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// Copyright 2019 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 <stddef.h>
#include <stdint.h>
#include <memory>
#include "base/base_export.h"
#include "base/macros.h"
namespace base {
// 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 in bytes.
size_t size() const { return size_; }
// The buffer to store the stack.
const std::unique_ptr<uint8_t[]> buffer_;
// The size in bytes of the requested buffer allocation. The actual allocation
// is larger to accommodate alignment requirements.
const size_t size_;
} // namespace base