stackwalker_ppc.cc

// Copyright (c) 2010 Google Inc.
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// stackwalker_ppc.cc: ppc-specific stackwalker.
//
// See stackwalker_ppc.h for documentation.
//
// Author: Mark Mentovai


#include "processor/stackwalker_ppc.h"
#include "google_breakpad/processor/call_stack.h"
#include "google_breakpad/processor/memory_region.h"
#include "google_breakpad/processor/stack_frame_cpu.h"
#include "processor/logging.h"

namespace google_breakpad {


StackwalkerPPC::StackwalkerPPC(const SystemInfo* system_info,
                               const MDRawContextPPC* context,
                               MemoryRegion* memory,
                               const CodeModules* modules,
                               StackFrameSymbolizer* resolver_helper)
    : Stackwalker(system_info, memory, modules, resolver_helper),
      context_(context) {
  if (memory_ && memory_->GetBase() + memory_->GetSize() - 1 > 0xffffffff) {
    // This implementation only covers 32-bit ppc CPUs.  The limits of the
    // supplied stack are invalid.  Mark memory_ = NULL, which will cause
    // stackwalking to fail.
    BPLOG(ERROR) << "Memory out of range for stackwalking: " <<
                    HexString(memory_->GetBase()) << "+" <<
                    HexString(memory_->GetSize());
    memory_ = NULL;
  }
}


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

  StackFramePPC* frame = new StackFramePPC();

  // 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 = StackFramePPC::CONTEXT_VALID_ALL;
  frame->trust = StackFrame::FRAME_TRUST_CONTEXT;
  frame->instruction = frame->context.srr0;

  return frame;
}


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

  // The instruction pointers for previous frames are saved on the stack.
  // The typical ppc calling convention is for the called procedure to store
  // its return address in the calling procedure's stack frame at 8(%r1),
  // and to allocate its own stack frame by decrementing %r1 (the stack
  // pointer) and saving the old value of %r1 at 0(%r1).  Because the ppc has
  // no hardware stack, there is no distinction between the stack pointer and
  // frame pointer, and what is typically thought of as the frame pointer on
  // an x86 is usually referred to as the stack pointer on a ppc.

  StackFramePPC* last_frame = static_cast<StackFramePPC*>(
      stack->frames()->back());

  // A caller frame must reside higher in memory than its callee frames.
  // Anything else is an error, or an indication that we've reached the
  // end of the stack.
  uint32_t stack_pointer;
  if (!memory_->GetMemoryAtAddress(last_frame->context.gpr[1],
                                   &stack_pointer) ||
      stack_pointer <= last_frame->context.gpr[1]) {
    return NULL;
  }

  // Mac OS X/Darwin gives 1 as the return address from the bottom-most
  // frame in a stack (a thread's entry point).  I haven't found any
  // documentation on this, but 0 or 1 would be bogus return addresses,
  // so check for them here and return false (end of stack) when they're
  // hit to avoid having a phantom frame.
  uint32_t instruction;
  if (!memory_->GetMemoryAtAddress(stack_pointer + 8, &instruction) ||
      instruction <= 1) {
    return NULL;
  }

  StackFramePPC* frame = new StackFramePPC();

  frame->context = last_frame->context;
  frame->context.srr0 = instruction;
  frame->context.gpr[1] = stack_pointer;
  frame->context_validity = StackFramePPC::CONTEXT_VALID_SRR0 |
                            StackFramePPC::CONTEXT_VALID_GPR1;
  frame->trust = StackFrame::FRAME_TRUST_FP;

  // frame->context.srr0 is the return address, which is one instruction
  // past the branch that caused us to arrive at the callee.  Set
  // frame_ppc->instruction to four less than that.  Since all ppc
  // instructions are 4 bytes wide, this is the address of the branch
  // instruction.  This allows source line information to match up with the
  // line that contains a function call.  Callers that require the exact
  // return address value may access the context.srr0 field of StackFramePPC.
  frame->instruction = frame->context.srr0 - 4;

  return frame;
}


}  // namespace google_breakpad