| // Copyright 2017 The Abseil Authors. | |
| // | |
| // Licensed under the Apache License, Version 2.0 (the "License"); | |
| // you may not use this file except in compliance with the License. | |
| // You may obtain a copy of the License at | |
| // | |
| // https://www.apache.org/licenses/LICENSE-2.0 | |
| // | |
| // Unless required by applicable law or agreed to in writing, software | |
| // distributed under the License is distributed on an "AS IS" BASIS, | |
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | |
| // See the License for the specific language governing permissions and | |
| // limitations under the License. | |
| // | |
| // Portable implementation - just use glibc | |
| // | |
| // Note: The glibc implementation may cause a call to malloc. | |
| // This can cause a deadlock in HeapProfiler. | |
| // Sometimes, we can try to get a stack trace from within a stack | |
| // trace, because we don't block signals inside this code (which would be too | |
| // expensive: the two extra system calls per stack trace do matter here). | |
| // That can cause a self-deadlock. | |
| // Protect against such reentrant call by failing to get a stack trace. | |
| // | |
| // We use __thread here because the code here is extremely low level -- it is | |
| // called while collecting stack traces from within malloc and mmap, and thus | |
| // can not call anything which might call malloc or mmap itself. | |
| static __thread int recursive = 0; | |
| // The stack trace function might be invoked very early in the program's | |
| // execution (e.g. from the very first malloc if using tcmalloc). Also, the | |
| // glibc implementation itself will trigger malloc the first time it is called. | |
| // As such, we suppress usage of backtrace during this early stage of execution. | |
| static std::atomic<bool> disable_stacktraces(true); // Disabled until healthy. | |
| // Waiting until static initializers run seems to be late enough. | |
| // This file is included into stacktrace.cc so this will only run once. | |
| ABSL_ATTRIBUTE_UNUSED static int stacktraces_enabler = []() { | |
| void* unused_stack[1]; | |
| // Force the first backtrace to happen early to get the one-time shared lib | |
| // loading (allocation) out of the way. After the first call it is much safer | |
| // to use backtrace from a signal handler if we crash somewhere later. | |
| backtrace(unused_stack, 1); | |
| disable_stacktraces.store(false, std::memory_order_relaxed); | |
| return 0; | |
| }(); | |
| template <bool IS_STACK_FRAMES, bool IS_WITH_CONTEXT> | |
| static int UnwindImpl(void** result, int* sizes, int max_depth, int skip_count, | |
| const void *ucp, int *min_dropped_frames) { | |
| if (recursive || disable_stacktraces.load(std::memory_order_relaxed)) { | |
| return 0; | |
| } | |
| ++recursive; | |
| static_cast<void>(ucp); // Unused. | |
| static const int kStackLength = 64; | |
| void * stack[kStackLength]; | |
| int size; | |
| size = backtrace(stack, kStackLength); | |
| skip_count++; // we want to skip the current frame as well | |
| int result_count = size - skip_count; | |
| if (result_count < 0) | |
| result_count = 0; | |
| if (result_count > max_depth) | |
| result_count = max_depth; | |
| for (int i = 0; i < result_count; i++) | |
| result[i] = stack[i + skip_count]; | |
| if (IS_STACK_FRAMES) { | |
| // No implementation for finding out the stack frame sizes yet. | |
| memset(sizes, 0, sizeof(*sizes) * static_cast<size_t>(result_count)); | |
| } | |
| if (min_dropped_frames != nullptr) { | |
| if (size - skip_count - max_depth > 0) { | |
| *min_dropped_frames = size - skip_count - max_depth; | |
| } else { | |
| *min_dropped_frames = 0; | |
| } | |
| } | |
| --recursive; | |
| return result_count; | |
| } | |
| namespace absl { | |
| ABSL_NAMESPACE_BEGIN | |
| namespace debugging_internal { | |
| bool StackTraceWorksForTest() { | |
| return true; | |
| } | |
| } // namespace debugging_internal | |
| ABSL_NAMESPACE_END | |
| } // namespace absl | |