IRExecutionUnit.cpp

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//===-- IRExecutionUnit.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 "llvm/ExecutionEngine/ExecutionEngine.h"
#include "llvm/ExecutionEngine/ObjectCache.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DiagnosticHandler.h"
#include "llvm/IR/DiagnosticInfo.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Module.h"
#include "llvm/Support/Error.h"
#include "llvm/Support/SourceMgr.h"
#include "llvm/Support/raw_ostream.h"
 
#include "lldb/Core/Debugger.h"
#include "lldb/Core/Disassembler.h"
#include "lldb/Core/Module.h"
#include "lldb/Core/Section.h"
#include "lldb/Expression/Expression.h"
#include "lldb/Expression/IRExecutionUnit.h"
#include "lldb/Expression/ObjectFileJIT.h"
#include "lldb/Host/HostInfo.h"
#include "lldb/Symbol/CompileUnit.h"
#include "lldb/Symbol/SymbolContext.h"
#include "lldb/Symbol/SymbolFile.h"
#include "lldb/Symbol/SymbolVendor.h"
#include "lldb/Target/ExecutionContext.h"
#include "lldb/Target/Language.h"
#include "lldb/Target/LanguageRuntime.h"
#include "lldb/Target/Target.h"
#include "lldb/Utility/DataBufferHeap.h"
#include "lldb/Utility/DataExtractor.h"
#include "lldb/Utility/LLDBAssert.h"
#include "lldb/Utility/LLDBLog.h"
#include "lldb/Utility/Log.h"
#include "lldb/lldb-defines.h"
 
#include <optional>
 
using namespace lldb_private;
 
IRExecutionUnit::IRExecutionUnit(std::unique_ptr<llvm::LLVMContext> &context_up,
                                 std::unique_ptr<llvm::Module> &module_up,
                                 ConstString &name,
                                 const lldb::TargetSP &target_sp,
                                 const SymbolContext &sym_ctx,
                                 std::vector<std::string> &cpu_features)
    : IRMemoryMap(target_sp), m_context_up(context_up.release()),
      m_module_up(module_up.release()), m_module(m_module_up.get()),
      m_cpu_features(cpu_features), m_name(name), m_sym_ctx(sym_ctx),
      m_did_jit(false), m_function_load_addr(LLDB_INVALID_ADDRESS),
      m_function_end_load_addr(LLDB_INVALID_ADDRESS),
      m_reported_allocations(false), m_preferred_modules() {}
 
lldb::addr_t IRExecutionUnit::WriteNow(const uint8_t *bytes, size_t size,
                                       Status &error) {
  const bool zero_memory = false;
  auto address_or_error =
      Malloc(size, 8, lldb::ePermissionsWritable | lldb::ePermissionsReadable,
             eAllocationPolicyMirror, zero_memory);
  if (!address_or_error) {
    error = Status::FromError(address_or_error.takeError());
    return LLDB_INVALID_ADDRESS;
  }
  lldb::addr_t allocation_process_addr = *address_or_error;
 
  WriteMemory(allocation_process_addr, bytes, size, error);
 
  if (!error.Success()) {
    Status err;
    Free(allocation_process_addr, err);
 
    return LLDB_INVALID_ADDRESS;
  }
 
  if (Log *log = GetLog(LLDBLog::Expressions)) {
    DataBufferHeap my_buffer(size, 0);
    Status err;
    ReadMemory(my_buffer.GetBytes(), allocation_process_addr, size, err);
 
    if (err.Success()) {
      DataExtractor my_extractor(my_buffer.GetBytes(), my_buffer.GetByteSize(),
                                 lldb::eByteOrderBig, 8);
      my_extractor.PutToLog(log, 0, my_buffer.GetByteSize(),
                            allocation_process_addr, 16,
                            DataExtractor::TypeUInt8);
    }
  }
 
  return allocation_process_addr;
}
 
void IRExecutionUnit::FreeNow(lldb::addr_t allocation) {
  if (allocation == LLDB_INVALID_ADDRESS)
    return;
 
  Status err;
 
  Free(allocation, err);
}
 
Status IRExecutionUnit::DisassembleFunction(Stream &stream,
                                            lldb::ProcessSP &process_wp) {
  Log *log = GetLog(LLDBLog::Expressions);
 
  ExecutionContext exe_ctx(process_wp);
 
  Status ret;
 
  ret.Clear();
 
  lldb::addr_t func_local_addr = LLDB_INVALID_ADDRESS;
  lldb::addr_t func_remote_addr = LLDB_INVALID_ADDRESS;
 
  for (JittedFunction &function : m_jitted_functions) {
    if (function.m_name == m_name) {
      func_local_addr = function.m_local_addr;
      func_remote_addr = function.m_remote_addr;
    }
  }
 
  if (func_local_addr == LLDB_INVALID_ADDRESS) {
    ret = Status::FromErrorStringWithFormat(
        "Couldn't find function %s for disassembly", m_name.AsCString());
    return ret;
  }
 
  LLDB_LOGF(log,
            "Found function, has local address 0x%" PRIx64
            " and remote address 0x%" PRIx64,
            (uint64_t)func_local_addr, (uint64_t)func_remote_addr);
 
  std::pair<lldb::addr_t, lldb::addr_t> func_range;
 
  func_range = GetRemoteRangeForLocal(func_local_addr);
 
  if (func_range.first == 0 && func_range.second == 0) {
    ret = Status::FromErrorStringWithFormat(
        "Couldn't find code range for function %s", m_name.AsCString());
    return ret;
  }
 
  LLDB_LOGF(log, "Function's code range is [0x%" PRIx64 "+0x%" PRIx64 "]",
            func_range.first, func_range.second);
 
  Target *target = exe_ctx.GetTargetPtr();
  if (!target) {
    ret = Status::FromErrorString("Couldn't find the target");
    return ret;
  }
 
  lldb::WritableDataBufferSP buffer_sp(
      new DataBufferHeap(func_range.second, 0));
 
  Process *process = exe_ctx.GetProcessPtr();
  Status err;
  process->ReadMemory(func_remote_addr, buffer_sp->GetBytes(),
                      buffer_sp->GetByteSize(), err);
 
  if (!err.Success()) {
    ret = Status::FromErrorStringWithFormat("Couldn't read from process: %s",
                                            err.AsCString("unknown error"));
    return ret;
  }
 
  ArchSpec arch(target->GetArchitecture());
 
  const char *plugin_name = nullptr;
  const char *flavor_string = nullptr;
  const char *cpu_string = nullptr;
  const char *features_string = nullptr;
  lldb::DisassemblerSP disassembler_sp = Disassembler::FindPlugin(
      arch, flavor_string, cpu_string, features_string, plugin_name);
 
  if (!disassembler_sp) {
    ret = Status::FromErrorStringWithFormat(
        "Unable to find disassembler plug-in for %s architecture.",
        arch.GetArchitectureName());
    return ret;
  }
 
  if (!process) {
    ret = Status::FromErrorString("Couldn't find the process");
    return ret;
  }
 
  DataExtractor extractor(buffer_sp, process->GetByteOrder(),
                          target->GetArchitecture().GetAddressByteSize());
 
  if (log) {
    LLDB_LOGF(log, "Function data has contents:");
    extractor.PutToLog(log, 0, extractor.GetByteSize(), func_remote_addr, 16,
                       DataExtractor::TypeUInt8);
  }
 
  disassembler_sp->DecodeInstructions(Address(func_remote_addr), extractor, 0,
                                      UINT32_MAX, false, false);
 
  InstructionList &instruction_list = disassembler_sp->GetInstructionList();
  instruction_list.Dump(&stream, true, true, /*show_control_flow_kind=*/false,
                        &exe_ctx);
 
  return ret;
}
 
namespace {
struct IRExecDiagnosticHandler : public llvm::DiagnosticHandler {
  Status *err;
  IRExecDiagnosticHandler(Status *err) : err(err) {}
  bool handleDiagnostics(const llvm::DiagnosticInfo &DI) override {
    if (DI.getSeverity() == llvm::DS_Error) {
      const auto &DISM = llvm::cast<llvm::DiagnosticInfoSrcMgr>(DI);
      if (err && err->Success()) {
        *err = Status::FromErrorStringWithFormat(
            "IRExecution error: %s",
            DISM.getSMDiag().getMessage().str().c_str());
      }
    }
 
    return true;
  }
};
} // namespace
 
void IRExecutionUnit::ReportSymbolLookupError(ConstString name) {
  m_failed_lookups.push_back(name);
}
 
void IRExecutionUnit::GetRunnableInfo(Status &error, lldb::addr_t &func_addr,
                                      lldb::addr_t &func_end) {
  lldb::ProcessSP process_sp(GetProcessWP().lock());
 
  static std::recursive_mutex s_runnable_info_mutex;
 
  func_addr = LLDB_INVALID_ADDRESS;
  func_end = LLDB_INVALID_ADDRESS;
 
  if (!process_sp) {
    error =
        Status::FromErrorString("Couldn't write the JIT compiled code into the "
                                "process because the process is invalid");
    return;
  }
 
  if (m_did_jit) {
    func_addr = m_function_load_addr;
    func_end = m_function_end_load_addr;
 
    return;
  };
 
  std::lock_guard<std::recursive_mutex> guard(s_runnable_info_mutex);
 
  m_did_jit = true;
 
  Log *log = GetLog(LLDBLog::Expressions);
 
  std::string error_string;
 
  if (log) {
    std::string s;
    llvm::raw_string_ostream oss(s);
 
    m_module->print(oss, nullptr);
 
    LLDB_LOGF(log, "Module being sent to JIT: \n%s", s.c_str());
  }
 
  m_module_up->getContext().setDiagnosticHandler(
      std::make_unique<IRExecDiagnosticHandler>(&error));
 
  llvm::EngineBuilder builder(std::move(m_module_up));
  llvm::Triple triple(m_module->getTargetTriple());
 
  builder.setEngineKind(llvm::EngineKind::JIT)
      .setErrorStr(&error_string)
      .setRelocationModel(triple.isOSBinFormatMachO() ? llvm::Reloc::PIC_
                                                      : llvm::Reloc::Static)
      .setMCJITMemoryManager(std::make_unique<MemoryManager>(*this))
      .setOptLevel(llvm::CodeGenOptLevel::Less);
 
  // Resulted jitted code can be placed too far from the code in the binary
  // and thus can contain more than +-2GB jumps, that are not available
  // in RISC-V without large code model.
  if (triple.isRISCV64())
    builder.setCodeModel(llvm::CodeModel::Large);
 
  llvm::StringRef mArch;
  llvm::StringRef mCPU;
  llvm::SmallVector<std::string, 0> mAttrs;
 
  for (std::string &feature : m_cpu_features)
    mAttrs.push_back(feature);
 
  llvm::TargetMachine *target_machine =
      builder.selectTarget(triple, mArch, mCPU, mAttrs);
 
  m_execution_engine_up.reset(builder.create(target_machine));
 
  if (!m_execution_engine_up) {
    error = Status::FromErrorStringWithFormat("Couldn't JIT the function: %s",
                                              error_string.c_str());
    return;
  }
 
  m_strip_underscore =
      (m_execution_engine_up->getDataLayout().getGlobalPrefix() == '_');
 
  class ObjectDumper : public llvm::ObjectCache {
  public:
    ObjectDumper(FileSpec output_dir)  : m_out_dir(output_dir) {}
    void notifyObjectCompiled(const llvm::Module *module,
                              llvm::MemoryBufferRef object) override {
      int fd = 0;
      llvm::SmallVector<char, 256> result_path;
      std::string object_name_model =
          "jit-object-" + module->getModuleIdentifier() + "-%%%.o";
      FileSpec model_spec 
          = m_out_dir.CopyByAppendingPathComponent(object_name_model);
      std::string model_path = model_spec.GetPath();
 
      std::error_code result 
        = llvm::sys::fs::createUniqueFile(model_path, fd, result_path);
      if (!result) {
          llvm::raw_fd_ostream fds(fd, true);
          fds.write(object.getBufferStart(), object.getBufferSize());
      }
    }
    std::unique_ptr<llvm::MemoryBuffer>
    getObject(const llvm::Module *module) override  {
      // Return nothing - we're just abusing the object-cache mechanism to dump
      // objects.
      return nullptr;
  }
  private:
    FileSpec m_out_dir;
  };
 
  FileSpec save_objects_dir = process_sp->GetTarget().GetSaveJITObjectsDir();
  if (save_objects_dir) {
    m_object_cache_up = std::make_unique<ObjectDumper>(save_objects_dir);
    m_execution_engine_up->setObjectCache(m_object_cache_up.get());
  }
 
  // Make sure we see all sections, including ones that don't have
  // relocations...
  m_execution_engine_up->setProcessAllSections(true);
 
  m_execution_engine_up->DisableLazyCompilation();
 
  for (llvm::Function &function : *m_module) {
    if (function.isDeclaration() || function.hasPrivateLinkage())
      continue;
 
    const bool external = !function.hasLocalLinkage();
 
    void *fun_ptr = m_execution_engine_up->getPointerToFunction(&function);
 
    if (!error.Success()) {
      // We got an error through our callback!
      return;
    }
 
    if (!fun_ptr) {
      error = Status::FromErrorStringWithFormat(
          "'%s' was in the JITted module but wasn't lowered",
          function.getName().str().c_str());
      return;
    }
    m_jitted_functions.push_back(JittedFunction(
        function.getName().str().c_str(), external, reinterpret_cast<uintptr_t>(fun_ptr)));
  }
 
  CommitAllocations(process_sp);
  ReportAllocations(*m_execution_engine_up);
 
  // We have to do this after calling ReportAllocations because for the MCJIT,
  // getGlobalValueAddress will cause the JIT to perform all relocations.  That
  // can only be done once, and has to happen after we do the remapping from
  // local -> remote. That means we don't know the local address of the
  // Variables, but we don't need that for anything, so that's okay.
 
  std::function<void(llvm::GlobalValue &)> RegisterOneValue = [this](
      llvm::GlobalValue &val) {
    if (val.hasExternalLinkage() && !val.isDeclaration()) {
      uint64_t var_ptr_addr =
          m_execution_engine_up->getGlobalValueAddress(val.getName().str());
 
      lldb::addr_t remote_addr = GetRemoteAddressForLocal(var_ptr_addr);
 
      // This is a really unfortunae API that sometimes returns local addresses
      // and sometimes returns remote addresses, based on whether the variable
      // was relocated during ReportAllocations or not.
 
      if (remote_addr == LLDB_INVALID_ADDRESS) {
        remote_addr = var_ptr_addr;
      }
 
      if (var_ptr_addr != 0)
        m_jitted_global_variables.push_back(JittedGlobalVariable(
            val.getName().str().c_str(), LLDB_INVALID_ADDRESS, remote_addr));
    }
  };
 
  for (llvm::GlobalVariable &global_var : m_module->globals()) {
    RegisterOneValue(global_var);
  }
 
  for (llvm::GlobalAlias &global_alias : m_module->aliases()) {
    RegisterOneValue(global_alias);
  }
 
  WriteData(process_sp);
 
  if (m_failed_lookups.size()) {
    StreamString ss;
 
    ss.PutCString("Couldn't look up symbols:\n");
 
    bool emitNewLine = false;
 
    for (ConstString failed_lookup : m_failed_lookups) {
      if (emitNewLine)
        ss.PutCString("\n");
      emitNewLine = true;
      ss.PutCString("  ");
      ss.PutCString(Mangled(failed_lookup).GetDemangledName().GetStringRef());
    }
 
    m_failed_lookups.clear();
    ss.PutCString(
        "\nHint: The expression tried to call a function that is not present "
        "in the target, perhaps because it was optimized out by the compiler.");
    error = Status(ss.GetString().str());
 
    return;
  }
 
  m_function_load_addr = LLDB_INVALID_ADDRESS;
  m_function_end_load_addr = LLDB_INVALID_ADDRESS;
 
  for (JittedFunction &jitted_function : m_jitted_functions) {
    jitted_function.m_remote_addr =
        GetRemoteAddressForLocal(jitted_function.m_local_addr);
 
    if (!m_name.IsEmpty() && jitted_function.m_name == m_name) {
      AddrRange func_range =
          GetRemoteRangeForLocal(jitted_function.m_local_addr);
      m_function_end_load_addr = func_range.first + func_range.second;
      m_function_load_addr = jitted_function.m_remote_addr;
    }
  }
 
  if (log) {
    LLDB_LOGF(log, "Code can be run in the target.");
 
    StreamString disassembly_stream;
 
    Status err = DisassembleFunction(disassembly_stream, process_sp);
 
    if (!err.Success()) {
      LLDB_LOGF(log, "Couldn't disassemble function : %s",
                err.AsCString("unknown error"));
    } else {
      LLDB_LOGF(log, "Function disassembly:\n%s", disassembly_stream.GetData());
    }
 
    LLDB_LOGF(log, "Sections: ");
    for (AllocationRecord &record : m_records) {
      if (record.m_process_address != LLDB_INVALID_ADDRESS) {
        record.dump(log);
 
        DataBufferHeap my_buffer(record.m_size, 0);
        Status err;
        ReadMemory(my_buffer.GetBytes(), record.m_process_address,
                   record.m_size, err);
 
        if (err.Success()) {
          DataExtractor my_extractor(my_buffer.GetBytes(),
                                     my_buffer.GetByteSize(),
                                     lldb::eByteOrderBig, 8);
          my_extractor.PutToLog(log, 0, my_buffer.GetByteSize(),
                                record.m_process_address, 16,
                                DataExtractor::TypeUInt8);
        }
      } else {
        record.dump(log);
 
        DataExtractor my_extractor((const void *)record.m_host_address,
                                   record.m_size, lldb::eByteOrderBig, 8);
        my_extractor.PutToLog(log, 0, record.m_size, record.m_host_address, 16,
                              DataExtractor::TypeUInt8);
      }
    }
  }
 
  func_addr = m_function_load_addr;
  func_end = m_function_end_load_addr;
}
 
IRExecutionUnit::~IRExecutionUnit() {
  m_module_up.reset();
  m_execution_engine_up.reset();
  m_context_up.reset();
}
 
IRExecutionUnit::MemoryManager::MemoryManager(IRExecutionUnit &parent)
    : m_default_mm_up(new llvm::SectionMemoryManager()), m_parent(parent) {}
 
IRExecutionUnit::MemoryManager::~MemoryManager() = default;
 
lldb::SectionType IRExecutionUnit::GetSectionTypeFromSectionName(
    const llvm::StringRef &name, IRExecutionUnit::AllocationKind alloc_kind) {
  lldb::SectionType sect_type = lldb::eSectionTypeCode;
  switch (alloc_kind) {
  case AllocationKind::Stub:
    sect_type = lldb::eSectionTypeCode;
    break;
  case AllocationKind::Code:
    sect_type = lldb::eSectionTypeCode;
    break;
  case AllocationKind::Data:
    sect_type = lldb::eSectionTypeData;
    break;
  case AllocationKind::Global:
    sect_type = lldb::eSectionTypeData;
    break;
  case AllocationKind::Bytes:
    sect_type = lldb::eSectionTypeOther;
    break;
  }
 
  if (!name.empty()) {
    if (name == "__text" || name == ".text")
      sect_type = lldb::eSectionTypeCode;
    else if (name == "__data" || name == ".data")
      sect_type = lldb::eSectionTypeCode;
    else if (name.starts_with("__debug_") || name.starts_with(".debug_")) {
      const uint32_t name_idx = name[0] == '_' ? 8 : 7;
      llvm::StringRef dwarf_name(name.substr(name_idx));
      sect_type = ObjectFile::GetDWARFSectionTypeFromName(dwarf_name);
    } else if (name.starts_with("__apple_") || name.starts_with(".apple_"))
      sect_type = lldb::eSectionTypeInvalid;
    else if (name == "__objc_imageinfo")
      sect_type = lldb::eSectionTypeOther;
  }
  return sect_type;
}
 
uint8_t *IRExecutionUnit::MemoryManager::allocateCodeSection(
    uintptr_t Size, unsigned Alignment, unsigned SectionID,
    llvm::StringRef SectionName) {
  Log *log = GetLog(LLDBLog::Expressions);
 
  uint8_t *return_value = m_default_mm_up->allocateCodeSection(
      Size, Alignment, SectionID, SectionName);
 
  m_parent.m_records.push_back(AllocationRecord(
      (uintptr_t)return_value,
      lldb::ePermissionsReadable | lldb::ePermissionsExecutable,
      GetSectionTypeFromSectionName(SectionName, AllocationKind::Code), Size,
      Alignment, SectionID, SectionName.str().c_str()));
 
  LLDB_LOGF(log,
            "IRExecutionUnit::allocateCodeSection(Size=0x%" PRIx64
            ", Alignment=%u, SectionID=%u) = %p",
            (uint64_t)Size, Alignment, SectionID, (void *)return_value);
 
  if (m_parent.m_reported_allocations) {
    Status err;
    lldb::ProcessSP process_sp =
        m_parent.GetBestExecutionContextScope()->CalculateProcess();
 
    m_parent.CommitOneAllocation(process_sp, err, m_parent.m_records.back());
  }
 
  return return_value;
}
 
uint8_t *IRExecutionUnit::MemoryManager::allocateDataSection(
    uintptr_t Size, unsigned Alignment, unsigned SectionID,
    llvm::StringRef SectionName, bool IsReadOnly) {
  Log *log = GetLog(LLDBLog::Expressions);
 
  uint8_t *return_value = m_default_mm_up->allocateDataSection(
      Size, Alignment, SectionID, SectionName, IsReadOnly);
 
  uint32_t permissions = lldb::ePermissionsReadable;
  if (!IsReadOnly)
    permissions |= lldb::ePermissionsWritable;
  m_parent.m_records.push_back(AllocationRecord(
      (uintptr_t)return_value, permissions,
      GetSectionTypeFromSectionName(SectionName, AllocationKind::Data), Size,
      Alignment, SectionID, SectionName.str().c_str()));
  LLDB_LOGF(log,
            "IRExecutionUnit::allocateDataSection(Size=0x%" PRIx64
            ", Alignment=%u, SectionID=%u) = %p",
            (uint64_t)Size, Alignment, SectionID, (void *)return_value);
 
  if (m_parent.m_reported_allocations) {
    Status err;
    lldb::ProcessSP process_sp =
        m_parent.GetBestExecutionContextScope()->CalculateProcess();
 
    m_parent.CommitOneAllocation(process_sp, err, m_parent.m_records.back());
  }
 
  return return_value;
}
 
void IRExecutionUnit::CollectCandidateCNames(std::vector<ConstString> &C_names,
                                             ConstString name) {
  if (m_strip_underscore && name.AsCString()[0] == '_')
    C_names.insert(C_names.begin(), ConstString(&name.AsCString()[1]));
  C_names.push_back(name);
}
 
void IRExecutionUnit::CollectCandidateCPlusPlusNames(
    std::vector<ConstString> &CPP_names,
    const std::vector<ConstString> &C_names, const SymbolContext &sc) {
  if (auto *cpp_lang = Language::FindPlugin(lldb::eLanguageTypeC_plus_plus)) {
    for (const ConstString &name : C_names) {
      Mangled mangled(name);
      if (cpp_lang->SymbolNameFitsToLanguage(mangled)) {
        if (ConstString best_alternate =
                cpp_lang->FindBestAlternateFunctionMangledName(mangled, sc)) {
          CPP_names.push_back(best_alternate);
        }
      }
 
      std::vector<ConstString> alternates =
          cpp_lang->GenerateAlternateFunctionManglings(name);
      CPP_names.insert(CPP_names.end(), alternates.begin(), alternates.end());
 
      // As a last-ditch fallback, try the base name for C++ names.  It's
      // terrible, but the DWARF doesn't always encode "extern C" correctly.
      ConstString basename =
          cpp_lang->GetDemangledFunctionNameWithoutArguments(mangled);
      CPP_names.push_back(basename);
    }
  }
}
 
class LoadAddressResolver {
public:
  LoadAddressResolver(Target &target, bool &symbol_was_missing_weak)
      : m_target(target), m_symbol_was_missing_weak(symbol_was_missing_weak) {}
 
  std::optional<lldb::addr_t> Resolve(SymbolContextList &sc_list) {
    if (sc_list.IsEmpty())
      return std::nullopt;
 
    lldb::addr_t load_address = LLDB_INVALID_ADDRESS;
 
    // Missing_weak_symbol will be true only if we found only weak undefined
    // references to this symbol.
    m_symbol_was_missing_weak = true;
 
    for (auto candidate_sc : sc_list.SymbolContexts()) {
      // Only symbols can be weak undefined.
      if (!candidate_sc.symbol ||
          candidate_sc.symbol->GetType() != lldb::eSymbolTypeUndefined ||
          !candidate_sc.symbol->IsWeak())
        m_symbol_was_missing_weak = false;
 
      // First try the symbol.
      if (candidate_sc.symbol) {
        load_address = candidate_sc.symbol->ResolveCallableAddress(m_target);
        if (load_address == LLDB_INVALID_ADDRESS) {
          Address addr = candidate_sc.symbol->GetAddress();
          load_address = m_target.GetProcessSP()
                             ? addr.GetLoadAddress(&m_target)
                             : addr.GetFileAddress();
        }
      }
 
      // If that didn't work, try the function.
      if (load_address == LLDB_INVALID_ADDRESS && candidate_sc.function) {
        Address addr = candidate_sc.function->GetAddress();
        load_address = m_target.GetProcessSP()
                           ? addr.GetCallableLoadAddress(&m_target)
                           : addr.GetFileAddress();
      }
 
      // We found a load address.
      if (load_address != LLDB_INVALID_ADDRESS) {
        // If the load address is external, we're done.
        const bool is_external =
            (candidate_sc.function) ||
            (candidate_sc.symbol && candidate_sc.symbol->IsExternal());
        if (is_external)
          return load_address;
 
        // Otherwise, remember the best internal load address.
        if (m_best_internal_load_address == LLDB_INVALID_ADDRESS)
          m_best_internal_load_address = load_address;
      }
    }
 
    // You test the address of a weak symbol against NULL to see if it is
    // present. So we should return 0 for a missing weak symbol.
    if (m_symbol_was_missing_weak)
      return 0;
 
    return std::nullopt;
  }
 
  lldb::addr_t GetBestInternalLoadAddress() const {
    return m_best_internal_load_address;
  }
 
private:
  Target &m_target;
  bool &m_symbol_was_missing_weak;
  lldb::addr_t m_best_internal_load_address = LLDB_INVALID_ADDRESS;
};
 
/// Returns address of the function referred to by the special function call
/// label \c label.
static llvm::Expected<lldb::addr_t>
ResolveFunctionCallLabel(FunctionCallLabel &label,
                         const lldb_private::SymbolContext &sc,
                         bool &symbol_was_missing_weak) {
  symbol_was_missing_weak = false;
 
  if (!sc.target_sp)
    return llvm::createStringError("target not available.");
 
  auto module_sp = sc.target_sp->GetImages().FindModule(label.module_id);
  if (!module_sp)
    return llvm::createStringError(
        llvm::formatv("failed to find module by UID {0}", label.module_id));
 
  auto *symbol_file = module_sp->GetSymbolFile();
  if (!symbol_file)
    return llvm::createStringError(
        llvm::formatv("no SymbolFile found on module {0:x}.", module_sp.get()));
 
  auto sc_or_err = symbol_file->ResolveFunctionCallLabel(label);
  if (!sc_or_err)
    return llvm::joinErrors(
        llvm::createStringError("failed to resolve function by UID:"),
        sc_or_err.takeError());
 
  SymbolContextList sc_list;
  sc_list.Append(*sc_or_err);
 
  LoadAddressResolver resolver(*sc.target_sp, symbol_was_missing_weak);
  lldb::addr_t resolved_addr =
      resolver.Resolve(sc_list).value_or(LLDB_INVALID_ADDRESS);
  if (resolved_addr == LLDB_INVALID_ADDRESS)
    return llvm::createStringError("couldn't resolve address for function");
 
  return resolved_addr;
}
 
lldb::addr_t
IRExecutionUnit::FindInSymbols(const std::vector<ConstString> &names,
                               const lldb_private::SymbolContext &sc,
                               bool &symbol_was_missing_weak) {
  symbol_was_missing_weak = false;
 
  Target *target = sc.target_sp.get();
  if (!target) {
    // We shouldn't be doing any symbol lookup at all without a target.
    return LLDB_INVALID_ADDRESS;
  }
 
  ModuleList non_local_images = target->GetImages();
  // We'll process module_sp and any preferred modules separately, before the
  // other modules.
  non_local_images.Remove(sc.module_sp);
  for (size_t i = 0; i < m_preferred_modules.GetSize(); ++i)
    non_local_images.Remove(m_preferred_modules.GetModuleAtIndex(i));
 
  LoadAddressResolver resolver(*target, symbol_was_missing_weak);
 
  ModuleFunctionSearchOptions function_options;
  function_options.include_symbols = true;
  function_options.include_inlines = false;
 
  for (const ConstString &name : names) {
    // The lookup order here is as follows:
    // 1) Functions in `sc.module_sp`
    // 2) Functions in the preferred modules list
    // 3) Functions in the other modules
    // 4) Symbols in `sc.module_sp`
    // 5) Symbols in the preferred modules list
    // 6) Symbols in the other modules
    if (sc.module_sp) {
      SymbolContextList sc_list;
      sc.module_sp->FindFunctions(name, CompilerDeclContext(),
                                  lldb::eFunctionNameTypeFull, function_options,
                                  sc_list);
      if (auto load_addr = resolver.Resolve(sc_list))
        return *load_addr;
    }
 
    {
      SymbolContextList sc_list;
      m_preferred_modules.FindFunctions(name, lldb::eFunctionNameTypeFull,
                                        function_options, sc_list);
      if (auto load_addr = resolver.Resolve(sc_list))
        return *load_addr;
    }
 
    {
      SymbolContextList sc_list;
      non_local_images.FindFunctions(name, lldb::eFunctionNameTypeFull,
                                     function_options, sc_list);
      if (auto load_addr = resolver.Resolve(sc_list))
        return *load_addr;
    }
 
    if (sc.module_sp) {
      SymbolContextList sc_list;
      sc.module_sp->FindSymbolsWithNameAndType(name, lldb::eSymbolTypeAny,
                                               sc_list);
      if (auto load_addr = resolver.Resolve(sc_list))
        return *load_addr;
    }
 
    {
      SymbolContextList sc_list;
      m_preferred_modules.FindSymbolsWithNameAndType(name, lldb::eSymbolTypeAny,
                                                     sc_list);
      if (auto load_addr = resolver.Resolve(sc_list))
        return *load_addr;
    }
 
    {
      SymbolContextList sc_list;
      non_local_images.FindSymbolsWithNameAndType(name, lldb::eSymbolTypeAny,
                                                  sc_list);
      if (auto load_addr = resolver.Resolve(sc_list))
        return *load_addr;
    }
 
    lldb::addr_t best_internal_load_address =
        resolver.GetBestInternalLoadAddress();
    if (best_internal_load_address != LLDB_INVALID_ADDRESS)
      return best_internal_load_address;
  }
 
  return LLDB_INVALID_ADDRESS;
}
 
lldb::addr_t
IRExecutionUnit::FindInRuntimes(const std::vector<ConstString> &names,
                                const lldb_private::SymbolContext &sc) {
  lldb::TargetSP target_sp = sc.target_sp;
 
  if (!target_sp) {
    return LLDB_INVALID_ADDRESS;
  }
 
  lldb::ProcessSP process_sp = sc.target_sp->GetProcessSP();
 
  if (!process_sp) {
    return LLDB_INVALID_ADDRESS;
  }
 
  for (const ConstString &name : names) {
    for (LanguageRuntime *runtime : process_sp->GetLanguageRuntimes()) {
      lldb::addr_t symbol_load_addr = runtime->LookupRuntimeSymbol(name);
 
      if (symbol_load_addr != LLDB_INVALID_ADDRESS)
        return symbol_load_addr;
    }
  }
 
  return LLDB_INVALID_ADDRESS;
}
 
lldb::addr_t IRExecutionUnit::FindInUserDefinedSymbols(
    const std::vector<ConstString> &names,
    const lldb_private::SymbolContext &sc) {
  lldb::TargetSP target_sp = sc.target_sp;
 
  for (const ConstString &name : names) {
    lldb::addr_t symbol_load_addr = target_sp->GetPersistentSymbol(name);
 
    if (symbol_load_addr != LLDB_INVALID_ADDRESS)
      return symbol_load_addr;
  }
 
  return LLDB_INVALID_ADDRESS;
}
 
lldb::addr_t IRExecutionUnit::FindSymbol(lldb_private::ConstString name,
                                         bool &missing_weak) {
  if (name.GetStringRef().starts_with(FunctionCallLabelPrefix)) {
    auto label_or_err = FunctionCallLabel::fromString(name);
    if (!label_or_err) {
      LLDB_LOG_ERROR(GetLog(LLDBLog::Expressions), label_or_err.takeError(),
                     "failed to create FunctionCallLabel from '{1}': {0}",
                     name.GetStringRef());
      return LLDB_INVALID_ADDRESS;
    }
 
    if (auto addr_or_err =
            ResolveFunctionCallLabel(*label_or_err, m_sym_ctx, missing_weak)) {
      return *addr_or_err;
    } else {
      LLDB_LOG_ERROR(GetLog(LLDBLog::Expressions), addr_or_err.takeError(),
                     "Failed to resolve function call label '{1}': {0}",
                     name.GetStringRef());
 
      // Fall back to lookup by name despite error in resolving the label.
      // May happen in practice if the definition of a function lives in
      // a different lldb_private::Module than it's declaration. Meaning
      // we couldn't pin-point it using the information encoded in the label.
      name.SetString(label_or_err->lookup_name);
    }
  }
 
  // TODO: now with function call labels, do we still need to
  // generate alternate manglings?
 
  std::vector<ConstString> candidate_C_names;
  std::vector<ConstString> candidate_CPlusPlus_names;
 
  CollectCandidateCNames(candidate_C_names, name);
 
  lldb::addr_t ret = FindInSymbols(candidate_C_names, m_sym_ctx, missing_weak);
  if (ret != LLDB_INVALID_ADDRESS)
    return ret;
 
  // If we find the symbol in runtimes or user defined symbols it can't be
  // a missing weak symbol.
  missing_weak = false;
  ret = FindInRuntimes(candidate_C_names, m_sym_ctx);
  if (ret != LLDB_INVALID_ADDRESS)
    return ret;
 
  ret = FindInUserDefinedSymbols(candidate_C_names, m_sym_ctx);
  if (ret != LLDB_INVALID_ADDRESS)
    return ret;
 
  CollectCandidateCPlusPlusNames(candidate_CPlusPlus_names, candidate_C_names,
                                 m_sym_ctx);
  ret = FindInSymbols(candidate_CPlusPlus_names, m_sym_ctx, missing_weak);
  return ret;
}
 
void IRExecutionUnit::GetStaticInitializers(
    std::vector<lldb::addr_t> &static_initializers) {
  Log *log = GetLog(LLDBLog::Expressions);
 
  llvm::GlobalVariable *global_ctors =
      m_module->getNamedGlobal("llvm.global_ctors");
  if (!global_ctors) {
    LLDB_LOG(log, "Couldn't find llvm.global_ctors.");
    return;
  }
  auto *ctor_array =
      llvm::dyn_cast<llvm::ConstantArray>(global_ctors->getInitializer());
  if (!ctor_array) {
    LLDB_LOG(log, "llvm.global_ctors not a ConstantArray.");
    return;
  }
 
  for (llvm::Use &ctor_use : ctor_array->operands()) {
    auto *ctor_struct = llvm::dyn_cast<llvm::ConstantStruct>(ctor_use);
    if (!ctor_struct)
      continue;
    // this is standardized
    lldbassert(ctor_struct->getNumOperands() == 3);
    auto *ctor_function =
        llvm::dyn_cast<llvm::Function>(ctor_struct->getOperand(1));
    if (!ctor_function) {
      LLDB_LOG(log, "global_ctor doesn't contain an llvm::Function");
      continue;
    }
 
    ConstString ctor_function_name(ctor_function->getName().str());
    LLDB_LOG(log, "Looking for callable jitted function with name {0}.",
             ctor_function_name);
 
    for (JittedFunction &jitted_function : m_jitted_functions) {
      if (ctor_function_name != jitted_function.m_name)
        continue;
      if (jitted_function.m_remote_addr == LLDB_INVALID_ADDRESS) {
        LLDB_LOG(log, "Found jitted function with invalid address.");
        continue;
      }
      static_initializers.push_back(jitted_function.m_remote_addr);
      LLDB_LOG(log, "Calling function at address {0:x}.",
               jitted_function.m_remote_addr);
      break;
    }
  }
}
 
llvm::JITSymbol 
IRExecutionUnit::MemoryManager::findSymbol(const std::string &Name) {
    bool missing_weak = false;
    uint64_t addr = GetSymbolAddressAndPresence(Name, missing_weak);
    // This is a weak symbol:
    if (missing_weak) 
      return llvm::JITSymbol(addr, 
          llvm::JITSymbolFlags::Exported | llvm::JITSymbolFlags::Weak);
    else
      return llvm::JITSymbol(addr, llvm::JITSymbolFlags::Exported);
}
 
uint64_t
IRExecutionUnit::MemoryManager::getSymbolAddress(const std::string &Name) {
  bool missing_weak = false;
  return GetSymbolAddressAndPresence(Name, missing_weak);
}
 
uint64_t 
IRExecutionUnit::MemoryManager::GetSymbolAddressAndPresence(
    const std::string &Name, bool &missing_weak) {
  Log *log = GetLog(LLDBLog::Expressions);
 
  ConstString name_cs(Name.c_str());
 
  lldb::addr_t ret = m_parent.FindSymbol(name_cs, missing_weak);
 
  if (ret == LLDB_INVALID_ADDRESS) {
    LLDB_LOGF(log,
              "IRExecutionUnit::getSymbolAddress(Name=\"%s\") = <not found>",
              Name.c_str());
 
    m_parent.ReportSymbolLookupError(name_cs);
    return 0;
  } else {
    LLDB_LOGF(log, "IRExecutionUnit::getSymbolAddress(Name=\"%s\") = %" PRIx64,
              Name.c_str(), ret);
    return ret;
  }
}
 
void *IRExecutionUnit::MemoryManager::getPointerToNamedFunction(
    const std::string &Name, bool AbortOnFailure) {
  return (void *)getSymbolAddress(Name);
}
 
lldb::addr_t
IRExecutionUnit::GetRemoteAddressForLocal(lldb::addr_t local_address) {
  Log *log = GetLog(LLDBLog::Expressions);
 
  for (AllocationRecord &record : m_records) {
    if (local_address >= record.m_host_address &&
        local_address < record.m_host_address + record.m_size) {
      if (record.m_process_address == LLDB_INVALID_ADDRESS)
        return LLDB_INVALID_ADDRESS;
 
      lldb::addr_t ret =
          record.m_process_address + (local_address - record.m_host_address);
 
      LLDB_LOGF(log,
                "IRExecutionUnit::GetRemoteAddressForLocal() found 0x%" PRIx64
                " in [0x%" PRIx64 "..0x%" PRIx64 "], and returned 0x%" PRIx64
                " from [0x%" PRIx64 "..0x%" PRIx64 "].",
                local_address, (uint64_t)record.m_host_address,
                (uint64_t)record.m_host_address + (uint64_t)record.m_size, ret,
                record.m_process_address,
                record.m_process_address + record.m_size);
 
      return ret;
    }
  }
 
  return LLDB_INVALID_ADDRESS;
}
 
IRExecutionUnit::AddrRange
IRExecutionUnit::GetRemoteRangeForLocal(lldb::addr_t local_address) {
  for (AllocationRecord &record : m_records) {
    if (local_address >= record.m_host_address &&
        local_address < record.m_host_address + record.m_size) {
      if (record.m_process_address == LLDB_INVALID_ADDRESS)
        return AddrRange(0, 0);
 
      return AddrRange(record.m_process_address, record.m_size);
    }
  }
 
  return AddrRange(0, 0);
}
 
bool IRExecutionUnit::CommitOneAllocation(lldb::ProcessSP &process_sp,
                                          Status &error,
                                          AllocationRecord &record) {
  if (record.m_process_address != LLDB_INVALID_ADDRESS) {
    return true;
  }
 
  switch (record.m_sect_type) {
  case lldb::eSectionTypeInvalid:
  case lldb::eSectionTypeDWARFDebugAbbrev:
  case lldb::eSectionTypeDWARFDebugAddr:
  case lldb::eSectionTypeDWARFDebugAranges:
  case lldb::eSectionTypeDWARFDebugCuIndex:
  case lldb::eSectionTypeDWARFDebugFrame:
  case lldb::eSectionTypeDWARFDebugInfo:
  case lldb::eSectionTypeDWARFDebugLine:
  case lldb::eSectionTypeDWARFDebugLoc:
  case lldb::eSectionTypeDWARFDebugLocLists:
  case lldb::eSectionTypeDWARFDebugMacInfo:
  case lldb::eSectionTypeDWARFDebugPubNames:
  case lldb::eSectionTypeDWARFDebugPubTypes:
  case lldb::eSectionTypeDWARFDebugRanges:
  case lldb::eSectionTypeDWARFDebugStr:
  case lldb::eSectionTypeDWARFDebugStrOffsets:
  case lldb::eSectionTypeDWARFAppleNames:
  case lldb::eSectionTypeDWARFAppleTypes:
  case lldb::eSectionTypeDWARFAppleNamespaces:
  case lldb::eSectionTypeDWARFAppleObjC:
  case lldb::eSectionTypeDWARFGNUDebugAltLink:
    error.Clear();
    break;
  default:
    const bool zero_memory = false;
    if (auto address_or_error =
            Malloc(record.m_size, record.m_alignment, record.m_permissions,
                   eAllocationPolicyProcessOnly, zero_memory))
      record.m_process_address = *address_or_error;
    else
      error = Status::FromError(address_or_error.takeError());
    break;
  }
 
  return error.Success();
}
 
bool IRExecutionUnit::CommitAllocations(lldb::ProcessSP &process_sp) {
  bool ret = true;
 
  lldb_private::Status err;
 
  for (AllocationRecord &record : m_records) {
    ret = CommitOneAllocation(process_sp, err, record);
 
    if (!ret) {
      break;
    }
  }
 
  if (!ret) {
    for (AllocationRecord &record : m_records) {
      if (record.m_process_address != LLDB_INVALID_ADDRESS) {
        Free(record.m_process_address, err);
        record.m_process_address = LLDB_INVALID_ADDRESS;
      }
    }
  }
 
  return ret;
}
 
void IRExecutionUnit::ReportAllocations(llvm::ExecutionEngine &engine) {
  m_reported_allocations = true;
 
  for (AllocationRecord &record : m_records) {
    if (record.m_process_address == LLDB_INVALID_ADDRESS)
      continue;
 
    if (record.m_section_id == eSectionIDInvalid)
      continue;
 
    engine.mapSectionAddress((void *)record.m_host_address,
                             record.m_process_address);
  }
 
  // Trigger re-application of relocations.
  engine.finalizeObject();
}
 
bool IRExecutionUnit::WriteData(lldb::ProcessSP &process_sp) {
  bool wrote_something = false;
  for (AllocationRecord &record : m_records) {
    if (record.m_process_address != LLDB_INVALID_ADDRESS) {
      lldb_private::Status err;
      WriteMemory(record.m_process_address, (uint8_t *)record.m_host_address,
                  record.m_size, err);
      if (err.Success())
        wrote_something = true;
    }
  }
  return wrote_something;
}
 
void IRExecutionUnit::AllocationRecord::dump(Log *log) {
  if (!log)
    return;
 
  LLDB_LOGF(log,
            "[0x%llx+0x%llx]->0x%llx (alignment %d, section ID %d, name %s)",
            (unsigned long long)m_host_address, (unsigned long long)m_size,
            (unsigned long long)m_process_address, (unsigned)m_alignment,
            (unsigned)m_section_id, m_name.c_str());
}
 
lldb::ByteOrder IRExecutionUnit::GetByteOrder() const {
  ExecutionContext exe_ctx(GetBestExecutionContextScope());
  return exe_ctx.GetByteOrder();
}
 
uint32_t IRExecutionUnit::GetAddressByteSize() const {
  ExecutionContext exe_ctx(GetBestExecutionContextScope());
  return exe_ctx.GetAddressByteSize();
}
 
void IRExecutionUnit::PopulateSymtab(lldb_private::ObjectFile *obj_file,
                                     lldb_private::Symtab &symtab) {
  // No symbols yet...
}
 
void IRExecutionUnit::PopulateSectionList(
    lldb_private::ObjectFile *obj_file,
    lldb_private::SectionList &section_list) {
  for (AllocationRecord &record : m_records) {
    if (record.m_size > 0) {
      lldb::SectionSP section_sp(new lldb_private::Section(
          obj_file->GetModule(), obj_file, record.m_section_id,
          ConstString(record.m_name), record.m_sect_type,
          record.m_process_address, record.m_size,
          record.m_host_address, // file_offset (which is the host address for
                                 // the data)
          record.m_size,         // file_size
          0,
          record.m_permissions)); // flags
      section_list.AddSection(section_sp);
    }
  }
}
 
ArchSpec IRExecutionUnit::GetArchitecture() {
  ExecutionContext exe_ctx(GetBestExecutionContextScope());
  if(Target *target = exe_ctx.GetTargetPtr())
    return target->GetArchitecture();
  return ArchSpec();
}
 
lldb::ModuleSP IRExecutionUnit::GetJITModule() {
  ExecutionContext exe_ctx(GetBestExecutionContextScope());
  Target *target = exe_ctx.GetTargetPtr();
  if (!target)
    return nullptr;
 
  auto Delegate = std::static_pointer_cast<lldb_private::ObjectFileJITDelegate>(
      shared_from_this());
 
  lldb::ModuleSP jit_module_sp =
      lldb_private::Module::CreateModuleFromObjectFile<ObjectFileJIT>(Delegate);
  if (!jit_module_sp)
    return nullptr;
 
  bool changed = false;
  jit_module_sp->SetLoadAddress(*target, 0, true, changed);
  return jit_module_sp;
}