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// 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
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// 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.
#include <execinfo.h>
#include <atomic>
#include <cstring>
#include "absl/debugging/stacktrace.h"
#include "absl/base/attributes.h"
// 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.
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;
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];
// No implementation for finding out the stack frame sizes yet.
memset(sizes, 0, sizeof(*sizes) * 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;
return result_count;
namespace absl {
namespace debugging_internal {
bool StackTraceWorksForTest() {
return false;
} // namespace debugging_internal
} // namespace absl