1 // Copyright (c) 2010 Google Inc.
2 // All rights reserved.
3 //
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5 // modification, are permitted provided that the following conditions are
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7 //
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17 //
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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