[compiler-rt] r224834 - tsan: fix trace initialization during thread id reuse

[Dmitry Vyukov]

Author: dvyukov
Date: Thu Dec 25 04:32:25 2014
New Revision: 224834

URL: http://llvm.org/viewvc/llvm-project?rev=224834&view=rev
Log:
tsan: fix trace initialization during thread id reuse

The current code leaves the first event in the trace part uninitialized
(from the previous thread). It can cause unpredictable behavior
during stack/mutexset restoration.
Initialize the first event to a fake harmless memory access.


Modified:
    compiler-rt/trunk/lib/tsan/rtl/tsan_rtl_thread.cc

Modified: compiler-rt/trunk/lib/tsan/rtl/tsan_rtl_thread.cc
URL: http://llvm.org/viewvc/llvm-project/compiler-rt/trunk/lib/tsan/rtl/tsan_rtl_thread.cc?rev=224834&r1=224833&r2=224834&view=diff
==============================================================================
--- compiler-rt/trunk/lib/tsan/rtl/tsan_rtl_thread.cc (original)
+++ compiler-rt/trunk/lib/tsan/rtl/tsan_rtl_thread.cc Thu Dec 25 04:32:25 2014
@@ -111,15 +111,13 @@ void ThreadContext::OnStarted(void *arg)
     thr->dd_pt = ctx->dd->CreatePhysicalThread();
     thr->dd_lt = ctx->dd->CreateLogicalThread(unique_id);
   }
+  thr->fast_state.SetHistorySize(flags()->history_size);
+  // Commit switch to the new part of the trace.
+  // TraceAddEvent will reset stack0/mset0 in the new part for us.
+  TraceAddEvent(thr, thr->fast_state, EventTypeMop, 0);
+
   thr->fast_synch_epoch = epoch0;
   AcquireImpl(thr, 0, &sync);
-  thr->fast_state.SetHistorySize(flags()->history_size);
-  const uptr trace = (epoch0 / kTracePartSize) % TraceParts();
-  Trace *thr_trace = ThreadTrace(thr->tid);
-  TraceHeader *hdr = &thr_trace->headers[trace];
-  hdr->epoch0 = epoch0;
-  ObtainCurrentStack(thr, 0, &hdr->stack0);
-  hdr->mset0 = thr->mset;
   StatInc(thr, StatSyncAcquire);
   sync.Reset(&thr->clock_cache);
   DPrintf("#%d: ThreadStart epoch=%zu stk_addr=%zx stk_size=%zx "