arch/arm64/fault_handler_arm64.cc

/*
 * Copyright (C) 2014 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 "base/macros.h"
#include "globals.h"
#include "base/logging.h"
#include "base/hex_dump.h"
#include "registers_arm64.h"
#include "mirror/art_method.h"
#include "mirror/art_method-inl.h"
#include "thread.h"
#include "thread-inl.h"

extern "C" void art_quick_throw_stack_overflow_from_signal();
extern "C" void art_quick_throw_null_pointer_exception();
extern "C" void art_quick_implicit_suspend();

//
// ARM64 specific fault handler functions.
//

namespace art {

void FaultManager::GetMethodAndReturnPCAndSP(siginfo_t* siginfo, void* context,
                                             mirror::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->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 x0.
  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(kArm64));
  if (overflow_addr == fault_addr) {
    *out_method = reinterpret_cast<mirror::ArtMethod*>(sc->regs[0]);
  } else {
    // The method is at the top of the stack.
    *out_method = (reinterpret_cast<StackReference<mirror::ArtMethod>* >(*out_sp)[0]).AsMirrorPtr();
  }

  // Work out the return PC.  This will be the address of the instruction
  // following the faulting ldr/str instruction.
  VLOG(signals) << "pc: " << std::hex
      << static_cast<void*>(reinterpret_cast<uint8_t*>(sc->pc));

  *out_return_pc = sc->pc + 4;
}

bool NullPointerHandler::Action(int sig, siginfo_t* info, void* context) {
  // The code that looks for the catch location needs to know the value of the
  // 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.

  struct ucontext *uc = reinterpret_cast<struct ucontext*>(context);
  struct sigcontext *sc = reinterpret_cast<struct sigcontext*>(&uc->uc_mcontext);

  sc->regs[30] = sc->pc + 4;      // LR needs to point to gc map location

  sc->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:
//      0xf7223228: f9405640  ldr x0, [x18, #168]
// .. some intervening instructions
//      0xf7223230: f9400000  ldr x0, [x0]

// The offset from r18 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, siginfo_t* info, void* context) {
  // These are the instructions to check for.  The first one is the ldr x0,[r18,#xxx]
  // where xxx is the offset of the suspend trigger.
  uint32_t checkinst1 = 0xf9400240 | (Thread::ThreadSuspendTriggerOffset<8>().Int32Value() << 7);
  uint32_t checkinst2 = 0xf9400000;

  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->pc);
  uint8_t* ptr1 = ptr2 - 4;
  VLOG(signals) << "checking suspend";

  uint32_t inst2 = *reinterpret_cast<uint32_t*>(ptr2);
  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 - 80;   // Compiler will hoist to a max of 20 instructions.
  bool found = false;
  while (ptr1 > limit) {
    uint32_t inst1 = *reinterpret_cast<uint32_t*>(ptr1);
    VLOG(signals) << "inst1: " << std::hex << inst1 << " checkinst1: " << checkinst1;
    if (inst1 == checkinst1) {
      found = true;
      break;
    }
    ptr1 -= 4;
  }
  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 + 4).  PC points to the
    // ldr x0,[x0,#0] instruction (r0 will be 0, set by the trigger).

    sc->regs[30] = sc->pc + 4;
    sc->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;
}

bool StackOverflowHandler::Action(int sig, siginfo_t* info, 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->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(kArm64);

  Thread* self = reinterpret_cast<Thread*>(sc->regs[art::arm64::TR]);
  CHECK_EQ(self, Thread::Current());
  uintptr_t pregion = reinterpret_cast<uintptr_t>(self->GetStackEnd()) -
      Thread::kStackOverflowProtectedSize;

  // 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;
  }

  // We know this is a stack overflow.  We need to move the sp to the overflow region
  // that exists below the protected region.  Determine the address of the next
  // available valid address below the protected region.
  uintptr_t prevsp = sp;
  sp = pregion;
  VLOG(signals) << "setting sp to overflow region at " << std::hex << sp;

  // Since the compiler puts the implicit overflow
  // check before the callee save instructions, the SP is already pointing to
  // the previous frame.
  VLOG(signals) << "previous frame: " << std::hex << prevsp;

  // Now establish the stack pointer for the signal return.
  sc->sp = prevsp;

  // Tell the stack overflow code where the new stack pointer should be.
  sc->regs[art::arm64::IP0] = sp;      // aka x16

  // Now arrange for the signal handler to return to art_quick_throw_stack_overflow_from_signal.
  // 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_from_signal).
  sc->pc = reinterpret_cast<uintptr_t>(art_quick_throw_stack_overflow_from_signal);

  // The kernel will now return to the address in sc->pc.
  return true;
}
}       // namespace art