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      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