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#include "fault_handler.h"
18#include <sys/ucontext.h>
19
20#include "art_method.h"
21#include "base/hex_dump.h"
22#include "base/logging.h"
23#include "base/macros.h"
24#include "globals.h"
25#include "quick_method_frame_info_mips.h"
26#include "registers_mips.h"
27#include "thread-inl.h"
28
29extern "C" void art_quick_throw_stack_overflow();
30extern "C" void art_quick_throw_null_pointer_exception_from_signal();
31
32//
33// Mips specific fault handler functions.
34//
35
36namespace art {
37
38void FaultManager::GetMethodAndReturnPcAndSp(siginfo_t* siginfo, void* context,
39                                             ArtMethod** out_method,
40                                             uintptr_t* out_return_pc, uintptr_t* out_sp) {
41  struct ucontext* uc = reinterpret_cast<struct ucontext*>(context);
42  struct sigcontext *sc = reinterpret_cast<struct sigcontext*>(&uc->uc_mcontext);
43  *out_sp = static_cast<uintptr_t>(sc->sc_regs[mips::SP]);
44  VLOG(signals) << "sp: " << *out_sp;
45  if (*out_sp == 0) {
46    return;
47  }
48
49  // In the case of a stack overflow, the stack is not valid and we can't
50  // get the method from the top of the stack.  However it's in r0.
51  uintptr_t* fault_addr = reinterpret_cast<uintptr_t*>(siginfo->si_addr);  // BVA addr
52  uintptr_t* overflow_addr = reinterpret_cast<uintptr_t*>(
53      reinterpret_cast<uint8_t*>(*out_sp) - GetStackOverflowReservedBytes(kMips));
54  if (overflow_addr == fault_addr) {
55    *out_method = reinterpret_cast<ArtMethod*>(sc->sc_regs[mips::A0]);
56  } else {
57    // The method is at the top of the stack.
58    *out_method = *reinterpret_cast<ArtMethod**>(*out_sp);
59  }
60
61  // Work out the return PC.  This will be the address of the instruction
62  // following the faulting ldr/str instruction.
63
64  VLOG(signals) << "pc: " << std::hex
65      << static_cast<void*>(reinterpret_cast<uint8_t*>(sc->sc_pc));
66
67  *out_return_pc = sc->sc_pc + 4;
68}
69
70bool NullPointerHandler::Action(int sig ATTRIBUTE_UNUSED, siginfo_t* info, void* context) {
71  if (!IsValidImplicitCheck(info)) {
72    return false;
73  }
74  // The code that looks for the catch location needs to know the value of the
75  // PC at the point of call.  For Null checks we insert a GC map that is immediately after
76  // the load/store instruction that might cause the fault.
77
78  struct ucontext *uc = reinterpret_cast<struct ucontext*>(context);
79  struct sigcontext *sc = reinterpret_cast<struct sigcontext*>(&uc->uc_mcontext);
80
81  // Decrement $sp by the frame size of the kSaveEverything method and store
82  // the fault address in the padding right after the ArtMethod*.
83  sc->sc_regs[mips::SP] -= mips::MipsCalleeSaveFrameSize(Runtime::kSaveEverything);
84  uintptr_t* padding = reinterpret_cast<uintptr_t*>(sc->sc_regs[mips::SP]) + /* ArtMethod* */ 1;
85  *padding = reinterpret_cast<uintptr_t>(info->si_addr);
86
87  sc->sc_regs[mips::RA] = sc->sc_pc + 4;      // RA needs to point to gc map location
88  sc->sc_pc = reinterpret_cast<uintptr_t>(art_quick_throw_null_pointer_exception_from_signal);
89  // Note: This entrypoint does not rely on T9 pointing to it, so we may as well preserve T9.
90  VLOG(signals) << "Generating null pointer exception";
91  return true;
92}
93
94bool SuspensionHandler::Action(int sig ATTRIBUTE_UNUSED, siginfo_t* info ATTRIBUTE_UNUSED,
95                               void* context ATTRIBUTE_UNUSED) {
96  return false;
97}
98
99// Stack overflow fault handler.
100//
101// This checks that the fault address is equal to the current stack pointer
102// minus the overflow region size (16K typically). The instruction that
103// generates this signal is:
104//
105// lw zero, -16384(sp)
106//
107// It will fault if sp is inside the protected region on the stack.
108//
109// If we determine this is a stack overflow we need to move the stack pointer
110// to the overflow region below the protected region.
111
112bool StackOverflowHandler::Action(int sig ATTRIBUTE_UNUSED, siginfo_t* info, void* context) {
113  struct ucontext* uc = reinterpret_cast<struct ucontext*>(context);
114  struct sigcontext *sc = reinterpret_cast<struct sigcontext*>(&uc->uc_mcontext);
115  VLOG(signals) << "stack overflow handler with sp at " << std::hex << &uc;
116  VLOG(signals) << "sigcontext: " << std::hex << sc;
117
118  uintptr_t sp = sc->sc_regs[mips::SP];
119  VLOG(signals) << "sp: " << std::hex << sp;
120
121  uintptr_t fault_addr = reinterpret_cast<uintptr_t>(info->si_addr);  // BVA addr
122  VLOG(signals) << "fault_addr: " << std::hex << fault_addr;
123  VLOG(signals) << "checking for stack overflow, sp: " << std::hex << sp <<
124    ", fault_addr: " << fault_addr;
125
126  uintptr_t overflow_addr = sp - GetStackOverflowReservedBytes(kMips);
127
128  // Check that the fault address is the value expected for a stack overflow.
129  if (fault_addr != overflow_addr) {
130    VLOG(signals) << "Not a stack overflow";
131    return false;
132  }
133
134  VLOG(signals) << "Stack overflow found";
135
136  // Now arrange for the signal handler to return to art_quick_throw_stack_overflow_from.
137  // The value of RA must be the same as it was when we entered the code that
138  // caused this fault.  This will be inserted into a callee save frame by
139  // the function to which this handler returns (art_quick_throw_stack_overflow).
140  sc->sc_pc = reinterpret_cast<uintptr_t>(art_quick_throw_stack_overflow);
141  sc->sc_regs[mips::T9] = sc->sc_pc;          // make sure T9 points to the function
142
143  // The kernel will now return to the address in sc->arm_pc.
144  return true;
145}
146}       // namespace art
147