_REGISTER_STUB(r27, "fp", LLDB_REGNUM_GENERIC_FP),
+    DEFINE_GENERIC_REGISTER_STUB(r28, "sp", LLDB_REGNUM_GENERIC_SP),
+    DEFINE_REGISTER_STUB(r29, "ilink"),
+    DEFINE_REGISTER_STUB(r30, nullptr),
+    DEFINE_GENERIC_REGISTER_STUB(r31, "blink", LLDB_REGNUM_GENERIC_RA),
+    DEFINE_REGISTER_STUB(r32, nullptr),
+    DEFINE_REGISTER_STUB(r33, nullptr),
+    DEFINE_REGISTER_STUB(r34, nullptr),
+    DEFINE_REGISTER_STUB(r35, nullptr),
+    DEFINE_REGISTER_STUB(r36, nullptr),
+    DEFINE_REGISTER_STUB(r37, nullptr),
+    DEFINE_REGISTER_STUB(r38, nullptr),
+    DEFINE_REGISTER_STUB(r39, nullptr),
+    DEFINE_REGISTER_STUB(r40, nullptr),
+    DEFINE_REGISTER_STUB(r41, nullptr),
+    DEFINE_REGISTER_STUB(r42, nullptr),
+    DEFINE_REGISTER_STUB(r43, nullptr),
+    DEFINE_REGISTER_STUB(r44, nullptr),
+    DEFINE_REGISTER_STUB(r45, nullptr),
+    DEFINE_REGISTER_STUB(r46, nullptr),
+    DEFINE_REGISTER_STUB(r47, nullptr),
+    DEFINE_REGISTER_STUB(r48, nullptr),
+    DEFINE_REGISTER_STUB(r49, nullptr),
+    DEFINE_REGISTER_STUB(r50, nullptr),
+    DEFINE_REGISTER_STUB(r51, nullptr),
+    DEFINE_REGISTER_STUB(r52, nullptr),
+    DEFINE_REGISTER_STUB(r53, nullptr),
+    DEFINE_REGISTER_STUB(r54, nullptr),
+    DEFINE_REGISTER_STUB(r55, nullptr),
+    DEFINE_REGISTER_STUB(r56, nullptr),
+    DEFINE_REGISTER_STUB(r57, nullptr),
+    DEFINE_REGISTER_STUB(r58, "accl"),
+    DEFINE_REGISTER_STUB(r59, "acch"),
+    DEFINE_REGISTER_STUB(r60, "lp_count"),
+    DEFINE_REGISTER_STUB(r63, "pcl"),
+    DEFINE_GENERIC_REGISTER_STUB(pc, nullptr, LLDB_REGNUM_GENERIC_PC),
+    DEFINE_GENERIC_REGISTER_STUB(status32, nullptr, LLDB_REGNUM_GENERIC_FLAGS)} };
+} // namespace dwarf
+} // namespace
+
+const RegisterInfo *ABISysV_arc::GetRegisterInfoArray(uint32_t &count) {
+  count = dwarf::g_register_infos.size();
+  return dwarf::g_register_infos.data();
+}
+
+size_t ABISysV_arc::GetRedZoneSize() const { return 0; }
+
+bool ABISysV_arc::IsRegisterFileReduced(RegisterContext &reg_ctx) const {
+  if (!m_is_reg_file_reduced) {
+    const auto *const rf_build_reg = reg_ctx.GetRegisterInfoByName("rf_build");
+    
+    const auto reg_value = reg_ctx.ReadRegisterAsUnsigned(rf_build_reg,
+                                                          /*fail_value*/ 0);
+    // RF_BUILD "Number of Entries" bit.
+    const uint32_t rf_entries_bit = 1U << 9U;
+    m_is_reg_file_reduced = (reg_value | rf_entries_bit) != 0;
+  }
+
+  return m_is_reg_file_reduced.getValueOr(false);
+}
+
+//------------------------------------------------------------------
+// Static Functions
+//------------------------------------------------------------------
+
+ABISP ABISysV_arc::CreateInstance(ProcessSP process_sp, const ArchSpec &arch) {
+  return llvm::Triple::arc == arch.GetTriple().getArch() ?
+      ABISP(new ABISysV_arc(std::move(process_sp), MakeMCRegisterInfo(arch))) :
+      ABISP();
+}
+
+namespace {
+const size_t word_size = 4U;
+const size_t reg_size = word_size;
+
+inline size_t AugmentArgSize(size_t size_in_bytes) {
+  return llvm::alignTo(size_in_bytes, word_size);
+}
+
+size_t TotalArgsSizeInWords(const llvm::ArrayRef<ABI::CallArgument> &args) {
+  size_t total_size = 0;
+  for (const auto &arg : args)
+    total_size +=
+        (ABI::CallArgument::TargetValue == arg.type ? AugmentArgSize(arg.size)
+                                                    : reg_size) /
+        word_size;
+
+  return total_size;
+}
+} // namespace
+
+bool ABISysV_arc::PrepareTrivialCall(Thread &thread, addr_t sp,
+                                     addr_t func_addr, addr_t return_addr,
+                                     llvm::ArrayRef<addr_t> args) const {
+  // We don't use the traditional trivial call specialized for jit.
+  return false;
+}
+
+bool ABISysV_arc::PrepareTrivialCall(Thread &thread, addr_t sp, addr_t pc,
+    addr_t ra, llvm::Type &prototype,
+    llvm::ArrayRef<ABI::CallArgument> args) const {
+  auto reg_ctx = thread.GetRegisterContext();
+  if (!reg_ctx)
+    return false;
+
+  uint32_t pc_reg = reg_ctx->ConvertRegisterKindToRegisterNumber(
+      eRegisterKindGeneric, LLDB_REGNUM_GENERIC_PC);
+  if (pc_reg == LLDB_INVALID_REGNUM)
+    return false;
+
+  uint32_t ra_reg = reg_ctx->ConvertRegisterKindToRegisterNumber(
+      eRegisterKindGeneric, LLDB_REGNUM_GENERIC_RA);
+  if (ra_reg == LLDB_INVALID_REGNUM)
+    return false;
+
+  uint32_t sp_reg = reg_ctx->ConvertRegisterKindToRegisterNumber(
+      eRegisterKindGeneric, LLDB_REGNUM_GENERIC_SP);
+  if (sp_reg == LLDB_INVALID_REGNUM)
+    return false;
+
+  Status error;
+  ProcessSP process = thread.GetProcess();
+  if (!process)
+    return false;
+
+  // Push host data onto target.
+  for (const auto &arg : args) {
+    // Skip over target values.
+    if (arg.type == ABI::CallArgument::TargetValue)
+      continue;
+
+    // Create space on the stack for this data 4-byte aligned.
+    sp -= AugmentArgSize(arg.size);
+
+    if (process->WriteMemory(sp, arg.data_up.get(), arg.size, error) < arg.size
+        || error.Fail())
+      return false;
+
+    // Update the argument with the target pointer.
+    *const_cast<addr_t *>(&arg.value) = sp;
+  }
+
+  // Make sure number of parameters matches prototype.
+  assert(!prototype.isFunctionVarArg());
+  assert(prototype.getFunctionNumParams() == args.size());
+  
+  const size_t regs_for_args_count = IsRegisterFileReduced(*reg_ctx) ? 4U : 8U;
+
+  // Number of arguments passed on stack.
+  auto args_size = TotalArgsSizeInWords(args);
+  auto on_stack =
+      args_size <= regs_for_args_count ? 0 : args_size - regs_for_args_count;
+  auto offset = on_stack * word_size;
+
+  uint8_t reg_value[reg_size];
+  size_t reg_index = LLDB_REGNUM_GENERIC_ARG1;
+
+  for (const auto &arg : args) {
+    auto value = reinterpret_cast<const uint8_t *>(&arg.value);
+    auto size =
+        ABI::CallArgument::TargetValue == arg.type ? arg.size : reg_size;
+
+    // Pass arguments via registers.
+    while (size > 0 && reg_index < regs_for_args_count) {
+      size_t byte_index = 0;
+      auto end = size < reg_size ? size : reg_size;
+
+      while (byte_index < end) {
+        reg_value[byte_index++] = *(value++);
+        --size;
+      }
+
+      while (byte_index < reg_size) {
+        reg_value[byte_index++] = 0;
+      }
+
+      RegisterValue reg_val_obj(reg_value, reg_size, eByteOrderLittle);
+      if (!reg_ctx->WriteRegister(
+            reg_ctx->GetRegisterInfo(eRegisterKindGeneric, reg_index),
+            reg_val_obj))
+        return false;
+
+      // NOTE: It's unsafe to iterate through LLDB_REGNUM_GENERICs.
+      ++reg_index;
+    }
+
+    if (reg_index < regs_for_args_count || size == 0)
+      continue;
+
+    // Remaining arguments are passed on the stack.
+    if (process->WriteMemory(sp - offset, value, size, error) < size ||
+        !error.Success())
+      return false;
+
+    offset -= AugmentArgSize(size);
+  }
+
+  // Set stack pointer immediately below arguments.
+  sp -= on_stack * word_size;
+
+  // Update registers with current function call state.
+  reg_ctx->WriteRegisterFromUnsigned(pc_reg, pc);
+  reg_ctx->WriteRegisterFromUnsigned(ra_reg, ra);
+  reg_ctx->WriteRegisterFromUnsigned(sp_reg, sp);
+
+  return true;
+}
+
+bool ABISysV_arc::GetArgumentValues(Thread &thread, ValueList &values) const {
+  return false;
+}
+
+Status ABISysV_arc::SetReturnValueObject(StackFrameSP &frame_sp,
+                                         ValueObjectSP &new_value_sp) {
+  Status result;
+  if (!new_value_sp) {
+    result.SetErrorString("Empty value object for return value.");
+    return result;
+  }
+
+  CompilerType compiler_type = new_value_sp->GetCompilerType();
+  if (!compiler_type) {
+    result.SetErrorString("Null clang type for return value.");
+    return result;
+  }
+
+  auto &reg_ctx = *frame_sp->GetThread()->GetRegisterContext();
+
+  bool is_signed = false;
+  if (!compiler_type.IsIntegerOrEnumerationType(is_signed) &&
+      !compiler_type.IsPointerType()) {
+    result.SetErrorString("We don't support returning other types at present");
+    return result;
+  }
+
+  DataExtractor data;
+  size_t num_bytes = new_value_sp->GetData(data, result);
+
+  if (result.Fail()) {
+    result.SetErrorStringWithFormat(
+        "Couldn't convert return value to raw data: %s", result.AsCString());
+    return result;
+  }
+
+  if (num_bytes <= 2 * reg_size) {
+    offset_t offset = 0;
+    uint64_t raw_value = data.GetMaxU64(&offset, num_bytes);
+
+    auto reg_info =
+        reg_ctx.GetRegisterInfo(eRegisterKindGeneric, LLDB_REGNUM_GENERIC_ARG1);
+    if (!reg_ctx.WriteRegisterFromUnsigned(reg_info, raw_value)) {
+      result.SetErrorStringWithFormat("Couldn't write value to register %s",
+                                      reg_info->name);
+      return result;
+    }
+
+    if (num_bytes <= reg_size)
+      return result; // Successfully written.
+
+    raw_value >>= 32;
+    reg_info =
+        reg_ctx.GetRegisterInfo(eRegisterKindGeneric, LLDB_REGNUM_GENERIC_ARG2);
+    if (!reg_ctx.WriteRegisterFromUnsigned(reg_info, raw_value)) {
+      result.SetErrorStringWithFormat("Couldn't write value to register %s",
+                                      reg_info->name);
+    }
+
+    return result;
+  }
+
+  result.SetErrorString(
+      "We don't support returning large integer values at present.");
+  return result;
+}
+
+namespace {
+template <typename T>
+void SetInteger(Scalar &scalar, uint64_t raw_value, bool is_signed) {
+  raw_value &= std::numeric_limits<T>::max();
+  if (is_signed)
+    scalar = static_cast<typename std::make_signed<T>::type>(raw_value);
+  else
+    scalar = static_cast<T>(raw_value);
+}
+
+bool SetSizedInteger(Scalar &scalar, uint64_t raw_value, uint8_t size_in_bytes,
+                     bool is_signed) {
+  switch (size_in_bytes) {
+  default:
+    return false;
+
+  case sizeof(uint64_t):
+    SetInteger<uint64_t>(scalar, raw_value, is_signed);
+    break;
+
+  case sizeof(uint32_t):
+    SetInteger<uint32_t>(scalar, raw_value, is_signed);
+    break;
+
+  case sizeof(uint16_t):
+    SetInteger<uint16_t>(scalar, raw_value, is_signed);
+    break;
+
+  case sizeof(uint8_t):
+    SetInteger<uint8_t>(scalar, raw_value, is_signed);
+    break;
+  }
+
+  return true;
+}
+
+bool SetSizedFloat(Scalar &scalar, uint64_t raw_value, uint8_t size_in_bytes) {
+  switch (size_in_bytes) {
+  default:
+    return false;
+
+  case sizeof(uint64_t):
+    scalar = *reinterpret_cast<double *>(&raw_value);
+    break;
+
+  case sizeof(uint32_t):
+    scalar = *reinterpret_cast<float *>(&raw_value);
+    break;
+  }
+
+  return true;
+}
+
+uint64_t ReadRawValue(const RegisterContextSP &reg_ctx, uint8_t size_in_bytes) {
+  auto reg_info_r0 =
+      reg_ctx->GetRegisterInfo(eRegisterKindGeneric, LLDB_REGNUM_GENERIC_ARG1);
+
+  // Extract the register context so we can read arguments from registers.
+  uint64_t raw_value =
+      reg_ctx->ReadRegisterAsUnsigned(reg_info_r0, 0) & UINT32_MAX;
+
+  if (sizeof(uint64_t) == size_in_bytes)
+    raw_value |= (reg_ctx->ReadRegisterAsUnsigned(
+                      reg_ctx->GetRegisterInfo(eRegisterKindGeneric,
+                                               LLDB_REGNUM_GENERIC_ARG2), 0) &
+                  UINT64_MAX) << 32U;
+
+  return raw_value;
+}
+} // namespace
+
+ValueObjectSP
+ABISysV_arc::GetReturnValueObjectSimple(Thread &thread,
+                                        CompilerType &compiler_type) const {
+  if (!compiler_type)
+    return ValueObjectSP();
+
+  auto reg_ctx = thread.GetRegisterContext();
+  if (!reg_ctx)
+    return ValueObjectSP();
+
+  Value value;
+  value.SetCompilerType(compiler_type);
+
+  const uint32_t type_flags = compiler_type.GetTypeInfo();
+  // Integer return type.
+  if (type_flags & eTypeIsInteger) {
+    const size_t byte_size = compiler_type.GetByteSize(nullptr).getValueOr(0);
+    auto raw_value = ReadRawValue(reg_ctx, byte_size);
+
+    const bool is_signed = (type_flags & eTypeIsSigned) != 0;
+    if (!SetSizedInteger(value.GetScalar(), raw_value, byte_size, is_signed))
+      return ValueObjectSP();
+
+    value.SetValueType(Value::eValueTypeScalar);
+  }
+  // Pointer return type.
+  else if (type_flags & eTypeIsPointer) {
+    auto reg_info_r0 = reg_ctx->GetRegisterInfo(eRegisterKindGeneric,
+                                                LLDB_REGNUM_GENERIC_ARG1);
+    value.GetScalar() = reg_ctx->ReadRegisterAsUnsigned(reg_info_r0, 0);
+
+    value.SetValueType(Value::eValueTypeScalar);
+  }
+  // Floating point return type.
+  else if (type_flags & eTypeIsFloat) {
+    uint32_t float_count = 0;
+    bool is_complex = false;
+
+    if (compiler_type.IsFloatingPointType(float_count, is_complex) &&
+        1 == float_count && !is_complex) {
+      const size_t byte_size = compiler_type.GetByteSize(nullptr).getValueOr(0);
+      auto raw_value = ReadRawValue(reg_ctx, byte_size);
+
+      if (!SetSizedFloat(value.GetScalar(), raw_value, byte_size))
+        return ValueObjectSP();
+    }
+  }
+  // Unsupported return type.
+  else
+    return ValueObjectSP();
+
+  return ValueObjectConstResult::Create(thread.GetStackFrameAtIndex(0).get(),
+                                        value, ConstString(""));
+}
+
+ValueObjectSP ABISysV_arc::GetReturnValueObjectImpl(
+    Thread &thread, CompilerType &return_compiler_type) const {
+  ValueObjectSP return_valobj_sp;
+
+  if (!return_compiler_type)
+    return return_valobj_sp;
+
+  ExecutionContext exe_ctx(thread.shared_from_this());
+  return GetReturnValueObjectSimple(thread, return_compiler_type);
+}
+
+ValueObjectSP ABISysV_arc::GetReturnValueObjectImpl(Thread &thread,
+                                                    llvm::Type &retType) const {
+  auto reg_ctx = thread.GetRegisterContext();
+  if (!reg_ctx)
+    return ValueObjectSP();
+
+  Value value;
+  // Void return type.
+  if (retType.isVoidTy()) {
+    value.GetScalar() = 0;
+  }
+  // Integer return type.
+  else if (retType.isIntegerTy()) {
+    size_t byte_size = retType.getPrimitiveSizeInBits();
+    if (1 != byte_size) // For boolian type.
+      byte_size /= CHAR_BIT;
+
+    auto raw_value = ReadRawValue(reg_ctx, byte_size);
+
+    const bool is_signed = false; // IR Type doesn't provide this info.
+    if (!SetSizedInteger(value.GetScalar(), raw_value, byte_size, is_signed))
+      return ValueObjectSP();
+  }
+  // Pointer return type.
+  else if (retType.isPointerTy()) {
+    auto reg_info_r0 = reg_ctx->GetRegisterInfo(eRegisterKindGeneric,
+                                                LLDB_REGNUM_GENERIC_ARG1);
+    value.GetScalar() = reg_ctx->ReadRegisterAsUnsigned(reg_info_r0, 0);
+    value.SetValueType(Value::eValueTypeScalar);
+  }
+  // Floating point return type.
+  else if (retType.isFloatingPointTy()) {
+    const size_t byte_size = retType.getPrimitiveSizeInBits() / CHAR_BIT;
+    auto raw_value = ReadRawValue(reg_ctx, byte_size);
+
+    if (!SetSizedFloat(value.GetScalar(), raw_value, byte_size))
+      return ValueObjectSP();
+  }
+  // Unsupported return type.
+  else
+    return ValueObjectSP();
+
+  return ValueObjectConstResult::Create(thread.GetStackFrameAtIndex(0).get(),
+                                        value, ConstString(""));
+}
+
+bool ABISysV_arc::CreateFunctionEntryUnwindPlan(UnwindPlan &unwind_plan) {
+  unwind_plan.Clear();
+  unwind_plan.SetRegisterKind(eRegisterKindDWARF);
+
+  UnwindPlan::RowSP row(new UnwindPlan::Row);
+
+  // Our Call Frame Address is the stack pointer value.
+  row->GetCFAValue().SetIsRegisterPlusOffset(dwarf::sp, 0);
+
+  // The previous PC is in the BLINK.
+  row->SetRegisterLocationToRegister(dwarf::pc, dwarf::blink, true);
+  unwind_plan.AppendRow(row);
+
+  // All other registers are the same.
+  unwind_plan.SetSourceName("arc at-func-entry default");
+  unwind_plan.SetSourcedFromCompiler(eLazyBoolNo);
+
+  return true;
+}
+
+bool ABISysV_arc::CreateDefaultUnwindPlan(UnwindPlan &unwind_plan) {
+  return false;
+}
+
+bool ABISysV_arc::RegisterIsVolatile(const RegisterInfo *reg_info) {
+  if (nullptr == reg_info)
+    return false;
+
+  // Volatile registers are: r0..r12.
+  uint32_t regnum = reg_info->kinds[eRegisterKindDWARF];
+  if (regnum <= 12)
+    return true;
+
+  static const std::string ra_reg_name = "blink";
+  return ra_reg_name == reg_info->name;
+}
+
+void ABISysV_arc::Initialize() {
+  PluginManager::RegisterPlugin(GetPluginNameStatic(),
+                                "System V ABI for ARC targets", CreateInstance);
+}
+
+void ABISysV_arc::Terminate() {
+  PluginManager::UnregisterPlugin(CreateInstance);
+}
+
+ConstString ABISysV_arc::GetPluginNameStatic() {
+  static ConstString g_name("sysv-arc");
+  return g_name;
+}
+
+//------------------------------------------------------------------
+// PluginInterface protocol
+//------------------------------------------------------------------
+
+ConstString ABISysV_arc::GetPluginName() {
+  return GetPluginNameStatic();
+}
+
+uint32_t ABISysV_arc::GetPluginVersion() { return 1; }

lldb/source/Plugins/ABI/SysV-arc/CMakeLists.txt

+add_lldb_library(lldbPluginABISysV_arc PLUGIN
+  ABISysV_arc.cpp
+
+  LINK_LIBS
+    lldbCore
+    lldbSymbol
+    lldbTarget
+    lldbPluginProcessUtility
+  LINK_COMPONENTS
+    Support
+  )