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 "art_method-inl.h"
21#include "base/macros.h"
22#include "globals.h"
23#include "base/logging.h"
24#include "base/hex_dump.h"
25#include "registers_mips.h"
26#include "thread.h"
27#include "thread-inl.h"
28
29extern "C" void art_quick_throw_stack_overflow();
30extern "C" void art_quick_throw_null_pointer_exception();
31
32//
33// Mips specific fault handler functions.
34//
35
36namespace art {
37
38void FaultManager::HandleNestedSignal(int sig ATTRIBUTE_UNUSED, siginfo_t* info ATTRIBUTE_UNUSED,
39                                      void* context ATTRIBUTE_UNUSED) {
40}
41
42void FaultManager::GetMethodAndReturnPcAndSp(siginfo_t* siginfo, void* context,
43                                             ArtMethod** out_method,
44                                             uintptr_t* out_return_pc, uintptr_t* out_sp) {
45  struct ucontext* uc = reinterpret_cast<struct ucontext*>(context);
46  struct sigcontext *sc = reinterpret_cast<struct sigcontext*>(&uc->uc_mcontext);
47  *out_sp = static_cast<uintptr_t>(sc->sc_regs[29]);   // SP register
48  VLOG(signals) << "sp: " << *out_sp;
49  if (*out_sp == 0) {
50    return;
51  }
52
53  // In the case of a stack overflow, the stack is not valid and we can't
54  // get the method from the top of the stack.  However it's in r0.
55  uintptr_t* fault_addr = reinterpret_cast<uintptr_t*>(siginfo->si_addr);  // BVA addr
56  uintptr_t* overflow_addr = reinterpret_cast<uintptr_t*>(
57      reinterpret_cast<uint8_t*>(*out_sp) - GetStackOverflowReservedBytes(kMips));
58  if (overflow_addr == fault_addr) {
59    *out_method = reinterpret_cast<ArtMethod*>(sc->sc_regs[4]);  // A0 register
60  } else {
61    // The method is at the top of the stack.
62    *out_method = *reinterpret_cast<ArtMethod**>(*out_sp);
63  }
64
65  // Work out the return PC.  This will be the address of the instruction
66  // following the faulting ldr/str instruction.
67
68  VLOG(signals) << "pc: " << std::hex
69      << static_cast<void*>(reinterpret_cast<uint8_t*>(sc->sc_pc));
70
71  *out_return_pc = sc->sc_pc + 4;
72}
73
74bool NullPointerHandler::Action(int sig ATTRIBUTE_UNUSED, siginfo_t* info ATTRIBUTE_UNUSED,
75                                void* context) {
76  // The code that looks for the catch location needs to know the value of the
77  // PC at the point of call.  For Null checks we insert a GC map that is immediately after
78  // the load/store instruction that might cause the fault.
79
80  struct ucontext *uc = reinterpret_cast<struct ucontext*>(context);
81  struct sigcontext *sc = reinterpret_cast<struct sigcontext*>(&uc->uc_mcontext);
82
83  sc->sc_regs[31] = sc->sc_pc + 4;      // RA needs to point to gc map location
84  sc->sc_pc = reinterpret_cast<uintptr_t>(art_quick_throw_null_pointer_exception);
85  sc->sc_regs[25] = sc->sc_pc;          // make sure T9 points to the function
86  VLOG(signals) << "Generating null pointer exception";
87  return true;
88}
89
90bool SuspensionHandler::Action(int sig ATTRIBUTE_UNUSED, siginfo_t* info ATTRIBUTE_UNUSED,
91                               void* context ATTRIBUTE_UNUSED) {
92  return false;
93}
94
95// Stack overflow fault handler.
96//
97// This checks that the fault address is equal to the current stack pointer
98// minus the overflow region size (16K typically). The instruction that
99// generates this signal is:
100//
101// lw zero, -16384(sp)
102//
103// It will fault if sp is inside the protected region on the stack.
104//
105// If we determine this is a stack overflow we need to move the stack pointer
106// to the overflow region below the protected region.
107
108bool StackOverflowHandler::Action(int sig ATTRIBUTE_UNUSED, siginfo_t* info, void* context) {
109  struct ucontext* uc = reinterpret_cast<struct ucontext*>(context);
110  struct sigcontext *sc = reinterpret_cast<struct sigcontext*>(&uc->uc_mcontext);
111  VLOG(signals) << "stack overflow handler with sp at " << std::hex << &uc;
112  VLOG(signals) << "sigcontext: " << std::hex << sc;
113
114  uintptr_t sp = sc->sc_regs[29];  // SP register
115  VLOG(signals) << "sp: " << std::hex << sp;
116
117  uintptr_t fault_addr = reinterpret_cast<uintptr_t>(info->si_addr);  // BVA addr
118  VLOG(signals) << "fault_addr: " << std::hex << fault_addr;
119  VLOG(signals) << "checking for stack overflow, sp: " << std::hex << sp <<
120    ", fault_addr: " << fault_addr;
121
122  uintptr_t overflow_addr = sp - GetStackOverflowReservedBytes(kMips);
123
124  // Check that the fault address is the value expected for a stack overflow.
125  if (fault_addr != overflow_addr) {
126    VLOG(signals) << "Not a stack overflow";
127    return false;
128  }
129
130  VLOG(signals) << "Stack overflow found";
131
132  // Now arrange for the signal handler to return to art_quick_throw_stack_overflow_from.
133  // The value of RA must be the same as it was when we entered the code that
134  // caused this fault.  This will be inserted into a callee save frame by
135  // the function to which this handler returns (art_quick_throw_stack_overflow).
136  sc->sc_pc = reinterpret_cast<uintptr_t>(art_quick_throw_stack_overflow);
137  sc->sc_regs[25] = sc->sc_pc;          // make sure T9 points to the function
138
139  // The kernel will now return to the address in sc->arm_pc.
140  return true;
141}
142}       // namespace art
143