[SanitizerCoverage] Add stack depth tracing instrumentation.

Summary:
Augment SanitizerCoverage to insert maximum stack depth tracing for
use by libFuzzer.  The new instrumentation is enabled by the flag
-fsanitize-coverage=stack-depth and is compatible with the existing
trace-pc-guard coverage.  The user must also declare the following
global variable in their code:
  thread_local uintptr_t __sancov_lowest_stack

https://bugs.llvm.org/show_bug.cgi?id=33857

Reviewers: vitalybuka, kcc

Reviewed By: vitalybuka

Subscribers: kubamracek, hiraditya, cfe-commits, llvm-commits

Differential Revision: https://reviews.llvm.org/D36839

llvm-svn: 311186

1 files changed, 3 insertions, 14 deletions

diff --git a/llvm/lib/Fuzzer/FuzzerTracePC.h b/llvm/lib/Fuzzer/FuzzerTracePC.h
index 40827b32828..56f1820f79e 100644
--- a/llvm/lib/Fuzzer/FuzzerTracePC.h
+++ b/llvm/lib/Fuzzer/FuzzerTracePC.h
@@ -120,19 +120,8 @@ class TracePC {
     return PCs()[Idx];
   }
 
-  void RecordCurrentStack() {
-    uintptr_t Stack = GetCurrentStack();
-    if (Stack < LowestStack)
-      LowestStack = Stack;
-  }
-  void RecordInitialStack() {
-    InitialStack = GetCurrentStack();
-    LowestStack = InitialStack;
-  }
-  uintptr_t GetCurrentStack() const {
-    return reinterpret_cast<uintptr_t>(__builtin_frame_address(0));
-  }
-  uintptr_t GetMaxStackOffset() const { return InitialStack - LowestStack; }
+  void RecordInitialStack();
+  uintptr_t GetMaxStackOffset() const;
 
   template<class CallBack>
   void ForEachObservedPC(CallBack CB) {
@@ -167,7 +156,7 @@ private:
   std::set<uintptr_t> ObservedPCs;
 
   ValueBitMap ValueProfileMap;
-  uintptr_t InitialStack, LowestStack;  // Assume stack grows down.
+  uintptr_t InitialStack;
 };
 
 template <class Callback>