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diff --git a/src/processor/stackwalker_x86.cc b/src/processor/stackwalker_x86.cc
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+// Copyright (C) 2006 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// stackwalker_x86.cc: x86-specific stackwalker.
+//
+// See stackwalker_x86.h for documentation.
+//
+// Author: Mark Mentovai
+
+
+#include "processor/stackwalker_x86.h"
+#include "processor/minidump.h"
+
+
+namespace google_airbag {
+
+
+StackwalkerX86::StackwalkerX86(MinidumpContext*    context,
+                               MemoryRegion*       memory,
+                               MinidumpModuleList* modules)
+    : Stackwalker(memory, modules)
+    , last_frame_pointer_(0) {
+  if (memory_->GetBase() + memory_->GetSize() - 1 > 0xffffffff) {
+    // The x86 is a 32-bit CPU, the limits of the supplied stack are invalid.
+    // Mark memory_ = NULL, which will cause stackwalking to fail.
+    memory_ = NULL;
+  }
+
+  // TODO(mmentovai): verify that |context| is x86 when Minidump supports
+  // other CPU types.
+  context_ = context->context();
+}
+
+
+bool StackwalkerX86::GetContextFrame(StackFrame* frame) {
+  if (!context_ || !memory_ || !frame)
+    return false;
+
+  // The frame and instruction pointers are stored directly in registers,
+  // so pull them straight out of the CPU context structure.
+  frame->frame_pointer = last_frame_pointer_ = context_->ebp;
+  frame->instruction = context_->eip;
+
+  return true;
+}
+
+
+bool StackwalkerX86::GetCallerFrame(StackFrame* frame) {
+  if (!memory_ || !frame)
+    return false;
+
+  // The frame and instruction pointers for previous frames are saved on the
+  // stack.  The typical x86 calling convention, when frame pointers are
+  // present, is for the calling procedure to use CALL, which pushes the
+  // return address onto the stack and sets the instruction pointer (%eip)
+  // to the entry point of the called routine.  The called routine's then
+  // PUSHes the calling routine's frame pointer (%ebp) onto the stack before
+  // copying the stack pointer (%esp) to the frame pointer (%ebp).  Therefore,
+  // the calling procedure's frame pointer is always available by
+  // dereferencing the called procedure's frame pointer, and the return
+  // address is always available at the memory location immediately above
+  // the address pointed to by the called procedure's frame pointer.
+
+  // If there is no frame pointer, determining the layout of the stack is
+  // considerably more difficult, requiring debugging information.  This
+  // stackwalker doesn't attempt to solve that problem (at this point).
+
+  // 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 frame_pointer;
+  if (!memory_->GetMemoryAtAddress(last_frame_pointer_, &frame_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 (frame_pointer <= last_frame_pointer_)
+    return false;
+
+  u_int32_t instruction;
+  if (!memory_->GetMemoryAtAddress(last_frame_pointer_ + 4, &instruction))
+    return false;
+
+  frame->frame_pointer = last_frame_pointer_ = frame_pointer;
+  frame->instruction = instruction;
+
+  return true;
+}
+
+
+} // namespace google_airbag