src/processor/stackwalker_mips.cc - 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