1//===-- UnwindLLDB.cpp ----------------------------------------------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8
9#include "lldb/Target/UnwindLLDB.h"
10#include "lldb/Core/Module.h"
11#include "lldb/Symbol/FuncUnwinders.h"
12#include "lldb/Symbol/Function.h"
13#include "lldb/Symbol/UnwindPlan.h"
14#include "lldb/Target/ABI.h"
15#include "lldb/Target/Process.h"
16#include "lldb/Target/RegisterContext.h"
17#include "lldb/Target/RegisterContextUnwind.h"
18#include "lldb/Target/Target.h"
19#include "lldb/Target/Thread.h"
20#include "lldb/Utility/LLDBLog.h"
21#include "lldb/Utility/Log.h"
22
23using namespace lldb;
24using namespace lldb_private;
25
26UnwindLLDB::UnwindLLDB(Thread &thread)
27 : Unwind(thread), m_frames(), m_unwind_complete(false),
28 m_user_supplied_trap_handler_functions() {
29 ProcessSP process_sp(thread.GetProcess());
30 if (process_sp) {
31 Args args;
32 process_sp->GetTarget().GetUserSpecifiedTrapHandlerNames(args);
33 size_t count = args.GetArgumentCount();
34 for (size_t i = 0; i < count; i++) {
35 const char *func_name = args.GetArgumentAtIndex(idx: i);
36 m_user_supplied_trap_handler_functions.push_back(x: ConstString(func_name));
37 }
38 }
39}
40
41uint32_t UnwindLLDB::DoGetFrameCount() {
42 if (!m_unwind_complete) {
43//#define DEBUG_FRAME_SPEED 1
44#if DEBUG_FRAME_SPEED
45#define FRAME_COUNT 10000
46 using namespace std::chrono;
47 auto time_value = steady_clock::now();
48#endif
49 if (!AddFirstFrame())
50 return 0;
51
52 ProcessSP process_sp(m_thread.GetProcess());
53 ABI *abi = process_sp ? process_sp->GetABI().get() : nullptr;
54
55 while (AddOneMoreFrame(abi)) {
56#if DEBUG_FRAME_SPEED
57 if ((m_frames.size() % FRAME_COUNT) == 0) {
58 const auto now = steady_clock::now();
59 const auto delta_t = now - time_value;
60 printf("%u frames in %.9f ms (%g frames/sec)\n", FRAME_COUNT,
61 duration<double, std::milli>(delta_t).count(),
62 (float)FRAME_COUNT / duration<double>(delta_t).count());
63 time_value = now;
64 }
65#endif
66 }
67 }
68 return m_frames.size();
69}
70
71bool UnwindLLDB::AddFirstFrame() {
72 if (m_frames.size() > 0)
73 return true;
74
75 ProcessSP process_sp(m_thread.GetProcess());
76 ABI *abi = process_sp ? process_sp->GetABI().get() : nullptr;
77
78 // First, set up the 0th (initial) frame
79 CursorSP first_cursor_sp(new Cursor());
80 RegisterContextLLDBSP reg_ctx_sp(new RegisterContextUnwind(
81 m_thread, RegisterContextLLDBSP(), first_cursor_sp->sctx, 0, *this));
82 if (reg_ctx_sp.get() == nullptr)
83 goto unwind_done;
84
85 if (!reg_ctx_sp->IsValid())
86 goto unwind_done;
87
88 if (!reg_ctx_sp->GetCFA(cfa&: first_cursor_sp->cfa))
89 goto unwind_done;
90
91 if (!reg_ctx_sp->ReadPC(start_pc&: first_cursor_sp->start_pc))
92 goto unwind_done;
93
94 // Everything checks out, so release the auto pointer value and let the
95 // cursor own it in its shared pointer
96 first_cursor_sp->reg_ctx_lldb_sp = reg_ctx_sp;
97 m_frames.push_back(x: first_cursor_sp);
98
99 // Update the Full Unwind Plan for this frame if not valid
100 UpdateUnwindPlanForFirstFrameIfInvalid(abi);
101
102 return true;
103
104unwind_done:
105 Log *log = GetLog(mask: LLDBLog::Unwind);
106 if (log) {
107 LLDB_LOGF(log, "th%d Unwind of this thread is complete.",
108 m_thread.GetIndexID());
109 }
110 m_unwind_complete = true;
111 return false;
112}
113
114UnwindLLDB::CursorSP UnwindLLDB::GetOneMoreFrame(ABI *abi) {
115 assert(m_frames.size() != 0 &&
116 "Get one more frame called with empty frame list");
117
118 // If we've already gotten to the end of the stack, don't bother to try
119 // again...
120 if (m_unwind_complete)
121 return nullptr;
122
123 Log *log = GetLog(mask: LLDBLog::Unwind);
124
125 CursorSP prev_frame = m_frames.back();
126 uint32_t cur_idx = m_frames.size();
127
128 CursorSP cursor_sp(new Cursor());
129 RegisterContextLLDBSP reg_ctx_sp(new RegisterContextUnwind(
130 m_thread, prev_frame->reg_ctx_lldb_sp, cursor_sp->sctx, cur_idx, *this));
131
132 uint64_t max_stack_depth = m_thread.GetMaxBacktraceDepth();
133
134 // We want to detect an unwind that cycles erroneously and stop backtracing.
135 // Don't want this maximum unwind limit to be too low -- if you have a
136 // backtrace with an "infinitely recursing" bug, it will crash when the stack
137 // blows out and the first 35,000 frames are uninteresting - it's the top
138 // most 5 frames that you actually care about. So you can't just cap the
139 // unwind at 10,000 or something. Realistically anything over around 200,000
140 // is going to blow out the stack space. If we're still unwinding at that
141 // point, we're probably never going to finish.
142 if (cur_idx >= max_stack_depth) {
143 LLDB_LOGF(log,
144 "%*sFrame %d unwound too many frames, assuming unwind has "
145 "gone astray, stopping.",
146 cur_idx < 100 ? cur_idx : 100, "", cur_idx);
147 return nullptr;
148 }
149
150 if (reg_ctx_sp.get() == nullptr) {
151 // If the RegisterContextUnwind has a fallback UnwindPlan, it will switch to
152 // that and return true. Subsequent calls to TryFallbackUnwindPlan() will
153 // return false.
154 if (prev_frame->reg_ctx_lldb_sp->TryFallbackUnwindPlan()) {
155 // TryFallbackUnwindPlan for prev_frame succeeded and updated
156 // reg_ctx_lldb_sp field of prev_frame. However, cfa field of prev_frame
157 // still needs to be updated. Hence updating it.
158 if (!(prev_frame->reg_ctx_lldb_sp->GetCFA(cfa&: prev_frame->cfa)))
159 return nullptr;
160
161 return GetOneMoreFrame(abi);
162 }
163
164 LLDB_LOGF(log, "%*sFrame %d did not get a RegisterContext, stopping.",
165 cur_idx < 100 ? cur_idx : 100, "", cur_idx);
166 return nullptr;
167 }
168
169 if (!reg_ctx_sp->IsValid()) {
170 // We failed to get a valid RegisterContext. See if the regctx below this
171 // on the stack has a fallback unwind plan it can use. Subsequent calls to
172 // TryFallbackUnwindPlan() will return false.
173 if (prev_frame->reg_ctx_lldb_sp->TryFallbackUnwindPlan()) {
174 // TryFallbackUnwindPlan for prev_frame succeeded and updated
175 // reg_ctx_lldb_sp field of prev_frame. However, cfa field of prev_frame
176 // still needs to be updated. Hence updating it.
177 if (!(prev_frame->reg_ctx_lldb_sp->GetCFA(cfa&: prev_frame->cfa)))
178 return nullptr;
179
180 return GetOneMoreFrame(abi);
181 }
182
183 LLDB_LOGF(log,
184 "%*sFrame %d invalid RegisterContext for this frame, "
185 "stopping stack walk",
186 cur_idx < 100 ? cur_idx : 100, "", cur_idx);
187 return nullptr;
188 }
189 if (!reg_ctx_sp->GetCFA(cfa&: cursor_sp->cfa)) {
190 // If the RegisterContextUnwind has a fallback UnwindPlan, it will switch to
191 // that and return true. Subsequent calls to TryFallbackUnwindPlan() will
192 // return false.
193 if (prev_frame->reg_ctx_lldb_sp->TryFallbackUnwindPlan()) {
194 // TryFallbackUnwindPlan for prev_frame succeeded and updated
195 // reg_ctx_lldb_sp field of prev_frame. However, cfa field of prev_frame
196 // still needs to be updated. Hence updating it.
197 if (!(prev_frame->reg_ctx_lldb_sp->GetCFA(cfa&: prev_frame->cfa)))
198 return nullptr;
199
200 return GetOneMoreFrame(abi);
201 }
202
203 LLDB_LOGF(log,
204 "%*sFrame %d did not get CFA for this frame, stopping stack walk",
205 cur_idx < 100 ? cur_idx : 100, "", cur_idx);
206 return nullptr;
207 }
208 if (abi && !abi->CallFrameAddressIsValid(cfa: cursor_sp->cfa)) {
209 // On Mac OS X, the _sigtramp asynchronous signal trampoline frame may not
210 // have its (constructed) CFA aligned correctly -- don't do the abi
211 // alignment check for these.
212 if (!reg_ctx_sp->IsTrapHandlerFrame()) {
213 // See if we can find a fallback unwind plan for THIS frame. It may be
214 // that the UnwindPlan we're using for THIS frame was bad and gave us a
215 // bad CFA. If that's not it, then see if we can change the UnwindPlan
216 // for the frame below us ("NEXT") -- see if using that other UnwindPlan
217 // gets us a better unwind state.
218 if (!reg_ctx_sp->TryFallbackUnwindPlan() ||
219 !reg_ctx_sp->GetCFA(cfa&: cursor_sp->cfa) ||
220 !abi->CallFrameAddressIsValid(cfa: cursor_sp->cfa)) {
221 if (prev_frame->reg_ctx_lldb_sp->TryFallbackUnwindPlan()) {
222 // TryFallbackUnwindPlan for prev_frame succeeded and updated
223 // reg_ctx_lldb_sp field of prev_frame. However, cfa field of
224 // prev_frame still needs to be updated. Hence updating it.
225 if (!(prev_frame->reg_ctx_lldb_sp->GetCFA(cfa&: prev_frame->cfa)))
226 return nullptr;
227
228 return GetOneMoreFrame(abi);
229 }
230
231 LLDB_LOGF(log,
232 "%*sFrame %d did not get a valid CFA for this frame, "
233 "stopping stack walk",
234 cur_idx < 100 ? cur_idx : 100, "", cur_idx);
235 return nullptr;
236 } else {
237 LLDB_LOGF(log,
238 "%*sFrame %d had a bad CFA value but we switched the "
239 "UnwindPlan being used and got one that looks more "
240 "realistic.",
241 cur_idx < 100 ? cur_idx : 100, "", cur_idx);
242 }
243 }
244 }
245 if (!reg_ctx_sp->ReadPC(start_pc&: cursor_sp->start_pc)) {
246 // If the RegisterContextUnwind has a fallback UnwindPlan, it will switch to
247 // that and return true. Subsequent calls to TryFallbackUnwindPlan() will
248 // return false.
249 if (prev_frame->reg_ctx_lldb_sp->TryFallbackUnwindPlan()) {
250 // TryFallbackUnwindPlan for prev_frame succeeded and updated
251 // reg_ctx_lldb_sp field of prev_frame. However, cfa field of prev_frame
252 // still needs to be updated. Hence updating it.
253 if (!(prev_frame->reg_ctx_lldb_sp->GetCFA(cfa&: prev_frame->cfa)))
254 return nullptr;
255
256 return GetOneMoreFrame(abi);
257 }
258
259 LLDB_LOGF(log,
260 "%*sFrame %d did not get PC for this frame, stopping stack walk",
261 cur_idx < 100 ? cur_idx : 100, "", cur_idx);
262 return nullptr;
263 }
264
265 // Invalid code addresses should not appear on the stack *unless* we're
266 // directly below a trap handler frame (in this case, the invalid address is
267 // likely the cause of the trap).
268 if (abi && !abi->CodeAddressIsValid(pc: cursor_sp->start_pc) &&
269 !prev_frame->reg_ctx_lldb_sp->IsTrapHandlerFrame()) {
270 // If the RegisterContextUnwind has a fallback UnwindPlan, it will switch to
271 // that and return true. Subsequent calls to TryFallbackUnwindPlan() will
272 // return false.
273 if (prev_frame->reg_ctx_lldb_sp->TryFallbackUnwindPlan()) {
274 // TryFallbackUnwindPlan for prev_frame succeeded and updated
275 // reg_ctx_lldb_sp field of prev_frame. However, cfa field of prev_frame
276 // still needs to be updated. Hence updating it.
277 if (!(prev_frame->reg_ctx_lldb_sp->GetCFA(cfa&: prev_frame->cfa)))
278 return nullptr;
279
280 return GetOneMoreFrame(abi);
281 }
282
283 LLDB_LOGF(log, "%*sFrame %d did not get a valid PC, stopping stack walk",
284 cur_idx < 100 ? cur_idx : 100, "", cur_idx);
285 return nullptr;
286 }
287 // Infinite loop where the current cursor is the same as the previous one...
288 if (prev_frame->start_pc == cursor_sp->start_pc &&
289 prev_frame->cfa == cursor_sp->cfa) {
290 LLDB_LOGF(log,
291 "th%d pc of this frame is the same as the previous frame and "
292 "CFAs for both frames are identical -- stopping unwind",
293 m_thread.GetIndexID());
294 return nullptr;
295 }
296
297 cursor_sp->reg_ctx_lldb_sp = reg_ctx_sp;
298 return cursor_sp;
299}
300
301void UnwindLLDB::UpdateUnwindPlanForFirstFrameIfInvalid(ABI *abi) {
302 // This function is called for First Frame only.
303 assert(m_frames.size() == 1 && "No. of cursor frames are not 1");
304
305 bool old_m_unwind_complete = m_unwind_complete;
306 CursorSP old_m_candidate_frame = m_candidate_frame;
307
308 // Try to unwind 2 more frames using the Unwinder. It uses Full UnwindPlan
309 // and if Full UnwindPlan fails, then uses FallBack UnwindPlan. Also update
310 // the cfa of Frame 0 (if required).
311 AddOneMoreFrame(abi);
312
313 // Remove all the frames added by above function as the purpose of using
314 // above function was just to check whether Unwinder of Frame 0 works or not.
315 for (uint32_t i = 1; i < m_frames.size(); i++)
316 m_frames.pop_back();
317
318 // Restore status after calling AddOneMoreFrame
319 m_unwind_complete = old_m_unwind_complete;
320 m_candidate_frame = old_m_candidate_frame;
321}
322
323bool UnwindLLDB::AddOneMoreFrame(ABI *abi) {
324 Log *log = GetLog(mask: LLDBLog::Unwind);
325
326 // Frame zero is a little different
327 if (m_frames.empty())
328 return false;
329
330 // If we've already gotten to the end of the stack, don't bother to try
331 // again...
332 if (m_unwind_complete)
333 return false;
334
335 CursorSP new_frame = m_candidate_frame;
336 if (new_frame == nullptr)
337 new_frame = GetOneMoreFrame(abi);
338
339 if (new_frame == nullptr) {
340 LLDB_LOGF(log, "th%d Unwind of this thread is complete.",
341 m_thread.GetIndexID());
342 m_unwind_complete = true;
343 return false;
344 }
345
346 m_frames.push_back(x: new_frame);
347
348 // If we can get one more frame further then accept that we get back a
349 // correct frame.
350 m_candidate_frame = GetOneMoreFrame(abi);
351 if (m_candidate_frame)
352 return true;
353
354 // We can't go further from the frame returned by GetOneMore frame. Lets try
355 // to get a different frame with using the fallback unwind plan.
356 if (!m_frames[m_frames.size() - 2]
357 ->reg_ctx_lldb_sp->TryFallbackUnwindPlan()) {
358 // We don't have a valid fallback unwind plan. Accept the frame as it is.
359 // This is a valid situation when we are at the bottom of the stack.
360 return true;
361 }
362
363 // Remove the possibly incorrect frame from the frame list and try to add a
364 // different one with the newly selected fallback unwind plan.
365 m_frames.pop_back();
366 CursorSP new_frame_v2 = GetOneMoreFrame(abi);
367 if (new_frame_v2 == nullptr) {
368 // We haven't got a new frame from the fallback unwind plan. Accept the
369 // frame from the original unwind plan. This is a valid situation when we
370 // are at the bottom of the stack.
371 m_frames.push_back(x: new_frame);
372 return true;
373 }
374
375 // Push the new frame to the list and try to continue from this frame. If we
376 // can get a new frame then accept it as the correct one.
377 m_frames.push_back(x: new_frame_v2);
378 m_candidate_frame = GetOneMoreFrame(abi);
379 if (m_candidate_frame) {
380 // If control reached here then TryFallbackUnwindPlan had succeeded for
381 // Cursor::m_frames[m_frames.size() - 2]. It also succeeded to Unwind next
382 // 2 frames i.e. m_frames[m_frames.size() - 1] and a frame after that. For
383 // Cursor::m_frames[m_frames.size() - 2], reg_ctx_lldb_sp field was already
384 // updated during TryFallbackUnwindPlan call above. However, cfa field
385 // still needs to be updated. Hence updating it here and then returning.
386 return m_frames[m_frames.size() - 2]->reg_ctx_lldb_sp->GetCFA(
387 cfa&: m_frames[m_frames.size() - 2]->cfa);
388 }
389
390 // The new frame hasn't helped in unwinding. Fall back to the original one as
391 // the default unwind plan is usually more reliable then the fallback one.
392 m_frames.pop_back();
393 m_frames.push_back(x: new_frame);
394 return true;
395}
396
397bool UnwindLLDB::DoGetFrameInfoAtIndex(uint32_t idx, addr_t &cfa, addr_t &pc,
398 bool &behaves_like_zeroth_frame) {
399 if (m_frames.size() == 0) {
400 if (!AddFirstFrame())
401 return false;
402 }
403
404 ProcessSP process_sp(m_thread.GetProcess());
405 ABI *abi = process_sp ? process_sp->GetABI().get() : nullptr;
406
407 while (idx >= m_frames.size() && AddOneMoreFrame(abi))
408 ;
409
410 if (idx < m_frames.size()) {
411 cfa = m_frames[idx]->cfa;
412 pc = m_frames[idx]->start_pc;
413 if (idx == 0) {
414 // Frame zero always behaves like it.
415 behaves_like_zeroth_frame = true;
416 } else if (m_frames[idx - 1]->reg_ctx_lldb_sp->IsTrapHandlerFrame()) {
417 // This could be an asynchronous signal, thus the
418 // pc might point to the interrupted instruction rather
419 // than a post-call instruction
420 behaves_like_zeroth_frame = true;
421 } else if (m_frames[idx]->reg_ctx_lldb_sp->IsTrapHandlerFrame()) {
422 // This frame may result from signal processing installing
423 // a pointer to the first byte of a signal-return trampoline
424 // in the return address slot of the frame below, so this
425 // too behaves like the zeroth frame (i.e. the pc might not
426 // be pointing just past a call in it)
427 behaves_like_zeroth_frame = true;
428 } else if (m_frames[idx]->reg_ctx_lldb_sp->BehavesLikeZerothFrame()) {
429 behaves_like_zeroth_frame = true;
430 } else {
431 behaves_like_zeroth_frame = false;
432 }
433 return true;
434 }
435 return false;
436}
437
438lldb::RegisterContextSP
439UnwindLLDB::DoCreateRegisterContextForFrame(StackFrame *frame) {
440 lldb::RegisterContextSP reg_ctx_sp;
441 uint32_t idx = frame->GetConcreteFrameIndex();
442
443 if (idx == 0) {
444 return m_thread.GetRegisterContext();
445 }
446
447 if (m_frames.size() == 0) {
448 if (!AddFirstFrame())
449 return reg_ctx_sp;
450 }
451
452 ProcessSP process_sp(m_thread.GetProcess());
453 ABI *abi = process_sp ? process_sp->GetABI().get() : nullptr;
454
455 while (idx >= m_frames.size()) {
456 if (!AddOneMoreFrame(abi))
457 break;
458 }
459
460 const uint32_t num_frames = m_frames.size();
461 if (idx < num_frames) {
462 Cursor *frame_cursor = m_frames[idx].get();
463 reg_ctx_sp = frame_cursor->reg_ctx_lldb_sp;
464 }
465 return reg_ctx_sp;
466}
467
468UnwindLLDB::RegisterContextLLDBSP
469UnwindLLDB::GetRegisterContextForFrameNum(uint32_t frame_num) {
470 RegisterContextLLDBSP reg_ctx_sp;
471 if (frame_num < m_frames.size())
472 reg_ctx_sp = m_frames[frame_num]->reg_ctx_lldb_sp;
473 return reg_ctx_sp;
474}
475
476bool UnwindLLDB::SearchForSavedLocationForRegister(
477 uint32_t lldb_regnum,
478 lldb_private::UnwindLLDB::ConcreteRegisterLocation &regloc,
479 uint32_t starting_frame_num, bool pc_reg) {
480 int64_t frame_num = starting_frame_num;
481 if (static_cast<size_t>(frame_num) >= m_frames.size())
482 return false;
483
484 // Never interrogate more than one level while looking for the saved pc
485 // value. If the value isn't saved by frame_num, none of the frames lower on
486 // the stack will have a useful value.
487 if (pc_reg) {
488 UnwindLLDB::RegisterSearchResult result;
489 result = m_frames[frame_num]->reg_ctx_lldb_sp->SavedLocationForRegister(
490 lldb_regnum, regloc);
491 return result == UnwindLLDB::RegisterSearchResult::eRegisterFound;
492 }
493 while (frame_num >= 0) {
494 UnwindLLDB::RegisterSearchResult result;
495 result = m_frames[frame_num]->reg_ctx_lldb_sp->SavedLocationForRegister(
496 lldb_regnum, regloc);
497
498 // We descended down to the live register context aka stack frame 0 and are
499 // reading the value out of a live register.
500 if (result == UnwindLLDB::RegisterSearchResult::eRegisterFound &&
501 regloc.type == UnwindLLDB::ConcreteRegisterLocation::
502 eRegisterInLiveRegisterContext) {
503 return true;
504 }
505
506 // If we have unwind instructions saying that register N is saved in
507 // register M in the middle of the stack (and N can equal M here, meaning
508 // the register was not used in this function), then change the register
509 // number we're looking for to M and keep looking for a concrete location
510 // down the stack, or an actual value from a live RegisterContext at frame
511 // 0.
512 if (result == UnwindLLDB::RegisterSearchResult::eRegisterFound &&
513 regloc.type ==
514 UnwindLLDB::ConcreteRegisterLocation::eRegisterInRegister &&
515 frame_num > 0) {
516 result = UnwindLLDB::RegisterSearchResult::eRegisterNotFound;
517 lldb_regnum = regloc.location.register_number;
518 }
519
520 if (result == UnwindLLDB::RegisterSearchResult::eRegisterFound)
521 return true;
522 if (result == UnwindLLDB::RegisterSearchResult::eRegisterIsVolatile)
523 return false;
524 frame_num--;
525 }
526 return false;
527}
528

source code of lldb/source/Target/UnwindLLDB.cpp