llvm/lldb/source/Plugins/Process/Utility/UnwindLLDB.cpp

//===-- UnwindLLDB.cpp -------------------------------------*- C++ -*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//

#include "lldb/Core/Module.h"
#include "lldb/Core/Log.h"
#include "lldb/Symbol/FuncUnwinders.h"
#include "lldb/Symbol/Function.h"
#include "lldb/Symbol/UnwindPlan.h"
#include "lldb/Target/ABI.h"
#include "lldb/Target/Thread.h"
#include "lldb/Target/Target.h"
#include "lldb/Target/Process.h"
#include "lldb/Target/RegisterContext.h"

#include "UnwindLLDB.h"
#include "RegisterContextLLDB.h"

using namespace lldb;
using namespace lldb_private;

UnwindLLDB::UnwindLLDB (Thread &thread) :
    Unwind (thread),
    m_frames(),
    m_unwind_complete(false),
    m_user_supplied_trap_handler_functions()
{
    ProcessSP process_sp(thread.GetProcess());
    if (process_sp)
    {
        Args args;
        process_sp->GetTarget().GetUserSpecifiedTrapHandlerNames (args);
        size_t count = args.GetArgumentCount();
        for (size_t i = 0; i < count; i++)
        {
            const char *func_name = args.GetArgumentAtIndex(i);
            m_user_supplied_trap_handler_functions.push_back (ConstString (func_name));
        }
    }
}

uint32_t
UnwindLLDB::DoGetFrameCount()
{
    if (!m_unwind_complete)
    {
//#define DEBUG_FRAME_SPEED 1
#if DEBUG_FRAME_SPEED
#define FRAME_COUNT 10000
        TimeValue time_value (TimeValue::Now());
#endif
        if (!AddFirstFrame ())
            return 0;

        ProcessSP process_sp (m_thread.GetProcess());
        ABI *abi = process_sp ? process_sp->GetABI().get() : NULL;

        while (AddOneMoreFrame (abi))
        {
#if DEBUG_FRAME_SPEED
            if ((m_frames.size() % FRAME_COUNT) == 0)
            {
                TimeValue now(TimeValue::Now());
                uint64_t delta_t = now - time_value;
                printf ("%u frames in %" PRIu64 ".%09llu ms (%g frames/sec)\n",
                        FRAME_COUNT,
                        delta_t / TimeValue::NanoSecPerSec, 
                        delta_t % TimeValue::NanoSecPerSec,
                        (float)FRAME_COUNT / ((float)delta_t / (float)TimeValue::NanoSecPerSec));
                time_value = now;
            }
#endif
        }
    }
    return m_frames.size ();
}

bool
UnwindLLDB::AddFirstFrame ()
{
    if (m_frames.size() > 0)
        return true;
        
    // First, set up the 0th (initial) frame
    CursorSP first_cursor_sp(new Cursor ());
    RegisterContextLLDBSP reg_ctx_sp (new RegisterContextLLDB (m_thread, 
                                                               RegisterContextLLDBSP(), 
                                                               first_cursor_sp->sctx, 
                                                               0, *this));
    if (reg_ctx_sp.get() == NULL)
        goto unwind_done;
    
    if (!reg_ctx_sp->IsValid())
        goto unwind_done;

    if (!reg_ctx_sp->GetCFA (first_cursor_sp->cfa))
        goto unwind_done;

    if (!reg_ctx_sp->ReadPC (first_cursor_sp->start_pc))
        goto unwind_done;

    // Everything checks out, so release the auto pointer value and let the
    // cursor own it in its shared pointer
    first_cursor_sp->reg_ctx_lldb_sp = reg_ctx_sp;
    m_frames.push_back (first_cursor_sp);
    return true;

unwind_done:
    Log *log(GetLogIfAllCategoriesSet (LIBLLDB_LOG_UNWIND));
    if (log)
    {
        log->Printf ("th%d Unwind of this thread is complete.", m_thread.GetIndexID());
    }
    m_unwind_complete = true;
    return false;
}

UnwindLLDB::CursorSP
UnwindLLDB::GetOneMoreFrame (ABI* abi)
{
    assert (m_frames.size() != 0 && "Get one more frame called with empty frame list");

    // If we've already gotten to the end of the stack, don't bother to try again...
    if (m_unwind_complete)
        return nullptr;
        
    Log *log(GetLogIfAllCategoriesSet (LIBLLDB_LOG_UNWIND));

    CursorSP prev_frame = m_frames.back();
    uint32_t cur_idx = m_frames.size();

    CursorSP cursor_sp(new Cursor ());
    RegisterContextLLDBSP reg_ctx_sp(new RegisterContextLLDB (m_thread, 
                                                              prev_frame->reg_ctx_lldb_sp, 
                                                              cursor_sp->sctx, 
                                                              cur_idx, 
                                                              *this));

    // We want to detect an unwind that cycles erroneously and stop backtracing.
    // Don't want this maximum unwind limit to be too low -- if you have a backtrace
    // with an "infinitely recursing" bug, it will crash when the stack blows out
    // and the first 35,000 frames are uninteresting - it's the top most 5 frames that
    // you actually care about.  So you can't just cap the unwind at 10,000 or something.
    // Realistically anything over around 200,000 is going to blow out the stack space.
    // If we're still unwinding at that point, we're probably never going to finish.
    if (cur_idx > 300000)
    {
        if (log)
            log->Printf ("%*sFrame %d unwound too many frames, assuming unwind has gone astray, stopping.", 
                         cur_idx < 100 ? cur_idx : 100, "", cur_idx);
        return nullptr;
    }

    if (reg_ctx_sp.get() == NULL)
    {
        // If the RegisterContextLLDB has a fallback UnwindPlan, it will switch to that and return
        // true.  Subsequent calls to TryFallbackUnwindPlan() will return false.
        if (prev_frame->reg_ctx_lldb_sp->TryFallbackUnwindPlan())
            return GetOneMoreFrame (abi);

        if (log)
            log->Printf ("%*sFrame %d did not get a RegisterContext, stopping.",
                         cur_idx < 100 ? cur_idx : 100, "", cur_idx);
        return nullptr;
    }

    if (!reg_ctx_sp->IsValid())
    {
        // We failed to get a valid RegisterContext.
        // See if the regctx below this on the stack has a fallback unwind plan it can use.
        // Subsequent calls to TryFallbackUnwindPlan() will return false.
        if (prev_frame->reg_ctx_lldb_sp->TryFallbackUnwindPlan())
            return GetOneMoreFrame (abi);

        if (log)
            log->Printf("%*sFrame %d invalid RegisterContext for this frame, stopping stack walk", 
                        cur_idx < 100 ? cur_idx : 100, "", cur_idx);
        return nullptr;
    }
    if (!reg_ctx_sp->GetCFA (cursor_sp->cfa))
    {
        // If the RegisterContextLLDB has a fallback UnwindPlan, it will switch to that and return
        // true.  Subsequent calls to TryFallbackUnwindPlan() will return false.
        if (prev_frame->reg_ctx_lldb_sp->TryFallbackUnwindPlan())
            return GetOneMoreFrame (abi);

        if (log)
            log->Printf("%*sFrame %d did not get CFA for this frame, stopping stack walk",
                        cur_idx < 100 ? cur_idx : 100, "", cur_idx);
        return nullptr;
    }
    if (abi && !abi->CallFrameAddressIsValid(cursor_sp->cfa))
    {
        // On Mac OS X, the _sigtramp asynchronous signal trampoline frame may not have
        // its (constructed) CFA aligned correctly -- don't do the abi alignment check for
        // these.
        if (reg_ctx_sp->IsTrapHandlerFrame() == false)
        {
            // See if we can find a fallback unwind plan for THIS frame.  It may be
            // that the UnwindPlan we're using for THIS frame was bad and gave us a
            // bad CFA.  
            // If that's not it, then see if we can change the UnwindPlan for the frame
            // below us ("NEXT") -- see if using that other UnwindPlan gets us a better
            // unwind state.
            if (reg_ctx_sp->TryFallbackUnwindPlan() == false
                || reg_ctx_sp->GetCFA (cursor_sp->cfa) == false
                || abi->CallFrameAddressIsValid(cursor_sp->cfa) == false)
            {
                if (prev_frame->reg_ctx_lldb_sp->TryFallbackUnwindPlan())
                    return GetOneMoreFrame (abi);

                if (log)
                    log->Printf("%*sFrame %d did not get a valid CFA for this frame, stopping stack walk",
                                cur_idx < 100 ? cur_idx : 100, "", cur_idx);
                return nullptr;
            }
            else
            {
                if (log)
                    log->Printf("%*sFrame %d had a bad CFA value but we switched the UnwindPlan being used and got one that looks more realistic.",
                                cur_idx < 100 ? cur_idx : 100, "", cur_idx);
            }
        }
    }
    if (!reg_ctx_sp->ReadPC (cursor_sp->start_pc))
    {
        // If the RegisterContextLLDB has a fallback UnwindPlan, it will switch to that and return
        // true.  Subsequent calls to TryFallbackUnwindPlan() will return false.
        if (prev_frame->reg_ctx_lldb_sp->TryFallbackUnwindPlan())
            return GetOneMoreFrame (abi);

        if (log)
            log->Printf("%*sFrame %d did not get PC for this frame, stopping stack walk",
                        cur_idx < 100 ? cur_idx : 100, "", cur_idx);
        return nullptr;
    }
    if (abi && !abi->CodeAddressIsValid (cursor_sp->start_pc))
    {
        // If the RegisterContextLLDB has a fallback UnwindPlan, it will switch to that and return
        // true.  Subsequent calls to TryFallbackUnwindPlan() will return false.
        if (prev_frame->reg_ctx_lldb_sp->TryFallbackUnwindPlan())
            return GetOneMoreFrame (abi);

        if (log)
            log->Printf("%*sFrame %d did not get a valid PC, stopping stack walk",
                        cur_idx < 100 ? cur_idx : 100, "", cur_idx);
        return nullptr;
    }
    // Infinite loop where the current cursor is the same as the previous one...
    if (prev_frame->start_pc == cursor_sp->start_pc && prev_frame->cfa == cursor_sp->cfa)
    {
        if (log)
            log->Printf ("th%d pc of this frame is the same as the previous frame and CFAs for both frames are identical -- stopping unwind", m_thread.GetIndexID());
        return nullptr;
    }

    cursor_sp->reg_ctx_lldb_sp = reg_ctx_sp;
    return cursor_sp;
}

bool
UnwindLLDB::AddOneMoreFrame (ABI *abi)
{
    Log *log(GetLogIfAllCategoriesSet (LIBLLDB_LOG_UNWIND));

    // Frame zero is a little different
    if (m_frames.empty())
        return false;

    // If we've already gotten to the end of the stack, don't bother to try again...
    if (m_unwind_complete)
        return false;

    CursorSP new_frame = m_candidate_frame;
    if (new_frame == nullptr)
        new_frame = GetOneMoreFrame(abi);

    if (new_frame == nullptr)
    {
        if (log)
            log->Printf ("th%d Unwind of this thread is complete.", m_thread.GetIndexID());
        m_unwind_complete = true;
        return false;
    }

    m_frames.push_back(new_frame);

    // If we can get one more frame further then accept that we get back a correct frame.
    m_candidate_frame = GetOneMoreFrame(abi);
    if (m_candidate_frame)
        return true;

    // We can't go further from the frame returned by GetOneMore frame. Lets try to get a
    // different frame with using the fallback unwind plan.
    if (!m_frames[m_frames.size() - 2]->reg_ctx_lldb_sp->TryFallbackUnwindPlan())
    {
        // We don't have a valid fallback unwind plan. Accept the frame as it is. This is a
        // valid situation when we are at the bottom of the stack.
        return true;
    }

    // Remove the possibly incorrect frame from the frame list and try to add a different one with
    // the newly selected fallback unwind plan.
    m_frames.pop_back();
    CursorSP new_frame_v2 = GetOneMoreFrame(abi);
    if (new_frame_v2 == nullptr)
    {
        // We haven't got a new frame from the fallback unwind plan. Accept the frame from the
        // original unwind plan. This is a valid situation when we are at the bottom of the stack.
        m_frames.push_back(new_frame);
        return true;
    }

    // Push the new frame to the list and try to continue from this frame. If we can get a new frame
    // then accept it as the correct one.
    m_frames.push_back(new_frame_v2);
    m_candidate_frame = GetOneMoreFrame(abi);
    if (m_candidate_frame)
        return true;

    // The new frame isn't helped in unwinding. Fall back to the original one as the default unwind
    // plan is usually more reliable then the fallback one.
    m_frames.pop_back();
    m_frames.push_back(new_frame);
    return true;
}

bool
UnwindLLDB::DoGetFrameInfoAtIndex (uint32_t idx, addr_t& cfa, addr_t& pc)
{
    if (m_frames.size() == 0)
    {
        if (!AddFirstFrame())
            return false;
    }

    ProcessSP process_sp (m_thread.GetProcess());
    ABI *abi = process_sp ? process_sp->GetABI().get() : NULL;

    while (idx >= m_frames.size() && AddOneMoreFrame (abi))
        ;

    if (idx < m_frames.size ())
    {
        cfa = m_frames[idx]->cfa;
        pc = m_frames[idx]->start_pc;
        return true;
    }
    return false;
}

lldb::RegisterContextSP
UnwindLLDB::DoCreateRegisterContextForFrame (StackFrame *frame)
{
    lldb::RegisterContextSP reg_ctx_sp;
    uint32_t idx = frame->GetConcreteFrameIndex ();

    if (idx == 0)
    {
        return m_thread.GetRegisterContext();
    }

    if (m_frames.size() == 0)
    {
        if (!AddFirstFrame())
            return reg_ctx_sp;
    }

    ProcessSP process_sp (m_thread.GetProcess());
    ABI *abi = process_sp ? process_sp->GetABI().get() : NULL;

    while (idx >= m_frames.size())
    {
        if (!AddOneMoreFrame (abi))
            break;
    }

    const uint32_t num_frames = m_frames.size();
    if (idx < num_frames)
    {
        Cursor *frame_cursor = m_frames[idx].get();
        reg_ctx_sp = frame_cursor->reg_ctx_lldb_sp;
    }
    return reg_ctx_sp;
}

UnwindLLDB::RegisterContextLLDBSP
UnwindLLDB::GetRegisterContextForFrameNum (uint32_t frame_num)
{
    RegisterContextLLDBSP reg_ctx_sp;
    if (frame_num < m_frames.size())
        reg_ctx_sp = m_frames[frame_num]->reg_ctx_lldb_sp;
    return reg_ctx_sp;
}

bool
UnwindLLDB::SearchForSavedLocationForRegister (uint32_t lldb_regnum, lldb_private::UnwindLLDB::RegisterLocation &regloc, uint32_t starting_frame_num, bool pc_reg)
{
    int64_t frame_num = starting_frame_num;
    if (static_cast<size_t>(frame_num) >= m_frames.size())
        return false;

    // Never interrogate more than one level while looking for the saved pc value.  If the value
    // isn't saved by frame_num, none of the frames lower on the stack will have a useful value.
    if (pc_reg)
    {
        UnwindLLDB::RegisterSearchResult result;
        result = m_frames[frame_num]->reg_ctx_lldb_sp->SavedLocationForRegister (lldb_regnum, regloc);
        if (result == UnwindLLDB::RegisterSearchResult::eRegisterFound)
          return true;
        else
          return false;
    }
    while (frame_num >= 0)
    {
        UnwindLLDB::RegisterSearchResult result;
        result = m_frames[frame_num]->reg_ctx_lldb_sp->SavedLocationForRegister (lldb_regnum, regloc);

        // We descended down to the live register context aka stack frame 0 and are reading the value
        // out of a live register.
        if (result == UnwindLLDB::RegisterSearchResult::eRegisterFound
            && regloc.type == UnwindLLDB::RegisterLocation::eRegisterInLiveRegisterContext)
        {
            return true;
        }

        // If we have unwind instructions saying that register N is saved in register M in the middle of
        // the stack (and N can equal M here, meaning the register was not used in this function), then
        // change the register number we're looking for to M and keep looking for a concrete  location 
        // down the stack, or an actual value from a live RegisterContext at frame 0.
        if (result == UnwindLLDB::RegisterSearchResult::eRegisterFound
            && regloc.type == UnwindLLDB::RegisterLocation::eRegisterInRegister
            && frame_num > 0)
        {
            result = UnwindLLDB::RegisterSearchResult::eRegisterNotFound;
            lldb_regnum = regloc.location.register_number;
        }

        if (result == UnwindLLDB::RegisterSearchResult::eRegisterFound)
            return true;
        if (result == UnwindLLDB::RegisterSearchResult::eRegisterIsVolatile)
            return false;
        frame_num--;
    }
    return false;
}