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+// Copyright (c) 2006, 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_ppc.cc: ppc-specific stackwalker.
+//
+// See stackwalker_ppc.h for documentation.
+//
+// Author: Mark Mentovai
+
+
+#include "processor/stackwalker_ppc.h"
+#include "processor/minidump.h"
+
+namespace google_airbag {
+
+
+StackwalkerPPC::StackwalkerPPC(const MDRawContextPPC *context,
+                               MemoryRegion *memory,
+                               MinidumpModuleList *modules,
+                               SymbolSupplier *supplier)
+    : Stackwalker(memory, modules, supplier),
+      context_(context) {
+  if (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.
+    memory_ = NULL;
+  }
+}
+
+
+bool StackwalkerPPC::GetContextFrame(StackFrame *frame) {
+  if (!context_ || !memory_ || !frame)
+    return false;
+
+  // The stack frame and instruction pointers are stored directly in
+  // registers, so pull them straight out of the CPU context structure.
+  frame->frame_pointer = context_->gpr[1];
+  frame->instruction = context_->srr0;
+
+  return true;
+}
+
+
+bool StackwalkerPPC::GetCallerFrame(StackFrame *frame,
+                                    const StackFrames *walked_frames) {
+  if (!memory_ || !frame || !walked_frames)
+    return false;
+
+  // The stack frame and 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.
+
+  u_int32_t last_stack_pointer = walked_frames->back().frame_pointer;
+
+  // Don't pass frame.frame_pointer or frame.instruction directly
+  // ReadMemory, because their types are too wide (64-bit), and we
+  // specifically want to read 32-bit quantities for both.
+  u_int32_t stack_pointer;
+  if (!memory_->GetMemoryAtAddress(last_stack_pointer, &stack_pointer))
+    return false;
+
+  // 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.
+  if (stack_pointer <= last_stack_pointer)
+    return false;
+
+  u_int32_t instruction;
+  if (!memory_->GetMemoryAtAddress(stack_pointer + 8, &instruction))
+    return false;
+
+  // 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.
+  if (instruction <= 1)
+    return false;
+
+  frame->frame_pointer = stack_pointer;
+  frame->instruction = instruction;
+
+  return true;
+}
+
+
+} // namespace google_airbag