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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,
SymbolSupplier* supplier,
void* supplier_data)
: Stackwalker(memory, modules, supplier, supplier_data),
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
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