stackwalker_arm.cc

// Copyright (c) 2010 Google Inc.
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// stackwalker_arm.cc: arm-specific stackwalker.
//
// See stackwalker_arm.h for documentation.
//
// Author: Mark Mentovai, Ted Mielczarek, Jim Blandy

#include <vector>

#include "common/scoped_ptr.h"
#include "google_breakpad/processor/call_stack.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/stackwalker_arm.h"

namespace google_breakpad {


StackwalkerARM::StackwalkerARM(const SystemInfo* system_info,
                               const MDRawContextARM* context,
                               int fp_register,
                               MemoryRegion* memory,
                               const CodeModules* modules,
                               StackFrameSymbolizer* resolver_helper)
    : Stackwalker(system_info, memory, modules, resolver_helper),
      context_(context), fp_register_(fp_register),
      context_frame_validity_(StackFrameARM::CONTEXT_VALID_ALL) { }


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

  StackFrameARM* frame = new StackFrameARM();

  // The instruction pointer is stored directly in a register (r15), so pull it
  // straight out of the CPU context structure.
  frame->context = *context_;
  frame->context_validity = context_frame_validity_;
  frame->trust = StackFrame::FRAME_TRUST_CONTEXT;
  frame->instruction = frame->context.iregs[MD_CONTEXT_ARM_REG_PC];

  return frame;
}

StackFrameARM* StackwalkerARM::GetCallerByCFIFrameInfo(
    const vector<StackFrame*> &frames,
    CFIFrameInfo* cfi_frame_info) {
  StackFrameARM* last_frame = static_cast<StackFrameARM*>(frames.back());

  static const char* register_names[] = {
    "r0",  "r1",  "r2",  "r3",  "r4",  "r5",  "r6",  "r7",
    "r8",  "r9",  "r10", "r11", "r12", "sp",  "lr",  "pc",
    "f0",  "f1",  "f2",  "f3",  "f4",  "f5",  "f6",  "f7",
    "fps", "cpsr",
    NULL
  };

  // Populate a dictionary with the valid register values in last_frame.
  CFIFrameInfo::RegisterValueMap<uint32_t> callee_registers;
  for (int i = 0; register_names[i]; i++)
    if (last_frame->context_validity & StackFrameARM::RegisterValidFlag(i))
      callee_registers[register_names[i]] = last_frame->context.iregs[i];

  // Use the STACK CFI data to recover the caller's register values.
  CFIFrameInfo::RegisterValueMap<uint32_t> caller_registers;
  if (!cfi_frame_info->FindCallerRegs(callee_registers, *memory_,
                                      &caller_registers))
    return NULL;

  // Construct a new stack frame given the values the CFI recovered.
  scoped_ptr<StackFrameARM> frame(new StackFrameARM());
  for (int i = 0; register_names[i]; i++) {
    CFIFrameInfo::RegisterValueMap<uint32_t>::iterator entry =
      caller_registers.find(register_names[i]);
    if (entry != caller_registers.end()) {
      // We recovered the value of this register; fill the context with the
      // value from caller_registers.
      frame->context_validity |= StackFrameARM::RegisterValidFlag(i);
      frame->context.iregs[i] = entry->second;
    } else if (4 <= i && i <= 11 && (last_frame->context_validity &
                                     StackFrameARM::RegisterValidFlag(i))) {
      // If the STACK CFI data doesn't mention some callee-saves register, and
      // it is valid in the callee, assume the callee has not yet changed it.
      // Registers r4 through r11 are callee-saves, according to the Procedure
      // Call Standard for the ARM Architecture, which the Linux ABI follows.
      frame->context_validity |= StackFrameARM::RegisterValidFlag(i);
      frame->context.iregs[i] = last_frame->context.iregs[i];
    }
  }
  // If the CFI doesn't recover the PC explicitly, then use .ra.
  if (!(frame->context_validity & StackFrameARM::CONTEXT_VALID_PC)) {
    CFIFrameInfo::RegisterValueMap<uint32_t>::iterator entry =
      caller_registers.find(".ra");
    if (entry != caller_registers.end()) {
      if (fp_register_ == -1) {
        frame->context_validity |= StackFrameARM::CONTEXT_VALID_PC;
        frame->context.iregs[MD_CONTEXT_ARM_REG_PC] = entry->second;
      } else {
        // The CFI updated the link register and not the program counter.
        // Handle getting the program counter from the link register.
        frame->context_validity |= StackFrameARM::CONTEXT_VALID_PC;
        frame->context_validity |= StackFrameARM::CONTEXT_VALID_LR;
        frame->context.iregs[MD_CONTEXT_ARM_REG_LR] = entry->second;
        frame->context.iregs[MD_CONTEXT_ARM_REG_PC] =
            last_frame->context.iregs[MD_CONTEXT_ARM_REG_LR];
      }
    }
  }
  // If the CFI doesn't recover the SP explicitly, then use .cfa.
  if (!(frame->context_validity & StackFrameARM::CONTEXT_VALID_SP)) {
    CFIFrameInfo::RegisterValueMap<uint32_t>::iterator entry =
      caller_registers.find(".cfa");
    if (entry != caller_registers.end()) {
      frame->context_validity |= StackFrameARM::CONTEXT_VALID_SP;
      frame->context.iregs[MD_CONTEXT_ARM_REG_SP] = entry->second;
    }
  }

  // If we didn't recover the PC and the SP, then the frame isn't very useful.
  static const int essentials = (StackFrameARM::CONTEXT_VALID_SP
                                 | StackFrameARM::CONTEXT_VALID_PC);
  if ((frame->context_validity & essentials) != essentials)
    return NULL;

  frame->trust = StackFrame::FRAME_TRUST_CFI;
  return frame.release();
}

StackFrameARM* StackwalkerARM::GetCallerByStackScan(
    const vector<StackFrame*> &frames) {
  StackFrameARM* last_frame = static_cast<StackFrameARM*>(frames.back());
  uint32_t last_sp = last_frame->context.iregs[MD_CONTEXT_ARM_REG_SP];
  uint32_t caller_sp, caller_pc;

  if (!ScanForReturnAddress(last_sp, &caller_sp, &caller_pc,
                            frames.size() == 1 /* is_context_frame */)) {
    // No plausible return address was 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 += 4;

  // Create a new stack frame (ownership will be transferred to the caller)
  // and fill it in.
  StackFrameARM* frame = new StackFrameARM();

  frame->trust = StackFrame::FRAME_TRUST_SCAN;
  frame->context = last_frame->context;
  frame->context.iregs[MD_CONTEXT_ARM_REG_PC] = caller_pc;
  frame->context.iregs[MD_CONTEXT_ARM_REG_SP] = caller_sp;
  frame->context_validity = StackFrameARM::CONTEXT_VALID_PC |
                            StackFrameARM::CONTEXT_VALID_SP;

  return frame;
}

StackFrameARM* StackwalkerARM::GetCallerByFramePointer(
    const vector<StackFrame*> &frames) {
  StackFrameARM* last_frame = static_cast<StackFrameARM*>(frames.back());

  if (!(last_frame->context_validity &
        StackFrameARM::RegisterValidFlag(fp_register_))) {
    return NULL;
  }

  uint32_t last_fp = last_frame->context.iregs[fp_register_];

  uint32_t caller_fp = 0;
  if (last_fp && !memory_->GetMemoryAtAddress(last_fp, &caller_fp)) {
    BPLOG(ERROR) << "Unable to read caller_fp from last_fp: 0x"
                 << std::hex << last_fp;
    return NULL;
  }

  uint32_t caller_lr = 0;
  if (last_fp && !memory_->GetMemoryAtAddress(last_fp + 4, &caller_lr)) {
    BPLOG(ERROR) << "Unable to read caller_lr from last_fp + 4: 0x"
                 << std::hex << (last_fp + 4);
    return NULL;
  }

  uint32_t caller_sp = last_fp ? last_fp + 8 :
      last_frame->context.iregs[MD_CONTEXT_ARM_REG_SP];

  // Create a new stack frame (ownership will be transferred to the caller)
  // and fill it in.
  StackFrameARM* frame = new StackFrameARM();

  frame->trust = StackFrame::FRAME_TRUST_FP;
  frame->context = last_frame->context;
  frame->context.iregs[fp_register_] = caller_fp;
  frame->context.iregs[MD_CONTEXT_ARM_REG_SP] = caller_sp;
  frame->context.iregs[MD_CONTEXT_ARM_REG_PC] =
      last_frame->context.iregs[MD_CONTEXT_ARM_REG_LR];
  frame->context.iregs[MD_CONTEXT_ARM_REG_LR] = caller_lr;
  frame->context_validity = StackFrameARM::CONTEXT_VALID_PC |
                            StackFrameARM::CONTEXT_VALID_LR |
                            StackFrameARM::RegisterValidFlag(fp_register_) |
                            StackFrameARM::CONTEXT_VALID_SP;
  return frame;
}

StackFrame* StackwalkerARM::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();
  StackFrameARM* last_frame = static_cast<StackFrameARM*>(frames.back());
  scoped_ptr<StackFrameARM> 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())
    frame.reset(GetCallerByCFIFrameInfo(frames, cfi_frame_info.get()));

  // If CFI failed, or there wasn't CFI available, fall back
  // to frame pointer, if this is configured.
  if (fp_register_ >= 0 && !frame.get())
    frame.reset(GetCallerByFramePointer(frames));

  // If everuthing failed, fall back to stack scanning.
  if (stack_scan_allowed && !frame.get())
    frame.reset(GetCallerByStackScan(frames));

  // If nothing worked, tell the caller.
  if (!frame.get())
    return NULL;


  // An instruction address of zero marks the end of the stack.
  if (frame->context.iregs[MD_CONTEXT_ARM_REG_PC] == 0)
    return NULL;

  // If the new stack pointer is at a lower address than the old, then
  // that's clearly incorrect. Treat this as end-of-stack to enforce
  // progress and avoid infinite loops.
  if (frame->context.iregs[MD_CONTEXT_ARM_REG_SP]
      < last_frame->context.iregs[MD_CONTEXT_ARM_REG_SP])
    return NULL;

  // The new frame's context's PC is the return address, which is one
  // instruction past the instruction that caused us to arrive at the
  // callee. Set new_frame->instruction to one less than the PC. This won't
  // reference the beginning of the call instruction, but it's at least
  // within it, which is sufficient to get the source line information to
  // match up with the line that contains the function call. Callers that
  // require the exact return address value may access
  // frame->context.iregs[MD_CONTEXT_ARM_REG_PC].
  frame->instruction = frame->context.iregs[MD_CONTEXT_ARM_REG_PC] - 2;

  return frame.release();
}


}  // namespace google_breakpad