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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.
- #ifndef BASE_PROFILER_STACK_BUFFER_H_
- #define BASE_PROFILER_STACK_BUFFER_H_
- #include <stddef.h>
- #include <stdint.h>
- #include <memory>
- #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<uintptr_t, AlignedFreeDeleter> buffer_;
- };
- } // namespace base
- #endif // BASE_PROFILER_STACK_BUFFER_H_
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