From cf6ac12e23f162e93e291e66f0852b2ccf06ce62 Mon Sep 17 00:00:00 2001
From: Alexey Samsonov <samsonov@google.com>
Date: Wed, 13 Nov 2013 15:20:10 +0000
Subject: [PATCH] [Sanitizer] Use same PC threshold in slow unwinder on all
 platforms

llvm-svn: 194580
---
 .../lib/sanitizer_common/sanitizer_linux_libcdep.cc        | 2 +-
 compiler-rt/lib/sanitizer_common/sanitizer_stacktrace.cc   | 7 +++++--
 compiler-rt/lib/sanitizer_common/sanitizer_stacktrace.h    | 2 +-
 3 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_linux_libcdep.cc b/compiler-rt/lib/sanitizer_common/sanitizer_linux_libcdep.cc
index eba6eb9682fe..f6de9f1f815a 100644
--- a/compiler-rt/lib/sanitizer_common/sanitizer_linux_libcdep.cc
+++ b/compiler-rt/lib/sanitizer_common/sanitizer_linux_libcdep.cc
@@ -161,7 +161,7 @@ void StackTrace::SlowUnwindStack(uptr pc, uptr max_depth) {
   UnwindTraceArg arg = {this, Min(max_depth + 1, kStackTraceMax)};
   _Unwind_Backtrace(Unwind_Trace, &arg);
   // We need to pop a few frames so that pc is on top.
-  uptr to_pop = LocatePcInTrace(pc, 64, 6);
+  uptr to_pop = LocatePcInTrace(pc, 6);
   // trace[0] belongs to the current function so we always pop it.
   if (to_pop == 0)
     to_pop = 1;
diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_stacktrace.cc b/compiler-rt/lib/sanitizer_common/sanitizer_stacktrace.cc
index f03490b8c4eb..8e591189dc5c 100644
--- a/compiler-rt/lib/sanitizer_common/sanitizer_stacktrace.cc
+++ b/compiler-rt/lib/sanitizer_common/sanitizer_stacktrace.cc
@@ -152,9 +152,12 @@ static bool MatchPc(uptr cur_pc, uptr trace_pc, uptr threshold) {
 }
 
 uptr
-StackTrace::LocatePcInTrace(uptr pc, uptr pc_threshold, uptr max_pc_depth) {
+StackTrace::LocatePcInTrace(uptr pc, uptr max_pc_depth) {
+  // 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 = 64;
   for (uptr i = 0; i < max_pc_depth && i < size; ++i) {
-    if (MatchPc(pc, trace[i], pc_threshold))
+    if (MatchPc(pc, trace[i], kPcThreshold))
       return i;
   }
   return 0;
diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_stacktrace.h b/compiler-rt/lib/sanitizer_common/sanitizer_stacktrace.h
index 88f0a03b1117..73474e65b6a7 100644
--- a/compiler-rt/lib/sanitizer_common/sanitizer_stacktrace.h
+++ b/compiler-rt/lib/sanitizer_common/sanitizer_stacktrace.h
@@ -69,7 +69,7 @@ struct StackTrace {
                        uptr max_depth);
   void SlowUnwindStack(uptr pc, uptr max_depth);
   void PopStackFrames(uptr count);
-  uptr LocatePcInTrace(uptr pc, uptr pc_threshold = 0, uptr max_pc_depth = -1);
+  uptr LocatePcInTrace(uptr pc, uptr max_pc_depth = -1);
 };
 
 }  // namespace __sanitizer