text: //===-- sanitizer_stacktrace.cc -------------------------------------------===//
  //
  //                     The LLVM Compiler Infrastructure
  //
  // This file is distributed under the University of Illinois Open Source
  // License. See LICENSE.TXT for details.
  //
  //===----------------------------------------------------------------------===//
  //
  // This file is shared between AddressSanitizer and ThreadSanitizer
  // run-time libraries.
  //===----------------------------------------------------------------------===//
  
  #include "sanitizer_common.h"
  #include "sanitizer_flags.h"
  #include "sanitizer_stacktrace.h"
  
  namespace __sanitizer {
  
  uptr StackTrace::GetNextInstructionPc(uptr pc) {
  #if defined(__mips__)
    return pc + 8;
  #else
    return pc + 1;
  #endif
  }
  
  uptr StackTrace::GetCurrentPc() {
    return GET_CALLER_PC();
  }
  
  void BufferedStackTrace::Init(const uptr *pcs, uptr cnt, uptr extra_top_pc) {
    size = cnt + !!extra_top_pc;
    CHECK_LE(size, kStackTraceMax);
    internal_memcpy(trace_buffer, pcs, cnt * sizeof(trace_buffer[0]));
    if (extra_top_pc)
      trace_buffer[cnt] = extra_top_pc;
    top_frame_bp = 0;
  }
  
  // Check if given pointer points into allocated stack area.
  static inline bool IsValidFrame(uptr frame, uptr stack_top, uptr stack_bottom) {
    return frame > stack_bottom && frame < stack_top - 2 * sizeof (uhwptr);
  }
  
  // In GCC on ARM bp points to saved lr, not fp, so we should check the next
  // cell in stack to be a saved frame pointer. GetCanonicFrame returns the
  // pointer to saved frame pointer in any case.
  static inline uhwptr *GetCanonicFrame(uptr bp,
                                        uptr stack_top,
                                        uptr stack_bottom) {
  #ifdef __arm__
    if (!IsValidFrame(bp, stack_top, stack_bottom)) return 0;
    uhwptr *bp_prev = (uhwptr *)bp;
    if (IsValidFrame((uptr)bp_prev[0], stack_top, stack_bottom)) return bp_prev;
    // The next frame pointer does not look right. This could be a GCC frame, step
    // back by 1 word and try again.
    if (IsValidFrame((uptr)bp_prev[-1], stack_top, stack_bottom))
      return bp_prev - 1;
    // Nope, this does not look right either. This means the frame after next does
    // not have a valid frame pointer, but we can still extract the caller PC.
    // Unfortunately, there is no way to decide between GCC and LLVM frame
    // layouts. Assume LLVM.
    return bp_prev;
  #else
    return (uhwptr*)bp;
  #endif
  }
  
  void BufferedStackTrace::FastUnwindStack(uptr pc, uptr bp, uptr stack_top,
                                           uptr stack_bottom, u32 max_depth) {
    CHECK_GE(max_depth, 2);
    trace_buffer[0] = pc;
    size = 1;
    if (stack_top < 4096) return;  // Sanity check for stack top.
    uhwptr *frame = GetCanonicFrame(bp, stack_top, stack_bottom);
    // Lowest possible address that makes sense as the next frame pointer.
    // Goes up as we walk the stack.
    uptr bottom = stack_bottom;
    // Avoid infinite loop when frame == frame[0] by using frame > prev_frame.
    while (IsValidFrame((uptr)frame, stack_top, bottom) &&
           IsAligned((uptr)frame, sizeof(*frame)) &&
           size < max_depth) {
      uhwptr pc1 = frame[1];
      if (pc1 != pc) {
        trace_buffer[size++] = (uptr) pc1;
      }
      bottom = (uptr)frame;
      frame = GetCanonicFrame((uptr)frame[0], stack_top, bottom);
    }
  }
  
  static bool MatchPc(uptr cur_pc, uptr trace_pc, uptr threshold) {
    return cur_pc - trace_pc <= threshold || trace_pc - cur_pc <= threshold;
  }
  
  void BufferedStackTrace::PopStackFrames(uptr count) {
    CHECK_LT(count, size);
    size -= count;
    for (uptr i = 0; i < size; ++i) {
      trace_buffer[i] = trace_buffer[i + count];
    }
  }
  
  uptr BufferedStackTrace::LocatePcInTrace(uptr pc) {
    // Use threshold to find PC in stack trace, as PC we want to unwind from may
    // slightly differ from return address in the actual unwinded stack trace.
    const int kPcThreshold = 304;
    for (uptr i = 0; i < size; ++i) {
      if (MatchPc(pc, trace[i], kPcThreshold))
        return i;
    }
    return 0;
  }
  
  }  // namespace __sanitizer
  