[ASan] Clarify that AsanThread objects are allocated only via mmap(). No functionality change.

llvm-svn: 195840

compiler-rt/lib/asan/asan_allocator.h

@@ -91,16 +91,12 @@ class AsanChunkFifoList: public IntrusiveList<AsanChunk> {
 };
 
 struct AsanThreadLocalMallocStorage {
-  explicit AsanThreadLocalMallocStorage(LinkerInitialized x)
-      { }
-  AsanThreadLocalMallocStorage() {
-    CHECK(REAL(memset));
-    REAL(memset)(this, 0, sizeof(AsanThreadLocalMallocStorage));
-  }
-
   uptr quarantine_cache[16];
   uptr allocator2_cache[96 * (512 * 8 + 16)];  // Opaque.
   void CommitBack();
+ private:
+  // These objects are allocated via mmap() and are zero-initialized.
+  AsanThreadLocalMallocStorage() {}
 };
 
 void *asan_memalign(uptr alignment, uptr size, StackTrace *stack,

compiler-rt/lib/asan/asan_stats.h

@@ -47,9 +47,9 @@ struct AsanStats {
   uptr malloc_large;
   uptr malloc_small_slow;
 
-  // Ctor for global AsanStats (accumulated stats and main thread stats).
+  // Ctor for global AsanStats (accumulated stats for dead threads).
   explicit AsanStats(LinkerInitialized) { }
-  // Default ctor for thread-local stats.
+  // Creates empty stats.
   AsanStats();
 
   void Print();  // Prints formatted stats to stderr.

compiler-rt/lib/asan/asan_thread.cc

@@ -81,7 +81,6 @@ AsanThread *AsanThread::Create(thread_callback_t start_routine,
   AsanThread *thread = (AsanThread*)MmapOrDie(size, __FUNCTION__);
   thread->start_routine_ = start_routine;
   thread->arg_ = arg;
-  thread->context_ = 0;
 
   return thread;
 }

compiler-rt/lib/asan/asan_thread.h

@@ -101,14 +101,15 @@ class AsanThread {
   // True is this thread is currently unwinding stack (i.e. collecting a stack
   // trace). Used to prevent deadlocks on platforms where libc unwinder calls
   // malloc internally. See PR17116 for more details.
-  bool isUnwinding() const { return unwinding; }
-  void setUnwinding(bool b) { unwinding = b; }
+  bool isUnwinding() const { return unwinding_; }
+  void setUnwinding(bool b) { unwinding_ = b; }
 
   AsanThreadLocalMallocStorage &malloc_storage() { return malloc_storage_; }
   AsanStats &stats() { return stats_; }
 
  private:
-  AsanThread() : unwinding(false) {}
+  // NOTE: There is no AsanThread constructor. It is allocated
+  // via mmap() and *must* be valid in zero-initialized state.
   void SetThreadStackAndTls();
   void ClearShadowForThreadStackAndTLS();
   FakeStack *AsyncSignalSafeLazyInitFakeStack();
@@ -116,18 +117,18 @@ class AsanThread {
   AsanThreadContext *context_;
   thread_callback_t start_routine_;
   void *arg_;
-  uptr  stack_top_;
-  uptr  stack_bottom_;
+  uptr stack_top_;
+  uptr stack_bottom_;
   // stack_size_ == stack_top_ - stack_bottom_;
   // It needs to be set in a async-signal-safe manner.
-  uptr  stack_size_;
+  uptr stack_size_;
   uptr tls_begin_;
   uptr tls_end_;
 
   FakeStack *fake_stack_;
   AsanThreadLocalMallocStorage malloc_storage_;
   AsanStats stats_;
-  bool unwinding;
+  bool unwinding_;
 };
 
 // ScopedUnwinding is a scope for stacktracing member of a context