// 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. #ifndef BASE_PROFILER_STACK_BUFFER_H_ #define BASE_PROFILER_STACK_BUFFER_H_ #include #include #include #include "base/base_export.h" #include "base/memory/aligned_memory.h" #include "build/build_config.h" namespace base { // This class contains a buffer for stack copies that can be shared across // multiple instances of StackSampler. class BASE_EXPORT StackBuffer { public: // 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); explicit StackBuffer(size_t buffer_size); StackBuffer(const StackBuffer&) = delete; StackBuffer& operator=(const StackBuffer&) = delete; ~StackBuffer(); // Returns a kPlatformStackAlignment-aligned pointer to the stack buffer. uintptr_t* buffer() const { // Aligned during allocation. return buffer_.get(); } // Size in bytes. size_t size() const { return size_; } #if BUILDFLAG(IS_CHROMEOS) // Tell the kernel that we no longer need the data currently in the upper // parts of the buffer and that the kernel may discard it to free up space. // Specifically, the bytes from |(uint8_t*)buffer + retained_bytes| to the // end of the buffer may be discarded, while the bytes from |buffer| to // |(uint8_t*)buffer + retained_bytes - 1| will not be affected. // The program can still write to that part of the buffer, but should not read // from that part of buffer until after the next write. (The contents of that // part of the buffer are undefined.) // After calling this function, there may be a page fault on the next write to // that area, so it should only be called when parts of the buffer were // written to and will probably not be written to again soon. void MarkUpperBufferContentsAsUnneeded(size_t retained_bytes); #endif private: // The size in bytes of the requested buffer allocation. const size_t size_; // The buffer to store the stack. Already aligned. const std::unique_ptr buffer_; }; } // namespace base #endif // BASE_PROFILER_STACK_BUFFER_H_