1//===--- Stack.cpp - Utilities for dealing with stack space ---------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8///
9/// \file
10/// Defines utilities for dealing with stack allocation and stack space.
11///
12//===----------------------------------------------------------------------===//
13
14#include "clang/Basic/Stack.h"
15#include "llvm/ADT/Optional.h"
16#include "llvm/Support/CrashRecoveryContext.h"
17
18#ifdef _MSC_VER
19#include <intrin.h>  // for _AddressOfReturnAddress
20#endif
21
22static LLVM_THREAD_LOCAL void *BottomOfStack = nullptr;
23
24static void *getStackPointer() {
25#if __GNUC__ || __has_builtin(__builtin_frame_address)
26  return __builtin_frame_address(0);
27#elif defined(_MSC_VER)
28  return _AddressOfReturnAddress();
29#else
30  char CharOnStack = 0;
31  // The volatile store here is intended to escape the local variable, to
32  // prevent the compiler from optimizing CharOnStack into anything other
33  // than a char on the stack.
34  //
35  // Tested on: MSVC 2015 - 2019, GCC 4.9 - 9, Clang 3.2 - 9, ICC 13 - 19.
36  char *volatile Ptr = &CharOnStack;
37  return Ptr;
38#endif
39}
40
41void clang::noteBottomOfStack() {
42  if (!BottomOfStack)
43    BottomOfStack = getStackPointer();
44}
45
46bool clang::isStackNearlyExhausted() {
47  // We consider 256 KiB to be sufficient for any code that runs between checks
48  // for stack size.
49  constexpr size_t SufficientStack = 256 << 10;
50
51  // If we don't know where the bottom of the stack is, hope for the best.
52  if (!BottomOfStack)
53    return false;
54
55  intptr_t StackDiff = (intptr_t)getStackPointer() - (intptr_t)BottomOfStack;
56  size_t StackUsage = (size_t)std::abs(StackDiff);
57
58  // If the stack pointer has a surprising value, we do not understand this
59  // stack usage scheme. (Perhaps the target allocates new stack regions on
60  // demand for us.) Don't try to guess what's going on.
61  if (StackUsage > DesiredStackSize)
62    return false;
63
64  return StackUsage >= DesiredStackSize - SufficientStack;
65}
66
67void clang::runWithSufficientStackSpaceSlow(llvm::function_ref<void()> Diag,
68                                            llvm::function_ref<void()> Fn) {
69  llvm::CrashRecoveryContext CRC;
70  CRC.RunSafelyOnThread([&] {
71    noteBottomOfStack();
72    Diag();
73    Fn();
74  }, DesiredStackSize);
75}
76