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