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1 // Copyright (c) 2010 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
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13 // distribution.
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16 // this software without specific prior written permission.
17 //
18 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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28 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
29 
30 // stackwalker_ppc.cc: ppc-specific stackwalker.
31 //
32 // See stackwalker_ppc.h for documentation.
33 //
34 // Author: Mark Mentovai
35 
36 
37 #include "processor/stackwalker_ppc.h"
38 #include "google_breakpad/processor/call_stack.h"
39 #include "google_breakpad/processor/memory_region.h"
40 #include "google_breakpad/processor/stack_frame_cpu.h"
41 #include "processor/logging.h"
42 
43 namespace google_breakpad {
44 
45 
StackwalkerPPC(const SystemInfo * system_info,const MDRawContextPPC * context,MemoryRegion * memory,const CodeModules * modules,StackFrameSymbolizer * resolver_helper)46 StackwalkerPPC::StackwalkerPPC(const SystemInfo* system_info,
47                                const MDRawContextPPC* context,
48                                MemoryRegion* memory,
49                                const CodeModules* modules,
50                                StackFrameSymbolizer* resolver_helper)
51     : Stackwalker(system_info, memory, modules, resolver_helper),
52       context_(context) {
53   if (memory_ && memory_->GetBase() + memory_->GetSize() - 1 > 0xffffffff) {
54     // This implementation only covers 32-bit ppc CPUs.  The limits of the
55     // supplied stack are invalid.  Mark memory_ = NULL, which will cause
56     // stackwalking to fail.
57     BPLOG(ERROR) << "Memory out of range for stackwalking: " <<
58                     HexString(memory_->GetBase()) << "+" <<
59                     HexString(memory_->GetSize());
60     memory_ = NULL;
61   }
62 }
63 
64 
GetContextFrame()65 StackFrame* StackwalkerPPC::GetContextFrame() {
66   if (!context_) {
67     BPLOG(ERROR) << "Can't get context frame without context";
68     return NULL;
69   }
70 
71   StackFramePPC* frame = new StackFramePPC();
72 
73   // The instruction pointer is stored directly in a register, so pull it
74   // straight out of the CPU context structure.
75   frame->context = *context_;
76   frame->context_validity = StackFramePPC::CONTEXT_VALID_ALL;
77   frame->trust = StackFrame::FRAME_TRUST_CONTEXT;
78   frame->instruction = frame->context.srr0;
79 
80   return frame;
81 }
82 
83 
GetCallerFrame(const CallStack * stack,bool stack_scan_allowed)84 StackFrame* StackwalkerPPC::GetCallerFrame(const CallStack* stack,
85                                            bool stack_scan_allowed) {
86   if (!memory_ || !stack) {
87     BPLOG(ERROR) << "Can't get caller frame without memory or stack";
88     return NULL;
89   }
90 
91   // The instruction pointers for previous frames are saved on the stack.
92   // The typical ppc calling convention is for the called procedure to store
93   // its return address in the calling procedure's stack frame at 8(%r1),
94   // and to allocate its own stack frame by decrementing %r1 (the stack
95   // pointer) and saving the old value of %r1 at 0(%r1).  Because the ppc has
96   // no hardware stack, there is no distinction between the stack pointer and
97   // frame pointer, and what is typically thought of as the frame pointer on
98   // an x86 is usually referred to as the stack pointer on a ppc.
99 
100   StackFramePPC* last_frame = static_cast<StackFramePPC*>(
101       stack->frames()->back());
102 
103   // A caller frame must reside higher in memory than its callee frames.
104   // Anything else is an error, or an indication that we've reached the
105   // end of the stack.
106   uint32_t stack_pointer;
107   if (!memory_->GetMemoryAtAddress(last_frame->context.gpr[1],
108                                    &stack_pointer) ||
109       stack_pointer <= last_frame->context.gpr[1]) {
110     return NULL;
111   }
112 
113   // Mac OS X/Darwin gives 1 as the return address from the bottom-most
114   // frame in a stack (a thread's entry point).  I haven't found any
115   // documentation on this, but 0 or 1 would be bogus return addresses,
116   // so check for them here and return false (end of stack) when they're
117   // hit to avoid having a phantom frame.
118   uint32_t instruction;
119   if (!memory_->GetMemoryAtAddress(stack_pointer + 8, &instruction) ||
120       instruction <= 1) {
121     return NULL;
122   }
123 
124   StackFramePPC* frame = new StackFramePPC();
125 
126   frame->context = last_frame->context;
127   frame->context.srr0 = instruction;
128   frame->context.gpr[1] = stack_pointer;
129   frame->context_validity = StackFramePPC::CONTEXT_VALID_SRR0 |
130                             StackFramePPC::CONTEXT_VALID_GPR1;
131   frame->trust = StackFrame::FRAME_TRUST_FP;
132 
133   // frame->context.srr0 is the return address, which is one instruction
134   // past the branch that caused us to arrive at the callee.  Set
135   // frame_ppc->instruction to four less than that.  Since all ppc
136   // instructions are 4 bytes wide, this is the address of the branch
137   // instruction.  This allows source line information to match up with the
138   // line that contains a function call.  Callers that require the exact
139   // return address value may access the context.srr0 field of StackFramePPC.
140   frame->instruction = frame->context.srr0 - 4;
141 
142   return frame;
143 }
144 
145 
146 }  // namespace google_breakpad
147