clang/lib/Basic/Stack.cpp

   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 }