tsan: print a meaningful frame for stack races

[dvyukov]

Summary

Depends on D110631.

compiler-rt/lib/tsan/rtl/tsan_rtl_thread.cpp

if (!args->thr)  // GCD workers don't have a parent thread.
     return;
   args->thr->fast_state.IncrementEpoch();
   // Can't increment epoch w/o writing to the trace as well.
   TraceAddEvent(args->thr, args->thr->fast_state, EventTypeMop, 0);
   ReleaseImpl(args->thr, 0, &sync);
   creation_stack_id = CurrentStackId(args->thr, args->pc);
 }
 
+extern "C" void __tsan_stack_initialization() {}
+
 struct OnStartedArgs {
   ThreadState *thr;
   uptr stk_addr;
   uptr stk_size;
   uptr tls_addr;
   uptr tls_size;
 };
 
#if !SANITIZER_GO
   if (ctx->after_multithreaded_fork) {
     thr->ignore_interceptors++;
     ThreadIgnoreBegin(thr, 0);
     ThreadIgnoreSyncBegin(thr, 0);
   }
 #endif
 
 #if !SANITIZER_GO
+  // Don't imitate stack/TLS writes for the main thread,
+  // because its initialization is synchronized with all
+  // subsequent threads anyway.
   if (tid != kMainTid) {
-    if (stk_addr && stk_size)
-      MemoryRangeImitateWrite(thr, /*pc=*/1, stk_addr, stk_size);
+    if (stk_addr && stk_size) {
+      const uptr pc = StackTrace::GetNextInstructionPc(
+          reinterpret_cast<uptr>(__tsan_stack_initialization));
+      MemoryRangeImitateWrite(thr, pc, stk_addr, stk_size);
+    }
 
     if (tls_addr && tls_size)
       ImitateTlsWrite(thr, tls_addr, tls_size);
   }
 #endif
 }
 
 void ThreadContext::OnStarted(void *arg) {