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 
22 static LLVM_THREAD_LOCAL void *BottomOfStack = nullptr;
23 
24 static 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 
41 void clang::noteBottomOfStack() {
42   if (!BottomOfStack)
43     BottomOfStack = getStackPointer();
44 }
45 
46 bool 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 
67 void 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