1// Copyright 2000 - 2007 Google Inc. 2// All rights reserved. 3// 4// Author: Sanjay Ghemawat 5// 6// Portable implementation - just use glibc 7// 8// Note: The glibc implementation may cause a call to malloc. 9// This can cause a deadlock in HeapProfiler. 10 11#ifndef ABSL_DEBUGGING_INTERNAL_STACKTRACE_GENERIC_INL_H_ 12#define ABSL_DEBUGGING_INTERNAL_STACKTRACE_GENERIC_INL_H_ 13 14#include <execinfo.h> 15#include <atomic> 16#include <cstring> 17 18#include "absl/debugging/stacktrace.h" 19#include "absl/base/attributes.h" 20 21// Sometimes, we can try to get a stack trace from within a stack 22// trace, because we don't block signals inside this code (which would be too 23// expensive: the two extra system calls per stack trace do matter here). 24// That can cause a self-deadlock. 25// Protect against such reentrant call by failing to get a stack trace. 26// 27// We use __thread here because the code here is extremely low level -- it is 28// called while collecting stack traces from within malloc and mmap, and thus 29// can not call anything which might call malloc or mmap itself. 30static __thread int recursive = 0; 31 32// The stack trace function might be invoked very early in the program's 33// execution (e.g. from the very first malloc if using tcmalloc). Also, the 34// glibc implementation itself will trigger malloc the first time it is called. 35// As such, we suppress usage of backtrace during this early stage of execution. 36static std::atomic<bool> disable_stacktraces(true); // Disabled until healthy. 37// Waiting until static initializers run seems to be late enough. 38// This file is included into stacktrace.cc so this will only run once. 39ABSL_ATTRIBUTE_UNUSED static int stacktraces_enabler = []() { 40 void* unused_stack[1]; 41 // Force the first backtrace to happen early to get the one-time shared lib 42 // loading (allocation) out of the way. After the first call it is much safer 43 // to use backtrace from a signal handler if we crash somewhere later. 44 backtrace(unused_stack, 1); 45 disable_stacktraces.store(false, std::memory_order_relaxed); 46 return 0; 47}(); 48 49template <bool IS_STACK_FRAMES, bool IS_WITH_CONTEXT> 50static int UnwindImpl(void** result, int* sizes, int max_depth, int skip_count, 51 const void *ucp, int *min_dropped_frames) { 52 if (recursive || disable_stacktraces.load(std::memory_order_relaxed)) { 53 return 0; 54 } 55 ++recursive; 56 57 static_cast<void>(ucp); // Unused. 58 static const int kStackLength = 64; 59 void * stack[kStackLength]; 60 int size; 61 62 size = backtrace(stack, kStackLength); 63 skip_count++; // we want to skip the current frame as well 64 int result_count = size - skip_count; 65 if (result_count < 0) 66 result_count = 0; 67 if (result_count > max_depth) 68 result_count = max_depth; 69 for (int i = 0; i < result_count; i++) 70 result[i] = stack[i + skip_count]; 71 72 if (IS_STACK_FRAMES) { 73 // No implementation for finding out the stack frame sizes yet. 74 memset(sizes, 0, sizeof(*sizes) * result_count); 75 } 76 if (min_dropped_frames != nullptr) { 77 if (size - skip_count - max_depth > 0) { 78 *min_dropped_frames = size - skip_count - max_depth; 79 } else { 80 *min_dropped_frames = 0; 81 } 82 } 83 84 --recursive; 85 86 return result_count; 87} 88 89namespace absl { 90ABSL_NAMESPACE_BEGIN 91namespace debugging_internal { 92bool StackTraceWorksForTest() { 93 return true; 94} 95} // namespace debugging_internal 96ABSL_NAMESPACE_END 97} // namespace absl 98 99#endif // ABSL_DEBUGGING_INTERNAL_STACKTRACE_GENERIC_INL_H_ 100