1 // Copyright 2019 The Chromium Authors. All rights reserved. 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/macros.h" 14 15 namespace base { 16 17 // This class contains a buffer for stack copies that can be shared across 18 // multiple instances of StackSampler. 19 class BASE_EXPORT StackBuffer { 20 public: 21 // The expected alignment of the stack on the current platform. Windows and 22 // System V AMD64 ABIs on x86, x64, and ARM require the stack to be aligned 23 // to twice the pointer size. Excepted from this requirement is code setting 24 // up the stack during function calls (between pushing the return address 25 // and the end of the function prologue). The profiler will sometimes 26 // encounter this exceptional case for leaf frames. 27 static constexpr size_t kPlatformStackAlignment = 2 * sizeof(uintptr_t); 28 29 StackBuffer(size_t buffer_size); 30 ~StackBuffer(); 31 32 // Returns a kPlatformStackAlignment-aligned pointer to the stack buffer. buffer()33 uintptr_t* buffer() const { 34 // Return the first address in the buffer aligned to 35 // kPlatformStackAlignment. The buffer is guaranteed to have enough space 36 // for size() bytes beyond this value. 37 return reinterpret_cast<uintptr_t*>( 38 (reinterpret_cast<uintptr_t>(buffer_.get()) + kPlatformStackAlignment - 39 1) & 40 ~(kPlatformStackAlignment - 1)); 41 } 42 43 // Size in bytes. size()44 size_t size() const { return size_; } 45 46 private: 47 // The buffer to store the stack. 48 const std::unique_ptr<uint8_t[]> buffer_; 49 50 // The size in bytes of the requested buffer allocation. The actual allocation 51 // is larger to accommodate alignment requirements. 52 const size_t size_; 53 54 DISALLOW_COPY_AND_ASSIGN(StackBuffer); 55 }; 56 57 } // namespace base 58 59 #endif // BASE_PROFILER_STACK_BUFFER_H_ 60