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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 // In GCC on ARM bp points to saved lr, not fp, so we should check the next
     44 // cell in stack to be a saved frame pointer. GetCanonicFrame returns the
     45 // pointer to saved frame pointer in any case.
     46 static inline uhwptr *GetCanonicFrame(uptr bp,
     47                                       uptr stack_top,
     48                                       uptr stack_bottom) {
     49 #ifdef __arm__
     50   if (!IsValidFrame(bp, stack_top, stack_bottom)) return 0;
     51   uhwptr *bp_prev = (uhwptr *)bp;
     52   if (IsValidFrame((uptr)bp_prev[0], stack_top, stack_bottom)) return bp_prev;
     53   // The next frame pointer does not look right. This could be a GCC frame, step
     54   // back by 1 word and try again.
     55   if (IsValidFrame((uptr)bp_prev[-1], stack_top, stack_bottom))
     56     return bp_prev - 1;
     57   // Nope, this does not look right either. This means the frame after next does
     58   // not have a valid frame pointer, but we can still extract the caller PC.
     59   // Unfortunately, there is no way to decide between GCC and LLVM frame
     60   // layouts. Assume LLVM.
     61   return bp_prev;
     62 #else
     63   return (uhwptr*)bp;
     64 #endif
     65 }
     66 
     67 void BufferedStackTrace::FastUnwindStack(uptr pc, uptr bp, uptr stack_top,
     68                                          uptr stack_bottom, u32 max_depth) {
     69   const uptr kPageSize = GetPageSizeCached();
     70   CHECK_GE(max_depth, 2);
     71   trace_buffer[0] = pc;
     72   size = 1;
     73   if (stack_top < 4096) return;  // Sanity check for stack top.
     74   uhwptr *frame = GetCanonicFrame(bp, stack_top, stack_bottom);
     75   // Lowest possible address that makes sense as the next frame pointer.
     76   // Goes up as we walk the stack.
     77   uptr bottom = stack_bottom;
     78   // Avoid infinite loop when frame == frame[0] by using frame > prev_frame.
     79   while (IsValidFrame((uptr)frame, stack_top, bottom) &&
     80          IsAligned((uptr)frame, sizeof(*frame)) &&
     81          size < max_depth) {
     82 #ifdef __powerpc__
     83     // PowerPC ABIs specify that the return address is saved at offset
     84     // 16 of the *caller's* stack frame.  Thus we must dereference the
     85     // back chain to find the caller frame before extracting it.
     86     uhwptr *caller_frame = (uhwptr*)frame[0];
     87     if (!IsValidFrame((uptr)caller_frame, stack_top, bottom) ||
     88         !IsAligned((uptr)caller_frame, sizeof(uhwptr)))
     89       break;
     90     uhwptr pc1 = caller_frame[2];
     91 #elif defined(__s390__)
     92     uhwptr pc1 = frame[14];
     93 #else
     94     uhwptr pc1 = frame[1];
     95 #endif
     96     // Let's assume that any pointer in the 0th page (i.e. <0x1000 on i386 and
     97     // x86_64) is invalid and stop unwinding here.  If we're adding support for
     98     // a platform where this isn't true, we need to reconsider this check.
     99     if (pc1 < kPageSize)
    100       break;
    101     if (pc1 != pc) {
    102       trace_buffer[size++] = (uptr) pc1;
    103     }
    104     bottom = (uptr)frame;
    105     frame = GetCanonicFrame((uptr)frame[0], stack_top, bottom);
    106   }
    107 }
    108 
    109 static bool MatchPc(uptr cur_pc, uptr trace_pc, uptr threshold) {
    110   return cur_pc - trace_pc <= threshold || trace_pc - cur_pc <= threshold;
    111 }
    112 
    113 void BufferedStackTrace::PopStackFrames(uptr count) {
    114   CHECK_LT(count, size);
    115   size -= count;
    116   for (uptr i = 0; i < size; ++i) {
    117     trace_buffer[i] = trace_buffer[i + count];
    118   }
    119 }
    120 
    121 uptr BufferedStackTrace::LocatePcInTrace(uptr pc) {
    122   // Use threshold to find PC in stack trace, as PC we want to unwind from may
    123   // slightly differ from return address in the actual unwinded stack trace.
    124   const int kPcThreshold = 350;
    125   for (uptr i = 0; i < size; ++i) {
    126     if (MatchPc(pc, trace[i], kPcThreshold))
    127       return i;
    128   }
    129   return 0;
    130 }
    131 
    132 }  // namespace __sanitizer
    133