StackFrameList.cpp

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//===-- StackFrameList.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 "lldb/Target/StackFrameList.h"
#include "lldb/Breakpoint/Breakpoint.h"
#include "lldb/Breakpoint/BreakpointLocation.h"
#include "lldb/Core/Debugger.h"
#include "lldb/Core/SourceManager.h"
#include "lldb/Host/StreamFile.h"
#include "lldb/Symbol/Block.h"
#include "lldb/Symbol/Function.h"
#include "lldb/Symbol/Symbol.h"
#include "lldb/Target/Process.h"
#include "lldb/Target/RegisterContext.h"
#include "lldb/Target/StackFrame.h"
#include "lldb/Target/StackFrameRecognizer.h"
#include "lldb/Target/StopInfo.h"
#include "lldb/Target/SyntheticFrameProvider.h"
#include "lldb/Target/Target.h"
#include "lldb/Target/Thread.h"
#include "lldb/Target/Unwind.h"
#include "lldb/Utility/LLDBLog.h"
#include "lldb/Utility/Log.h"
#include "lldb/Utility/Policy.h"
#include "llvm/ADT/ScopeExit.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/Support/ConvertUTF.h"
 
#include <memory>
 
//#define DEBUG_STACK_FRAMES 1
 
using namespace lldb;
using namespace lldb_private;
 
// StackFrameList constructor
StackFrameList::StackFrameList(Thread &thread,
                               const lldb::StackFrameListSP &prev_frames_sp,
                               bool show_inline_frames,
                               lldb::frame_list_id_t provider_id)
    : m_thread(thread), m_prev_frames_sp(prev_frames_sp), m_frames(),
      m_selected_frame_idx(), m_concrete_frames_fetched(0),
      m_current_inlined_depth(UINT32_MAX),
      m_current_inlined_pc(LLDB_INVALID_ADDRESS),
      m_show_inlined_frames(show_inline_frames), m_identifier(provider_id) {
  if (prev_frames_sp) {
    m_current_inlined_depth = prev_frames_sp->m_current_inlined_depth;
    m_current_inlined_pc = prev_frames_sp->m_current_inlined_pc;
  }
}
 
StackFrameList::~StackFrameList() {
  // Call clear since this takes a lock and clears the stack frame list in case
  // another thread is currently using this stack frame list
  Clear();
}
 
SyntheticStackFrameList::SyntheticStackFrameList(
    Thread &thread, lldb::StackFrameListSP input_frames,
    const lldb::StackFrameListSP &prev_frames_sp, bool show_inline_frames,
    lldb::SyntheticFrameProviderSP provider_sp, uint64_t provider_id)
    : StackFrameList(thread, prev_frames_sp, show_inline_frames, provider_id),
      m_input_frames(std::move(input_frames)),
      m_provider(std::move(provider_sp)) {}
 
bool SyntheticStackFrameList::FetchFramesUpTo(
    uint32_t end_idx, InterruptionControl allow_interrupt) {
 
  // Use the provider to generate frames lazily.
  if (m_provider) {
    // Count how many synthetic frames already exist so we assign unique CFAs
    // to new ones. This must not be a local initialized to zero — when
    // FetchFramesUpTo is called incrementally (first for a small range, then
    // for the full stack), a zero-initialized counter would hand out duplicate
    // CFA values, creating StackID collisions for PC-less synthetic frames.
    size_t num_synthetic_frames = 0;
    for (const auto &f : m_frames) {
      if (f && f->IsSynthetic())
        num_synthetic_frames++;
    }
 
    // Keep fetching until we reach end_idx or the provider returns an error.
    for (uint32_t idx = m_frames.size(); idx <= end_idx; idx++) {
      if (allow_interrupt &&
          m_thread.GetProcess()->GetTarget().GetDebugger().InterruptRequested())
        return true;
 
      // Ensure the provider sees its parent StackFrameList, not the
      // synthetic list being constructed. In a chain A->B->C, provider C
      // must consult B's output - using its own list would be nonsensical.
      // This also applies when the provider runs commands or expressions:
      // any path that fetches a StackFrameList should transparently get the
      // parent list. As a side benefit, this avoids circular re-entrancy and
      // deadlocks on the private state thread.
      m_thread.PushProviderFrameList(m_input_frames);
      auto clear_active_frames =
          llvm::scope_exit([&]() { m_thread.PopProviderFrameList(); });
      auto frame_or_err = m_provider->GetFrameAtIndex(idx);
 
      if (!frame_or_err) {
        // Provider returned error - we've reached the end.
        LLDB_LOG_ERROR(GetLog(LLDBLog::Thread), frame_or_err.takeError(),
                       "Frame provider reached end at index {1}: {0}", idx);
        SetAllFramesFetched();
        break;
      }
      StackFrameSP frame_sp = *frame_or_err;
      // Synthetic frames can provide a CFA.  If they haven't, set it to the
      // frame index which will at least order the frames on this stop.
      if (frame_sp->IsSynthetic() && !frame_sp->GetStackID().IsValid())
        frame_sp->GetStackID().SetCFA(num_synthetic_frames++,
                                      GetThread().GetProcess().get());
      // Set the frame list weak pointer so ExecutionContextRef can resolve
      // the frame without calling Thread::GetStackFrameList().
      frame_sp->m_frame_list_id = GetIdentifier();
      m_frames.push_back(frame_sp);
    }
 
    return false; // Not interrupted.
  }
 
  // If no provider, fall back to the base implementation.
  return StackFrameList::FetchFramesUpTo(end_idx, allow_interrupt);
}
 
void StackFrameList::CalculateCurrentInlinedDepth() {
  uint32_t cur_inlined_depth = GetCurrentInlinedDepth();
  if (cur_inlined_depth == UINT32_MAX) {
    ResetCurrentInlinedDepth();
  }
}
 
uint32_t StackFrameList::GetCurrentInlinedDepth() {
  std::lock_guard<std::mutex> guard(m_inlined_depth_mutex);
  if (m_show_inlined_frames && m_current_inlined_pc != LLDB_INVALID_ADDRESS) {
    lldb::addr_t cur_pc = m_thread.GetRegisterContext()->GetPC();
    if (cur_pc != m_current_inlined_pc) {
      m_current_inlined_pc = LLDB_INVALID_ADDRESS;
      m_current_inlined_depth = UINT32_MAX;
      LLDB_LOGF_VERBOSE(
          GetLog(LLDBLog::Step),
          "GetCurrentInlinedDepth: invalidating current inlined depth.\n");
    }
    return m_current_inlined_depth;
  } else {
    return UINT32_MAX;
  }
}
 
void StackFrameList::ResetCurrentInlinedDepth() {
  if (!m_show_inlined_frames)
    return;
 
  StopInfoSP stop_info_sp = m_thread.GetStopInfo();
  if (!stop_info_sp)
    return;
 
  bool inlined = true;
  auto inline_depth = stop_info_sp->GetSuggestedStackFrameIndex(inlined);
  // We're only adjusting the inlined stack here.
  Log *log = GetLog(LLDBLog::Step);
  if (inline_depth) {
    std::lock_guard<std::mutex> guard(m_inlined_depth_mutex);
    m_current_inlined_depth = *inline_depth;
    m_current_inlined_pc = m_thread.GetRegisterContext()->GetPC();
 
    LLDB_LOGF_VERBOSE(log,
                      "ResetCurrentInlinedDepth: setting inlined "
                      "depth: %d 0x%" PRIx64 ".\n",
                      m_current_inlined_depth, m_current_inlined_pc);
  } else {
    std::lock_guard<std::mutex> guard(m_inlined_depth_mutex);
    m_current_inlined_pc = LLDB_INVALID_ADDRESS;
    m_current_inlined_depth = UINT32_MAX;
    LLDB_LOGF_VERBOSE(
        log, "ResetCurrentInlinedDepth: Invalidating current inlined depth.\n");
  }
}
 
bool StackFrameList::DecrementCurrentInlinedDepth() {
  if (m_show_inlined_frames) {
    uint32_t current_inlined_depth = GetCurrentInlinedDepth();
    if (current_inlined_depth != UINT32_MAX) {
      if (current_inlined_depth > 0) {
        std::lock_guard<std::mutex> guard(m_inlined_depth_mutex);
        m_current_inlined_depth--;
        return true;
      }
    }
  }
  return false;
}
 
void StackFrameList::SetCurrentInlinedDepth(uint32_t new_depth) {
  std::lock_guard<std::mutex> guard(m_inlined_depth_mutex);
  m_current_inlined_depth = new_depth;
  if (new_depth == UINT32_MAX)
    m_current_inlined_pc = LLDB_INVALID_ADDRESS;
  else
    m_current_inlined_pc = m_thread.GetRegisterContext()->GetPC();
}
 
bool StackFrameList::WereAllFramesFetched() const {
  llvm::sys::ScopedReader guard(m_list_mutex);
  return GetAllFramesFetched();
}
 
/// A sequence of calls that comprise some portion of a backtrace. Each frame
/// is represented as a pair of a callee and an address within the callee.
struct CallDescriptor {
  SymbolContext callee;
  CallEdge::AddrType address_type = CallEdge::AddrType::Call;
  addr_t address = LLDB_INVALID_ADDRESS;
};
using CallSequence = std::vector<CallDescriptor>;
 
/// Find the unique path through the call graph from \p begin (with return PC
/// \p return_pc) to \p end. On success this path is stored into \p path, and
/// on failure \p path is unchanged.
/// This function doesn't currently access StackFrameLists at all, it only looks
/// at the frame set in the ExecutionContext it passes around.
static void FindInterveningFrames(Function &begin, Function &end,
                                  ExecutionContext &exe_ctx, Target &target,
                                  addr_t return_pc, CallSequence &path,
                                  ModuleList &images, Log *log) {
  LLDB_LOG_VERBOSE(log, "Finding frames between {0} and {1}, retn-pc={2:x}",
                   begin.GetDisplayName(), end.GetDisplayName(), return_pc);
 
  // Find a non-tail calling edge with the correct return PC.
  if (log)
    for (const auto &edge : begin.GetCallEdges())
      LLDB_LOG_VERBOSE(log,
                       "FindInterveningFrames: found call with retn-PC = {0:x}",
                       edge->GetReturnPCAddress(begin, target));
  CallEdge *first_edge = begin.GetCallEdgeForReturnAddress(return_pc, target);
  if (!first_edge) {
    LLDB_LOG_VERBOSE(log,
                     "No call edge outgoing from {0} with retn-PC == {1:x}",
                     begin.GetDisplayName(), return_pc);
    return;
  }
 
  // The first callee may not be resolved, or there may be nothing to fill in.
  SymbolContext first_callee = first_edge->GetCallee(images, exe_ctx);
  if (!first_callee.function) {
    LLDB_LOG_VERBOSE(log, "Could not resolve callee");
    return;
  }
  if (first_callee.function == &end) {
    LLDB_LOG_VERBOSE(
        log, "Not searching further, first callee is {0} (retn-PC: {1:x})",
        end.GetDisplayName(), return_pc);
    return;
  }
 
  // Run DFS on the tail-calling edges out of the first callee to find \p end.
  // Fully explore the set of functions reachable from the first edge via tail
  // calls in order to detect ambiguous executions.
  struct DFS {
    CallSequence active_path = {};
    CallSequence solution_path = {};
    llvm::SmallPtrSet<Function *, 2> visited_nodes = {};
    bool ambiguous = false;
    Function *end;
    ModuleList &images;
    Target &target;
    ExecutionContext &context;
 
    DFS(Function *end, ModuleList &images, Target &target,
        ExecutionContext &context)
        : end(end), images(images), target(target), context(context) {}
 
    void search(CallEdge &first_edge, const SymbolContext &first_callee,
                CallSequence &path) {
      dfs(first_edge, first_callee);
      if (!ambiguous)
        path = std::move(solution_path);
    }
 
    void dfs(CallEdge &current_edge, const SymbolContext &callee) {
      // Found a path to the target function.
      if (callee.function == end) {
        if (solution_path.empty())
          solution_path = active_path;
        else
          ambiguous = true;
        return;
      }
 
      // Terminate the search if tail recursion is found, or more generally if
      // there's more than one way to reach a target. This errs on the side of
      // caution: it conservatively stops searching when some solutions are
      // still possible to save time in the average case.
      if (!visited_nodes.insert(callee.function).second) {
        ambiguous = true;
        return;
      }
 
      // Search the calls made from this callee.
      active_path.push_back(CallDescriptor{callee});
      for (const auto &edge : callee.function->GetTailCallingEdges()) {
        SymbolContext next_callee = edge->GetCallee(images, context);
        if (!next_callee.function)
          continue;
 
        std::tie(active_path.back().address_type, active_path.back().address) =
            edge->GetCallerAddress(*callee.function, target);
 
        dfs(*edge, next_callee);
        if (ambiguous)
          return;
      }
      active_path.pop_back();
    }
  };
 
  DFS(&end, images, target, exe_ctx).search(*first_edge, first_callee, path);
}
 
/// Given that \p next_frame will be appended to the frame list, synthesize
/// tail call frames between the current end of the list and \p next_frame.
/// If any frames are added, adjust the frame index of \p next_frame.
///
///   --------------
///   |    ...     | <- Completed frames.
///   --------------
///   | prev_frame |
///   --------------
///   |    ...     | <- Artificial frames inserted here.
///   --------------
///   | next_frame |
///   --------------
///   |    ...     | <- Not-yet-visited frames.
///   --------------
void StackFrameList::SynthesizeTailCallFrames(StackFrame &next_frame) {
  // Cannot synthesize tail call frames when the stack is empty (there is no
  // "previous" frame).
  if (m_frames.empty())
    return;
 
  TargetSP target_sp = next_frame.CalculateTarget();
  if (!target_sp)
    return;
 
  lldb::RegisterContextSP next_reg_ctx_sp = next_frame.GetRegisterContext();
  if (!next_reg_ctx_sp)
    return;
 
  Log *log = GetLog(LLDBLog::Step);
 
  StackFrame &prev_frame = *m_frames.back().get();
 
  // Find the functions prev_frame and next_frame are stopped in. The function
  // objects are needed to search the lazy call graph for intervening frames.
  Function *prev_func =
      prev_frame.GetSymbolContext(eSymbolContextFunction).function;
  if (!prev_func) {
    LLDB_LOG(log, "SynthesizeTailCallFrames: can't find previous function");
    return;
  }
  Function *next_func =
      next_frame.GetSymbolContext(eSymbolContextFunction).function;
  if (!next_func) {
    LLDB_LOG(log, "SynthesizeTailCallFrames: can't find next function");
    return;
  }
 
  // Try to find the unique sequence of (tail) calls which led from next_frame
  // to prev_frame.
  CallSequence path;
  addr_t return_pc = next_reg_ctx_sp->GetPC();
  Target &target = *target_sp.get();
  ModuleList &images = next_frame.CalculateTarget()->GetImages();
  ExecutionContext exe_ctx(target_sp, /*get_process=*/true);
  exe_ctx.SetFramePtr(&next_frame);
  FindInterveningFrames(*next_func, *prev_func, exe_ctx, target, return_pc,
                        path, images, log);
 
  // Push synthetic tail call frames.
  for (const auto &calleeInfo : llvm::reverse(path)) {
    Function *callee = calleeInfo.callee.function;
    uint32_t frame_idx = m_frames.size();
    uint32_t concrete_frame_idx = next_frame.GetConcreteFrameIndex();
    addr_t cfa = LLDB_INVALID_ADDRESS;
    bool cfa_is_valid = false;
    addr_t pc = calleeInfo.address;
    // If the callee address refers to the call instruction, we do not want to
    // subtract 1 from this value.
    const bool artificial = true;
    const bool behaves_like_zeroth_frame =
        calleeInfo.address_type == CallEdge::AddrType::Call;
    SymbolContext sc;
    callee->CalculateSymbolContext(&sc);
    auto synth_frame = std::make_shared<StackFrame>(
        m_thread.shared_from_this(), frame_idx, concrete_frame_idx, cfa,
        cfa_is_valid, pc, StackFrame::Kind::Regular, artificial,
        behaves_like_zeroth_frame, &sc);
    synth_frame->m_frame_list_id = GetIdentifier();
    m_frames.push_back(synth_frame);
    LLDB_LOG(log, "Pushed frame {0} at {1:x}", callee->GetDisplayName(), pc);
  }
 
  // If any frames were created, adjust next_frame's index.
  if (!path.empty())
    next_frame.SetFrameIndex(m_frames.size());
}
 
uint32_t StackFrameList::SynthesizeInlineFrames(StackFrameSP frame_sp,
                                                addr_t cfa) {
  SymbolContext unwind_sc =
      frame_sp->GetSymbolContext(eSymbolContextBlock | eSymbolContextFunction);
  if (!unwind_sc.block)
    return 0;
 
  TargetSP target_sp = m_thread.CalculateTarget();
  uint32_t concrete_frame_idx = frame_sp->GetConcreteFrameIndex();
  Address curr_frame_address(frame_sp->GetFrameCodeAddressForSymbolication());
 
  SymbolContext next_frame_sc;
  Address next_frame_address;
  uint32_t num_inlined_frames = 0;
 
  const bool behaves_like_zeroth_frame = frame_sp->m_behaves_like_zeroth_frame;
 
  while (unwind_sc.GetParentOfInlinedScope(curr_frame_address, next_frame_sc,
                                           next_frame_address)) {
    next_frame_sc.line_entry.ApplyFileMappings(target_sp);
    StackFrameSP inline_frame_sp = std::make_shared<StackFrame>(
        m_thread.shared_from_this(), m_frames.size(), concrete_frame_idx,
        frame_sp->GetRegisterContextSP(), cfa, next_frame_address,
        behaves_like_zeroth_frame, &next_frame_sc);
 
    inline_frame_sp->m_frame_list_id = GetIdentifier();
    m_frames.push_back(inline_frame_sp);
    unwind_sc = next_frame_sc;
    curr_frame_address = next_frame_address;
    ++num_inlined_frames;
  }
 
  return num_inlined_frames;
}
 
bool StackFrameList::GetFramesUpTo(uint32_t end_idx,
                                   InterruptionControl allow_interrupt) {
  // GetFramesUpTo is always called with the intent to add frames, so get the
  // writer lock:
  llvm::sys::ScopedWriter guard(m_list_mutex);
  // Now that we have the lock, check to make sure someone didn't get there
  // ahead of us:
  if (m_frames.size() > end_idx || GetAllFramesFetched())
    return false;
 
  // Do not fetch frames for an invalid thread.
  bool was_interrupted = false;
  if (!m_thread.IsValid())
    return false;
 
  // lock the writer side of m_list_mutex as we're going to add frames here:
  if (!m_show_inlined_frames) {
    if (end_idx < m_concrete_frames_fetched)
      return false;
    // We're adding concrete frames now:
    // FIXME: This should also be interruptible:
    FetchOnlyConcreteFramesUpTo(end_idx);
    return false;
  }
 
  // We're adding concrete and inlined frames now:
  was_interrupted = FetchFramesUpTo(end_idx, allow_interrupt);
 
#if defined(DEBUG_STACK_FRAMES)
  s.PutCString("\n\nNew frames:\n");
  Dump(&s);
  s.EOL();
#endif
  return was_interrupted;
}
 
void StackFrameList::FetchOnlyConcreteFramesUpTo(uint32_t end_idx) {
  assert(m_thread.IsValid() && "Expected valid thread");
  assert(m_frames.size() <= end_idx && "Expected there to be frames to fill");
 
  Unwind &unwinder = m_thread.GetUnwinder();
 
  if (end_idx < m_concrete_frames_fetched)
    return;
 
  uint32_t num_frames = unwinder.GetFramesUpTo(end_idx);
  if (num_frames <= end_idx + 1) {
    // Done unwinding.
    m_concrete_frames_fetched = UINT32_MAX;
  }
 
  // Don't create the frames eagerly. Defer this work to GetFrameAtIndex,
  // which can lazily query the unwinder to create frames.
  m_frames.resize(num_frames);
}
 
bool StackFrameList::FetchFramesUpTo(uint32_t end_idx,
                                     InterruptionControl allow_interrupt) {
  Unwind &unwinder = m_thread.GetUnwinder();
  bool was_interrupted = false;
 
#if defined(DEBUG_STACK_FRAMES)
  StreamFile s(stdout, false);
#endif
  // If we are hiding some frames from the outside world, we need to add
  // those onto the total count of frames to fetch.  However, we don't need
  // to do that if end_idx is 0 since in that case we always get the first
  // concrete frame and all the inlined frames below it...  And of course, if
  // end_idx is UINT32_MAX that means get all, so just do that...
 
  uint32_t inlined_depth = 0;
  if (end_idx > 0 && end_idx != UINT32_MAX) {
    inlined_depth = GetCurrentInlinedDepth();
    if (inlined_depth != UINT32_MAX) {
      if (end_idx > 0)
        end_idx += inlined_depth;
    }
  }
 
  StackFrameSP unwind_frame_sp;
  Debugger &dbg = m_thread.GetProcess()->GetTarget().GetDebugger();
  do {
    uint32_t idx = m_concrete_frames_fetched++;
    lldb::addr_t pc = LLDB_INVALID_ADDRESS;
    lldb::addr_t cfa = LLDB_INVALID_ADDRESS;
    bool behaves_like_zeroth_frame = (idx == 0);
    if (idx == 0) {
      // We might have already created frame zero, only create it if we need
      // to.
      if (m_frames.empty()) {
        RegisterContextSP reg_ctx_sp(m_thread.GetRegisterContext());
 
        if (reg_ctx_sp) {
          const bool success = unwinder.GetFrameInfoAtIndex(
              idx, cfa, pc, behaves_like_zeroth_frame);
          // There shouldn't be any way not to get the frame info for frame
          // 0. But if the unwinder can't make one, lets make one by hand
          // with the SP as the CFA and see if that gets any further.
          if (!success) {
            cfa = reg_ctx_sp->GetSP();
            pc = reg_ctx_sp->GetPC();
          }
 
          unwind_frame_sp = std::make_shared<StackFrame>(
              m_thread.shared_from_this(), m_frames.size(), idx, reg_ctx_sp,
              cfa, pc, behaves_like_zeroth_frame, nullptr);
          unwind_frame_sp->m_frame_list_id = GetIdentifier();
          m_frames.push_back(unwind_frame_sp);
        }
      } else {
        unwind_frame_sp = m_frames.front();
        cfa = unwind_frame_sp->m_id.GetCallFrameAddressWithoutMetadata();
      }
    } else {
      // Check for interruption when building the frames.
      // Do the check in idx > 0 so that we'll always create a 0th frame.
      if (allow_interrupt &&
          INTERRUPT_REQUESTED(dbg, "Interrupted having fetched {0} frames",
                              m_frames.size())) {
        was_interrupted = true;
        break;
      }
 
      const bool success =
          unwinder.GetFrameInfoAtIndex(idx, cfa, pc, behaves_like_zeroth_frame);
      if (!success) {
        // We've gotten to the end of the stack.
        SetAllFramesFetched();
        break;
      }
      const bool cfa_is_valid = true;
      unwind_frame_sp = std::make_shared<StackFrame>(
          m_thread.shared_from_this(), m_frames.size(), idx, cfa, cfa_is_valid,
          pc, StackFrame::Kind::Regular, false, behaves_like_zeroth_frame,
          nullptr);
 
      // Create synthetic tail call frames between the previous frame and the
      // newly-found frame. The new frame's index may change after this call,
      // although its concrete index will stay the same.
      SynthesizeTailCallFrames(*unwind_frame_sp.get());
 
      unwind_frame_sp->m_frame_list_id = GetIdentifier();
      m_frames.push_back(unwind_frame_sp);
    }
 
    assert(unwind_frame_sp);
    SynthesizeInlineFrames(unwind_frame_sp, cfa);
  } while (m_frames.size() - 1 < end_idx);
 
  // Don't try to merge till you've calculated all the frames in this stack.
  if (GetAllFramesFetched() && m_prev_frames_sp) {
    StackFrameList *prev_frames = m_prev_frames_sp.get();
    StackFrameList *curr_frames = this;
 
#if defined(DEBUG_STACK_FRAMES)
    s.PutCString("\nprev_frames:\n");
    prev_frames->Dump(&s);
    s.PutCString("\ncurr_frames:\n");
    curr_frames->Dump(&s);
    s.EOL();
#endif
    size_t curr_frame_num, prev_frame_num;
 
    for (curr_frame_num = curr_frames->m_frames.size(),
        prev_frame_num = prev_frames->m_frames.size();
         curr_frame_num > 0 && prev_frame_num > 0;
         --curr_frame_num, --prev_frame_num) {
      const size_t curr_frame_idx = curr_frame_num - 1;
      const size_t prev_frame_idx = prev_frame_num - 1;
      StackFrameSP curr_frame_sp(curr_frames->m_frames[curr_frame_idx]);
      StackFrameSP prev_frame_sp(prev_frames->m_frames[prev_frame_idx]);
 
#if defined(DEBUG_STACK_FRAMES)
      s.Printf("\n\nCurr frame #%u ", curr_frame_idx);
      if (curr_frame_sp)
        curr_frame_sp->Dump(&s, true, false);
      else
        s.PutCString("NULL");
      s.Printf("\nPrev frame #%u ", prev_frame_idx);
      if (prev_frame_sp)
        prev_frame_sp->Dump(&s, true, false);
      else
        s.PutCString("NULL");
#endif
 
      StackFrame *curr_frame = curr_frame_sp.get();
      StackFrame *prev_frame = prev_frame_sp.get();
 
      if (curr_frame == nullptr || prev_frame == nullptr)
        break;
 
      // Check the stack ID to make sure they are equal.
      if (curr_frame->GetStackID() != prev_frame->GetStackID())
        break;
 
      // Only adopt a frame that a list with this identifier produced. A frame
      // from another layer of the provider chain, scripted or borrowed, can
      // share its StackID with a frame of this list without being
      // interchangeable with it. Skipping it is safe because the merge only
      // carries cached state onto a frame this list has already unwound
      // correctly.
      if (prev_frame->GetContainingStackFrameListIdentifier() !=
          GetIdentifier())
        continue;
 
      prev_frame->UpdatePreviousFrameFromCurrentFrame(*curr_frame);
      // Now copy the fixed up previous frame into the current frames so the
      // pointer doesn't change.
      m_frames[curr_frame_idx] = prev_frame_sp;
 
#if defined(DEBUG_STACK_FRAMES)
      s.PutCString("\n    Copying previous frame to current frame");
#endif
    }
    // We are done with the old stack frame list, we can release it now.
    m_prev_frames_sp.reset();
  }
  // Don't report interrupted if we happen to have gotten all the frames:
  if (!GetAllFramesFetched())
    return was_interrupted;
  return false;
}
 
uint32_t StackFrameList::GetNumFrames(bool can_create) {
  if (!WereAllFramesFetched() && can_create) {
    // Don't allow interrupt or we might not return the correct count
    GetFramesUpTo(UINT32_MAX, DoNotAllowInterruption);
  }
  uint32_t frame_idx;
  {
    llvm::sys::ScopedReader guard(m_list_mutex);
    frame_idx = GetVisibleStackFrameIndex(m_frames.size());
  }
  return frame_idx;
}
 
void StackFrameList::Dump(Stream *s) {
  if (s == nullptr)
    return;
 
  llvm::sys::ScopedReader guard(m_list_mutex);
 
  const_iterator pos, begin = m_frames.begin(), end = m_frames.end();
  for (pos = begin; pos != end; ++pos) {
    StackFrame *frame = (*pos).get();
    s->Printf("%p: ", static_cast<void *>(frame));
    if (frame) {
      frame->GetStackID().Dump(s);
      frame->DumpUsingSettingsFormat(s);
    } else
      s->Printf("frame #%u", (uint32_t)std::distance(begin, pos));
    s->EOL();
  }
  s->EOL();
}
 
StackFrameSP StackFrameList::GetFrameAtIndex(uint32_t idx) {
  StackFrameSP frame_sp;
  uint32_t original_idx = idx;
 
  // We're going to consult the m_frames.size, but if there are already
  // enough frames for our request we don't want to block other readers, so
  // first acquire the shared lock:
  { // Scope for shared lock:
    llvm::sys::ScopedReader guard(m_list_mutex);
 
    uint32_t inlined_depth = GetCurrentInlinedDepth();
    if (inlined_depth != UINT32_MAX)
      idx += inlined_depth;
 
    if (idx < m_frames.size())
      frame_sp = m_frames[idx];
 
    if (frame_sp)
      return frame_sp;
  } // End of reader lock scope
 
  // GetFramesUpTo will fill m_frames with as many frames as you asked for, if
  // there are that many.  If there weren't then you asked for too many frames.
  // GetFramesUpTo returns true if interrupted:
  if (GetFramesUpTo(idx, AllowInterruption)) {
    Log *log = GetLog(LLDBLog::Thread);
    LLDB_LOG(log, "GetFrameAtIndex was interrupted");
    return {};
  }
 
  { // Now we're accessing m_frames as a reader, so acquire the reader lock.
    llvm::sys::ScopedReader guard(m_list_mutex);
    if (idx < m_frames.size()) {
      frame_sp = m_frames[idx];
    } else if (original_idx == 0) {
      // There should ALWAYS be a frame at index 0.  If something went wrong
      // with the CurrentInlinedDepth such that there weren't as many frames as
      // we thought taking that into account, then reset the current inlined
      // depth and return the real zeroth frame.
      if (m_frames.empty()) {
        // Why do we have a thread with zero frames, that should not ever
        // happen...
        assert(!m_thread.IsValid() && "A valid thread has no frames.");
      } else {
        ResetCurrentInlinedDepth();
        frame_sp = m_frames[original_idx];
      }
    }
  } // End of reader lock scope
 
  return frame_sp;
}
 
StackFrameSP
StackFrameList::GetFrameWithConcreteFrameIndex(uint32_t unwind_idx) {
  // First try assuming the unwind index is the same as the frame index. The
  // unwind index is always greater than or equal to the frame index, so it is
  // a good place to start. If we have inlined frames we might have 5 concrete
  // frames (frame unwind indexes go from 0-4), but we might have 15 frames
  // after we make all the inlined frames. Most of the time the unwind frame
  // index (or the concrete frame index) is the same as the frame index.
  uint32_t frame_idx = unwind_idx;
  StackFrameSP frame_sp(GetFrameAtIndex(frame_idx));
  while (frame_sp) {
    if (frame_sp->GetFrameIndex() == unwind_idx)
      break;
    frame_sp = GetFrameAtIndex(++frame_idx);
  }
  return frame_sp;
}
 
static bool CompareStackID(const StackFrameSP &stack_sp,
                           const StackID &stack_id) {
  return stack_sp->GetStackID().IsYoungerThan(stack_id);
}
 
StackFrameSP StackFrameList::GetFrameWithStackID(const StackID &stack_id) {
  StackFrameSP frame_sp;
 
  if (stack_id.IsValid()) {
    uint32_t frame_idx = 0;
    {
      // First see if the frame is already realized.  This is the scope for
      // the shared mutex:
      llvm::sys::ScopedReader guard(m_list_mutex);
      // Do a binary search in case the stack frame is already in our cache
      collection::const_iterator pos =
          llvm::lower_bound(m_frames, stack_id, CompareStackID);
      if (pos != m_frames.end() && (*pos)->GetStackID() == stack_id)
        return *pos;
    }
    // If we needed to add more frames, we would get to here.
    do {
      frame_sp = GetFrameAtIndex(frame_idx);
      if (frame_sp && frame_sp->GetStackID() == stack_id)
        break;
      frame_idx++;
    } while (frame_sp);
  }
  return frame_sp;
}
 
bool StackFrameList::SetFrameAtIndex(uint32_t idx, StackFrameSP &frame_sp) {
  llvm::sys::ScopedWriter guard(m_list_mutex);
  if (idx >= m_frames.size())
    m_frames.resize(idx + 1);
  // Make sure allocation succeeded by checking bounds again
  if (idx < m_frames.size()) {
    m_frames[idx] = frame_sp;
    return true;
  }
  return false; // resize failed, out of memory?
}
 
void StackFrameList::SelectMostRelevantFrame() {
  // Don't call into the frame recognizers while evaluating an expression on
  // the private state thread, as they can cause code to run in the inferior
  // process, and that can cause deadlocks when fetching stop events for the
  // expression.
  Policy policy = PolicyStack::Get().Current();
  if (!policy.capabilities.can_run_frame_recognizers)
    return;
 
  Log *log = GetLog(LLDBLog::Thread);
 
  // Only the top frame should be recognized.
  StackFrameSP frame_sp = GetFrameAtIndex(0);
  if (!frame_sp) {
    LLDB_LOG(log, "Failed to construct Frame #0");
    return;
  }
 
  RecognizedStackFrameSP recognized_frame_sp = frame_sp->GetRecognizedFrame();
 
  if (recognized_frame_sp) {
    if (StackFrameSP most_relevant_frame_sp =
            recognized_frame_sp->GetMostRelevantFrame()) {
      LLDB_LOG(log, "Found most relevant frame at index {0}",
               most_relevant_frame_sp->GetFrameIndex());
      SetSelectedFrame(most_relevant_frame_sp.get());
      return;
    }
  }
  LLDB_LOG(log, "Frame #0 not recognized");
 
  // If this thread has a non-trivial StopInfo, then let it suggest
  // a most relevant frame:
  StopInfoSP stop_info_sp = m_thread.GetStopInfo();
  uint32_t stack_idx = 0;
  bool found_relevant = false;
  if (stop_info_sp) {
    // Here we're only asking the stop info if it wants to adjust the real stack
    // index.  We have to ask about the m_inlined_stack_depth in
    // Thread::ShouldStop since the plans need to reason with that info.
    bool inlined = false;
    std::optional<uint32_t> stack_opt =
        stop_info_sp->GetSuggestedStackFrameIndex(inlined);
    if (stack_opt) {
      stack_idx = *stack_opt;
      found_relevant = true;
    }
  }
 
  frame_sp = GetFrameAtIndex(stack_idx);
  if (!frame_sp)
    LLDB_LOG(log, "Stop info suggested relevant frame {0} but it didn't exist",
             stack_idx);
  else if (found_relevant)
    LLDB_LOG(log, "Setting selected frame from stop info to {0}", stack_idx);
  // Note, we don't have to worry about "inlined" frames here, because we've
  // already calculated the inlined frame in Thread::ShouldStop, and
  // SetSelectedFrame will take care of that adjustment for us.
  SetSelectedFrame(frame_sp.get());
 
  if (!found_relevant)
    LLDB_LOG(log, "No relevant frame!");
}
 
uint32_t
StackFrameList::GetSelectedFrameIndex(SelectMostRelevant select_most_relevant) {
  std::lock_guard<std::recursive_mutex> guard(m_selected_frame_mutex);
 
  if (!m_selected_frame_idx && select_most_relevant)
    SelectMostRelevantFrame();
  if (!m_selected_frame_idx) {
    // If we aren't selecting the most relevant frame, and the selected frame
    // isn't set, then don't force a selection here, just return 0.
    if (!select_most_relevant)
      return 0;
    // If the inlined stack frame is set, then use that:
    m_selected_frame_idx = 0;
  }
  return *m_selected_frame_idx;
}
 
uint32_t StackFrameList::SetSelectedFrame(lldb_private::StackFrame *frame) {
  llvm::sys::ScopedReader guard(m_list_mutex);
  std::lock_guard<std::recursive_mutex> selected_frame_guard(
      m_selected_frame_mutex);
 
  const_iterator pos;
  const_iterator begin = m_frames.begin();
  const_iterator end = m_frames.end();
  m_selected_frame_idx = 0;
 
  for (pos = begin; pos != end; ++pos) {
    if (pos->get() == frame) {
      m_selected_frame_idx = std::distance(begin, pos);
      uint32_t inlined_depth = GetCurrentInlinedDepth();
      if (inlined_depth != UINT32_MAX)
        m_selected_frame_idx = *m_selected_frame_idx - inlined_depth;
      break;
    }
  }
  SetDefaultFileAndLineToSelectedFrame();
  return *m_selected_frame_idx;
}
 
bool StackFrameList::SetSelectedFrameByIndex(uint32_t idx) {
  StackFrameSP frame_sp(GetFrameAtIndex(idx));
  if (frame_sp) {
    SetSelectedFrame(frame_sp.get());
    return true;
  } else
    return false;
}
 
void StackFrameList::SetDefaultFileAndLineToSelectedFrame() {
  if (m_thread.GetID() ==
      m_thread.GetProcess()->GetThreadList().GetSelectedThread()->GetID()) {
    StackFrameSP frame_sp(
        GetFrameAtIndex(GetSelectedFrameIndex(DoNoSelectMostRelevantFrame)));
    if (frame_sp) {
      SymbolContext sc = frame_sp->GetSymbolContext(eSymbolContextLineEntry);
      if (sc.line_entry.GetFile())
        m_thread.CalculateTarget()->GetSourceManager().SetDefaultFileAndLine(
            sc.line_entry.file_sp, sc.line_entry.line);
    }
  }
}
 
// The thread has been run, reset the number stack frames to zero so we can
// determine how many frames we have lazily.
// Note, we don't actually re-use StackFrameLists, we always make a new
// StackFrameList every time we stop, and then copy frame information frame
// by frame from the old to the new StackFrameList.  So the comment above,
// does not describe how StackFrameLists are currently used.
// Clear is currently only used to clear the list in the destructor.
void StackFrameList::Clear() {
  llvm::sys::ScopedWriter guard(m_list_mutex);
  m_frames.clear();
  m_concrete_frames_fetched = 0;
  std::lock_guard<std::recursive_mutex> selected_frame_guard(
      m_selected_frame_mutex);
  m_selected_frame_idx.reset();
}
 
lldb::StackFrameSP
StackFrameList::GetStackFrameSPForStackFramePtr(StackFrame *stack_frame_ptr) {
  llvm::sys::ScopedReader guard(m_list_mutex);
  const_iterator pos;
  const_iterator begin = m_frames.begin();
  const_iterator end = m_frames.end();
  lldb::StackFrameSP ret_sp;
 
  for (pos = begin; pos != end; ++pos) {
    if (pos->get() == stack_frame_ptr) {
      ret_sp = (*pos);
      break;
    }
  }
  return ret_sp;
}
 
bool StackFrameList::IsNextFrameHidden(lldb_private::StackFrame &frame) {
  uint32_t frame_idx = frame.GetFrameIndex();
  StackFrameSP frame_sp = GetFrameAtIndex(frame_idx + 1);
  if (!frame_sp)
    return false;
  return frame_sp->IsHidden();
}
 
bool StackFrameList::IsPreviousFrameHidden(lldb_private::StackFrame &frame) {
  uint32_t frame_idx = frame.GetFrameIndex();
  if (frame_idx == 0)
    return false;
  StackFrameSP frame_sp = GetFrameAtIndex(frame_idx - 1);
  if (!frame_sp)
    return false;
  return frame_sp->IsHidden();
}
 
std::string StackFrameList::GetFrameMarker(lldb::StackFrameSP frame_sp,
                                           lldb::StackFrameSP selected_frame_sp,
                                           bool show_hidden_marker) {
  bool show_unicode_marker = Terminal::SupportsUnicode() && show_hidden_marker;
  if (frame_sp == selected_frame_sp)
    return show_unicode_marker ? " * " : "* ";
  if (!show_unicode_marker)
    return "  ";
  if (IsPreviousFrameHidden(*frame_sp))
    return reinterpret_cast<const char *>(u8"﹉ ");
  if (IsNextFrameHidden(*frame_sp))
    return reinterpret_cast<const char *>(u8"﹍ ");
  return "   ";
}
 
size_t StackFrameList::GetStatus(Stream &strm, uint32_t first_frame,
                                 uint32_t num_frames, bool show_frame_info,
                                 uint32_t num_frames_with_source,
                                 bool show_unique, bool show_hidden,
                                 bool show_hidden_marker,
                                 bool show_selected_frame) {
  size_t num_frames_displayed = 0;
 
  if (num_frames == 0)
    return 0;
 
  StackFrameSP frame_sp;
  uint32_t frame_idx = 0;
  uint32_t last_frame;
 
  // Don't let the last frame wrap around...
  if (num_frames == UINT32_MAX)
    last_frame = UINT32_MAX;
  else
    last_frame = first_frame + num_frames;
 
  StackFrameSP selected_frame_sp =
      m_thread.GetSelectedFrame(DoNoSelectMostRelevantFrame);
  std::string marker;
  for (frame_idx = first_frame; frame_idx < last_frame; ++frame_idx) {
    frame_sp = GetFrameAtIndex(frame_idx);
    if (!frame_sp)
      break;
 
    if (show_selected_frame)
      marker = GetFrameMarker(frame_sp, selected_frame_sp, show_hidden_marker);
    else
      marker = GetFrameMarker(frame_sp, /*selected_frame_sp=*/nullptr,
                              show_hidden_marker);
 
    // Hide uninteresting frames unless it's the selected frame.
    if (!show_hidden && frame_sp != selected_frame_sp && frame_sp->IsHidden())
      continue;
 
    // Check for interruption here.  If we're fetching arguments, this loop
    // can go slowly:
    Debugger &dbg = m_thread.GetProcess()->GetTarget().GetDebugger();
    if (INTERRUPT_REQUESTED(
            dbg, "Interrupted dumping stack for thread {0:x} with {1} shown.",
            m_thread.GetID(), num_frames_displayed))
      break;
 
    if (!frame_sp->GetStatus(strm, show_frame_info,
                             num_frames_with_source > (first_frame - frame_idx),
                             show_unique, marker))
      break;
    ++num_frames_displayed;
  }
 
  strm.IndentLess();
  return num_frames_displayed;
}
 
void StackFrameList::ClearSelectedFrameIndex() { m_selected_frame_idx.reset(); }