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// Copyright 2020 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "src/heap/cppgc/stack.h"
#include <limits>
#include "src/base/platform/platform.h"
#include "src/heap/cppgc/globals.h"
#include "src/heap/cppgc/sanitizers.h"
namespace cppgc {
namespace internal {
using IterateStackCallback = void (Stack::*)(StackVisitor*, intptr_t*) const;
extern "C" void PushAllRegistersAndIterateStack(const Stack*, StackVisitor*,
IterateStackCallback);
Stack::Stack(const void* stack_start) : stack_start_(stack_start) {}
bool Stack::IsOnStack(void* slot) const {
void* raw_slot = v8::base::Stack::GetStackSlot(slot);
return v8::base::Stack::GetCurrentStackPosition() <= raw_slot &&
raw_slot <= stack_start_;
}
namespace {
#ifdef V8_USE_ADDRESS_SANITIZER
// No ASAN support as accessing fake frames otherwise results in
// "stack-use-after-scope" warnings.
NO_SANITIZE_ADDRESS
void IterateAsanFakeFrameIfNecessary(StackVisitor* visitor,
void* asan_fake_stack,
const void* stack_start,
const void* stack_end, void* address) {
// When using ASAN fake stack a pointer to the fake frame is kept on the
// native frame. In case |addr| points to a fake frame of the current stack
// iterate the fake frame. Frame layout see
// https://github.com/google/sanitizers/wiki/AddressSanitizerUseAfterReturn
if (asan_fake_stack) {
void* fake_frame_begin;
void* fake_frame_end;
void* real_stack_frame = __asan_addr_is_in_fake_stack(
asan_fake_stack, address, &fake_frame_begin, &fake_frame_end);
if (real_stack_frame) {
// |address| points to a fake frame. Check that the fake frame is part
// of this stack.
if (stack_start >= real_stack_frame && real_stack_frame >= stack_end) {
// Iterate the fake frame.
for (void** current = reinterpret_cast<void**>(fake_frame_begin);
current < fake_frame_end; ++current) {
void* addr = *current;
if (addr == nullptr) continue;
visitor->VisitPointer(addr);
}
}
}
}
}
#endif // V8_USE_ADDRESS_SANITIZER
#ifdef CPPGC_SUPPORTS_CONSERVATIVE_STACK_SCAN
void IterateSafeStackIfNecessary(StackVisitor* visitor) {
#if defined(__has_feature)
#if __has_feature(safe_stack)
// Source:
// https://github.com/llvm/llvm-project/blob/master/compiler-rt/lib/safestack/safestack.cpp
constexpr size_t kSafeStackAlignmentBytes = 16;
void* stack_end = __builtin___get_unsafe_stack_ptr();
void* stack_start = __builtin___get_unsafe_stack_top();
CHECK_GT(stack_start, stack_end);
CHECK_EQ(0u, reinterpret_cast<uintptr_t>(stack_end) &
(kSafeStackAlignmentBytes - 1));
CHECK_EQ(0u, reinterpret_cast<uintptr_t>(stack_start) &
(kSafeStackAlignmentBytes - 1));
void** current = reinterpret_cast<void**>(stack_end);
for (; current < stack_start; ++current) {
void* address = *current;
if (address == nullptr) continue;
visitor->VisitPointer(address);
}
#endif // __has_feature(safe_stack)
#endif // defined(__has_feature)
}
#endif // CPPGC_SUPPORTS_CONSERVATIVE_STACK_SCAN
} // namespace
#ifdef CPPGC_SUPPORTS_CONSERVATIVE_STACK_SCAN
void Stack::IteratePointers(StackVisitor* visitor) const {
PushAllRegistersAndIterateStack(this, visitor, &Stack::IteratePointersImpl);
// No need to deal with callee-saved registers as they will be kept alive by
// the regular conservative stack iteration.
IterateSafeStackIfNecessary(visitor);
}
#endif // CPPGC_SUPPORTS_CONSERVATIVE_STACK_SCAN
// No ASAN support as method accesses redzones while walking the stack.
NO_SANITIZE_ADDRESS
void Stack::IteratePointersImpl(StackVisitor* visitor,
intptr_t* stack_end) const {
#ifdef V8_USE_ADDRESS_SANITIZER
void* asan_fake_stack = __asan_get_current_fake_stack();
#endif // V8_USE_ADDRESS_SANITIZER
// All supported platforms should have their stack aligned to at least
// sizeof(void*).
constexpr size_t kMinStackAlignment = sizeof(void*);
// Redzone should not contain any pointers as the iteration is always called
// from the assembly trampoline. If inline assembly is ever inlined through
// LTO this may become necessary.
constexpr size_t kRedZoneBytes = 128;
void** current = reinterpret_cast<void**>(
reinterpret_cast<uintptr_t>(stack_end - kRedZoneBytes));
CHECK_EQ(0u, reinterpret_cast<uintptr_t>(current) & (kMinStackAlignment - 1));
for (; current < stack_start_; ++current) {
// MSAN: Instead of unpoisoning the whole stack, the slot's value is copied
// into a local which is unpoisoned.
void* address = *current;
MSAN_UNPOISON(address, sizeof(address));
if (address == nullptr) continue;
visitor->VisitPointer(address);
#ifdef V8_USE_ADDRESS_SANITIZER
IterateAsanFakeFrameIfNecessary(visitor, asan_fake_stack, stack_start_,
stack_end, address);
#endif // V8_USE_ADDRESS_SANITIZER
}
}
} // namespace internal
} // namespace cppgc
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