From 3e8467b8b985efcd11c667d50efa69920cd3b108 Mon Sep 17 00:00:00 2001
From: Alexey Samsonov <samsonov@google.com>
Date: Tue, 4 Mar 2014 12:21:28 +0000
Subject: [PATCH] Avoid doing any work when unwinding stack traces with 0 or 1
 frame

llvm-svn: 202837
---
 .../lib/sanitizer_common/sanitizer_linux_libcdep.cc | 10 ++++------
 .../lib/sanitizer_common/sanitizer_stacktrace.cc    |  5 +----
 .../sanitizer_stacktrace_libcdep.cc                 | 13 +++++++++++--
 compiler-rt/lib/sanitizer_common/sanitizer_win.cc   |  1 +
 4 files changed, 17 insertions(+), 12 deletions(-)

diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_linux_libcdep.cc b/compiler-rt/lib/sanitizer_common/sanitizer_linux_libcdep.cc
index af6eb06a122b..7f810ed0b67d 100644
--- a/compiler-rt/lib/sanitizer_common/sanitizer_linux_libcdep.cc
+++ b/compiler-rt/lib/sanitizer_common/sanitizer_linux_libcdep.cc
@@ -223,9 +223,8 @@ _Unwind_Reason_Code Unwind_Trace(struct _Unwind_Context *ctx, void *param) {
 }
 
 void StackTrace::SlowUnwindStack(uptr pc, uptr max_depth) {
+  CHECK_GE(max_depth, 2);
   size = 0;
-  if (max_depth == 0)
-    return;
   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.
@@ -239,14 +238,12 @@ void StackTrace::SlowUnwindStack(uptr pc, uptr max_depth) {
 
 void StackTrace::SlowUnwindStackWithContext(uptr pc, void *context,
                                             uptr max_depth) {
+  CHECK_GE(max_depth, 2);
   if (!unwind_backtrace_signal_arch) {
     SlowUnwindStack(pc, max_depth);
     return;
   }
 
-  size = 0;
-  if (max_depth == 0) return;
-
   void *map = acquire_my_map_info_list();
   CHECK(map);
   InternalScopedBuffer<backtrace_frame_t> frames(kStackTraceMax);
@@ -256,8 +253,9 @@ void StackTrace::SlowUnwindStackWithContext(uptr pc, void *context,
                                           /* ignore_depth */ 0, max_depth);
   release_my_map_info_list(map);
   if (res < 0) return;
-  CHECK((uptr)res <= kStackTraceMax);
+  CHECK_LE((uptr)res, kStackTraceMax);
 
+  size = 0;
   // +2 compensate for libcorkscrew unwinder returning addresses of call
   // instructions instead of raw return addresses.
   for (sptr i = 0; i < res; ++i)
diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_stacktrace.cc b/compiler-rt/lib/sanitizer_common/sanitizer_stacktrace.cc
index dbacedc14c12..df1475737479 100644
--- a/compiler-rt/lib/sanitizer_common/sanitizer_stacktrace.cc
+++ b/compiler-rt/lib/sanitizer_common/sanitizer_stacktrace.cc
@@ -36,10 +36,7 @@ uptr StackTrace::GetCurrentPc() {
 void StackTrace::FastUnwindStack(uptr pc, uptr bp,
                                  uptr stack_top, uptr stack_bottom,
                                  uptr max_depth) {
-  if (max_depth == 0) {
-    size = 0;
-    return;
-  }
+  CHECK_GE(max_depth, 2);
   trace[0] = pc;
   size = 1;
   uptr *frame = (uptr *)bp;
diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_stacktrace_libcdep.cc b/compiler-rt/lib/sanitizer_common/sanitizer_stacktrace_libcdep.cc
index 4784c200f032..d7d5e9e4a2c5 100644
--- a/compiler-rt/lib/sanitizer_common/sanitizer_stacktrace_libcdep.cc
+++ b/compiler-rt/lib/sanitizer_common/sanitizer_stacktrace_libcdep.cc
@@ -66,6 +66,17 @@ void StackTrace::PrintStack(const uptr *addr, uptr size) {
 void StackTrace::Unwind(uptr max_depth, uptr pc, uptr bp, void *context,
                         uptr stack_top, uptr stack_bottom,
                         bool request_fast_unwind) {
+  top_frame_bp = (max_depth > 0) ? bp : 0;
+  // Avoid doing any work for small max_depth.
+  if (max_depth == 0) {
+    size = 0;
+    return;
+  }
+  if (max_depth == 1) {
+    size = 1;
+    trace[0] = pc;
+    return;
+  }
   if (!WillUseFastUnwind(request_fast_unwind)) {
     if (context)
       SlowUnwindStackWithContext(pc, context, max_depth);
@@ -74,8 +85,6 @@ void StackTrace::Unwind(uptr max_depth, uptr pc, uptr bp, void *context,
   } else {
     FastUnwindStack(pc, bp, stack_top, stack_bottom, max_depth);
   }
-
-  top_frame_bp = size ? bp : 0;
 }
 
 }  // namespace __sanitizer
diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_win.cc b/compiler-rt/lib/sanitizer_common/sanitizer_win.cc
index 162f37ddce2e..21f92b3b6130 100644
--- a/compiler-rt/lib/sanitizer_common/sanitizer_win.cc
+++ b/compiler-rt/lib/sanitizer_common/sanitizer_win.cc
@@ -417,6 +417,7 @@ void GetThreadStackAndTls(bool main, uptr *stk_addr, uptr *stk_size,
 }
 
 void StackTrace::SlowUnwindStack(uptr pc, uptr max_depth) {
+  CHECK_GE(max_depth, 2);
   // FIXME: CaptureStackBackTrace might be too slow for us.
   // FIXME: Compare with StackWalk64.
   // FIXME: Look at LLVMUnhandledExceptionFilter in Signals.inc