//===--- Stack.cpp - Utilities for dealing with stack space ---------------===//

//

// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.

// See https://llvm.org/LICENSE.txt for license information.

// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception

//

//===----------------------------------------------------------------------===//

///

/// \file

/// Defines utilities for dealing with stack allocation and stack space.

///

//===----------------------------------------------------------------------===//

#include "clang/Basic/Stack.h"

#include "llvm/ADT/Optional.h"

#include "llvm/Support/CrashRecoveryContext.h"

#ifdef _MSC_VER

#include <intrin.h>  // for _AddressOfReturnAddress

#endif

static LLVM_THREAD_LOCAL void *BottomOfStack = nullptr;

static void *getStackPointer() {

#if __GNUC__ || __has_builtin(__builtin_frame_address)

  return __builtin_frame_address(0);

#elif defined(_MSC_VER)

  return _AddressOfReturnAddress();

#else

  char CharOnStack = 0;

  // The volatile store here is intended to escape the local variable, to

  // prevent the compiler from optimizing CharOnStack into anything other

  // than a char on the stack.

  //

  // Tested on: MSVC 2015 - 2019, GCC 4.9 - 9, Clang 3.2 - 9, ICC 13 - 19.

  char *volatile Ptr = &CharOnStack;

  return Ptr;

#endif

}

void clang::noteBottomOfStack() {

  if (!BottomOfStack)

    BottomOfStack = getStackPointer();

}

bool clang::isStackNearlyExhausted() {

  // We consider 256 KiB to be sufficient for any code that runs between checks

  // for stack size.

  constexpr size_t SufficientStack = 256 << 10;

  // If we don't know where the bottom of the stack is, hope for the best.

  if (!BottomOfStack)

    return false;

  intptr_t StackDiff = (intptr_t)getStackPointer() - (intptr_t)BottomOfStack;

  size_t StackUsage = (size_t)std::abs(StackDiff);

  // If the stack pointer has a surprising value, we do not understand this

  // stack usage scheme. (Perhaps the target allocates new stack regions on

  // demand for us.) Don't try to guess what's going on.

  if (StackUsage > DesiredStackSize)

    return false;

  return StackUsage >= DesiredStackSize - SufficientStack;

}

void clang::runWithSufficientStackSpaceSlow(llvm::function_ref<void()> Diag,

                                            llvm::function_ref<void()> Fn) {

  llvm::CrashRecoveryContext CRC;

  CRC.RunSafelyOnThread([&] {

    noteBottomOfStack();

    Diag();

    Fn();

  }, DesiredStackSize);

}