llvm-project

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//===--- Stack.cpp - Utilities for dealing with stack space ---------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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///
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/// \file
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/// Defines utilities for dealing with stack allocation and stack space.
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///
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//===----------------------------------------------------------------------===//
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#include "clang/Basic/Stack.h"
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#include "llvm/Support/CrashRecoveryContext.h"
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#ifdef _MSC_VER
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#include <intrin.h>  // for _AddressOfReturnAddress
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#endif
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static LLVM_THREAD_LOCAL void *BottomOfStack = nullptr;
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static void *getStackPointer() {
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#if __GNUC__ || __has_builtin(__builtin_frame_address)
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  return __builtin_frame_address(0);
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#elif defined(_MSC_VER)
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  return _AddressOfReturnAddress();
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#else
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  char CharOnStack = 0;
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  // The volatile store here is intended to escape the local variable, to
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  // prevent the compiler from optimizing CharOnStack into anything other
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  // than a char on the stack.
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  //
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  // Tested on: MSVC 2015 - 2019, GCC 4.9 - 9, Clang 3.2 - 9, ICC 13 - 19.
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  char *volatile Ptr = &CharOnStack;
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  return Ptr;
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#endif
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}
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void clang::noteBottomOfStack() {
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  if (!BottomOfStack)
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    BottomOfStack = getStackPointer();
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}
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bool clang::isStackNearlyExhausted() {
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  // We consider 256 KiB to be sufficient for any code that runs between checks
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  // for stack size.
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  constexpr size_t SufficientStack = 256 << 10;
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  // If we don't know where the bottom of the stack is, hope for the best.
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  if (!BottomOfStack)
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    return false;
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  intptr_t StackDiff = (intptr_t)getStackPointer() - (intptr_t)BottomOfStack;
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  size_t StackUsage = (size_t)std::abs(StackDiff);
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  // If the stack pointer has a surprising value, we do not understand this
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  // stack usage scheme. (Perhaps the target allocates new stack regions on
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  // demand for us.) Don't try to guess what's going on.
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  if (StackUsage > DesiredStackSize)
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    return false;
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  return StackUsage >= DesiredStackSize - SufficientStack;
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}
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void clang::runWithSufficientStackSpaceSlow(llvm::function_ref<void()> Diag,
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                                            llvm::function_ref<void()> Fn) {
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  llvm::CrashRecoveryContext CRC;
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  CRC.RunSafelyOnThread([&] {
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    noteBottomOfStack();
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    Diag();
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    Fn();
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  }, DesiredStackSize);
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}
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