1 // Copyright 2019 The Chromium Authors 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 5 #ifndef BASE_PROFILER_STACK_BUFFER_H_ 6 #define BASE_PROFILER_STACK_BUFFER_H_ 7 8 #include <stddef.h> 9 #include <stdint.h> 10 #include <memory> 11 12 #include "base/base_export.h" 13 #include "base/memory/aligned_memory.h" 14 #include "build/build_config.h" 15 16 namespace base { 17 18 // This class contains a buffer for stack copies that can be shared across 19 // multiple instances of StackSampler. 20 class BASE_EXPORT StackBuffer { 21 public: 22 // The expected alignment of the stack on the current platform. Windows and 23 // System V AMD64 ABIs on x86, x64, and ARM require the stack to be aligned 24 // to twice the pointer size. Excepted from this requirement is code setting 25 // up the stack during function calls (between pushing the return address 26 // and the end of the function prologue). The profiler will sometimes 27 // encounter this exceptional case for leaf frames. 28 static constexpr size_t kPlatformStackAlignment = 2 * sizeof(uintptr_t); 29 30 explicit StackBuffer(size_t buffer_size); 31 32 StackBuffer(const StackBuffer&) = delete; 33 StackBuffer& operator=(const StackBuffer&) = delete; 34 35 ~StackBuffer(); 36 37 // Returns a kPlatformStackAlignment-aligned pointer to the stack buffer. buffer()38 uintptr_t* buffer() const { 39 // Aligned during allocation. 40 return buffer_.get(); 41 } 42 43 // Size in bytes. size()44 size_t size() const { return size_; } 45 46 #if BUILDFLAG(IS_CHROMEOS) 47 // Tell the kernel that we no longer need the data currently in the upper 48 // parts of the buffer and that the kernel may discard it to free up space. 49 // Specifically, the bytes from |(uint8_t*)buffer + retained_bytes| to the 50 // end of the buffer may be discarded, while the bytes from |buffer| to 51 // |(uint8_t*)buffer + retained_bytes - 1| will not be affected. 52 // The program can still write to that part of the buffer, but should not read 53 // from that part of buffer until after the next write. (The contents of that 54 // part of the buffer are undefined.) 55 // After calling this function, there may be a page fault on the next write to 56 // that area, so it should only be called when parts of the buffer were 57 // written to and will probably not be written to again soon. 58 void MarkUpperBufferContentsAsUnneeded(size_t retained_bytes); 59 #endif 60 61 private: 62 // The size in bytes of the requested buffer allocation. 63 const size_t size_; 64 65 // The buffer to store the stack. Already aligned. 66 const std::unique_ptr<uintptr_t, AlignedFreeDeleter> buffer_; 67 }; 68 69 } // namespace base 70 71 #endif // BASE_PROFILER_STACK_BUFFER_H_ 72