src/processor/stackwalker_mips.cc - platform/external/google-breakpad - Git at Google


            
            // Copyright (c) 2013 Google Inc.

            
            // All rights reserved.

            
            //

            
            // Redistribution and use in source and binary forms, with or without

            
            // modification, are permitted provided that the following conditions are

            
            // met:

            
            //

            
            //     * Redistributions of source code must retain the above copyright

            
            // notice, this list of conditions and the following disclaimer.

            
            //     * Redistributions in binary form must reproduce the above

            
            // copyright notice, this list of conditions and the following disclaimer

            
            // in the documentation and/or other materials provided with the

            
            // distribution.

            
            //     * Neither the name of Google Inc. nor the names of its

            
            // contributors may be used to endorse or promote products derived from

            
            // this software without specific prior written permission.

            
            //

            
            // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS

            
            // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT

            
            // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR

            
            // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT

            
            // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,

            
            // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT

            
            // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,

            
            // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY

            
            // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT

            
            // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE

            
            // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.


            // stackwalker_mips.cc: MIPS-specific stackwalker.

            
            //

            
            // See stackwalker_mips.h for documentation.

            
            //

            
            // Author: Tata Elxsi


            #include "common/scoped_ptr.h"

            
            #include "google_breakpad/processor/call_stack.h"

            
            #include "google_breakpad/processor/code_modules.h"

            
            #include "google_breakpad/processor/memory_region.h"

            
            #include "google_breakpad/processor/source_line_resolver_interface.h"

            
            #include "google_breakpad/processor/stack_frame_cpu.h"

            
            #include "processor/cfi_frame_info.h"

            
            #include "processor/logging.h"

            
            #include "processor/postfix_evaluator-inl.h"

            
            #include "processor/stackwalker_mips.h"

            
            #include "processor/windows_frame_info.h"

            
            #include "google_breakpad/common/minidump_cpu_mips.h"


            namespace google_breakpad {


            StackwalkerMIPS::StackwalkerMIPS(const SystemInfo* system_info,

            
                                             const MDRawContextMIPS* context,

            
                                             MemoryRegion* memory,

            
                                             const CodeModules* modules,

            
                                             StackFrameSymbolizer* resolver_helper)

            
            : Stackwalker(system_info, memory, modules, resolver_helper),

            
              context_(context) {

            
              if (memory_) {

            
                if (context_->context_flags & MD_CONTEXT_MIPS64 ) {

            
                  if (0xffffffffffffffff - memory_->GetBase() < memory_->GetSize() - 1) {

            
                    BPLOG(ERROR) << "Memory out of range for stackwalking mips64: "

            
                        << HexString(memory_->GetBase())

            
                        << "+"

            
                        << HexString(memory_->GetSize());

            
                    memory_ = NULL;

            
                  }

            
                } else {

            
                  if (0xffffffff - memory_->GetBase() < memory_->GetSize() - 1) {

            
                    BPLOG(ERROR) << "Memory out of range for stackwalking mips32: "

            
                        << HexString(memory_->GetBase())

            
                        << "+"

            
                        << HexString(memory_->GetSize());

            
                    memory_ = NULL;

            
                  }

            
                }

            
              }

            
            }


            StackFrame* StackwalkerMIPS::GetContextFrame() {

            
              if (!context_) {

            
                BPLOG(ERROR) << "Can't get context frame without context.";

            
                return NULL;

            
              }


              StackFrameMIPS* frame = new StackFrameMIPS();


              // The instruction pointer is stored directly in a register, so pull it

            
              // straight out of the CPU context structure.

            
              frame->context = *context_;

            
              frame->context_validity = StackFrameMIPS::CONTEXT_VALID_ALL;

            
              frame->trust = StackFrame::FRAME_TRUST_CONTEXT;

            
              frame->instruction = frame->context.epc;


              return frame;

            
            }


            // Register names for mips.

            
            static const char* const kRegisterNames[] = {

            
               "$zero", "$at", "$v0", "$v1", "$a0", "$a1", "$a2", "$a3", "$to", "$t1",

            
               "$t2",   "$t3", "$t4", "$t5", "$t6", "$t7", "$s0", "$s1", "$s2", "$s3",

            
               "$s4",   "$s5", "$s6", "$s7", "$t8", "$t9", "$k0", "$k1", "$gp", "$sp",

            
               "$fp",   "$ra", NULL

            
              // TODO(gordanac): add float point save registers

            
            };


            StackFrameMIPS* StackwalkerMIPS::GetCallerByCFIFrameInfo(

            
                const vector<StackFrame*>& frames,

            
                CFIFrameInfo* cfi_frame_info) {

            
              StackFrameMIPS* last_frame = static_cast<StackFrameMIPS*>(frames.back());


              if (context_->context_flags & MD_CONTEXT_MIPS) {

            
                uint32_t pc = 0;


                // Populate a dictionary with the valid register values in last_frame.

            
                CFIFrameInfo::RegisterValueMap<uint32_t> callee_registers;

            
                // Use the STACK CFI data to recover the caller's register values.

            
                CFIFrameInfo::RegisterValueMap<uint32_t> caller_registers;


                for (int i = 0; kRegisterNames[i]; ++i) {

            
                  caller_registers[kRegisterNames[i]] = last_frame->context.iregs[i];

            
                  callee_registers[kRegisterNames[i]] = last_frame->context.iregs[i];

            
                }


                if (!cfi_frame_info->FindCallerRegs(callee_registers, *memory_,

            
                    &caller_registers))  {

            
                  return NULL;

            
                }


                CFIFrameInfo::RegisterValueMap<uint32_t>::const_iterator entry =

            
                    caller_registers.find(".cfa");


                if (entry != caller_registers.end()) {

            
                  caller_registers["$sp"] = entry->second;

            
                }


                entry = caller_registers.find(".ra");

            
                if (entry != caller_registers.end()) {

            
                  caller_registers["$ra"] = entry->second;

            
                  pc = entry->second - 2 * sizeof(pc);

            
                }

            
                caller_registers["$pc"] = pc;

            
                // Construct a new stack frame given the values the CFI recovered.

            
                scoped_ptr<StackFrameMIPS> frame(new StackFrameMIPS());


                for (int i = 0; kRegisterNames[i]; ++i) {

            
                  CFIFrameInfo::RegisterValueMap<uint32_t>::const_iterator caller_entry =

            
                      caller_registers.find(kRegisterNames[i]);


                  if (caller_entry != caller_registers.end()) {

            
                    // The value of this register is recovered; fill the context with the

            
                    // value from caller_registers.

            
                    frame->context.iregs[i] = caller_entry->second;

            
                    frame->context_validity |= StackFrameMIPS::RegisterValidFlag(i);

            
                  } else if (((i >= INDEX_MIPS_REG_S0 && i <= INDEX_MIPS_REG_S7) ||

            
                      (i > INDEX_MIPS_REG_GP && i < INDEX_MIPS_REG_RA)) &&

            
                      (last_frame->context_validity &

            
                          StackFrameMIPS::RegisterValidFlag(i))) {

            
                    // If the STACK CFI data doesn't mention some callee-save register, and

            
                    // it is valid in the callee, assume the callee has not yet changed it.

            
                    // Calee-save registers according to the MIPS o32 ABI specification are:

            
                    // $s0 to $s7

            
                    // $sp, $s8

            
                    frame->context.iregs[i] = last_frame->context.iregs[i];

            
                    frame->context_validity |= StackFrameMIPS::RegisterValidFlag(i);

            
                  }

            
                }


                frame->context.epc = caller_registers["$pc"];

            
                frame->instruction = caller_registers["$pc"];

            
                frame->context_validity |= StackFrameMIPS::CONTEXT_VALID_PC;


                frame->context.iregs[MD_CONTEXT_MIPS_REG_RA] = caller_registers["$ra"];

            
                frame->context_validity |= StackFrameMIPS::CONTEXT_VALID_RA;


                frame->trust = StackFrame::FRAME_TRUST_CFI;


                return frame.release();

            
              } else {

            
                uint64_t pc = 0;


                // Populate a dictionary with the valid register values in last_frame.

            
                CFIFrameInfo::RegisterValueMap<uint64_t> callee_registers;

            
                // Use the STACK CFI data to recover the caller's register values.

            
                CFIFrameInfo::RegisterValueMap<uint64_t> caller_registers;


                for (int i = 0; kRegisterNames[i]; ++i) {

            
                  caller_registers[kRegisterNames[i]] = last_frame->context.iregs[i];

            
                  callee_registers[kRegisterNames[i]] = last_frame->context.iregs[i];

            
                }


                if (!cfi_frame_info->FindCallerRegs(callee_registers, *memory_,

            
                    &caller_registers))  {

            
                  return NULL;

            
                }


                CFIFrameInfo::RegisterValueMap<uint64_t>::const_iterator entry =

            
                    caller_registers.find(".cfa");


                if (entry != caller_registers.end()) {

            
                  caller_registers["$sp"] = entry->second;

            
                }


                entry = caller_registers.find(".ra");

            
                if (entry != caller_registers.end()) {

            
                  caller_registers["$ra"] = entry->second;

            
                  pc = entry->second - 2 * sizeof(pc);

            
                }

            
                caller_registers["$pc"] = pc;

            
                // Construct a new stack frame given the values the CFI recovered.

            
                scoped_ptr<StackFrameMIPS> frame(new StackFrameMIPS());


                for (int i = 0; kRegisterNames[i]; ++i) {

            
                  CFIFrameInfo::RegisterValueMap<uint64_t>::const_iterator caller_entry =

            
                      caller_registers.find(kRegisterNames[i]);


                  if (caller_entry != caller_registers.end()) {

            
                    // The value of this register is recovered; fill the context with the

            
                    // value from caller_registers.

            
                    frame->context.iregs[i] = caller_entry->second;

            
                    frame->context_validity |= StackFrameMIPS::RegisterValidFlag(i);

            
                  } else if (((i >= INDEX_MIPS_REG_S0 && i <= INDEX_MIPS_REG_S7) ||

            
                      (i >= INDEX_MIPS_REG_GP && i < INDEX_MIPS_REG_RA)) &&

            
                      (last_frame->context_validity &

            
                          StackFrameMIPS::RegisterValidFlag(i))) {

            
                    // If the STACK CFI data doesn't mention some callee-save register, and

            
                    // it is valid in the callee, assume the callee has not yet changed it.

            
                    // Calee-save registers according to the MIPS o32 ABI specification are:

            
                    // $s0 to $s7

            
                    // $sp, $s8

            
                    frame->context.iregs[i] = last_frame->context.iregs[i];

            
                    frame->context_validity |= StackFrameMIPS::RegisterValidFlag(i);

            
                  }

            
                }


                frame->context.epc = caller_registers["$pc"];

            
                frame->instruction = caller_registers["$pc"];

            
                frame->context_validity |= StackFrameMIPS::CONTEXT_VALID_PC;


                frame->context.iregs[MD_CONTEXT_MIPS_REG_RA] = caller_registers["$ra"];

            
                frame->context_validity |= StackFrameMIPS::CONTEXT_VALID_RA;


                frame->trust = StackFrame::FRAME_TRUST_CFI;


                return frame.release();

            
              }

            
            }


            StackFrame* StackwalkerMIPS::GetCallerFrame(const CallStack* stack,

            
                                                        bool stack_scan_allowed) {

            
              if (!memory_ || !stack) {

            
                BPLOG(ERROR) << "Can't get caller frame without memory or stack";

            
                return NULL;

            
              }


              const vector<StackFrame*>& frames = *stack->frames();

            
              StackFrameMIPS* last_frame = static_cast<StackFrameMIPS*>(frames.back());

            
              scoped_ptr<StackFrameMIPS> new_frame;


              // See if there is DWARF call frame information covering this address.

            
              scoped_ptr<CFIFrameInfo> cfi_frame_info(

            
                frame_symbolizer_->FindCFIFrameInfo(last_frame));

            
              if (cfi_frame_info.get())

            
                new_frame.reset(GetCallerByCFIFrameInfo(frames, cfi_frame_info.get()));


              // If caller frame is not found in CFI try analyzing the stack.

            
              if (stack_scan_allowed && !new_frame.get()) {

            
                new_frame.reset(GetCallerByStackScan(frames));

            
              }


              // If nothing worked, tell the caller.

            
              if (!new_frame.get()) {

            
                return NULL;

            
              }


              // Should we terminate the stack walk? (end-of-stack or broken invariant)

            
              if (TerminateWalk(new_frame->context.epc,

            
                                new_frame->context.iregs[MD_CONTEXT_MIPS_REG_SP],

            
                                last_frame->context.iregs[MD_CONTEXT_MIPS_REG_SP],

            
                                frames.size() == 1)) {

            
                return NULL;

            
              }


              return new_frame.release();

            
            }


            StackFrameMIPS* StackwalkerMIPS::GetCallerByStackScan(

            
                const vector<StackFrame*>& frames) {

            
              const uint32_t kMaxFrameStackSize = 1024;

            
              const uint32_t kMinArgsOnStack = 4;


              StackFrameMIPS* last_frame = static_cast<StackFrameMIPS*>(frames.back());


              if (context_->context_flags & MD_CONTEXT_MIPS) {

            
                uint32_t last_sp = last_frame->context.iregs[MD_CONTEXT_MIPS_REG_SP];

            
                uint32_t caller_pc, caller_sp, caller_fp;


                // Return address cannot be obtained directly.

            
                // Force stackwalking.


                // We cannot use frame pointer to get the return address.

            
                // We'll scan the stack for a

            
                // return address. This can happen if last_frame is executing code

            
                // for a module for which we don't have symbols.

            
                int count = kMaxFrameStackSize / sizeof(caller_pc);


                if (frames.size() > 1) {

            
                  // In case of mips32 ABI stack frame of a nonleaf function

            
                  // must have minimum stack frame assigned for 4 arguments (4 words).

            
                  // Move stack pointer for 4 words to avoid reporting non-existing frames

            
                  // for all frames except the topmost one.

            
                  // There is no way of knowing if topmost frame belongs to a leaf or

            
                  // a nonleaf function.

            
                  last_sp +=  kMinArgsOnStack * sizeof(caller_pc);

            
                  // Adjust 'count' so that return address is scanned only in limits

            
                  // of one stack frame.

            
                  count -= kMinArgsOnStack;

            
                }


                do {

            
                  // Scanning for return address from stack pointer of the last frame.

            
                  if (!ScanForReturnAddress(last_sp, &caller_sp, &caller_pc, count)) {

            
                    // If we can't find an instruction pointer even with stack scanning,

            
                    // give up.

            
                    BPLOG(ERROR) << " ScanForReturnAddress failed ";

            
                    return NULL;

            
                  }

            
                  // Get $fp stored in the stack frame.

            
                  if (!memory_->GetMemoryAtAddress(caller_sp - sizeof(caller_pc),

            
                      &caller_fp)) {

            
                    BPLOG(INFO) << " GetMemoryAtAddress for fp failed " ;

            
                    return NULL;

            
                  }


                  count = count - (caller_sp - last_sp) / sizeof(caller_pc);

            
                  // Now scan the next address in the stack.

            
                  last_sp = caller_sp + sizeof(caller_pc);

            
                } while ((caller_fp - caller_sp >= kMaxFrameStackSize) && count > 0);


                if (!count) {

            
                  BPLOG(INFO) << " No frame found " ;

            
                  return NULL;

            
                }


                // ScanForReturnAddress found a reasonable return address. Advance

            
                // $sp to the location above the one where the return address was

            
                // found.

            
                caller_sp += sizeof(caller_pc);

            
                // caller_pc is actually containing $ra value;

            
                // $pc is two instructions before $ra,

            
                // so the caller_pc needs to be decremented accordingly.

            
                caller_pc -= 2 * sizeof(caller_pc);


                // Create a new stack frame (ownership will be transferred to the caller)

            
                // and fill it in.

            
                StackFrameMIPS* frame = new StackFrameMIPS();

            
                frame->trust = StackFrame::FRAME_TRUST_SCAN;

            
                frame->context = last_frame->context;

            
                frame->context.epc = caller_pc;

            
                frame->context_validity |= StackFrameMIPS::CONTEXT_VALID_PC;

            
                frame->instruction = caller_pc;


                frame->context.iregs[MD_CONTEXT_MIPS_REG_SP] = caller_sp;

            
                frame->context_validity |= StackFrameMIPS::CONTEXT_VALID_SP;

            
                frame->context.iregs[MD_CONTEXT_MIPS_REG_FP] = caller_fp;

            
                frame->context_validity |= StackFrameMIPS::CONTEXT_VALID_FP;


                frame->context.iregs[MD_CONTEXT_MIPS_REG_RA] =

            
                    caller_pc + 2 * sizeof(caller_pc);

            
                frame->context_validity |= StackFrameMIPS::CONTEXT_VALID_RA;


                return frame;

            
              } else {

            
                uint64_t last_sp = last_frame->context.iregs[MD_CONTEXT_MIPS_REG_SP];

            
                uint64_t caller_pc, caller_sp, caller_fp;


                // Return address cannot be obtained directly.

            
                // Force stackwalking.


                // We cannot use frame pointer to get the return address.

            
                // We'll scan the stack for a

            
                // return address. This can happen if last_frame is executing code

            
                // for a module for which we don't have symbols.

            
                int count = kMaxFrameStackSize / sizeof(caller_pc);


                do {

            
                  // Scanning for return address from stack pointer of the last frame.

            
                  if (!ScanForReturnAddress(last_sp, &caller_sp, &caller_pc, count)) {

            
                    // If we can't find an instruction pointer even with stack scanning,

            
                    // give up.

            
                    BPLOG(ERROR) << " ScanForReturnAddress failed ";

            
                    return NULL;

            
                  }

            
                  // Get $fp stored in the stack frame.

            
                  if (!memory_->GetMemoryAtAddress(caller_sp - sizeof(caller_pc),

            
                      &caller_fp)) {

            
                    BPLOG(INFO) << " GetMemoryAtAddress for fp failed " ;

            
                    return NULL;

            
                  }


                  count = count - (caller_sp - last_sp) / sizeof(caller_pc);

            
                  // Now scan the next address in the stack.

            
                  last_sp = caller_sp + sizeof(caller_pc);

            
                } while ((caller_fp - caller_sp >= kMaxFrameStackSize) && count > 0);


                if (!count) {

            
                  BPLOG(INFO) << " No frame found " ;

            
                  return NULL;

            
                }


                // ScanForReturnAddress found a reasonable return address. Advance

            
                // $sp to the location above the one where the return address was

            
                // found.

            
                caller_sp += sizeof(caller_pc);

            
                // caller_pc is actually containing $ra value;

            
                // $pc is two instructions before $ra,

            
                // so the caller_pc needs to be decremented accordingly.

            
                caller_pc -= 2 * sizeof(caller_pc);


                // Create a new stack frame (ownership will be transferred to the caller)

            
                // and fill it in.

            
                StackFrameMIPS* frame = new StackFrameMIPS();

            
                frame->trust = StackFrame::FRAME_TRUST_SCAN;

            
                frame->context = last_frame->context;

            
                frame->context.epc = caller_pc;

            
                frame->context_validity |= StackFrameMIPS::CONTEXT_VALID_PC;

            
                frame->instruction = caller_pc;


                frame->context.iregs[MD_CONTEXT_MIPS_REG_SP] = caller_sp;

            
                frame->context_validity |= StackFrameMIPS::CONTEXT_VALID_SP;

            
                frame->context.iregs[MD_CONTEXT_MIPS_REG_FP] = caller_fp;

            
                frame->context_validity |= StackFrameMIPS::CONTEXT_VALID_FP;


                frame->context.iregs[MD_CONTEXT_MIPS_REG_RA] =

            
                    caller_pc + 2 * sizeof(caller_pc);

            
                frame->context_validity |= StackFrameMIPS::CONTEXT_VALID_RA;


                return frame;

            
              }

            
            }


            }  // namespace google_breakpad
	// Copyright (c) 2013 Google Inc.
	// All rights reserved.
	//
	// Redistribution and use in source and binary forms, with or without
	// modification, are permitted provided that the following conditions are
	// met:
	//
	// * Redistributions of source code must retain the above copyright
	// notice, this list of conditions and the following disclaimer.
	// * Redistributions in binary form must reproduce the above
	// copyright notice, this list of conditions and the following disclaimer
	// in the documentation and/or other materials provided with the
	// distribution.
	// * Neither the name of Google Inc. nor the names of its
	// contributors may be used to endorse or promote products derived from
	// this software without specific prior written permission.
	//
	// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
	// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
	// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
	// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
	// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
	// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
	// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
	// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
	// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
	// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
	// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

	// stackwalker_mips.cc: MIPS-specific stackwalker.
	//
	// See stackwalker_mips.h for documentation.
	//
	// Author: Tata Elxsi

	#include "common/scoped_ptr.h"
	#include "google_breakpad/processor/call_stack.h"
	#include "google_breakpad/processor/code_modules.h"
	#include "google_breakpad/processor/memory_region.h"
	#include "google_breakpad/processor/source_line_resolver_interface.h"
	#include "google_breakpad/processor/stack_frame_cpu.h"
	#include "processor/cfi_frame_info.h"
	#include "processor/logging.h"
	#include "processor/postfix_evaluator-inl.h"
	#include "processor/stackwalker_mips.h"
	#include "processor/windows_frame_info.h"
	#include "google_breakpad/common/minidump_cpu_mips.h"

	namespace google_breakpad {

	StackwalkerMIPS::StackwalkerMIPS(const SystemInfo* system_info,
	const MDRawContextMIPS* context,
	MemoryRegion* memory,
	const CodeModules* modules,
	StackFrameSymbolizer* resolver_helper)
	: Stackwalker(system_info, memory, modules, resolver_helper),
	context_(context) {
	if (memory_) {
	if (context_->context_flags & MD_CONTEXT_MIPS64 ) {
	if (0xffffffffffffffff - memory_->GetBase() < memory_->GetSize() - 1) {
	BPLOG(ERROR) << "Memory out of range for stackwalking mips64: "
	<< HexString(memory_->GetBase())
	<< "+"
	<< HexString(memory_->GetSize());
	memory_ = NULL;
	}
	} else {
	if (0xffffffff - memory_->GetBase() < memory_->GetSize() - 1) {
	BPLOG(ERROR) << "Memory out of range for stackwalking mips32: "
	<< HexString(memory_->GetBase())
	<< "+"
	<< HexString(memory_->GetSize());
	memory_ = NULL;
	}
	}
	}
	}

	StackFrame* StackwalkerMIPS::GetContextFrame() {
	if (!context_) {
	BPLOG(ERROR) << "Can't get context frame without context.";
	return NULL;
	}

	StackFrameMIPS* frame = new StackFrameMIPS();

	// The instruction pointer is stored directly in a register, so pull it
	// straight out of the CPU context structure.
	frame->context = *context_;
	frame->context_validity = StackFrameMIPS::CONTEXT_VALID_ALL;
	frame->trust = StackFrame::FRAME_TRUST_CONTEXT;
	frame->instruction = frame->context.epc;

	return frame;
	}

	// Register names for mips.
	static const char* const kRegisterNames[] = {
	"$zero", "$at", "$v0", "$v1", "$a0", "$a1", "$a2", "$a3", "$to", "$t1",
	"$t2", "$t3", "$t4", "$t5", "$t6", "$t7", "$s0", "$s1", "$s2", "$s3",
	"$s4", "$s5", "$s6", "$s7", "$t8", "$t9", "$k0", "$k1", "$gp", "$sp",
	"$fp", "$ra", NULL
	// TODO(gordanac): add float point save registers
	};

	StackFrameMIPS* StackwalkerMIPS::GetCallerByCFIFrameInfo(
	const vector<StackFrame*>& frames,
	CFIFrameInfo* cfi_frame_info) {
	StackFrameMIPS* last_frame = static_cast<StackFrameMIPS*>(frames.back());

	if (context_->context_flags & MD_CONTEXT_MIPS) {
	uint32_t pc = 0;

	// Populate a dictionary with the valid register values in last_frame.
	CFIFrameInfo::RegisterValueMap<uint32_t> callee_registers;
	// Use the STACK CFI data to recover the caller's register values.
	CFIFrameInfo::RegisterValueMap<uint32_t> caller_registers;

	for (int i = 0; kRegisterNames[i]; ++i) {
	caller_registers[kRegisterNames[i]] = last_frame->context.iregs[i];
	callee_registers[kRegisterNames[i]] = last_frame->context.iregs[i];
	}

	if (!cfi_frame_info->FindCallerRegs(callee_registers, *memory_,
	&caller_registers)) {
	return NULL;
	}

	CFIFrameInfo::RegisterValueMap<uint32_t>::const_iterator entry =
	caller_registers.find(".cfa");

	if (entry != caller_registers.end()) {
	caller_registers["$sp"] = entry->second;
	}

	entry = caller_registers.find(".ra");
	if (entry != caller_registers.end()) {
	caller_registers["$ra"] = entry->second;
	pc = entry->second - 2 * sizeof(pc);
	}
	caller_registers["$pc"] = pc;
	// Construct a new stack frame given the values the CFI recovered.
	scoped_ptr<StackFrameMIPS> frame(new StackFrameMIPS());

	for (int i = 0; kRegisterNames[i]; ++i) {
	CFIFrameInfo::RegisterValueMap<uint32_t>::const_iterator caller_entry =
	caller_registers.find(kRegisterNames[i]);

	if (caller_entry != caller_registers.end()) {
	// The value of this register is recovered; fill the context with the
	// value from caller_registers.
	frame->context.iregs[i] = caller_entry->second;
	frame->context_validity \|= StackFrameMIPS::RegisterValidFlag(i);
	} else if (((i >= INDEX_MIPS_REG_S0 && i <= INDEX_MIPS_REG_S7) \|\|
	(i > INDEX_MIPS_REG_GP && i < INDEX_MIPS_REG_RA)) &&
	(last_frame->context_validity &
	StackFrameMIPS::RegisterValidFlag(i))) {
	// If the STACK CFI data doesn't mention some callee-save register, and
	// it is valid in the callee, assume the callee has not yet changed it.
	// Calee-save registers according to the MIPS o32 ABI specification are:
	// $s0 to $s7
	// $sp, $s8
	frame->context.iregs[i] = last_frame->context.iregs[i];
	frame->context_validity \|= StackFrameMIPS::RegisterValidFlag(i);
	}
	}

	frame->context.epc = caller_registers["$pc"];
	frame->instruction = caller_registers["$pc"];
	frame->context_validity \|= StackFrameMIPS::CONTEXT_VALID_PC;

	frame->context.iregs[MD_CONTEXT_MIPS_REG_RA] = caller_registers["$ra"];
	frame->context_validity \|= StackFrameMIPS::CONTEXT_VALID_RA;

	frame->trust = StackFrame::FRAME_TRUST_CFI;

	return frame.release();
	} else {
	uint64_t pc = 0;

	// Populate a dictionary with the valid register values in last_frame.
	CFIFrameInfo::RegisterValueMap<uint64_t> callee_registers;
	// Use the STACK CFI data to recover the caller's register values.
	CFIFrameInfo::RegisterValueMap<uint64_t> caller_registers;

	for (int i = 0; kRegisterNames[i]; ++i) {
	caller_registers[kRegisterNames[i]] = last_frame->context.iregs[i];
	callee_registers[kRegisterNames[i]] = last_frame->context.iregs[i];
	}

	if (!cfi_frame_info->FindCallerRegs(callee_registers, *memory_,
	&caller_registers)) {
	return NULL;
	}

	CFIFrameInfo::RegisterValueMap<uint64_t>::const_iterator entry =
	caller_registers.find(".cfa");

	if (entry != caller_registers.end()) {
	caller_registers["$sp"] = entry->second;
	}

	entry = caller_registers.find(".ra");
	if (entry != caller_registers.end()) {
	caller_registers["$ra"] = entry->second;
	pc = entry->second - 2 * sizeof(pc);
	}
	caller_registers["$pc"] = pc;
	// Construct a new stack frame given the values the CFI recovered.
	scoped_ptr<StackFrameMIPS> frame(new StackFrameMIPS());

	for (int i = 0; kRegisterNames[i]; ++i) {
	CFIFrameInfo::RegisterValueMap<uint64_t>::const_iterator caller_entry =
	caller_registers.find(kRegisterNames[i]);

	if (caller_entry != caller_registers.end()) {
	// The value of this register is recovered; fill the context with the
	// value from caller_registers.
	frame->context.iregs[i] = caller_entry->second;
	frame->context_validity \|= StackFrameMIPS::RegisterValidFlag(i);
	} else if (((i >= INDEX_MIPS_REG_S0 && i <= INDEX_MIPS_REG_S7) \|\|
	(i >= INDEX_MIPS_REG_GP && i < INDEX_MIPS_REG_RA)) &&
	(last_frame->context_validity &
	StackFrameMIPS::RegisterValidFlag(i))) {
	// If the STACK CFI data doesn't mention some callee-save register, and
	// it is valid in the callee, assume the callee has not yet changed it.
	// Calee-save registers according to the MIPS o32 ABI specification are:
	// $s0 to $s7
	// $sp, $s8
	frame->context.iregs[i] = last_frame->context.iregs[i];
	frame->context_validity \|= StackFrameMIPS::RegisterValidFlag(i);
	}
	}

	frame->context.epc = caller_registers["$pc"];
	frame->instruction = caller_registers["$pc"];
	frame->context_validity \|= StackFrameMIPS::CONTEXT_VALID_PC;

	frame->context.iregs[MD_CONTEXT_MIPS_REG_RA] = caller_registers["$ra"];
	frame->context_validity \|= StackFrameMIPS::CONTEXT_VALID_RA;

	frame->trust = StackFrame::FRAME_TRUST_CFI;

	return frame.release();
	}
	}

	StackFrame* StackwalkerMIPS::GetCallerFrame(const CallStack* stack,
	bool stack_scan_allowed) {
	if (!memory_ \|\| !stack) {
	BPLOG(ERROR) << "Can't get caller frame without memory or stack";
	return NULL;
	}

	const vector<StackFrame>& frames = stack->frames();
	StackFrameMIPS* last_frame = static_cast<StackFrameMIPS*>(frames.back());
	scoped_ptr<StackFrameMIPS> new_frame;

	// See if there is DWARF call frame information covering this address.
	scoped_ptr<CFIFrameInfo> cfi_frame_info(
	frame_symbolizer_->FindCFIFrameInfo(last_frame));
	if (cfi_frame_info.get())
	new_frame.reset(GetCallerByCFIFrameInfo(frames, cfi_frame_info.get()));

	// If caller frame is not found in CFI try analyzing the stack.
	if (stack_scan_allowed && !new_frame.get()) {
	new_frame.reset(GetCallerByStackScan(frames));
	}

	// If nothing worked, tell the caller.
	if (!new_frame.get()) {
	return NULL;
	}

	// Should we terminate the stack walk? (end-of-stack or broken invariant)
	if (TerminateWalk(new_frame->context.epc,
	new_frame->context.iregs[MD_CONTEXT_MIPS_REG_SP],
	last_frame->context.iregs[MD_CONTEXT_MIPS_REG_SP],
	frames.size() == 1)) {
	return NULL;
	}

	return new_frame.release();
	}

	StackFrameMIPS* StackwalkerMIPS::GetCallerByStackScan(
	const vector<StackFrame*>& frames) {
	const uint32_t kMaxFrameStackSize = 1024;
	const uint32_t kMinArgsOnStack = 4;

	StackFrameMIPS* last_frame = static_cast<StackFrameMIPS*>(frames.back());

	if (context_->context_flags & MD_CONTEXT_MIPS) {
	uint32_t last_sp = last_frame->context.iregs[MD_CONTEXT_MIPS_REG_SP];
	uint32_t caller_pc, caller_sp, caller_fp;

	// Return address cannot be obtained directly.
	// Force stackwalking.

	// We cannot use frame pointer to get the return address.
	// We'll scan the stack for a
	// return address. This can happen if last_frame is executing code
	// for a module for which we don't have symbols.
	int count = kMaxFrameStackSize / sizeof(caller_pc);

	if (frames.size() > 1) {
	// In case of mips32 ABI stack frame of a nonleaf function
	// must have minimum stack frame assigned for 4 arguments (4 words).
	// Move stack pointer for 4 words to avoid reporting non-existing frames
	// for all frames except the topmost one.
	// There is no way of knowing if topmost frame belongs to a leaf or
	// a nonleaf function.
	last_sp += kMinArgsOnStack * sizeof(caller_pc);
	// Adjust 'count' so that return address is scanned only in limits
	// of one stack frame.
	count -= kMinArgsOnStack;
	}

	do {
	// Scanning for return address from stack pointer of the last frame.
	if (!ScanForReturnAddress(last_sp, &caller_sp, &caller_pc, count)) {
	// If we can't find an instruction pointer even with stack scanning,
	// give up.
	BPLOG(ERROR) << " ScanForReturnAddress failed ";
	return NULL;
	}
	// Get $fp stored in the stack frame.
	if (!memory_->GetMemoryAtAddress(caller_sp - sizeof(caller_pc),
	&caller_fp)) {
	BPLOG(INFO) << " GetMemoryAtAddress for fp failed " ;
	return NULL;
	}

	count = count - (caller_sp - last_sp) / sizeof(caller_pc);
	// Now scan the next address in the stack.
	last_sp = caller_sp + sizeof(caller_pc);
	} while ((caller_fp - caller_sp >= kMaxFrameStackSize) && count > 0);

	if (!count) {
	BPLOG(INFO) << " No frame found " ;
	return NULL;
	}

	// ScanForReturnAddress found a reasonable return address. Advance
	// $sp to the location above the one where the return address was
	// found.
	caller_sp += sizeof(caller_pc);
	// caller_pc is actually containing $ra value;
	// $pc is two instructions before $ra,
	// so the caller_pc needs to be decremented accordingly.
	caller_pc -= 2 * sizeof(caller_pc);

	// Create a new stack frame (ownership will be transferred to the caller)
	// and fill it in.
	StackFrameMIPS* frame = new StackFrameMIPS();
	frame->trust = StackFrame::FRAME_TRUST_SCAN;
	frame->context = last_frame->context;
	frame->context.epc = caller_pc;
	frame->context_validity \|= StackFrameMIPS::CONTEXT_VALID_PC;
	frame->instruction = caller_pc;

	frame->context.iregs[MD_CONTEXT_MIPS_REG_SP] = caller_sp;
	frame->context_validity \|= StackFrameMIPS::CONTEXT_VALID_SP;
	frame->context.iregs[MD_CONTEXT_MIPS_REG_FP] = caller_fp;
	frame->context_validity \|= StackFrameMIPS::CONTEXT_VALID_FP;

	frame->context.iregs[MD_CONTEXT_MIPS_REG_RA] =
	caller_pc + 2 * sizeof(caller_pc);
	frame->context_validity \|= StackFrameMIPS::CONTEXT_VALID_RA;

	return frame;
	} else {
	uint64_t last_sp = last_frame->context.iregs[MD_CONTEXT_MIPS_REG_SP];
	uint64_t caller_pc, caller_sp, caller_fp;

	// Return address cannot be obtained directly.
	// Force stackwalking.

	// We cannot use frame pointer to get the return address.
	// We'll scan the stack for a
	// return address. This can happen if last_frame is executing code
	// for a module for which we don't have symbols.
	int count = kMaxFrameStackSize / sizeof(caller_pc);

	do {
	// Scanning for return address from stack pointer of the last frame.
	if (!ScanForReturnAddress(last_sp, &caller_sp, &caller_pc, count)) {
	// If we can't find an instruction pointer even with stack scanning,
	// give up.
	BPLOG(ERROR) << " ScanForReturnAddress failed ";
	return NULL;
	}
	// Get $fp stored in the stack frame.
	if (!memory_->GetMemoryAtAddress(caller_sp - sizeof(caller_pc),
	&caller_fp)) {
	BPLOG(INFO) << " GetMemoryAtAddress for fp failed " ;
	return NULL;
	}

	count = count - (caller_sp - last_sp) / sizeof(caller_pc);
	// Now scan the next address in the stack.
	last_sp = caller_sp + sizeof(caller_pc);
	} while ((caller_fp - caller_sp >= kMaxFrameStackSize) && count > 0);

	if (!count) {
	BPLOG(INFO) << " No frame found " ;
	return NULL;
	}

	// ScanForReturnAddress found a reasonable return address. Advance
	// $sp to the location above the one where the return address was
	// found.
	caller_sp += sizeof(caller_pc);
	// caller_pc is actually containing $ra value;
	// $pc is two instructions before $ra,
	// so the caller_pc needs to be decremented accordingly.
	caller_pc -= 2 * sizeof(caller_pc);

	// Create a new stack frame (ownership will be transferred to the caller)
	// and fill it in.
	StackFrameMIPS* frame = new StackFrameMIPS();
	frame->trust = StackFrame::FRAME_TRUST_SCAN;
	frame->context = last_frame->context;
	frame->context.epc = caller_pc;
	frame->context_validity \|= StackFrameMIPS::CONTEXT_VALID_PC;
	frame->instruction = caller_pc;

	frame->context.iregs[MD_CONTEXT_MIPS_REG_SP] = caller_sp;
	frame->context_validity \|= StackFrameMIPS::CONTEXT_VALID_SP;
	frame->context.iregs[MD_CONTEXT_MIPS_REG_FP] = caller_fp;
	frame->context_validity \|= StackFrameMIPS::CONTEXT_VALID_FP;

	frame->context.iregs[MD_CONTEXT_MIPS_REG_RA] =
	caller_pc + 2 * sizeof(caller_pc);
	frame->context_validity \|= StackFrameMIPS::CONTEXT_VALID_RA;

	return frame;
	}
	}

	} // namespace google_breakpad