1// Copyright 2017 The Abseil Authors.
2//
3// Licensed under the Apache License, Version 2.0 (the "License");
4// you may not use this file except in compliance with the License.
5// You may obtain a copy of the License at
6//
7//      https://www.apache.org/licenses/LICENSE-2.0
8//
9// Unless required by applicable law or agreed to in writing, software
10// distributed under the License is distributed on an "AS IS" BASIS,
11// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12// See the License for the specific language governing permissions and
13// limitations under the License.
14//
15// Produces a stack trace for Windows.  Normally, one could use
16// stacktrace_x86-inl.h or stacktrace_x86_64-inl.h -- and indeed, that
17// should work for binaries compiled using MSVC in "debug" mode.
18// However, in "release" mode, Windows uses frame-pointer
19// optimization, which makes getting a stack trace very difficult.
20//
21// There are several approaches one can take.  One is to use Windows
22// intrinsics like StackWalk64.  These can work, but have restrictions
23// on how successful they can be.  Another attempt is to write a
24// version of stacktrace_x86-inl.h that has heuristic support for
25// dealing with FPO, similar to what WinDbg does (see
26// http://www.nynaeve.net/?p=97).  There are (non-working) examples of
27// these approaches, complete with TODOs, in stacktrace_win32-inl.h#1
28//
29// The solution we've ended up doing is to call the undocumented
30// windows function RtlCaptureStackBackTrace, which probably doesn't
31// work with FPO but at least is fast, and doesn't require a symbol
32// server.
33//
34// This code is inspired by a patch from David Vitek:
35//   https://code.google.com/p/google-perftools/issues/detail?id=83
36
37#ifndef ABSL_DEBUGGING_INTERNAL_STACKTRACE_WIN32_INL_H_
38#define ABSL_DEBUGGING_INTERNAL_STACKTRACE_WIN32_INL_H_
39
40#include <windows.h>    // for GetProcAddress and GetModuleHandle
41#include <cassert>
42
43typedef USHORT NTAPI RtlCaptureStackBackTrace_Function(
44    IN ULONG frames_to_skip,
45    IN ULONG frames_to_capture,
46    OUT PVOID *backtrace,
47    OUT PULONG backtrace_hash);
48
49// Load the function we need at static init time, where we don't have
50// to worry about someone else holding the loader's lock.
51static RtlCaptureStackBackTrace_Function* const RtlCaptureStackBackTrace_fn =
52   (RtlCaptureStackBackTrace_Function*)
53   GetProcAddress(GetModuleHandleA("ntdll.dll"), "RtlCaptureStackBackTrace");
54
55template <bool IS_STACK_FRAMES, bool IS_WITH_CONTEXT>
56static int UnwindImpl(void** result, int* sizes, int max_depth, int skip_count,
57                      const void*, int* min_dropped_frames) {
58  int n = 0;
59  if (!RtlCaptureStackBackTrace_fn) {
60    // can't find a stacktrace with no function to call
61  } else {
62    n = (int)RtlCaptureStackBackTrace_fn(skip_count + 2, max_depth, result, 0);
63  }
64  if (IS_STACK_FRAMES) {
65    // No implementation for finding out the stack frame sizes yet.
66    memset(sizes, 0, sizeof(*sizes) * n);
67  }
68  if (min_dropped_frames != nullptr) {
69    // Not implemented.
70    *min_dropped_frames = 0;
71  }
72  return n;
73}
74
75namespace absl {
76ABSL_NAMESPACE_BEGIN
77namespace debugging_internal {
78bool StackTraceWorksForTest() {
79  return false;
80}
81}  // namespace debugging_internal
82ABSL_NAMESPACE_END
83}  // namespace absl
84
85#endif  // ABSL_DEBUGGING_INTERNAL_STACKTRACE_WIN32_INL_H_
86