fault_handler_arm.cc revision 03c9785a8a6d712775cf406c4371d0227c44148f
1/* 2 * Copyright (C) 2008 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 18#include "fault_handler.h" 19#include <sys/ucontext.h> 20#include "base/macros.h" 21#include "base/hex_dump.h" 22#include "globals.h" 23#include "base/logging.h" 24#include "base/hex_dump.h" 25#include "instruction_set.h" 26#include "mirror/art_method.h" 27#include "mirror/art_method-inl.h" 28#include "thread.h" 29#include "thread-inl.h" 30 31// 32// ARM specific fault handler functions. 33// 34 35namespace art { 36 37extern "C" void art_quick_throw_null_pointer_exception(); 38extern "C" void art_quick_throw_stack_overflow(); 39extern "C" void art_quick_implicit_suspend(); 40 41// Get the size of a thumb2 instruction in bytes. 42static uint32_t GetInstructionSize(uint8_t* pc) { 43 uint16_t instr = pc[0] | pc[1] << 8; 44 bool is_32bit = ((instr & 0xF000) == 0xF000) || ((instr & 0xF800) == 0xE800); 45 uint32_t instr_size = is_32bit ? 4 : 2; 46 return instr_size; 47} 48 49void FaultManager::GetMethodAndReturnPcAndSp(siginfo_t* siginfo, void* context, 50 mirror::ArtMethod** out_method, 51 uintptr_t* out_return_pc, uintptr_t* out_sp) { 52 struct ucontext* uc = reinterpret_cast<struct ucontext*>(context); 53 struct sigcontext *sc = reinterpret_cast<struct sigcontext*>(&uc->uc_mcontext); 54 *out_sp = static_cast<uintptr_t>(sc->arm_sp); 55 VLOG(signals) << "sp: " << *out_sp; 56 if (*out_sp == 0) { 57 return; 58 } 59 60 // In the case of a stack overflow, the stack is not valid and we can't 61 // get the method from the top of the stack. However it's in r0. 62 uintptr_t* fault_addr = reinterpret_cast<uintptr_t*>(sc->fault_address); 63 uintptr_t* overflow_addr = reinterpret_cast<uintptr_t*>( 64 reinterpret_cast<uint8_t*>(*out_sp) - GetStackOverflowReservedBytes(kArm)); 65 if (overflow_addr == fault_addr) { 66 *out_method = reinterpret_cast<mirror::ArtMethod*>(sc->arm_r0); 67 } else { 68 // The method is at the top of the stack. 69 *out_method = reinterpret_cast<mirror::ArtMethod*>(reinterpret_cast<uintptr_t*>(*out_sp)[0]); 70 } 71 72 // Work out the return PC. This will be the address of the instruction 73 // following the faulting ldr/str instruction. This is in thumb mode so 74 // the instruction might be a 16 or 32 bit one. Also, the GC map always 75 // has the bottom bit of the PC set so we also need to set that. 76 77 // Need to work out the size of the instruction that caused the exception. 78 uint8_t* ptr = reinterpret_cast<uint8_t*>(sc->arm_pc); 79 VLOG(signals) << "pc: " << std::hex << static_cast<void*>(ptr); 80 uint32_t instr_size = GetInstructionSize(ptr); 81 82 *out_return_pc = (sc->arm_pc + instr_size) | 1; 83} 84 85bool NullPointerHandler::Action(int sig, siginfo_t* info, void* context) { 86 // The code that looks for the catch location needs to know the value of the 87 // ARM PC at the point of call. For Null checks we insert a GC map that is immediately after 88 // the load/store instruction that might cause the fault. However the mapping table has 89 // the low bits set for thumb mode so we need to set the bottom bit for the LR 90 // register in order to find the mapping. 91 92 // Need to work out the size of the instruction that caused the exception. 93 struct ucontext *uc = reinterpret_cast<struct ucontext*>(context); 94 struct sigcontext *sc = reinterpret_cast<struct sigcontext*>(&uc->uc_mcontext); 95 uint8_t* ptr = reinterpret_cast<uint8_t*>(sc->arm_pc); 96 97 uint32_t instr_size = GetInstructionSize(ptr); 98 sc->arm_lr = (sc->arm_pc + instr_size) | 1; // LR needs to point to gc map location 99 sc->arm_pc = reinterpret_cast<uintptr_t>(art_quick_throw_null_pointer_exception); 100 VLOG(signals) << "Generating null pointer exception"; 101 return true; 102} 103 104// A suspend check is done using the following instruction sequence: 105// 0xf723c0b2: f8d902c0 ldr.w r0, [r9, #704] ; suspend_trigger_ 106// .. some intervening instruction 107// 0xf723c0b6: 6800 ldr r0, [r0, #0] 108 109// The offset from r9 is Thread::ThreadSuspendTriggerOffset(). 110// To check for a suspend check, we examine the instructions that caused 111// the fault (at PC-4 and PC). 112bool SuspensionHandler::Action(int sig, siginfo_t* info, void* context) { 113 // These are the instructions to check for. The first one is the ldr r0,[r9,#xxx] 114 // where xxx is the offset of the suspend trigger. 115 uint32_t checkinst1 = 0xf8d90000 + Thread::ThreadSuspendTriggerOffset<4>().Int32Value(); 116 uint16_t checkinst2 = 0x6800; 117 118 struct ucontext* uc = reinterpret_cast<struct ucontext*>(context); 119 struct sigcontext *sc = reinterpret_cast<struct sigcontext*>(&uc->uc_mcontext); 120 uint8_t* ptr2 = reinterpret_cast<uint8_t*>(sc->arm_pc); 121 uint8_t* ptr1 = ptr2 - 4; 122 VLOG(signals) << "checking suspend"; 123 124 uint16_t inst2 = ptr2[0] | ptr2[1] << 8; 125 VLOG(signals) << "inst2: " << std::hex << inst2 << " checkinst2: " << checkinst2; 126 if (inst2 != checkinst2) { 127 // Second instruction is not good, not ours. 128 return false; 129 } 130 131 // The first instruction can a little bit up the stream due to load hoisting 132 // in the compiler. 133 uint8_t* limit = ptr1 - 40; // Compiler will hoist to a max of 20 instructions. 134 bool found = false; 135 while (ptr1 > limit) { 136 uint32_t inst1 = ((ptr1[0] | ptr1[1] << 8) << 16) | (ptr1[2] | ptr1[3] << 8); 137 VLOG(signals) << "inst1: " << std::hex << inst1 << " checkinst1: " << checkinst1; 138 if (inst1 == checkinst1) { 139 found = true; 140 break; 141 } 142 ptr1 -= 2; // Min instruction size is 2 bytes. 143 } 144 if (found) { 145 VLOG(signals) << "suspend check match"; 146 // This is a suspend check. Arrange for the signal handler to return to 147 // art_quick_implicit_suspend. Also set LR so that after the suspend check it 148 // will resume the instruction (current PC + 2). PC points to the 149 // ldr r0,[r0,#0] instruction (r0 will be 0, set by the trigger). 150 151 // NB: remember that we need to set the bottom bit of the LR register 152 // to switch to thumb mode. 153 VLOG(signals) << "arm lr: " << std::hex << sc->arm_lr; 154 VLOG(signals) << "arm pc: " << std::hex << sc->arm_pc; 155 sc->arm_lr = sc->arm_pc + 3; // +2 + 1 (for thumb) 156 sc->arm_pc = reinterpret_cast<uintptr_t>(art_quick_implicit_suspend); 157 158 // Now remove the suspend trigger that caused this fault. 159 Thread::Current()->RemoveSuspendTrigger(); 160 VLOG(signals) << "removed suspend trigger invoking test suspend"; 161 return true; 162 } 163 return false; 164} 165 166// Stack overflow fault handler. 167// 168// This checks that the fault address is equal to the current stack pointer 169// minus the overflow region size (16K typically). The instruction sequence 170// that generates this signal is: 171// 172// sub r12,sp,#16384 173// ldr.w r12,[r12,#0] 174// 175// The second instruction will fault if r12 is inside the protected region 176// on the stack. 177// 178// If we determine this is a stack overflow we need to move the stack pointer 179// to the overflow region below the protected region. 180 181bool StackOverflowHandler::Action(int sig, siginfo_t* info, void* context) { 182 struct ucontext* uc = reinterpret_cast<struct ucontext*>(context); 183 struct sigcontext *sc = reinterpret_cast<struct sigcontext*>(&uc->uc_mcontext); 184 VLOG(signals) << "stack overflow handler with sp at " << std::hex << &uc; 185 VLOG(signals) << "sigcontext: " << std::hex << sc; 186 187 uintptr_t sp = sc->arm_sp; 188 VLOG(signals) << "sp: " << std::hex << sp; 189 190 uintptr_t fault_addr = sc->fault_address; 191 VLOG(signals) << "fault_addr: " << std::hex << fault_addr; 192 VLOG(signals) << "checking for stack overflow, sp: " << std::hex << sp << 193 ", fault_addr: " << fault_addr; 194 195 uintptr_t overflow_addr = sp - GetStackOverflowReservedBytes(kArm); 196 197 // Check that the fault address is the value expected for a stack overflow. 198 if (fault_addr != overflow_addr) { 199 VLOG(signals) << "Not a stack overflow"; 200 return false; 201 } 202 203 VLOG(signals) << "Stack overflow found"; 204 205 // Now arrange for the signal handler to return to art_quick_throw_stack_overflow_from. 206 // The value of LR must be the same as it was when we entered the code that 207 // caused this fault. This will be inserted into a callee save frame by 208 // the function to which this handler returns (art_quick_throw_stack_overflow). 209 sc->arm_pc = reinterpret_cast<uintptr_t>(art_quick_throw_stack_overflow); 210 211 // The kernel will now return to the address in sc->arm_pc. 212 return true; 213} 214} // namespace art 215