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