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 20 #include <sys/ucontext.h> 21 #include "base/macros.h" 22 #include "base/hex_dump.h" 23 #include "globals.h" 24 #include "base/logging.h" 25 #include "base/hex_dump.h" 26 #include "instruction_set.h" 27 #include "mirror/art_method.h" 28 #include "mirror/art_method-inl.h" 29 #include "thread.h" 30 #include "thread-inl.h" 31 32 // 33 // ARM specific fault handler functions. 34 // 35 36 namespace art { 37 38 extern "C" void art_quick_throw_null_pointer_exception(); 39 extern "C" void art_quick_throw_stack_overflow(); 40 extern "C" void art_quick_implicit_suspend(); 41 42 // Get the size of a thumb2 instruction in bytes. 43 static uint32_t GetInstructionSize(uint8_t* pc) { 44 uint16_t instr = pc[0] | pc[1] << 8; 45 bool is_32bit = ((instr & 0xF000) == 0xF000) || ((instr & 0xF800) == 0xE800); 46 uint32_t instr_size = is_32bit ? 4 : 2; 47 return instr_size; 48 } 49 50 void FaultManager::HandleNestedSignal(int sig, siginfo_t* info, void* context) { 51 // Note that in this handler we set up the registers and return to 52 // longjmp directly rather than going through an assembly language stub. The 53 // reason for this is that longjmp is (currently) in ARM mode and that would 54 // require switching modes in the stub - incurring an unwanted relocation. 55 56 struct ucontext *uc = reinterpret_cast<struct ucontext*>(context); 57 struct sigcontext *sc = reinterpret_cast<struct sigcontext*>(&uc->uc_mcontext); 58 Thread* self = Thread::Current(); 59 CHECK(self != nullptr); // This will cause a SIGABRT if self is nullptr. 60 61 sc->arm_r0 = reinterpret_cast<uintptr_t>(*self->GetNestedSignalState()); 62 sc->arm_r1 = 1; 63 sc->arm_pc = reinterpret_cast<uintptr_t>(longjmp); 64 VLOG(signals) << "longjmp address: " << reinterpret_cast<void*>(sc->arm_pc); 65 } 66 67 void FaultManager::GetMethodAndReturnPcAndSp(siginfo_t* siginfo, void* context, 68 mirror::ArtMethod** out_method, 69 uintptr_t* out_return_pc, uintptr_t* out_sp) { 70 struct ucontext* uc = reinterpret_cast<struct ucontext*>(context); 71 struct sigcontext *sc = reinterpret_cast<struct sigcontext*>(&uc->uc_mcontext); 72 *out_sp = static_cast<uintptr_t>(sc->arm_sp); 73 VLOG(signals) << "sp: " << *out_sp; 74 if (*out_sp == 0) { 75 return; 76 } 77 78 // In the case of a stack overflow, the stack is not valid and we can't 79 // get the method from the top of the stack. However it's in r0. 80 uintptr_t* fault_addr = reinterpret_cast<uintptr_t*>(sc->fault_address); 81 uintptr_t* overflow_addr = reinterpret_cast<uintptr_t*>( 82 reinterpret_cast<uint8_t*>(*out_sp) - GetStackOverflowReservedBytes(kArm)); 83 if (overflow_addr == fault_addr) { 84 *out_method = reinterpret_cast<mirror::ArtMethod*>(sc->arm_r0); 85 } else { 86 // The method is at the top of the stack. 87 *out_method = reinterpret_cast<mirror::ArtMethod*>(reinterpret_cast<uintptr_t*>(*out_sp)[0]); 88 } 89 90 // Work out the return PC. This will be the address of the instruction 91 // following the faulting ldr/str instruction. This is in thumb mode so 92 // the instruction might be a 16 or 32 bit one. Also, the GC map always 93 // has the bottom bit of the PC set so we also need to set that. 94 95 // Need to work out the size of the instruction that caused the exception. 96 uint8_t* ptr = reinterpret_cast<uint8_t*>(sc->arm_pc); 97 VLOG(signals) << "pc: " << std::hex << static_cast<void*>(ptr); 98 uint32_t instr_size = GetInstructionSize(ptr); 99 100 *out_return_pc = (sc->arm_pc + instr_size) | 1; 101 } 102 103 bool NullPointerHandler::Action(int sig, siginfo_t* info, void* context) { 104 // The code that looks for the catch location needs to know the value of the 105 // ARM PC at the point of call. For Null checks we insert a GC map that is immediately after 106 // the load/store instruction that might cause the fault. However the mapping table has 107 // the low bits set for thumb mode so we need to set the bottom bit for the LR 108 // register in order to find the mapping. 109 110 // Need to work out the size of the instruction that caused the exception. 111 struct ucontext *uc = reinterpret_cast<struct ucontext*>(context); 112 struct sigcontext *sc = reinterpret_cast<struct sigcontext*>(&uc->uc_mcontext); 113 uint8_t* ptr = reinterpret_cast<uint8_t*>(sc->arm_pc); 114 115 uint32_t instr_size = GetInstructionSize(ptr); 116 sc->arm_lr = (sc->arm_pc + instr_size) | 1; // LR needs to point to gc map location 117 sc->arm_pc = reinterpret_cast<uintptr_t>(art_quick_throw_null_pointer_exception); 118 VLOG(signals) << "Generating null pointer exception"; 119 return true; 120 } 121 122 // A suspend check is done using the following instruction sequence: 123 // 0xf723c0b2: f8d902c0 ldr.w r0, [r9, #704] ; suspend_trigger_ 124 // .. some intervening instruction 125 // 0xf723c0b6: 6800 ldr r0, [r0, #0] 126 127 // The offset from r9 is Thread::ThreadSuspendTriggerOffset(). 128 // To check for a suspend check, we examine the instructions that caused 129 // the fault (at PC-4 and PC). 130 bool SuspensionHandler::Action(int sig, siginfo_t* info, void* context) { 131 // These are the instructions to check for. The first one is the ldr r0,[r9,#xxx] 132 // where xxx is the offset of the suspend trigger. 133 uint32_t checkinst1 = 0xf8d90000 + Thread::ThreadSuspendTriggerOffset<4>().Int32Value(); 134 uint16_t checkinst2 = 0x6800; 135 136 struct ucontext* uc = reinterpret_cast<struct ucontext*>(context); 137 struct sigcontext *sc = reinterpret_cast<struct sigcontext*>(&uc->uc_mcontext); 138 uint8_t* ptr2 = reinterpret_cast<uint8_t*>(sc->arm_pc); 139 uint8_t* ptr1 = ptr2 - 4; 140 VLOG(signals) << "checking suspend"; 141 142 uint16_t inst2 = ptr2[0] | ptr2[1] << 8; 143 VLOG(signals) << "inst2: " << std::hex << inst2 << " checkinst2: " << checkinst2; 144 if (inst2 != checkinst2) { 145 // Second instruction is not good, not ours. 146 return false; 147 } 148 149 // The first instruction can a little bit up the stream due to load hoisting 150 // in the compiler. 151 uint8_t* limit = ptr1 - 40; // Compiler will hoist to a max of 20 instructions. 152 bool found = false; 153 while (ptr1 > limit) { 154 uint32_t inst1 = ((ptr1[0] | ptr1[1] << 8) << 16) | (ptr1[2] | ptr1[3] << 8); 155 VLOG(signals) << "inst1: " << std::hex << inst1 << " checkinst1: " << checkinst1; 156 if (inst1 == checkinst1) { 157 found = true; 158 break; 159 } 160 ptr1 -= 2; // Min instruction size is 2 bytes. 161 } 162 if (found) { 163 VLOG(signals) << "suspend check match"; 164 // This is a suspend check. Arrange for the signal handler to return to 165 // art_quick_implicit_suspend. Also set LR so that after the suspend check it 166 // will resume the instruction (current PC + 2). PC points to the 167 // ldr r0,[r0,#0] instruction (r0 will be 0, set by the trigger). 168 169 // NB: remember that we need to set the bottom bit of the LR register 170 // to switch to thumb mode. 171 VLOG(signals) << "arm lr: " << std::hex << sc->arm_lr; 172 VLOG(signals) << "arm pc: " << std::hex << sc->arm_pc; 173 sc->arm_lr = sc->arm_pc + 3; // +2 + 1 (for thumb) 174 sc->arm_pc = reinterpret_cast<uintptr_t>(art_quick_implicit_suspend); 175 176 // Now remove the suspend trigger that caused this fault. 177 Thread::Current()->RemoveSuspendTrigger(); 178 VLOG(signals) << "removed suspend trigger invoking test suspend"; 179 return true; 180 } 181 return false; 182 } 183 184 // Stack overflow fault handler. 185 // 186 // This checks that the fault address is equal to the current stack pointer 187 // minus the overflow region size (16K typically). The instruction sequence 188 // that generates this signal is: 189 // 190 // sub r12,sp,#16384 191 // ldr.w r12,[r12,#0] 192 // 193 // The second instruction will fault if r12 is inside the protected region 194 // on the stack. 195 // 196 // If we determine this is a stack overflow we need to move the stack pointer 197 // to the overflow region below the protected region. 198 199 bool StackOverflowHandler::Action(int sig, siginfo_t* info, void* context) { 200 struct ucontext* uc = reinterpret_cast<struct ucontext*>(context); 201 struct sigcontext *sc = reinterpret_cast<struct sigcontext*>(&uc->uc_mcontext); 202 VLOG(signals) << "stack overflow handler with sp at " << std::hex << &uc; 203 VLOG(signals) << "sigcontext: " << std::hex << sc; 204 205 uintptr_t sp = sc->arm_sp; 206 VLOG(signals) << "sp: " << std::hex << sp; 207 208 uintptr_t fault_addr = sc->fault_address; 209 VLOG(signals) << "fault_addr: " << std::hex << fault_addr; 210 VLOG(signals) << "checking for stack overflow, sp: " << std::hex << sp << 211 ", fault_addr: " << fault_addr; 212 213 uintptr_t overflow_addr = sp - GetStackOverflowReservedBytes(kArm); 214 215 // Check that the fault address is the value expected for a stack overflow. 216 if (fault_addr != overflow_addr) { 217 VLOG(signals) << "Not a stack overflow"; 218 return false; 219 } 220 221 VLOG(signals) << "Stack overflow found"; 222 223 // Now arrange for the signal handler to return to art_quick_throw_stack_overflow_from. 224 // The value of LR must be the same as it was when we entered the code that 225 // caused this fault. This will be inserted into a callee save frame by 226 // the function to which this handler returns (art_quick_throw_stack_overflow). 227 sc->arm_pc = reinterpret_cast<uintptr_t>(art_quick_throw_stack_overflow); 228 229 // The kernel will now return to the address in sc->arm_pc. 230 return true; 231 } 232 } // namespace art 233
