1// Copyright 2017 The Abseil Authors. 2// 3// Licensed under the Apache License, Version 2.0 (the "License"); 4// you may not use this file except in compliance with the License. 5// You may obtain a copy of the License at 6// 7// https://www.apache.org/licenses/LICENSE-2.0 8// 9// Unless required by applicable law or agreed to in writing, software 10// distributed under the License is distributed on an "AS IS" BASIS, 11// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 12// See the License for the specific language governing permissions and 13// limitations under the License. 14// 15// Portable implementation - just use glibc 16// 17// Note: The glibc implementation may cause a call to malloc. 18// This can cause a deadlock in HeapProfiler. 19 20#ifndef ABSL_DEBUGGING_INTERNAL_STACKTRACE_GENERIC_INL_H_ 21#define ABSL_DEBUGGING_INTERNAL_STACKTRACE_GENERIC_INL_H_ 22 23#include <execinfo.h> 24#include <atomic> 25#include <cstring> 26 27#include "absl/debugging/stacktrace.h" 28#include "absl/base/attributes.h" 29 30// Sometimes, we can try to get a stack trace from within a stack 31// trace, because we don't block signals inside this code (which would be too 32// expensive: the two extra system calls per stack trace do matter here). 33// That can cause a self-deadlock. 34// Protect against such reentrant call by failing to get a stack trace. 35// 36// We use __thread here because the code here is extremely low level -- it is 37// called while collecting stack traces from within malloc and mmap, and thus 38// can not call anything which might call malloc or mmap itself. 39static __thread int recursive = 0; 40 41// The stack trace function might be invoked very early in the program's 42// execution (e.g. from the very first malloc if using tcmalloc). Also, the 43// glibc implementation itself will trigger malloc the first time it is called. 44// As such, we suppress usage of backtrace during this early stage of execution. 45static std::atomic<bool> disable_stacktraces(true); // Disabled until healthy. 46// Waiting until static initializers run seems to be late enough. 47// This file is included into stacktrace.cc so this will only run once. 48ABSL_ATTRIBUTE_UNUSED static int stacktraces_enabler = []() { 49 void* unused_stack[1]; 50 // Force the first backtrace to happen early to get the one-time shared lib 51 // loading (allocation) out of the way. After the first call it is much safer 52 // to use backtrace from a signal handler if we crash somewhere later. 53 backtrace(unused_stack, 1); 54 disable_stacktraces.store(false, std::memory_order_relaxed); 55 return 0; 56}(); 57 58template <bool IS_STACK_FRAMES, bool IS_WITH_CONTEXT> 59static int UnwindImpl(void** result, int* sizes, int max_depth, int skip_count, 60 const void *ucp, int *min_dropped_frames) { 61 if (recursive || disable_stacktraces.load(std::memory_order_relaxed)) { 62 return 0; 63 } 64 ++recursive; 65 66 static_cast<void>(ucp); // Unused. 67 static const int kStackLength = 64; 68 void * stack[kStackLength]; 69 int size; 70 71 size = backtrace(stack, kStackLength); 72 skip_count++; // we want to skip the current frame as well 73 int result_count = size - skip_count; 74 if (result_count < 0) 75 result_count = 0; 76 if (result_count > max_depth) 77 result_count = max_depth; 78 for (int i = 0; i < result_count; i++) 79 result[i] = stack[i + skip_count]; 80 81 if (IS_STACK_FRAMES) { 82 // No implementation for finding out the stack frame sizes yet. 83 memset(sizes, 0, sizeof(*sizes) * result_count); 84 } 85 if (min_dropped_frames != nullptr) { 86 if (size - skip_count - max_depth > 0) { 87 *min_dropped_frames = size - skip_count - max_depth; 88 } else { 89 *min_dropped_frames = 0; 90 } 91 } 92 93 --recursive; 94 95 return result_count; 96} 97 98namespace absl { 99ABSL_NAMESPACE_BEGIN 100namespace debugging_internal { 101bool StackTraceWorksForTest() { 102 return true; 103} 104} // namespace debugging_internal 105ABSL_NAMESPACE_END 106} // namespace absl 107 108#endif // ABSL_DEBUGGING_INTERNAL_STACKTRACE_GENERIC_INL_H_ 109