asan_fake_stack.h | Explore in Territory

//===-- asan_fake_stack.h ---------------------------------------*- C++ -*-===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// This file is a part of AddressSanitizer, an address sanity checker.
//
// ASan-private header for asan_fake_stack.cpp, implements FakeStack.
//===----------------------------------------------------------------------===//

#ifndef ASAN_FAKE_STACK_H
#define ASAN_FAKE_STACK_H

#include "sanitizer_common/sanitizer_common.h"

namespace __asan {

// Fake stack frame contains local variables of one function.
struct FakeFrame { … };

// For each thread we create a fake stack and place stack objects on this fake
// stack instead of the real stack. The fake stack is not really a stack but
// a fast malloc-like allocator so that when a function exits the fake stack
// is not popped but remains there for quite some time until gets used again.
// So, we poison the objects on the fake stack when function returns.
// It helps us find use-after-return bugs.
//
// The FakeStack objects is allocated by a single mmap call and has no other
// pointers. The size of the fake stack depends on the actual thread stack size
// and thus can not be a constant.
// stack_size is a power of two greater or equal to the thread's stack size;
// we store it as its logarithm (stack_size_log).
// FakeStack has kNumberOfSizeClasses (11) size classes, each size class
// is a power of two, starting from 64 bytes. Each size class occupies
// stack_size bytes and thus can allocate
// NumberOfFrames=(stack_size/BytesInSizeClass) fake frames (also a power of 2).
// For each size class we have NumberOfFrames allocation flags,
// each flag indicates whether the given frame is currently allocated.
// All flags for size classes 0 .. 10 are stored in a single contiguous region
// followed by another contiguous region which contains the actual memory for
// size classes. The addresses are computed by GetFlags and GetFrame without
// any memory accesses solely based on 'this' and stack_size_log.
// Allocate() flips the appropriate allocation flag atomically, thus achieving
// async-signal safety.
// This allocator does not have quarantine per se, but it tries to allocate the
// frames in round robin fashion to maximize the delay between a deallocation
// and the next allocation.
class FakeStack { … };

FakeStack *GetTLSFakeStack();
void SetTLSFakeStack(FakeStack *fs);

}  // namespace __asan

#endif  // ASAN_FAKE_STACK_H
llvm/compiler-rt/lib/asan/asan_fake_stack.h
