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// Copyright 2015 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include <memory>
#include "base/base_export.h"
#include "base/macros.h"
#include "base/threading/platform_thread.h"
namespace base {
class Unwinder;
class ModuleCache;
class ProfileBuilder;
class StackSamplerTestDelegate;
// StackSampler is an implementation detail of StackSamplingProfiler. It
// abstracts the native implementation required to record a set of stack frames
// for a given thread.
class BASE_EXPORT StackSampler {
// This class contains a buffer for stack copies that can be shared across
// multiple instances of StackSampler.
class BASE_EXPORT StackBuffer {
// The expected alignment of the stack on the current platform. Windows and
// System V AMD64 ABIs on x86, x64, and ARM require the stack to be aligned
// to twice the pointer size. Excepted from this requirement is code setting
// up the stack during function calls (between pushing the return address
// and the end of the function prologue). The profiler will sometimes
// encounter this exceptional case for leaf frames.
static constexpr size_t kPlatformStackAlignment = 2 * sizeof(uintptr_t);
StackBuffer(size_t buffer_size);
// Returns a kPlatformStackAlignment-aligned pointer to the stack buffer.
uintptr_t* buffer() const {
// Return the first address in the buffer aligned to
// kPlatformStackAlignment. The buffer is guaranteed to have enough space
// for size() bytes beyond this value.
return reinterpret_cast<uintptr_t*>(
(reinterpret_cast<uintptr_t>(buffer_.get()) +
kPlatformStackAlignment - 1) &
~(kPlatformStackAlignment - 1));
size_t size() const { return size_; }
// The buffer to store the stack.
const std::unique_ptr<uint8_t[]> buffer_;
// The size of the requested buffer allocation. The actual allocation is
// larger to accommodate alignment requirements.
const size_t size_;
virtual ~StackSampler();
// Creates a stack sampler that records samples for thread with |thread_id|.
// Returns null if this platform does not support stack sampling.
static std::unique_ptr<StackSampler> Create(
PlatformThreadId thread_id,
ModuleCache* module_cache,
StackSamplerTestDelegate* test_delegate);
// Gets the required size of the stack buffer.
static size_t GetStackBufferSize();
// Creates an instance of the a stack buffer that can be used for calls to
// any StackSampler object.
static std::unique_ptr<StackBuffer> CreateStackBuffer();
// The following functions are all called on the SamplingThread (not the
// thread being sampled).
// Adds an auxiliary unwinder to handle additional, non-native-code unwind
// scenarios.
virtual void AddAuxUnwinder(std::unique_ptr<Unwinder> unwinder) = 0;
// Records a set of frames and returns them.
virtual void RecordStackFrames(StackBuffer* stackbuffer,
ProfileBuilder* profile_builder) = 0;
// StackSamplerTestDelegate provides seams for test code to execute during stack
// collection.
class BASE_EXPORT StackSamplerTestDelegate {
virtual ~StackSamplerTestDelegate();
// Called after copying the stack and resuming the target thread, but prior to
// walking the stack. Invoked on the SamplingThread.
virtual void OnPreStackWalk() = 0;
} // namespace base