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llvm-project/lldb/source/Target/UnwindLLDB.cpp

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//===-- UnwindLLDB.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/UnwindLLDB.h"
#include "lldb/Core/Module.h"
#include "lldb/Symbol/FuncUnwinders.h"
#include "lldb/Symbol/Function.h"
#include "lldb/Symbol/UnwindPlan.h"
#include "lldb/Target/ABI.h"
#include "lldb/Target/Process.h"
#include "lldb/Target/RegisterContext.h"
#include "lldb/Target/RegisterContextUnwind.h"
#include "lldb/Target/Target.h"
#include "lldb/Target/Thread.h"
#include "lldb/Utility/LLDBLog.h"
#include "lldb/Utility/Log.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
using namespace std::chrono;
auto time_value = steady_clock::now();
#endif
if (!AddFirstFrame())
return 0;
ProcessSP process_sp(m_thread.GetProcess());
ABI *abi = process_sp ? process_sp->GetABI().get() : nullptr;
while (AddOneMoreFrame(abi)) {
#if DEBUG_FRAME_SPEED
if ((m_frames.size() % FRAME_COUNT) == 0) {
const auto now = steady_clock::now();
const auto delta_t = now - time_value;
printf("%u frames in %.9f ms (%g frames/sec)\n", FRAME_COUNT,
duration<double, std::milli>(delta_t).count(),
(float)FRAME_COUNT / duration<double>(delta_t).count());
time_value = now;
}
#endif
}
}
return m_frames.size();
}
bool UnwindLLDB::AddFirstFrame() {
if (m_frames.size() > 0)
return true;
ProcessSP process_sp(m_thread.GetProcess());
ABI *abi = process_sp ? process_sp->GetABI().get() : nullptr;
// First, set up the 0th (initial) frame
CursorSP first_cursor_sp(new Cursor());
RegisterContextLLDBSP reg_ctx_sp(new RegisterContextUnwind(
m_thread, RegisterContextLLDBSP(), first_cursor_sp->sctx, 0, *this));
if (reg_ctx_sp.get() == nullptr)
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);
// Update the Full Unwind Plan for this frame if not valid
UpdateUnwindPlanForFirstFrameIfInvalid(abi);
return true;
unwind_done:
Log *log = GetLog(LLDBLog::Unwind);
if (log) {
LLDB_LOGF(log, "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 = GetLog(LLDBLog::Unwind);
CursorSP prev_frame = m_frames.back();
uint32_t cur_idx = m_frames.size();
CursorSP cursor_sp(new Cursor());
RegisterContextLLDBSP reg_ctx_sp(new RegisterContextUnwind(
m_thread, prev_frame->reg_ctx_lldb_sp, cursor_sp->sctx, cur_idx, *this));
uint64_t max_stack_depth = m_thread.GetMaxBacktraceDepth();
// 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 >= max_stack_depth) {
LLDB_LOGF(log,
"%*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() == nullptr) {
// If the RegisterContextUnwind 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()) {
// TryFallbackUnwindPlan for prev_frame succeeded and updated
// reg_ctx_lldb_sp field of prev_frame. However, cfa field of prev_frame
// still needs to be updated. Hence updating it.
if (!(prev_frame->reg_ctx_lldb_sp->GetCFA(prev_frame->cfa)))
return nullptr;
return GetOneMoreFrame(abi);
}
LLDB_LOGF(log, "%*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()) {
// TryFallbackUnwindPlan for prev_frame succeeded and updated
// reg_ctx_lldb_sp field of prev_frame. However, cfa field of prev_frame
// still needs to be updated. Hence updating it.
if (!(prev_frame->reg_ctx_lldb_sp->GetCFA(prev_frame->cfa)))
return nullptr;
return GetOneMoreFrame(abi);
}
LLDB_LOGF(log,
"%*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 RegisterContextUnwind 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()) {
// TryFallbackUnwindPlan for prev_frame succeeded and updated
// reg_ctx_lldb_sp field of prev_frame. However, cfa field of prev_frame
// still needs to be updated. Hence updating it.
if (!(prev_frame->reg_ctx_lldb_sp->GetCFA(prev_frame->cfa)))
return nullptr;
return GetOneMoreFrame(abi);
}
LLDB_LOGF(log,
"%*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()) {
// 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() ||
!reg_ctx_sp->GetCFA(cursor_sp->cfa) ||
!abi->CallFrameAddressIsValid(cursor_sp->cfa)) {
if (prev_frame->reg_ctx_lldb_sp->TryFallbackUnwindPlan()) {
// TryFallbackUnwindPlan for prev_frame succeeded and updated
// reg_ctx_lldb_sp field of prev_frame. However, cfa field of
// prev_frame still needs to be updated. Hence updating it.
if (!(prev_frame->reg_ctx_lldb_sp->GetCFA(prev_frame->cfa)))
return nullptr;
return GetOneMoreFrame(abi);
}
LLDB_LOGF(log,
"%*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 {
LLDB_LOGF(log,
"%*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 RegisterContextUnwind 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()) {
// TryFallbackUnwindPlan for prev_frame succeeded and updated
// reg_ctx_lldb_sp field of prev_frame. However, cfa field of prev_frame
// still needs to be updated. Hence updating it.
if (!(prev_frame->reg_ctx_lldb_sp->GetCFA(prev_frame->cfa)))
return nullptr;
return GetOneMoreFrame(abi);
}
LLDB_LOGF(log,
"%*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 RegisterContextUnwind 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()) {
// TryFallbackUnwindPlan for prev_frame succeeded and updated
// reg_ctx_lldb_sp field of prev_frame. However, cfa field of prev_frame
// still needs to be updated. Hence updating it.
if (!(prev_frame->reg_ctx_lldb_sp->GetCFA(prev_frame->cfa)))
return nullptr;
return GetOneMoreFrame(abi);
}
LLDB_LOGF(log, "%*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) {
LLDB_LOGF(log,
"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;
}
void UnwindLLDB::UpdateUnwindPlanForFirstFrameIfInvalid(ABI *abi) {
// This function is called for First Frame only.
assert(m_frames.size() == 1 && "No. of cursor frames are not 1");
bool old_m_unwind_complete = m_unwind_complete;
CursorSP old_m_candidate_frame = m_candidate_frame;
// Try to unwind 2 more frames using the Unwinder. It uses Full UnwindPlan
// and if Full UnwindPlan fails, then uses FallBack UnwindPlan. Also update
// the cfa of Frame 0 (if required).
AddOneMoreFrame(abi);
// Remove all the frames added by above function as the purpose of using
// above function was just to check whether Unwinder of Frame 0 works or not.
for (uint32_t i = 1; i < m_frames.size(); i++)
m_frames.pop_back();
// Restore status after calling AddOneMoreFrame
m_unwind_complete = old_m_unwind_complete;
m_candidate_frame = old_m_candidate_frame;
}
bool UnwindLLDB::AddOneMoreFrame(ABI *abi) {
Log *log = GetLog(LLDBLog::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) {
LLDB_LOGF(log, "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) {
// If control reached here then TryFallbackUnwindPlan had succeeded for
// Cursor::m_frames[m_frames.size() - 2]. It also succeeded to Unwind next
// 2 frames i.e. m_frames[m_frames.size() - 1] and a frame after that. For
// Cursor::m_frames[m_frames.size() - 2], reg_ctx_lldb_sp field was already
// updated during TryFallbackUnwindPlan call above. However, cfa field
// still needs to be updated. Hence updating it here and then returning.
return m_frames[m_frames.size() - 2]->reg_ctx_lldb_sp->GetCFA(
m_frames[m_frames.size() - 2]->cfa);
}
// The new frame hasn'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,
bool &behaves_like_zeroth_frame) {
if (m_frames.size() == 0) {
if (!AddFirstFrame())
return false;
}
ProcessSP process_sp(m_thread.GetProcess());
ABI *abi = process_sp ? process_sp->GetABI().get() : nullptr;
while (idx >= m_frames.size() && AddOneMoreFrame(abi))
;
if (idx < m_frames.size()) {
cfa = m_frames[idx]->cfa;
pc = m_frames[idx]->start_pc;
if (idx == 0) {
// Frame zero always behaves like it.
behaves_like_zeroth_frame = true;
} else if (m_frames[idx - 1]->reg_ctx_lldb_sp->IsTrapHandlerFrame()) {
// This could be an asynchronous signal, thus the
// pc might point to the interrupted instruction rather
// than a post-call instruction
behaves_like_zeroth_frame = true;
} else if (m_frames[idx]->reg_ctx_lldb_sp->IsTrapHandlerFrame()) {
// This frame may result from signal processing installing
// a pointer to the first byte of a signal-return trampoline
// in the return address slot of the frame below, so this
// too behaves like the zeroth frame (i.e. the pc might not
// be pointing just past a call in it)
behaves_like_zeroth_frame = true;
} else if (m_frames[idx]->reg_ctx_lldb_sp->BehavesLikeZerothFrame()) {
behaves_like_zeroth_frame = true;
} else {
behaves_like_zeroth_frame = false;
}
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() : nullptr;
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);
return result == UnwindLLDB::RegisterSearchResult::eRegisterFound;
}
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;
}
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