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/*
* Copyright (C) 2008 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include "fault_handler.h"
#include <string.h>
#include <sys/mman.h>
#include <sys/ucontext.h>
#include "art_method-inl.h"
#include "base/logging.h" // For VLOG
#include "base/safe_copy.h"
#include "base/stl_util.h"
#include "dex/dex_file_types.h"
#include "mirror/class.h"
#include "mirror/object_reference.h"
#include "oat_quick_method_header.h"
#include "sigchain.h"
#include "thread-current-inl.h"
#include "verify_object-inl.h"
namespace art {
// Static fault manger object accessed by signal handler.
FaultManager fault_manager;
// This needs to be NO_INLINE since some debuggers do not read the inline-info to set a breakpoint
// if it isn't.
extern "C" NO_INLINE __attribute__((visibility("default"))) void art_sigsegv_fault() {
// Set a breakpoint here to be informed when a SIGSEGV is unhandled by ART.
VLOG(signals)<< "Caught unknown SIGSEGV in ART fault handler - chaining to next handler.";
}
// Signal handler called on SIGSEGV.
static bool art_fault_handler(int sig, siginfo_t* info, void* context) {
return fault_manager.HandleFault(sig, info, context);
}
#if defined(__linux__)
// Change to verify the safe implementations against the original ones.
constexpr bool kVerifySafeImpls = false;
// Provide implementations of ArtMethod::GetDeclaringClass and VerifyClassClass that use SafeCopy
// to safely dereference pointers which are potentially garbage.
// Only available on Linux due to availability of SafeCopy.
static mirror::Class* SafeGetDeclaringClass(ArtMethod* method)
REQUIRES_SHARED(Locks::mutator_lock_) {
char* method_declaring_class =
reinterpret_cast<char*>(method) + ArtMethod::DeclaringClassOffset().SizeValue();
// ArtMethod::declaring_class_ is a GcRoot<mirror::Class>.
// Read it out into as a CompressedReference directly for simplicity's sake.
mirror::CompressedReference<mirror::Class> cls;
ssize_t rc = SafeCopy(&cls, method_declaring_class, sizeof(cls));
CHECK_NE(-1, rc);
if (kVerifySafeImpls) {
ObjPtr<mirror::Class> actual_class = method->GetDeclaringClassUnchecked<kWithoutReadBarrier>();
CHECK_EQ(actual_class, cls.AsMirrorPtr());
}
if (rc != sizeof(cls)) {
return nullptr;
}
return cls.AsMirrorPtr();
}
static mirror::Class* SafeGetClass(mirror::Object* obj) REQUIRES_SHARED(Locks::mutator_lock_) {
char* obj_cls = reinterpret_cast<char*>(obj) + mirror::Object::ClassOffset().SizeValue();
mirror::HeapReference<mirror::Class> cls;
ssize_t rc = SafeCopy(&cls, obj_cls, sizeof(cls));
CHECK_NE(-1, rc);
if (kVerifySafeImpls) {
mirror::Class* actual_class = obj->GetClass<kVerifyNone>();
CHECK_EQ(actual_class, cls.AsMirrorPtr());
}
if (rc != sizeof(cls)) {
return nullptr;
}
return cls.AsMirrorPtr();
}
static bool SafeVerifyClassClass(mirror::Class* cls) REQUIRES_SHARED(Locks::mutator_lock_) {
mirror::Class* c_c = SafeGetClass(cls);
bool result = c_c != nullptr && c_c == SafeGetClass(c_c);
if (kVerifySafeImpls) {
CHECK_EQ(VerifyClassClass(cls), result);
}
return result;
}
#else
static mirror::Class* SafeGetDeclaringClass(ArtMethod* method_obj)
REQUIRES_SHARED(Locks::mutator_lock_) {
return method_obj->GetDeclaringClassUnchecked<kWithoutReadBarrier>().Ptr();
}
static bool SafeVerifyClassClass(mirror::Class* cls) REQUIRES_SHARED(Locks::mutator_lock_) {
return VerifyClassClass(cls);
}
#endif
FaultManager::FaultManager() : initialized_(false) {
sigaction(SIGSEGV, nullptr, &oldaction_);
}
FaultManager::~FaultManager() {
}
void FaultManager::Init() {
CHECK(!initialized_);
sigset_t mask;
sigfillset(&mask);
sigdelset(&mask, SIGABRT);
sigdelset(&mask, SIGBUS);
sigdelset(&mask, SIGFPE);
sigdelset(&mask, SIGILL);
sigdelset(&mask, SIGSEGV);
SigchainAction sa = {
.sc_sigaction = art_fault_handler,
.sc_mask = mask,
.sc_flags = 0UL,
};
AddSpecialSignalHandlerFn(SIGSEGV, &sa);
initialized_ = true;
}
void FaultManager::Release() {
if (initialized_) {
RemoveSpecialSignalHandlerFn(SIGSEGV, art_fault_handler);
initialized_ = false;
}
}
void FaultManager::Shutdown() {
if (initialized_) {
Release();
// Free all handlers.
STLDeleteElements(&generated_code_handlers_);
STLDeleteElements(&other_handlers_);
}
}
bool FaultManager::HandleFaultByOtherHandlers(int sig, siginfo_t* info, void* context) {
if (other_handlers_.empty()) {
return false;
}
Thread* self = Thread::Current();
DCHECK(self != nullptr);
DCHECK(Runtime::Current() != nullptr);
DCHECK(Runtime::Current()->IsStarted());
for (const auto& handler : other_handlers_) {
if (handler->Action(sig, info, context)) {
return true;
}
}
return false;
}
static const char* SignalCodeName(int sig, int code) {
if (sig != SIGSEGV) {
return "UNKNOWN";
} else {
switch (code) {
case SEGV_MAPERR: return "SEGV_MAPERR";
case SEGV_ACCERR: return "SEGV_ACCERR";
default: return "UNKNOWN";
}
}
}
static std::ostream& PrintSignalInfo(std::ostream& os, siginfo_t* info) {
os << " si_signo: " << info->si_signo << " (" << strsignal(info->si_signo) << ")\n"
<< " si_code: " << info->si_code
<< " (" << SignalCodeName(info->si_signo, info->si_code) << ")";
if (info->si_signo == SIGSEGV) {
os << "\n" << " si_addr: " << info->si_addr;
}
return os;
}
bool FaultManager::HandleFault(int sig, siginfo_t* info, void* context) {
if (VLOG_IS_ON(signals)) {
PrintSignalInfo(VLOG_STREAM(signals) << "Handling fault:" << "\n", info);
}
#ifdef TEST_NESTED_SIGNAL
// Simulate a crash in a handler.
raise(SIGSEGV);
#endif
if (IsInGeneratedCode(info, context, true)) {
VLOG(signals) << "in generated code, looking for handler";
for (const auto& handler : generated_code_handlers_) {
VLOG(signals) << "invoking Action on handler " << handler;
if (handler->Action(sig, info, context)) {
// We have handled a signal so it's time to return from the
// signal handler to the appropriate place.
return true;
}
}
}
// We hit a signal we didn't handle. This might be something for which
// we can give more information about so call all registered handlers to
// see if it is.
if (HandleFaultByOtherHandlers(sig, info, context)) {
return true;
}
// Set a breakpoint in this function to catch unhandled signals.
art_sigsegv_fault();
return false;
}
void FaultManager::AddHandler(FaultHandler* handler, bool generated_code) {
DCHECK(initialized_);
if (generated_code) {
generated_code_handlers_.push_back(handler);
} else {
other_handlers_.push_back(handler);
}
}
void FaultManager::RemoveHandler(FaultHandler* handler) {
auto it = std::find(generated_code_handlers_.begin(), generated_code_handlers_.end(), handler);
if (it != generated_code_handlers_.end()) {
generated_code_handlers_.erase(it);
return;
}
auto it2 = std::find(other_handlers_.begin(), other_handlers_.end(), handler);
if (it2 != other_handlers_.end()) {
other_handlers_.erase(it2);
return;
}
LOG(FATAL) << "Attempted to remove non existent handler " << handler;
}
// This function is called within the signal handler. It checks that
// the mutator_lock is held (shared). No annotalysis is done.
bool FaultManager::IsInGeneratedCode(siginfo_t* siginfo, void* context, bool check_dex_pc) {
// We can only be running Java code in the current thread if it
// is in Runnable state.
VLOG(signals) << "Checking for generated code";
Thread* thread = Thread::Current();
if (thread == nullptr) {
VLOG(signals) << "no current thread";
return false;
}
ThreadState state = thread->GetState();
if (state != kRunnable) {
VLOG(signals) << "not runnable";
return false;
}
// Current thread is runnable.
// Make sure it has the mutator lock.
if (!Locks::mutator_lock_->IsSharedHeld(thread)) {
VLOG(signals) << "no lock";
return false;
}
ArtMethod* method_obj = nullptr;
uintptr_t return_pc = 0;
uintptr_t sp = 0;
bool is_stack_overflow = false;
// Get the architecture specific method address and return address. These
// are in architecture specific files in arch/<arch>/fault_handler_<arch>.
GetMethodAndReturnPcAndSp(siginfo, context, &method_obj, &return_pc, &sp, &is_stack_overflow);
// If we don't have a potential method, we're outta here.
VLOG(signals) << "potential method: " << method_obj;
// TODO: Check linear alloc and image.
DCHECK_ALIGNED(ArtMethod::Size(kRuntimePointerSize), sizeof(void*))
<< "ArtMethod is not pointer aligned";
if (method_obj == nullptr || !IsAligned<sizeof(void*)>(method_obj)) {
VLOG(signals) << "no method";
return false;
}
// Verify that the potential method is indeed a method.
// TODO: check the GC maps to make sure it's an object.
// Check that the class pointer inside the object is not null and is aligned.
// No read barrier because method_obj may not be a real object.
mirror::Class* cls = SafeGetDeclaringClass(method_obj);
if (cls == nullptr) {
VLOG(signals) << "not a class";
return false;
}
if (!IsAligned<kObjectAlignment>(cls)) {
VLOG(signals) << "not aligned";
return false;
}
if (!SafeVerifyClassClass(cls)) {
VLOG(signals) << "not a class class";
return false;
}
const OatQuickMethodHeader* method_header = method_obj->GetOatQuickMethodHeader(return_pc);
// We can be certain that this is a method now. Check if we have a GC map
// at the return PC address.
if (true || kIsDebugBuild) {
VLOG(signals) << "looking for dex pc for return pc " << std::hex << return_pc;
uint32_t sought_offset = return_pc -
reinterpret_cast<uintptr_t>(method_header->GetEntryPoint());
VLOG(signals) << "pc offset: " << std::hex << sought_offset;
}
uint32_t dexpc = dex::kDexNoIndex;
if (is_stack_overflow) {
// If it's an implicit stack overflow check, the frame is not setup, so we
// just infer the dex PC as zero.
dexpc = 0;
} else {
CHECK_EQ(*reinterpret_cast<ArtMethod**>(sp), method_obj);
dexpc = method_header->ToDexPc(reinterpret_cast<ArtMethod**>(sp), return_pc, false);
}
VLOG(signals) << "dexpc: " << dexpc;
return !check_dex_pc || dexpc != dex::kDexNoIndex;
}
FaultHandler::FaultHandler(FaultManager* manager) : manager_(manager) {
}
//
// Null pointer fault handler
//
NullPointerHandler::NullPointerHandler(FaultManager* manager) : FaultHandler(manager) {
manager_->AddHandler(this, true);
}
//
// Suspension fault handler
//
SuspensionHandler::SuspensionHandler(FaultManager* manager) : FaultHandler(manager) {
manager_->AddHandler(this, true);
}
//
// Stack overflow fault handler
//
StackOverflowHandler::StackOverflowHandler(FaultManager* manager) : FaultHandler(manager) {
manager_->AddHandler(this, true);
}
//
// Stack trace handler, used to help get a stack trace from SIGSEGV inside of compiled code.
//
JavaStackTraceHandler::JavaStackTraceHandler(FaultManager* manager) : FaultHandler(manager) {
manager_->AddHandler(this, false);
}
bool JavaStackTraceHandler::Action(int sig ATTRIBUTE_UNUSED, siginfo_t* siginfo, void* context) {
// Make sure that we are in the generated code, but we may not have a dex pc.
bool in_generated_code = manager_->IsInGeneratedCode(siginfo, context, false);
if (in_generated_code) {
LOG(ERROR) << "Dumping java stack trace for crash in generated code";
ArtMethod* method = nullptr;
uintptr_t return_pc = 0;
uintptr_t sp = 0;
bool is_stack_overflow = false;
Thread* self = Thread::Current();
manager_->GetMethodAndReturnPcAndSp(
siginfo, context, &method, &return_pc, &sp, &is_stack_overflow);
// Inside of generated code, sp[0] is the method, so sp is the frame.
self->SetTopOfStack(reinterpret_cast<ArtMethod**>(sp));
self->DumpJavaStack(LOG_STREAM(ERROR));
}
return false; // Return false since we want to propagate the fault to the main signal handler.
}
} // namespace art