1 // Copyright (c) 2012 The Chromium Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 5 #include "base/debug/stack_trace.h" 6 7 #include <string.h> 8 9 #include <algorithm> 10 #include <sstream> 11 12 #include "base/logging.h" 13 #include "base/macros.h" 14 15 #if BUILDFLAG(CAN_UNWIND_WITH_FRAME_POINTERS) 16 17 #if defined(OS_LINUX) || defined(OS_ANDROID) 18 #include <pthread.h> 19 #include "base/process/process_handle.h" 20 #include "base/threading/platform_thread.h" 21 #endif 22 23 #if defined(OS_MACOSX) 24 #include <pthread.h> 25 #endif 26 27 #if defined(OS_LINUX) && defined(__GLIBC__) 28 extern "C" void* __libc_stack_end; 29 #endif 30 31 #endif // BUILDFLAG(CAN_UNWIND_WITH_FRAME_POINTERS) 32 33 namespace base { 34 namespace debug { 35 36 namespace { 37 38 #if BUILDFLAG(CAN_UNWIND_WITH_FRAME_POINTERS) 39 40 #if defined(__arm__) && defined(__GNUC__) && !defined(__clang__) 41 // GCC and LLVM generate slightly different frames on ARM, see 42 // https://llvm.org/bugs/show_bug.cgi?id=18505 - LLVM generates 43 // x86-compatible frame, while GCC needs adjustment. 44 constexpr size_t kStackFrameAdjustment = sizeof(uintptr_t); 45 #else 46 constexpr size_t kStackFrameAdjustment = 0; 47 #endif 48 49 uintptr_t GetNextStackFrame(uintptr_t fp) { 50 return reinterpret_cast<const uintptr_t*>(fp)[0] - kStackFrameAdjustment; 51 } 52 53 uintptr_t GetStackFramePC(uintptr_t fp) { 54 return reinterpret_cast<const uintptr_t*>(fp)[1]; 55 } 56 57 bool IsStackFrameValid(uintptr_t fp, uintptr_t prev_fp, uintptr_t stack_end) { 58 // With the stack growing downwards, older stack frame must be 59 // at a greater address that the current one. 60 if (fp <= prev_fp) return false; 61 62 // Assume huge stack frames are bogus. 63 if (fp - prev_fp > 100000) return false; 64 65 // Check alignment. 66 if (fp & (sizeof(uintptr_t) - 1)) return false; 67 68 if (stack_end) { 69 // Both fp[0] and fp[1] must be within the stack. 70 if (fp > stack_end - 2 * sizeof(uintptr_t)) return false; 71 72 // Additional check to filter out false positives. 73 if (GetStackFramePC(fp) < 32768) return false; 74 } 75 76 return true; 77 }; 78 79 // ScanStackForNextFrame() scans the stack for a valid frame to allow unwinding 80 // past system libraries. Only supported on Linux where system libraries are 81 // usually in the middle of the trace: 82 // 83 // TraceStackFramePointers 84 // <more frames from Chrome> 85 // base::WorkSourceDispatch <-- unwinding stops (next frame is invalid), 86 // g_main_context_dispatch ScanStackForNextFrame() is called 87 // <more frames from glib> 88 // g_main_context_iteration 89 // base::MessagePumpGlib::Run <-- ScanStackForNextFrame() finds valid frame, 90 // base::RunLoop::Run unwinding resumes 91 // <more frames from Chrome> 92 // __libc_start_main 93 // 94 // For stack scanning to be efficient it's very important for the thread to 95 // be started by Chrome. In that case we naturally terminate unwinding once 96 // we reach the origin of the stack (i.e. GetStackEnd()). If the thread is 97 // not started by Chrome (e.g. Android's main thread), then we end up always 98 // scanning area at the origin of the stack, wasting time and not finding any 99 // frames (since Android libraries don't have frame pointers). 100 // 101 // ScanStackForNextFrame() returns 0 if it couldn't find a valid frame 102 // (or if stack scanning is not supported on the current platform). 103 uintptr_t ScanStackForNextFrame(uintptr_t fp, uintptr_t stack_end) { 104 #if defined(OS_LINUX) 105 // Enough to resume almost all prematurely terminated traces. 106 constexpr size_t kMaxStackScanArea = 8192; 107 108 if (!stack_end) { 109 // Too dangerous to scan without knowing where the stack ends. 110 return 0; 111 } 112 113 fp += sizeof(uintptr_t); // current frame is known to be invalid 114 uintptr_t last_fp_to_scan = std::min(fp + kMaxStackScanArea, stack_end) - 115 sizeof(uintptr_t); 116 for (;fp <= last_fp_to_scan; fp += sizeof(uintptr_t)) { 117 uintptr_t next_fp = GetNextStackFrame(fp); 118 if (IsStackFrameValid(next_fp, fp, stack_end)) { 119 // Check two frames deep. Since stack frame is just a pointer to 120 // a higher address on the stack, it's relatively easy to find 121 // something that looks like one. However two linked frames are 122 // far less likely to be bogus. 123 uintptr_t next2_fp = GetNextStackFrame(next_fp); 124 if (IsStackFrameValid(next2_fp, next_fp, stack_end)) { 125 return fp; 126 } 127 } 128 } 129 #endif // defined(OS_LINUX) 130 131 return 0; 132 } 133 134 // Links stack frame |fp| to |parent_fp|, so that during stack unwinding 135 // TraceStackFramePointers() visits |parent_fp| after visiting |fp|. 136 // Both frame pointers must come from __builtin_frame_address(). 137 // Returns previous stack frame |fp| was linked to. 138 void* LinkStackFrames(void* fpp, void* parent_fp) { 139 uintptr_t fp = reinterpret_cast<uintptr_t>(fpp) - kStackFrameAdjustment; 140 void* prev_parent_fp = reinterpret_cast<void**>(fp)[0]; 141 reinterpret_cast<void**>(fp)[0] = parent_fp; 142 return prev_parent_fp; 143 } 144 145 #endif // BUILDFLAG(CAN_UNWIND_WITH_FRAME_POINTERS) 146 147 } // namespace 148 149 #if BUILDFLAG(CAN_UNWIND_WITH_FRAME_POINTERS) 150 uintptr_t GetStackEnd() { 151 #if defined(OS_ANDROID) 152 // Bionic reads proc/maps on every call to pthread_getattr_np() when called 153 // from the main thread. So we need to cache end of stack in that case to get 154 // acceptable performance. 155 // For all other threads pthread_getattr_np() is fast enough as it just reads 156 // values from its pthread_t argument. 157 static uintptr_t main_stack_end = 0; 158 159 bool is_main_thread = GetCurrentProcId() == PlatformThread::CurrentId(); 160 if (is_main_thread && main_stack_end) { 161 return main_stack_end; 162 } 163 164 uintptr_t stack_begin = 0; 165 size_t stack_size = 0; 166 pthread_attr_t attributes; 167 int error = pthread_getattr_np(pthread_self(), &attributes); 168 if (!error) { 169 error = pthread_attr_getstack( 170 &attributes, reinterpret_cast<void**>(&stack_begin), &stack_size); 171 pthread_attr_destroy(&attributes); 172 } 173 DCHECK(!error); 174 175 uintptr_t stack_end = stack_begin + stack_size; 176 if (is_main_thread) { 177 main_stack_end = stack_end; 178 } 179 return stack_end; // 0 in case of error 180 181 #elif defined(OS_LINUX) && defined(__GLIBC__) 182 183 if (GetCurrentProcId() == PlatformThread::CurrentId()) { 184 // For the main thread we have a shortcut. 185 return reinterpret_cast<uintptr_t>(__libc_stack_end); 186 } 187 188 // No easy way to get end of the stack for non-main threads, 189 // see crbug.com/617730. 190 #elif defined(OS_MACOSX) 191 return reinterpret_cast<uintptr_t>(pthread_get_stackaddr_np(pthread_self())); 192 #endif 193 194 // Don't know how to get end of the stack. 195 return 0; 196 } 197 #endif // BUILDFLAG(CAN_UNWIND_WITH_FRAME_POINTERS) 198 199 StackTrace::StackTrace() : StackTrace(arraysize(trace_)) {} 200 201 StackTrace::StackTrace(const void* const* trace, size_t count) { 202 count = std::min(count, arraysize(trace_)); 203 if (count) 204 memcpy(trace_, trace, count * sizeof(trace_[0])); 205 count_ = count; 206 } 207 208 const void *const *StackTrace::Addresses(size_t* count) const { 209 *count = count_; 210 if (count_) 211 return trace_; 212 return nullptr; 213 } 214 215 std::string StackTrace::ToString() const { 216 std::stringstream stream; 217 #if !defined(__UCLIBC__) && !defined(_AIX) 218 OutputToStream(&stream); 219 #endif 220 return stream.str(); 221 } 222 223 #if BUILDFLAG(CAN_UNWIND_WITH_FRAME_POINTERS) 224 225 size_t TraceStackFramePointers(const void** out_trace, 226 size_t max_depth, 227 size_t skip_initial) { 228 // Usage of __builtin_frame_address() enables frame pointers in this 229 // function even if they are not enabled globally. So 'fp' will always 230 // be valid. 231 uintptr_t fp = reinterpret_cast<uintptr_t>(__builtin_frame_address(0)) - 232 kStackFrameAdjustment; 233 234 uintptr_t stack_end = GetStackEnd(); 235 236 size_t depth = 0; 237 while (depth < max_depth) { 238 if (skip_initial != 0) { 239 skip_initial--; 240 } else { 241 out_trace[depth++] = reinterpret_cast<const void*>(GetStackFramePC(fp)); 242 } 243 244 uintptr_t next_fp = GetNextStackFrame(fp); 245 if (IsStackFrameValid(next_fp, fp, stack_end)) { 246 fp = next_fp; 247 continue; 248 } 249 250 next_fp = ScanStackForNextFrame(fp, stack_end); 251 if (next_fp) { 252 fp = next_fp; 253 continue; 254 } 255 256 // Failed to find next frame. 257 break; 258 } 259 260 return depth; 261 } 262 263 ScopedStackFrameLinker::ScopedStackFrameLinker(void* fp, void* parent_fp) 264 : fp_(fp), 265 parent_fp_(parent_fp), 266 original_parent_fp_(LinkStackFrames(fp, parent_fp)) {} 267 268 ScopedStackFrameLinker::~ScopedStackFrameLinker() { 269 void* previous_parent_fp = LinkStackFrames(fp_, original_parent_fp_); 270 CHECK_EQ(parent_fp_, previous_parent_fp) 271 << "Stack frame's parent pointer has changed!"; 272 } 273 274 #endif // BUILDFLAG(CAN_UNWIND_WITH_FRAME_POINTERS) 275 276 } // namespace debug 277 } // namespace base 278
