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      1 //===-- sanitizer_stacktrace.cc -------------------------------------------===//
      2 //
      3 //                     The LLVM Compiler Infrastructure
      4 //
      5 // This file is distributed under the University of Illinois Open Source
      6 // License. See LICENSE.TXT for details.
      7 //
      8 //===----------------------------------------------------------------------===//
      9 //
     10 // This file is shared between AddressSanitizer and ThreadSanitizer
     11 // run-time libraries.
     12 //===----------------------------------------------------------------------===//
     13 
     14 #include "sanitizer_common.h"
     15 #include "sanitizer_flags.h"
     16 #include "sanitizer_stacktrace.h"
     17 
     18 namespace __sanitizer {
     19 
     20 uptr StackTrace::GetNextInstructionPc(uptr pc) {
     21 #if defined(__mips__)
     22   return pc + 8;
     23 #elif defined(__powerpc__)
     24   return pc + 4;
     25 #else
     26   return pc + 1;
     27 #endif
     28 }
     29 
     30 uptr StackTrace::GetCurrentPc() {
     31   return GET_CALLER_PC();
     32 }
     33 
     34 void BufferedStackTrace::Init(const uptr *pcs, uptr cnt, uptr extra_top_pc) {
     35   size = cnt + !!extra_top_pc;
     36   CHECK_LE(size, kStackTraceMax);
     37   internal_memcpy(trace_buffer, pcs, cnt * sizeof(trace_buffer[0]));
     38   if (extra_top_pc)
     39     trace_buffer[cnt] = extra_top_pc;
     40   top_frame_bp = 0;
     41 }
     42 
     43 // Check if given pointer points into allocated stack area.
     44 static inline bool IsValidFrame(uptr frame, uptr stack_top, uptr stack_bottom) {
     45   return frame > stack_bottom && frame < stack_top - 2 * sizeof (uhwptr);
     46 }
     47 
     48 // In GCC on ARM bp points to saved lr, not fp, so we should check the next
     49 // cell in stack to be a saved frame pointer. GetCanonicFrame returns the
     50 // pointer to saved frame pointer in any case.
     51 static inline uhwptr *GetCanonicFrame(uptr bp,
     52                                       uptr stack_top,
     53                                       uptr stack_bottom) {
     54 #ifdef __arm__
     55   if (!IsValidFrame(bp, stack_top, stack_bottom)) return 0;
     56   uhwptr *bp_prev = (uhwptr *)bp;
     57   if (IsValidFrame((uptr)bp_prev[0], stack_top, stack_bottom)) return bp_prev;
     58   // The next frame pointer does not look right. This could be a GCC frame, step
     59   // back by 1 word and try again.
     60   if (IsValidFrame((uptr)bp_prev[-1], stack_top, stack_bottom))
     61     return bp_prev - 1;
     62   // Nope, this does not look right either. This means the frame after next does
     63   // not have a valid frame pointer, but we can still extract the caller PC.
     64   // Unfortunately, there is no way to decide between GCC and LLVM frame
     65   // layouts. Assume LLVM.
     66   return bp_prev;
     67 #else
     68   return (uhwptr*)bp;
     69 #endif
     70 }
     71 
     72 void BufferedStackTrace::FastUnwindStack(uptr pc, uptr bp, uptr stack_top,
     73                                          uptr stack_bottom, u32 max_depth) {
     74   CHECK_GE(max_depth, 2);
     75   trace_buffer[0] = pc;
     76   size = 1;
     77   if (stack_top < 4096) return;  // Sanity check for stack top.
     78   uhwptr *frame = GetCanonicFrame(bp, stack_top, stack_bottom);
     79   // Lowest possible address that makes sense as the next frame pointer.
     80   // Goes up as we walk the stack.
     81   uptr bottom = stack_bottom;
     82   // Avoid infinite loop when frame == frame[0] by using frame > prev_frame.
     83   while (IsValidFrame((uptr)frame, stack_top, bottom) &&
     84          IsAligned((uptr)frame, sizeof(*frame)) &&
     85          size < max_depth) {
     86 #ifdef __powerpc__
     87     // PowerPC ABIs specify that the return address is saved at offset
     88     // 16 of the *caller's* stack frame.  Thus we must dereference the
     89     // back chain to find the caller frame before extracting it.
     90     uhwptr *caller_frame = (uhwptr*)frame[0];
     91     if (!IsValidFrame((uptr)caller_frame, stack_top, bottom) ||
     92         !IsAligned((uptr)caller_frame, sizeof(uhwptr)))
     93       break;
     94     uhwptr pc1 = caller_frame[2];
     95 #else
     96     uhwptr pc1 = frame[1];
     97 #endif
     98     if (pc1 != pc) {
     99       trace_buffer[size++] = (uptr) pc1;
    100     }
    101     bottom = (uptr)frame;
    102     frame = GetCanonicFrame((uptr)frame[0], stack_top, bottom);
    103   }
    104 }
    105 
    106 static bool MatchPc(uptr cur_pc, uptr trace_pc, uptr threshold) {
    107   return cur_pc - trace_pc <= threshold || trace_pc - cur_pc <= threshold;
    108 }
    109 
    110 void BufferedStackTrace::PopStackFrames(uptr count) {
    111   CHECK_LT(count, size);
    112   size -= count;
    113   for (uptr i = 0; i < size; ++i) {
    114     trace_buffer[i] = trace_buffer[i + count];
    115   }
    116 }
    117 
    118 uptr BufferedStackTrace::LocatePcInTrace(uptr pc) {
    119   // Use threshold to find PC in stack trace, as PC we want to unwind from may
    120   // slightly differ from return address in the actual unwinded stack trace.
    121   const int kPcThreshold = 320;
    122   for (uptr i = 0; i < size; ++i) {
    123     if (MatchPc(pc, trace[i], kPcThreshold))
    124       return i;
    125   }
    126   return 0;
    127 }
    128 
    129 }  // namespace __sanitizer
    130