xref: /freebsd/contrib/llvm-project/lldb/source/Plugins/ABI/SystemZ/ABISysV_s390x.cpp (revision 06c3fb27)

//===-- ABISysV_s390x.cpp -------------------------------------------------===//
//
// 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_s390x.h"

#include "llvm/ADT/STLExtras.h"
#include "llvm/TargetParser/Triple.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/DataExtractor.h"
#include "lldb/Utility/LLDBLog.h"
#include "lldb/Utility/Log.h"
#include "lldb/Utility/RegisterValue.h"
#include "lldb/Utility/Status.h"
#include <optional>

using namespace lldb;
using namespace lldb_private;

LLDB_PLUGIN_DEFINE_ADV(ABISysV_s390x, ABISystemZ)

enum dwarf_regnums {
  // General Purpose Registers
  dwarf_r0_s390x = 0,
  dwarf_r1_s390x,
  dwarf_r2_s390x,
  dwarf_r3_s390x,
  dwarf_r4_s390x,
  dwarf_r5_s390x,
  dwarf_r6_s390x,
  dwarf_r7_s390x,
  dwarf_r8_s390x,
  dwarf_r9_s390x,
  dwarf_r10_s390x,
  dwarf_r11_s390x,
  dwarf_r12_s390x,
  dwarf_r13_s390x,
  dwarf_r14_s390x,
  dwarf_r15_s390x,
  // Floating Point Registers / Vector Registers 0-15
  dwarf_f0_s390x = 16,
  dwarf_f2_s390x,
  dwarf_f4_s390x,
  dwarf_f6_s390x,
  dwarf_f1_s390x,
  dwarf_f3_s390x,
  dwarf_f5_s390x,
  dwarf_f7_s390x,
  dwarf_f8_s390x,
  dwarf_f10_s390x,
  dwarf_f12_s390x,
  dwarf_f14_s390x,
  dwarf_f9_s390x,
  dwarf_f11_s390x,
  dwarf_f13_s390x,
  dwarf_f15_s390x,
  // Access Registers
  dwarf_acr0_s390x = 48,
  dwarf_acr1_s390x,
  dwarf_acr2_s390x,
  dwarf_acr3_s390x,
  dwarf_acr4_s390x,
  dwarf_acr5_s390x,
  dwarf_acr6_s390x,
  dwarf_acr7_s390x,
  dwarf_acr8_s390x,
  dwarf_acr9_s390x,
  dwarf_acr10_s390x,
  dwarf_acr11_s390x,
  dwarf_acr12_s390x,
  dwarf_acr13_s390x,
  dwarf_acr14_s390x,
  dwarf_acr15_s390x,
  // Program Status Word
  dwarf_pswm_s390x = 64,
  dwarf_pswa_s390x,
  // Vector Registers 16-31
  dwarf_v16_s390x = 68,
  dwarf_v18_s390x,
  dwarf_v20_s390x,
  dwarf_v22_s390x,
  dwarf_v17_s390x,
  dwarf_v19_s390x,
  dwarf_v21_s390x,
  dwarf_v23_s390x,
  dwarf_v24_s390x,
  dwarf_v26_s390x,
  dwarf_v28_s390x,
  dwarf_v30_s390x,
  dwarf_v25_s390x,
  dwarf_v27_s390x,
  dwarf_v29_s390x,
  dwarf_v31_s390x,
};

// RegisterKind: EHFrame, DWARF, Generic, Process Plugin, LLDB

#define DEFINE_REG(name, size, alt, generic)                                   \
  {                                                                            \
    #name, alt, size, 0, eEncodingUint, eFormatHex,                            \
        {dwarf_##name##_s390x, dwarf_##name##_s390x, generic,                  \
         LLDB_INVALID_REGNUM, LLDB_INVALID_REGNUM },                           \
         nullptr, nullptr, nullptr,                                            \
  }

static const RegisterInfo g_register_infos[] = {
    DEFINE_REG(r0, 8, nullptr, LLDB_INVALID_REGNUM),
    DEFINE_REG(r1, 8, nullptr, LLDB_INVALID_REGNUM),
    DEFINE_REG(r2, 8, nullptr, LLDB_REGNUM_GENERIC_ARG1),
    DEFINE_REG(r3, 8, nullptr, LLDB_REGNUM_GENERIC_ARG2),
    DEFINE_REG(r4, 8, nullptr, LLDB_REGNUM_GENERIC_ARG3),
    DEFINE_REG(r5, 8, nullptr, LLDB_REGNUM_GENERIC_ARG4),
    DEFINE_REG(r6, 8, nullptr, LLDB_REGNUM_GENERIC_ARG5),
    DEFINE_REG(r7, 8, nullptr, LLDB_INVALID_REGNUM),
    DEFINE_REG(r8, 8, nullptr, LLDB_INVALID_REGNUM),
    DEFINE_REG(r9, 8, nullptr, LLDB_INVALID_REGNUM),
    DEFINE_REG(r10, 8, nullptr, LLDB_INVALID_REGNUM),
    DEFINE_REG(r11, 8, nullptr, LLDB_REGNUM_GENERIC_FP),
    DEFINE_REG(r12, 8, nullptr, LLDB_INVALID_REGNUM),
    DEFINE_REG(r13, 8, nullptr, LLDB_INVALID_REGNUM),
    DEFINE_REG(r14, 8, nullptr, LLDB_INVALID_REGNUM),
    DEFINE_REG(r15, 8, "sp", LLDB_REGNUM_GENERIC_SP),
    DEFINE_REG(acr0, 4, nullptr, LLDB_INVALID_REGNUM),
    DEFINE_REG(acr1, 4, nullptr, LLDB_INVALID_REGNUM),
    DEFINE_REG(acr2, 4, nullptr, LLDB_INVALID_REGNUM),
    DEFINE_REG(acr3, 4, nullptr, LLDB_INVALID_REGNUM),
    DEFINE_REG(acr4, 4, nullptr, LLDB_INVALID_REGNUM),
    DEFINE_REG(acr5, 4, nullptr, LLDB_INVALID_REGNUM),
    DEFINE_REG(acr6, 4, nullptr, LLDB_INVALID_REGNUM),
    DEFINE_REG(acr7, 4, nullptr, LLDB_INVALID_REGNUM),
    DEFINE_REG(acr8, 4, nullptr, LLDB_INVALID_REGNUM),
    DEFINE_REG(acr9, 4, nullptr, LLDB_INVALID_REGNUM),
    DEFINE_REG(acr10, 4, nullptr, LLDB_INVALID_REGNUM),
    DEFINE_REG(acr11, 4, nullptr, LLDB_INVALID_REGNUM),
    DEFINE_REG(acr12, 4, nullptr, LLDB_INVALID_REGNUM),
    DEFINE_REG(acr13, 4, nullptr, LLDB_INVALID_REGNUM),
    DEFINE_REG(acr14, 4, nullptr, LLDB_INVALID_REGNUM),
    DEFINE_REG(acr15, 4, nullptr, LLDB_INVALID_REGNUM),
    DEFINE_REG(pswm, 8, nullptr, LLDB_REGNUM_GENERIC_FLAGS),
    DEFINE_REG(pswa, 8, nullptr, LLDB_REGNUM_GENERIC_PC),
    DEFINE_REG(f0, 8, nullptr, LLDB_INVALID_REGNUM),
    DEFINE_REG(f1, 8, nullptr, LLDB_INVALID_REGNUM),
    DEFINE_REG(f2, 8, nullptr, LLDB_INVALID_REGNUM),
    DEFINE_REG(f3, 8, nullptr, LLDB_INVALID_REGNUM),
    DEFINE_REG(f4, 8, nullptr, LLDB_INVALID_REGNUM),
    DEFINE_REG(f5, 8, nullptr, LLDB_INVALID_REGNUM),
    DEFINE_REG(f6, 8, nullptr, LLDB_INVALID_REGNUM),
    DEFINE_REG(f7, 8, nullptr, LLDB_INVALID_REGNUM),
    DEFINE_REG(f8, 8, nullptr, LLDB_INVALID_REGNUM),
    DEFINE_REG(f9, 8, nullptr, LLDB_INVALID_REGNUM),
    DEFINE_REG(f10, 8, nullptr, LLDB_INVALID_REGNUM),
    DEFINE_REG(f11, 8, nullptr, LLDB_INVALID_REGNUM),
    DEFINE_REG(f12, 8, nullptr, LLDB_INVALID_REGNUM),
    DEFINE_REG(f13, 8, nullptr, LLDB_INVALID_REGNUM),
    DEFINE_REG(f14, 8, nullptr, LLDB_INVALID_REGNUM),
    DEFINE_REG(f15, 8, nullptr, LLDB_INVALID_REGNUM),
};

static const uint32_t k_num_register_infos = std::size(g_register_infos);

const lldb_private::RegisterInfo *
ABISysV_s390x::GetRegisterInfoArray(uint32_t &count) {
  count = k_num_register_infos;
  return g_register_infos;
}

size_t ABISysV_s390x::GetRedZoneSize() const { return 0; }

// Static Functions

ABISP
ABISysV_s390x::CreateInstance(lldb::ProcessSP process_sp, const ArchSpec &arch) {
  if (arch.GetTriple().getArch() == llvm::Triple::systemz) {
    return ABISP(new ABISysV_s390x(std::move(process_sp), MakeMCRegisterInfo(arch)));
  }
  return ABISP();
}

bool ABISysV_s390x::PrepareTrivialCall(Thread &thread, addr_t sp,
                                       addr_t func_addr, addr_t return_addr,
                                       llvm::ArrayRef<addr_t> args) const {
  Log *log = GetLog(LLDBLog::Expressions);

  if (log) {
    StreamString s;
    s.Printf("ABISysV_s390x::PrepareTrivialCall (tid = 0x%" PRIx64
             ", sp = 0x%" PRIx64 ", func_addr = 0x%" PRIx64
             ", return_addr = 0x%" PRIx64,
             thread.GetID(), (uint64_t)sp, (uint64_t)func_addr,
             (uint64_t)return_addr);

    for (size_t i = 0; i < args.size(); ++i)
      s.Printf(", arg%" PRIu64 " = 0x%" PRIx64, static_cast<uint64_t>(i + 1),
               args[i]);
    s.PutCString(")");
    log->PutString(s.GetString());
  }

  RegisterContext *reg_ctx = thread.GetRegisterContext().get();
  if (!reg_ctx)
    return false;

  const RegisterInfo *pc_reg_info =
      reg_ctx->GetRegisterInfo(eRegisterKindGeneric, LLDB_REGNUM_GENERIC_PC);
  const RegisterInfo *sp_reg_info =
      reg_ctx->GetRegisterInfo(eRegisterKindGeneric, LLDB_REGNUM_GENERIC_SP);
  const RegisterInfo *ra_reg_info = reg_ctx->GetRegisterInfoByName("r14", 0);
  ProcessSP process_sp(thread.GetProcess());

  // Allocate a new stack frame and space for stack arguments if necessary

  addr_t arg_pos = 0;
  if (args.size() > 5) {
    sp -= 8 * (args.size() - 5);
    arg_pos = sp;
  }

  sp -= 160;

  // Process arguments

  for (size_t i = 0; i < args.size(); ++i) {
    if (i < 5) {
      const RegisterInfo *reg_info = reg_ctx->GetRegisterInfo(
          eRegisterKindGeneric, LLDB_REGNUM_GENERIC_ARG1 + i);
      LLDB_LOGF(log, "About to write arg%" PRIu64 " (0x%" PRIx64 ") into %s",
                static_cast<uint64_t>(i + 1), args[i], reg_info->name);
      if (!reg_ctx->WriteRegisterFromUnsigned(reg_info, args[i]))
        return false;
    } else {
      Status error;
      LLDB_LOGF(log, "About to write arg%" PRIu64 " (0x%" PRIx64 ") onto stack",
                static_cast<uint64_t>(i + 1), args[i]);
      if (!process_sp->WritePointerToMemory(arg_pos, args[i], error))
        return false;
      arg_pos += 8;
    }
  }

  // %r14 is set to the return address

  LLDB_LOGF(log, "Writing RA: 0x%" PRIx64, (uint64_t)return_addr);

  if (!reg_ctx->WriteRegisterFromUnsigned(ra_reg_info, return_addr))
    return false;

  // %r15 is set to the actual stack value.

  LLDB_LOGF(log, "Writing SP: 0x%" PRIx64, (uint64_t)sp);

  if (!reg_ctx->WriteRegisterFromUnsigned(sp_reg_info, sp))
    return false;

  // %pc is set to the address of the called function.

  LLDB_LOGF(log, "Writing PC: 0x%" PRIx64, (uint64_t)func_addr);

  if (!reg_ctx->WriteRegisterFromUnsigned(pc_reg_info, func_addr))
    return false;

  return true;
}

static bool ReadIntegerArgument(Scalar &scalar, unsigned int bit_width,
                                bool is_signed, Thread &thread,
                                uint32_t *argument_register_ids,
                                unsigned int &current_argument_register,
                                addr_t &current_stack_argument) {
  if (bit_width > 64)
    return false; // Scalar can't hold large integer arguments

  if (current_argument_register < 5) {
    scalar = thread.GetRegisterContext()->ReadRegisterAsUnsigned(
        argument_register_ids[current_argument_register], 0);
    current_argument_register++;
    if (is_signed)
      scalar.SignExtend(bit_width);
  } else {
    uint32_t byte_size = (bit_width + (8 - 1)) / 8;
    Status error;
    if (thread.GetProcess()->ReadScalarIntegerFromMemory(
            current_stack_argument + 8 - byte_size, byte_size, is_signed,
            scalar, error)) {
      current_stack_argument += 8;
      return true;
    }
    return false;
  }
  return true;
}

bool ABISysV_s390x::GetArgumentValues(Thread &thread, ValueList &values) const {
  unsigned int num_values = values.GetSize();
  unsigned int value_index;

  // Extract the register context so we can read arguments from registers

  RegisterContext *reg_ctx = thread.GetRegisterContext().get();

  if (!reg_ctx)
    return false;

  // Get the pointer to the first stack argument so we have a place to start
  // when reading data

  addr_t sp = reg_ctx->GetSP(0);

  if (!sp)
    return false;

  addr_t current_stack_argument = sp + 160;

  uint32_t argument_register_ids[5];

  argument_register_ids[0] =
      reg_ctx->GetRegisterInfo(eRegisterKindGeneric, LLDB_REGNUM_GENERIC_ARG1)
          ->kinds[eRegisterKindLLDB];
  argument_register_ids[1] =
      reg_ctx->GetRegisterInfo(eRegisterKindGeneric, LLDB_REGNUM_GENERIC_ARG2)
          ->kinds[eRegisterKindLLDB];
  argument_register_ids[2] =
      reg_ctx->GetRegisterInfo(eRegisterKindGeneric, LLDB_REGNUM_GENERIC_ARG3)
          ->kinds[eRegisterKindLLDB];
  argument_register_ids[3] =
      reg_ctx->GetRegisterInfo(eRegisterKindGeneric, LLDB_REGNUM_GENERIC_ARG4)
          ->kinds[eRegisterKindLLDB];
  argument_register_ids[4] =
      reg_ctx->GetRegisterInfo(eRegisterKindGeneric, LLDB_REGNUM_GENERIC_ARG5)
          ->kinds[eRegisterKindLLDB];

  unsigned int current_argument_register = 0;

  for (value_index = 0; value_index < num_values; ++value_index) {
    Value *value = values.GetValueAtIndex(value_index);

    if (!value)
      return false;

    // We currently only support extracting values with Clang QualTypes. Do we
    // care about others?
    CompilerType compiler_type = value->GetCompilerType();
    std::optional<uint64_t> bit_size = compiler_type.GetBitSize(&thread);
    if (!bit_size)
      return false;
    bool is_signed;

    if (compiler_type.IsIntegerOrEnumerationType(is_signed)) {
      ReadIntegerArgument(value->GetScalar(), *bit_size, is_signed, thread,
                          argument_register_ids, current_argument_register,
                          current_stack_argument);
    } else if (compiler_type.IsPointerType()) {
      ReadIntegerArgument(value->GetScalar(), *bit_size, false, thread,
                          argument_register_ids, current_argument_register,
                          current_stack_argument);
    }
  }

  return true;
}

Status ABISysV_s390x::SetReturnValueObject(lldb::StackFrameSP &frame_sp,
                                           lldb::ValueObjectSP &new_value_sp) {
  Status error;
  if (!new_value_sp) {
    error.SetErrorString("Empty value object for return value.");
    return error;
  }

  CompilerType compiler_type = new_value_sp->GetCompilerType();
  if (!compiler_type) {
    error.SetErrorString("Null clang type for return value.");
    return error;
  }

  Thread *thread = frame_sp->GetThread().get();

  bool is_signed;
  uint32_t count;
  bool is_complex;

  RegisterContext *reg_ctx = thread->GetRegisterContext().get();

  bool set_it_simple = false;
  if (compiler_type.IsIntegerOrEnumerationType(is_signed) ||
      compiler_type.IsPointerType()) {
    const RegisterInfo *reg_info = reg_ctx->GetRegisterInfoByName("r2", 0);

    DataExtractor data;
    Status data_error;
    size_t num_bytes = new_value_sp->GetData(data, data_error);
    if (data_error.Fail()) {
      error.SetErrorStringWithFormat(
          "Couldn't convert return value to raw data: %s",
          data_error.AsCString());
      return error;
    }
    lldb::offset_t offset = 0;
    if (num_bytes <= 8) {
      uint64_t raw_value = data.GetMaxU64(&offset, num_bytes);

      if (reg_ctx->WriteRegisterFromUnsigned(reg_info, raw_value))
        set_it_simple = true;
    } else {
      error.SetErrorString("We don't support returning longer than 64 bit "
                           "integer values at present.");
    }
  } else if (compiler_type.IsFloatingPointType(count, is_complex)) {
    if (is_complex)
      error.SetErrorString(
          "We don't support returning complex values at present");
    else {
      std::optional<uint64_t> bit_width =
          compiler_type.GetBitSize(frame_sp.get());
      if (!bit_width) {
        error.SetErrorString("can't get type size");
        return error;
      }
      if (*bit_width <= 64) {
        const RegisterInfo *f0_info = reg_ctx->GetRegisterInfoByName("f0", 0);
        RegisterValue f0_value;
        DataExtractor data;
        Status data_error;
        size_t num_bytes = new_value_sp->GetData(data, data_error);
        if (data_error.Fail()) {
          error.SetErrorStringWithFormat(
              "Couldn't convert return value to raw data: %s",
              data_error.AsCString());
          return error;
        }

        unsigned char buffer[8];
        ByteOrder byte_order = data.GetByteOrder();

        data.CopyByteOrderedData(0, num_bytes, buffer, 8, byte_order);
        f0_value.SetBytes(buffer, 8, byte_order);
        reg_ctx->WriteRegister(f0_info, f0_value);
        set_it_simple = true;
      } else {
        // FIXME - don't know how to do long doubles yet.
        error.SetErrorString(
            "We don't support returning float values > 64 bits at present");
      }
    }
  }

  if (!set_it_simple) {
    // Okay we've got a structure or something that doesn't fit in a simple
    // register. We should figure out where it really goes, but we don't
    // support this yet.
    error.SetErrorString("We only support setting simple integer and float "
                         "return types at present.");
  }

  return error;
}

ValueObjectSP ABISysV_s390x::GetReturnValueObjectSimple(
    Thread &thread, CompilerType &return_compiler_type) const {
  ValueObjectSP return_valobj_sp;
  Value value;

  if (!return_compiler_type)
    return return_valobj_sp;

  // value.SetContext (Value::eContextTypeClangType, return_value_type);
  value.SetCompilerType(return_compiler_type);

  RegisterContext *reg_ctx = thread.GetRegisterContext().get();
  if (!reg_ctx)
    return return_valobj_sp;

  const uint32_t type_flags = return_compiler_type.GetTypeInfo();
  if (type_flags & eTypeIsScalar) {
    value.SetValueType(Value::ValueType::Scalar);

    bool success = false;
    if (type_flags & eTypeIsInteger) {
      // Extract the register context so we can read arguments from registers.
      std::optional<uint64_t> byte_size =
          return_compiler_type.GetByteSize(&thread);
      if (!byte_size)
        return return_valobj_sp;
      uint64_t raw_value = thread.GetRegisterContext()->ReadRegisterAsUnsigned(
          reg_ctx->GetRegisterInfoByName("r2", 0), 0);
      const bool is_signed = (type_flags & eTypeIsSigned) != 0;
      switch (*byte_size) {
      default:
        break;

      case sizeof(uint64_t):
        if (is_signed)
          value.GetScalar() = (int64_t)(raw_value);
        else
          value.GetScalar() = (uint64_t)(raw_value);
        success = true;
        break;

      case sizeof(uint32_t):
        if (is_signed)
          value.GetScalar() = (int32_t)(raw_value & UINT32_MAX);
        else
          value.GetScalar() = (uint32_t)(raw_value & UINT32_MAX);
        success = true;
        break;

      case sizeof(uint16_t):
        if (is_signed)
          value.GetScalar() = (int16_t)(raw_value & UINT16_MAX);
        else
          value.GetScalar() = (uint16_t)(raw_value & UINT16_MAX);
        success = true;
        break;

      case sizeof(uint8_t):
        if (is_signed)
          value.GetScalar() = (int8_t)(raw_value & UINT8_MAX);
        else
          value.GetScalar() = (uint8_t)(raw_value & UINT8_MAX);
        success = true;
        break;
      }
    } else if (type_flags & eTypeIsFloat) {
      if (type_flags & eTypeIsComplex) {
        // Don't handle complex yet.
      } else {
        std::optional<uint64_t> byte_size =
            return_compiler_type.GetByteSize(&thread);
        if (byte_size && *byte_size <= sizeof(long double)) {
          const RegisterInfo *f0_info = reg_ctx->GetRegisterInfoByName("f0", 0);
          RegisterValue f0_value;
          if (reg_ctx->ReadRegister(f0_info, f0_value)) {
            DataExtractor data;
            if (f0_value.GetData(data)) {
              lldb::offset_t offset = 0;
              if (*byte_size == sizeof(float)) {
                value.GetScalar() = (float)data.GetFloat(&offset);
                success = true;
              } else if (*byte_size == sizeof(double)) {
                value.GetScalar() = (double)data.GetDouble(&offset);
                success = true;
              } else if (*byte_size == sizeof(long double)) {
                // Don't handle long double yet.
              }
            }
          }
        }
      }
    }

    if (success)
      return_valobj_sp = ValueObjectConstResult::Create(
          thread.GetStackFrameAtIndex(0).get(), value, ConstString(""));
  } else if (type_flags & eTypeIsPointer) {
    unsigned r2_id =
        reg_ctx->GetRegisterInfoByName("r2", 0)->kinds[eRegisterKindLLDB];
    value.GetScalar() =
        (uint64_t)thread.GetRegisterContext()->ReadRegisterAsUnsigned(r2_id, 0);
    value.SetValueType(Value::ValueType::Scalar);
    return_valobj_sp = ValueObjectConstResult::Create(
        thread.GetStackFrameAtIndex(0).get(), value, ConstString(""));
  }

  return return_valobj_sp;
}

ValueObjectSP ABISysV_s390x::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_valobj_sp = GetReturnValueObjectSimple(thread, return_compiler_type);
  if (return_valobj_sp)
    return return_valobj_sp;

  RegisterContextSP reg_ctx_sp = thread.GetRegisterContext();
  if (!reg_ctx_sp)
    return return_valobj_sp;

  if (return_compiler_type.IsAggregateType()) {
    // FIXME: This is just taking a guess, r2 may very well no longer hold the
    // return storage location.
    // If we are going to do this right, when we make a new frame we should
    // check to see if it uses a memory return, and if we are at the first
    // instruction and if so stash away the return location.  Then we would
    // only return the memory return value if we know it is valid.

    unsigned r2_id =
        reg_ctx_sp->GetRegisterInfoByName("r2", 0)->kinds[eRegisterKindLLDB];
    lldb::addr_t storage_addr =
        (uint64_t)thread.GetRegisterContext()->ReadRegisterAsUnsigned(r2_id, 0);
    return_valobj_sp = ValueObjectMemory::Create(
        &thread, "", Address(storage_addr, nullptr), return_compiler_type);
  }

  return return_valobj_sp;
}

bool ABISysV_s390x::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 + 160
  row->GetCFAValue().SetIsRegisterPlusOffset(dwarf_r15_s390x, 160);

  // The previous PC is in r14
  row->SetRegisterLocationToRegister(dwarf_pswa_s390x, dwarf_r14_s390x, true);

  // All other registers are the same.
  unwind_plan.AppendRow(row);
  unwind_plan.SetSourceName("s390x at-func-entry default");
  unwind_plan.SetSourcedFromCompiler(eLazyBoolNo);
  return true;
}

bool ABISysV_s390x::CreateDefaultUnwindPlan(UnwindPlan &unwind_plan) {
  // There's really no default way to unwind on s390x. Trust the .eh_frame CFI,
  // which should always be good.
  return false;
}

bool ABISysV_s390x::GetFallbackRegisterLocation(
    const RegisterInfo *reg_info,
    UnwindPlan::Row::RegisterLocation &unwind_regloc) {
  // If a volatile register is being requested, we don't want to forward the
  // next frame's register contents up the stack -- the register is not
  // retrievable at this frame.
  if (RegisterIsVolatile(reg_info)) {
    unwind_regloc.SetUndefined();
    return true;
  }

  return false;
}

bool ABISysV_s390x::RegisterIsVolatile(const RegisterInfo *reg_info) {
  return !RegisterIsCalleeSaved(reg_info);
}

bool ABISysV_s390x::RegisterIsCalleeSaved(const RegisterInfo *reg_info) {
  if (reg_info) {
    // Preserved registers are :
    //    r6-r13, r15
    //    f8-f15

    const char *name = reg_info->name;
    if (name[0] == 'r') {
      switch (name[1]) {
      case '6': // r6
      case '7': // r7
      case '8': // r8
      case '9': // r9
        return name[2] == '\0';

      case '1': // r10, r11, r12, r13, r15
        if ((name[2] >= '0' && name[2] <= '3') || name[2] == '5')
          return name[3] == '\0';
        break;

      default:
        break;
      }
    }
    if (name[0] == 'f') {
      switch (name[1]) {
      case '8': // r8
      case '9': // r9
        return name[2] == '\0';

      case '1': // r10, r11, r12, r13, r14, r15
        if (name[2] >= '0' && name[2] <= '5')
          return name[3] == '\0';
        break;

      default:
        break;
      }
    }

    // Accept shorter-variant versions
    if (name[0] == 's' && name[1] == 'p' && name[2] == '\0') // sp
      return true;
    if (name[0] == 'f' && name[1] == 'p' && name[2] == '\0') // fp
      return true;
    if (name[0] == 'p' && name[1] == 'c' && name[2] == '\0') // pc
      return true;
  }
  return false;
}

void ABISysV_s390x::Initialize() {
  PluginManager::RegisterPlugin(
      GetPluginNameStatic(), "System V ABI for s390x targets", CreateInstance);
}

void ABISysV_s390x::Terminate() {
  PluginManager::UnregisterPlugin(CreateInstance);
}