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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 <sys/ucontext.h>
#include "art_method-inl.h"
#include "base/macros.h"
#include "base/hex_dump.h"
#include "globals.h"
#include "base/logging.h"
#include "base/hex_dump.h"
#include "thread.h"
#include "thread-inl.h"
//
// ARM specific fault handler functions.
//
namespace art {
extern "C" void art_quick_throw_null_pointer_exception();
extern "C" void art_quick_throw_stack_overflow();
extern "C" void art_quick_implicit_suspend();
// Get the size of a thumb2 instruction in bytes.
static uint32_t GetInstructionSize(uint8_t* pc) {
uint16_t instr = pc[0] | pc[1] << 8;
bool is_32bit = ((instr & 0xF000) == 0xF000) || ((instr & 0xF800) == 0xE800);
uint32_t instr_size = is_32bit ? 4 : 2;
return instr_size;
}
void FaultManager::HandleNestedSignal(int sig ATTRIBUTE_UNUSED, siginfo_t* info ATTRIBUTE_UNUSED,
void* context) {
// Note that in this handler we set up the registers and return to
// longjmp directly rather than going through an assembly language stub. The
// reason for this is that longjmp is (currently) in ARM mode and that would
// require switching modes in the stub - incurring an unwanted relocation.
struct ucontext *uc = reinterpret_cast<struct ucontext*>(context);
struct sigcontext *sc = reinterpret_cast<struct sigcontext*>(&uc->uc_mcontext);
Thread* self = Thread::Current();
CHECK(self != nullptr); // This will cause a SIGABRT if self is null.
sc->arm_r0 = reinterpret_cast<uintptr_t>(*self->GetNestedSignalState());
sc->arm_r1 = 1;
sc->arm_pc = reinterpret_cast<uintptr_t>(longjmp);
VLOG(signals) << "longjmp address: " << reinterpret_cast<void*>(sc->arm_pc);
}
void FaultManager::GetMethodAndReturnPcAndSp(siginfo_t* siginfo ATTRIBUTE_UNUSED, void* context,
ArtMethod** out_method,
uintptr_t* out_return_pc, uintptr_t* out_sp) {
struct ucontext* uc = reinterpret_cast<struct ucontext*>(context);
struct sigcontext *sc = reinterpret_cast<struct sigcontext*>(&uc->uc_mcontext);
*out_sp = static_cast<uintptr_t>(sc->arm_sp);
VLOG(signals) << "sp: " << *out_sp;
if (*out_sp == 0) {
return;
}
// In the case of a stack overflow, the stack is not valid and we can't
// get the method from the top of the stack. However it's in r0.
uintptr_t* fault_addr = reinterpret_cast<uintptr_t*>(sc->fault_address);
uintptr_t* overflow_addr = reinterpret_cast<uintptr_t*>(
reinterpret_cast<uint8_t*>(*out_sp) - GetStackOverflowReservedBytes(kArm));
if (overflow_addr == fault_addr) {
*out_method = reinterpret_cast<ArtMethod*>(sc->arm_r0);
} else {
// The method is at the top of the stack.
*out_method = reinterpret_cast<ArtMethod*>(reinterpret_cast<uintptr_t*>(*out_sp)[0]);
}
// Work out the return PC. This will be the address of the instruction
// following the faulting ldr/str instruction. This is in thumb mode so
// the instruction might be a 16 or 32 bit one. Also, the GC map always
// has the bottom bit of the PC set so we also need to set that.
// Need to work out the size of the instruction that caused the exception.
uint8_t* ptr = reinterpret_cast<uint8_t*>(sc->arm_pc);
VLOG(signals) << "pc: " << std::hex << static_cast<void*>(ptr);
if (ptr == nullptr) {
// Somebody jumped to 0x0. Definitely not ours, and will definitely segfault below.
*out_method = nullptr;
return;
}
uint32_t instr_size = GetInstructionSize(ptr);
*out_return_pc = (sc->arm_pc + instr_size) | 1;
}
bool NullPointerHandler::Action(int sig ATTRIBUTE_UNUSED, siginfo_t* info ATTRIBUTE_UNUSED,
void* context) {
// The code that looks for the catch location needs to know the value of the
// ARM PC at the point of call. For Null checks we insert a GC map that is immediately after
// the load/store instruction that might cause the fault. However the mapping table has
// the low bits set for thumb mode so we need to set the bottom bit for the LR
// register in order to find the mapping.
// Need to work out the size of the instruction that caused the exception.
struct ucontext *uc = reinterpret_cast<struct ucontext*>(context);
struct sigcontext *sc = reinterpret_cast<struct sigcontext*>(&uc->uc_mcontext);
uint8_t* ptr = reinterpret_cast<uint8_t*>(sc->arm_pc);
uint32_t instr_size = GetInstructionSize(ptr);
sc->arm_lr = (sc->arm_pc + instr_size) | 1; // LR needs to point to gc map location
sc->arm_pc = reinterpret_cast<uintptr_t>(art_quick_throw_null_pointer_exception);
VLOG(signals) << "Generating null pointer exception";
return true;
}
// A suspend check is done using the following instruction sequence:
// 0xf723c0b2: f8d902c0 ldr.w r0, [r9, #704] ; suspend_trigger_
// .. some intervening instruction
// 0xf723c0b6: 6800 ldr r0, [r0, #0]
// The offset from r9 is Thread::ThreadSuspendTriggerOffset().
// To check for a suspend check, we examine the instructions that caused
// the fault (at PC-4 and PC).
bool SuspensionHandler::Action(int sig ATTRIBUTE_UNUSED, siginfo_t* info ATTRIBUTE_UNUSED,
void* context) {
// These are the instructions to check for. The first one is the ldr r0,[r9,#xxx]
// where xxx is the offset of the suspend trigger.
uint32_t checkinst1 = 0xf8d90000 + Thread::ThreadSuspendTriggerOffset<4>().Int32Value();
uint16_t checkinst2 = 0x6800;
struct ucontext* uc = reinterpret_cast<struct ucontext*>(context);
struct sigcontext *sc = reinterpret_cast<struct sigcontext*>(&uc->uc_mcontext);
uint8_t* ptr2 = reinterpret_cast<uint8_t*>(sc->arm_pc);
uint8_t* ptr1 = ptr2 - 4;
VLOG(signals) << "checking suspend";
uint16_t inst2 = ptr2[0] | ptr2[1] << 8;
VLOG(signals) << "inst2: " << std::hex << inst2 << " checkinst2: " << checkinst2;
if (inst2 != checkinst2) {
// Second instruction is not good, not ours.
return false;
}
// The first instruction can a little bit up the stream due to load hoisting
// in the compiler.
uint8_t* limit = ptr1 - 40; // Compiler will hoist to a max of 20 instructions.
bool found = false;
while (ptr1 > limit) {
uint32_t inst1 = ((ptr1[0] | ptr1[1] << 8) << 16) | (ptr1[2] | ptr1[3] << 8);
VLOG(signals) << "inst1: " << std::hex << inst1 << " checkinst1: " << checkinst1;
if (inst1 == checkinst1) {
found = true;
break;
}
ptr1 -= 2; // Min instruction size is 2 bytes.
}
if (found) {
VLOG(signals) << "suspend check match";
// This is a suspend check. Arrange for the signal handler to return to
// art_quick_implicit_suspend. Also set LR so that after the suspend check it
// will resume the instruction (current PC + 2). PC points to the
// ldr r0,[r0,#0] instruction (r0 will be 0, set by the trigger).
// NB: remember that we need to set the bottom bit of the LR register
// to switch to thumb mode.
VLOG(signals) << "arm lr: " << std::hex << sc->arm_lr;
VLOG(signals) << "arm pc: " << std::hex << sc->arm_pc;
sc->arm_lr = sc->arm_pc + 3; // +2 + 1 (for thumb)
sc->arm_pc = reinterpret_cast<uintptr_t>(art_quick_implicit_suspend);
// Now remove the suspend trigger that caused this fault.
Thread::Current()->RemoveSuspendTrigger();
VLOG(signals) << "removed suspend trigger invoking test suspend";
return true;
}
return false;
}
// Stack overflow fault handler.
//
// This checks that the fault address is equal to the current stack pointer
// minus the overflow region size (16K typically). The instruction sequence
// that generates this signal is:
//
// sub r12,sp,#16384
// ldr.w r12,[r12,#0]
//
// The second instruction will fault if r12 is inside the protected region
// on the stack.
//
// If we determine this is a stack overflow we need to move the stack pointer
// to the overflow region below the protected region.
bool StackOverflowHandler::Action(int sig ATTRIBUTE_UNUSED, siginfo_t* info ATTRIBUTE_UNUSED,
void* context) {
struct ucontext* uc = reinterpret_cast<struct ucontext*>(context);
struct sigcontext *sc = reinterpret_cast<struct sigcontext*>(&uc->uc_mcontext);
VLOG(signals) << "stack overflow handler with sp at " << std::hex << &uc;
VLOG(signals) << "sigcontext: " << std::hex << sc;
uintptr_t sp = sc->arm_sp;
VLOG(signals) << "sp: " << std::hex << sp;
uintptr_t fault_addr = sc->fault_address;
VLOG(signals) << "fault_addr: " << std::hex << fault_addr;
VLOG(signals) << "checking for stack overflow, sp: " << std::hex << sp <<
", fault_addr: " << fault_addr;
uintptr_t overflow_addr = sp - GetStackOverflowReservedBytes(kArm);
// Check that the fault address is the value expected for a stack overflow.
if (fault_addr != overflow_addr) {
VLOG(signals) << "Not a stack overflow";
return false;
}
VLOG(signals) << "Stack overflow found";
// Now arrange for the signal handler to return to art_quick_throw_stack_overflow_from.
// The value of LR must be the same as it was when we entered the code that
// caused this fault. This will be inserted into a callee save frame by
// the function to which this handler returns (art_quick_throw_stack_overflow).
sc->arm_pc = reinterpret_cast<uintptr_t>(art_quick_throw_stack_overflow);
// The kernel will now return to the address in sc->arm_pc.
return true;
}
} // namespace art
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