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1 // Copyright (c) 2013 Google Inc.
2 // All rights reserved.
3 //
4 // Redistribution and use in source and binary forms, with or without
5 // modification, are permitted provided that the following conditions are
6 // met:
7 //
8 //     * Redistributions of source code must retain the above copyright
9 // notice, this list of conditions and the following disclaimer.
10 //     * Redistributions in binary form must reproduce the above
11 // copyright notice, this list of conditions and the following disclaimer
12 // in the documentation and/or other materials provided with the
13 // distribution.
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15 // contributors may be used to endorse or promote products derived from
16 // this software without specific prior written permission.
17 //
18 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
19 // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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21 // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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27 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
28 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
29 
30 // stackwalker_arm64.cc: arm64-specific stackwalker.
31 //
32 // See stackwalker_arm64.h for documentation.
33 //
34 // Author: Mark Mentovai, Ted Mielczarek, Jim Blandy, Colin Blundell
35 
36 #include <vector>
37 
38 #include "common/scoped_ptr.h"
39 #include "google_breakpad/processor/call_stack.h"
40 #include "google_breakpad/processor/memory_region.h"
41 #include "google_breakpad/processor/source_line_resolver_interface.h"
42 #include "google_breakpad/processor/stack_frame_cpu.h"
43 #include "processor/cfi_frame_info.h"
44 #include "processor/logging.h"
45 #include "processor/stackwalker_arm64.h"
46 
47 namespace google_breakpad {
48 
49 
StackwalkerARM64(const SystemInfo * system_info,const MDRawContextARM64 * context,MemoryRegion * memory,const CodeModules * modules,StackFrameSymbolizer * resolver_helper)50 StackwalkerARM64::StackwalkerARM64(const SystemInfo* system_info,
51                                    const MDRawContextARM64* context,
52                                    MemoryRegion* memory,
53                                    const CodeModules* modules,
54                                    StackFrameSymbolizer* resolver_helper)
55     : Stackwalker(system_info, memory, modules, resolver_helper),
56       context_(context),
57       context_frame_validity_(StackFrameARM64::CONTEXT_VALID_ALL) { }
58 
59 
GetContextFrame()60 StackFrame* StackwalkerARM64::GetContextFrame() {
61   if (!context_) {
62     BPLOG(ERROR) << "Can't get context frame without context";
63     return NULL;
64   }
65 
66   StackFrameARM64* frame = new StackFrameARM64();
67 
68   // The instruction pointer is stored directly in a register (x32), so pull it
69   // straight out of the CPU context structure.
70   frame->context = *context_;
71   frame->context_validity = context_frame_validity_;
72   frame->trust = StackFrame::FRAME_TRUST_CONTEXT;
73   frame->instruction = frame->context.iregs[MD_CONTEXT_ARM64_REG_PC];
74 
75   return frame;
76 }
77 
GetCallerByCFIFrameInfo(const vector<StackFrame * > & frames,CFIFrameInfo * cfi_frame_info)78 StackFrameARM64* StackwalkerARM64::GetCallerByCFIFrameInfo(
79     const vector<StackFrame*> &frames,
80     CFIFrameInfo* cfi_frame_info) {
81   StackFrameARM64* last_frame = static_cast<StackFrameARM64*>(frames.back());
82 
83   static const char* register_names[] = {
84     "x0",  "x1",  "x2",  "x3",  "x4",  "x5",  "x6",  "x7",
85     "x8",  "x9",  "x10", "x11", "x12", "x13", "x14", "x15",
86     "x16", "x17", "x18", "x19", "x20", "x21", "x22", "x23",
87     "x24", "x25", "x26", "x27", "x28", "x29", "x30", "sp",
88     "pc",  NULL
89   };
90 
91   // Populate a dictionary with the valid register values in last_frame.
92   CFIFrameInfo::RegisterValueMap<uint64_t> callee_registers;
93   for (int i = 0; register_names[i]; i++) {
94     if (last_frame->context_validity & StackFrameARM64::RegisterValidFlag(i))
95       callee_registers[register_names[i]] = last_frame->context.iregs[i];
96   }
97 
98   // Use the STACK CFI data to recover the caller's register values.
99   CFIFrameInfo::RegisterValueMap<uint64_t> caller_registers;
100   if (!cfi_frame_info->FindCallerRegs(callee_registers, *memory_,
101                                       &caller_registers)) {
102     return NULL;
103   }
104   // Construct a new stack frame given the values the CFI recovered.
105   scoped_ptr<StackFrameARM64> frame(new StackFrameARM64());
106   for (int i = 0; register_names[i]; i++) {
107     CFIFrameInfo::RegisterValueMap<uint64_t>::iterator entry =
108       caller_registers.find(register_names[i]);
109     if (entry != caller_registers.end()) {
110       // We recovered the value of this register; fill the context with the
111       // value from caller_registers.
112       frame->context_validity |= StackFrameARM64::RegisterValidFlag(i);
113       frame->context.iregs[i] = entry->second;
114     } else if (19 <= i && i <= 29 && (last_frame->context_validity &
115                                       StackFrameARM64::RegisterValidFlag(i))) {
116       // If the STACK CFI data doesn't mention some callee-saves register, and
117       // it is valid in the callee, assume the callee has not yet changed it.
118       // Registers r19 through r29 are callee-saves, according to the Procedure
119       // Call Standard for the ARM AARCH64 Architecture, which the Linux ABI
120       // follows.
121       frame->context_validity |= StackFrameARM64::RegisterValidFlag(i);
122       frame->context.iregs[i] = last_frame->context.iregs[i];
123     }
124   }
125   // If the CFI doesn't recover the PC explicitly, then use .ra.
126   if (!(frame->context_validity & StackFrameARM64::CONTEXT_VALID_PC)) {
127     CFIFrameInfo::RegisterValueMap<uint64_t>::iterator entry =
128       caller_registers.find(".ra");
129     if (entry != caller_registers.end()) {
130       frame->context_validity |= StackFrameARM64::CONTEXT_VALID_PC;
131       frame->context.iregs[MD_CONTEXT_ARM64_REG_PC] = entry->second;
132     }
133   }
134   // If the CFI doesn't recover the SP explicitly, then use .cfa.
135   if (!(frame->context_validity & StackFrameARM64::CONTEXT_VALID_SP)) {
136     CFIFrameInfo::RegisterValueMap<uint64_t>::iterator entry =
137       caller_registers.find(".cfa");
138     if (entry != caller_registers.end()) {
139       frame->context_validity |= StackFrameARM64::CONTEXT_VALID_SP;
140       frame->context.iregs[MD_CONTEXT_ARM64_REG_SP] = entry->second;
141     }
142   }
143 
144   // If we didn't recover the PC and the SP, then the frame isn't very useful.
145   static const uint64_t essentials = (StackFrameARM64::CONTEXT_VALID_SP
146                                      | StackFrameARM64::CONTEXT_VALID_PC);
147   if ((frame->context_validity & essentials) != essentials)
148     return NULL;
149 
150   frame->trust = StackFrame::FRAME_TRUST_CFI;
151   return frame.release();
152 }
153 
GetCallerByStackScan(const vector<StackFrame * > & frames)154 StackFrameARM64* StackwalkerARM64::GetCallerByStackScan(
155     const vector<StackFrame*> &frames) {
156   StackFrameARM64* last_frame = static_cast<StackFrameARM64*>(frames.back());
157   uint64_t last_sp = last_frame->context.iregs[MD_CONTEXT_ARM64_REG_SP];
158   uint64_t caller_sp, caller_pc;
159 
160   if (!ScanForReturnAddress(last_sp, &caller_sp, &caller_pc,
161                             frames.size() == 1 /* is_context_frame */)) {
162     // No plausible return address was found.
163     return NULL;
164   }
165 
166   // ScanForReturnAddress found a reasonable return address. Advance
167   // %sp to the location above the one where the return address was
168   // found.
169   caller_sp += 8;
170 
171   // Create a new stack frame (ownership will be transferred to the caller)
172   // and fill it in.
173   StackFrameARM64* frame = new StackFrameARM64();
174 
175   frame->trust = StackFrame::FRAME_TRUST_SCAN;
176   frame->context = last_frame->context;
177   frame->context.iregs[MD_CONTEXT_ARM64_REG_PC] = caller_pc;
178   frame->context.iregs[MD_CONTEXT_ARM64_REG_SP] = caller_sp;
179   frame->context_validity = StackFrameARM64::CONTEXT_VALID_PC |
180                             StackFrameARM64::CONTEXT_VALID_SP;
181 
182   return frame;
183 }
184 
GetCallerByFramePointer(const vector<StackFrame * > & frames)185 StackFrameARM64* StackwalkerARM64::GetCallerByFramePointer(
186     const vector<StackFrame*> &frames) {
187   StackFrameARM64* last_frame = static_cast<StackFrameARM64*>(frames.back());
188 
189   uint64_t last_fp = last_frame->context.iregs[MD_CONTEXT_ARM64_REG_FP];
190 
191   uint64_t caller_fp = 0;
192   if (last_fp && !memory_->GetMemoryAtAddress(last_fp, &caller_fp)) {
193     BPLOG(ERROR) << "Unable to read caller_fp from last_fp: 0x"
194                  << std::hex << last_fp;
195     return NULL;
196   }
197 
198   uint64_t caller_lr = 0;
199   if (last_fp && !memory_->GetMemoryAtAddress(last_fp + 8, &caller_lr)) {
200     BPLOG(ERROR) << "Unable to read caller_lr from last_fp + 8: 0x"
201                  << std::hex << (last_fp + 8);
202     return NULL;
203   }
204 
205   uint64_t caller_sp = last_fp ? last_fp + 16 :
206       last_frame->context.iregs[MD_CONTEXT_ARM64_REG_SP];
207 
208   // Create a new stack frame (ownership will be transferred to the caller)
209   // and fill it in.
210   StackFrameARM64* frame = new StackFrameARM64();
211 
212   frame->trust = StackFrame::FRAME_TRUST_FP;
213   frame->context = last_frame->context;
214   frame->context.iregs[MD_CONTEXT_ARM64_REG_FP] = caller_fp;
215   frame->context.iregs[MD_CONTEXT_ARM64_REG_SP] = caller_sp;
216   frame->context.iregs[MD_CONTEXT_ARM64_REG_PC] =
217       last_frame->context.iregs[MD_CONTEXT_ARM64_REG_LR];
218   frame->context.iregs[MD_CONTEXT_ARM64_REG_LR] = caller_lr;
219   frame->context_validity = StackFrameARM64::CONTEXT_VALID_PC |
220                             StackFrameARM64::CONTEXT_VALID_LR |
221                             StackFrameARM64::CONTEXT_VALID_FP |
222                             StackFrameARM64::CONTEXT_VALID_SP;
223   return frame;
224 }
225 
GetCallerFrame(const CallStack * stack,bool stack_scan_allowed)226 StackFrame* StackwalkerARM64::GetCallerFrame(const CallStack* stack,
227                                              bool stack_scan_allowed) {
228   if (!memory_ || !stack) {
229     BPLOG(ERROR) << "Can't get caller frame without memory or stack";
230     return NULL;
231   }
232 
233   const vector<StackFrame*> &frames = *stack->frames();
234   StackFrameARM64* last_frame = static_cast<StackFrameARM64*>(frames.back());
235   scoped_ptr<StackFrameARM64> frame;
236 
237   // See if there is DWARF call frame information covering this address.
238   scoped_ptr<CFIFrameInfo> cfi_frame_info(
239       frame_symbolizer_->FindCFIFrameInfo(last_frame));
240   if (cfi_frame_info.get())
241     frame.reset(GetCallerByCFIFrameInfo(frames, cfi_frame_info.get()));
242 
243   // If CFI failed, or there wasn't CFI available, fall back to frame pointer.
244   if (!frame.get())
245     frame.reset(GetCallerByFramePointer(frames));
246 
247   // If everything failed, fall back to stack scanning.
248   if (stack_scan_allowed && !frame.get())
249     frame.reset(GetCallerByStackScan(frames));
250 
251   // If nothing worked, tell the caller.
252   if (!frame.get())
253     return NULL;
254 
255   // An instruction address of zero marks the end of the stack.
256   if (frame->context.iregs[MD_CONTEXT_ARM64_REG_PC] == 0)
257     return NULL;
258 
259   // If the new stack pointer is at a lower address than the old, then
260   // that's clearly incorrect. Treat this as end-of-stack to enforce
261   // progress and avoid infinite loops.
262   if (frame->context.iregs[MD_CONTEXT_ARM64_REG_SP]
263       < last_frame->context.iregs[MD_CONTEXT_ARM64_REG_SP])
264     return NULL;
265 
266   // The new frame's context's PC is the return address, which is one
267   // instruction past the instruction that caused us to arrive at the callee.
268   // ARM64 instructions have a uniform 4-byte encoding, so subtracting 4 off
269   // the return address gets back to the beginning of the call instruction.
270   // Callers that require the exact return address value may access
271   // frame->context.iregs[MD_CONTEXT_ARM64_REG_PC].
272   frame->instruction = frame->context.iregs[MD_CONTEXT_ARM64_REG_PC] - 4;
273 
274   return frame.release();
275 }
276 
277 
278 }  // namespace google_breakpad
279