text: /*
   * 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 "art_method.h"
  #include "base/enums.h"
  #include "base/hex_dump.h"
  #include "base/logging.h"  // For VLOG.
  #include "base/macros.h"
  #include "globals.h"
  #include "registers_arm64.h"
  #include "thread-current-inl.h"
  
  extern "C" void art_quick_throw_stack_overflow();
  extern "C" void art_quick_throw_null_pointer_exception_from_signal();
  extern "C" void art_quick_implicit_suspend();
  
  //
  // ARM64 specific fault handler functions.
  //
  
  namespace art {
  
  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->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(InstructionSet::kArm64));
    if (overflow_addr == fault_addr) {
      *out_method = reinterpret_cast<ArtMethod*>(sc->regs[0]);
    } else {
      // The method is at the top of the stack.
      *out_method = *reinterpret_cast<ArtMethod**>(*out_sp);
    }
  
    // 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 ATTRIBUTE_UNUSED, siginfo_t* info, void* context) {
    if (!IsValidImplicitCheck(info)) {
      return false;
    }
    // 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);
  
    // Push the gc map location to the stack and pass the fault address in LR.
    sc->sp -= sizeof(uintptr_t);
    *reinterpret_cast<uintptr_t*>(sc->sp) = sc->pc + 4;
    sc->regs[30] = reinterpret_cast<uintptr_t>(info->si_addr);
  
    sc->pc = reinterpret_cast<uintptr_t>(art_quick_throw_null_pointer_exception_from_signal);
    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 ATTRIBUTE_UNUSED, siginfo_t* info ATTRIBUTE_UNUSED,
                                 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<PointerSize::k64>().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 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->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(InstructionSet::kArm64);
  
    // 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.
    // 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->pc = reinterpret_cast<uintptr_t>(art_quick_throw_stack_overflow);
  
    // The kernel will now return to the address in sc->pc.
    return true;
  }
  }       // namespace art
  
  