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