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//===-- asan_fake_stack.h ---------------------------------------*- C++ -*-===//
// The LLVM Compiler Infrastructure
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
// This file is a part of AddressSanitizer, an address sanity checker.
// ASan-private header for
namespace __asan {
// Fake stack frame contains local variables of one function.
struct FakeFrame {
uptr magic; // Modified by the instrumented code.
uptr descr; // Modified by the instrumented code.
uptr pc; // Modified by the instrumented code.
u64 real_stack : 48;
u64 size_minus_one : 16;
// End of the first 32 bytes.
// The rest should not be used when the frame is active.
FakeFrame *next;
struct FakeFrameFifo {
void FifoPush(FakeFrame *node);
FakeFrame *FifoPop();
FakeFrame *first_, *last_;
template<uptr kMaxNumberOfFrames>
class FakeFrameLifo {
explicit FakeFrameLifo(LinkerInitialized) {}
FakeFrameLifo() : n_frames_(0) {}
void LifoPush(FakeFrame *node) {
CHECK_LT(n_frames_, kMaxNumberOfFrames);
frames_[n_frames_++] = node;
void LifoPop() {
FakeFrame *top() {
if (n_frames_ == 0)
return 0;
return frames_[n_frames_ - 1];
uptr n_frames_;
FakeFrame *frames_[kMaxNumberOfFrames];
// 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 poped 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.
// We can not rely on __asan_stack_free being called on every function exit,
// so we maintain a lifo list of all current fake frames and update it on every
// call to __asan_stack_malloc.
class FakeStack {
explicit FakeStack(LinkerInitialized x) : call_stack_(x) {}
void Init(uptr stack_size);
void StopUsingFakeStack() { alive_ = false; }
void Cleanup();
uptr AllocateStack(uptr size, uptr real_stack);
static void OnFree(uptr ptr, uptr size, uptr real_stack);
// Return the bottom of the maped region.
uptr AddrIsInFakeStack(uptr addr);
bool StackSize() { return stack_size_; }
static const uptr kMinStackFrameSizeLog = 9; // Min frame is 512B.
static const uptr kMaxStackFrameSizeLog = 16; // Max stack frame is 64K.
static const uptr kMaxStackMallocSize = 1 << kMaxStackFrameSizeLog;
static const uptr kNumberOfSizeClasses =
kMaxStackFrameSizeLog - kMinStackFrameSizeLog + 1;
static const uptr kMaxRecursionDepth = 1023;
bool AddrIsInSizeClass(uptr addr, uptr size_class);
// Each size class should be large enough to hold all frames.
uptr ClassMmapSize(uptr size_class);
uptr ClassSize(uptr size_class) {
return 1UL << (size_class + kMinStackFrameSizeLog);
void DeallocateFrame(FakeFrame *fake_frame);
uptr ComputeSizeClass(uptr alloc_size);
void AllocateOneSizeClass(uptr size_class);
uptr stack_size_;
bool alive_;
uptr allocated_size_classes_[kNumberOfSizeClasses];
FakeFrameFifo size_classes_[kNumberOfSizeClasses];
FakeFrameLifo<kMaxRecursionDepth> call_stack_;
} // namespace __asan