tsan: add a test for stack init race

[dvyukov]

Summary

Depends on D110538.

[kda]

Looks like this is breaking the bot: https://lab.llvm.org/buildbot/#/builders/70/builds/12193
Prepping revert...

To reproduce, follow directions here: https://github.com/google/sanitizers/wiki/SanitizerBotReproduceBuild

log snippet:

-- Testing: 434 tests, 80 workers --
Testing:  0.. 10.. 20.. 30.. 40.. 50.. 60.. 70.. 80..
FAIL: ThreadSanitizer-x86_64 :: stack_race3.cpp (389 of 434)
******************** TEST 'ThreadSanitizer-x86_64 :: stack_race3.cpp' FAILED ********************
Script:
--
: 'RUN: at line 1';      /b/sanitizer-x86_64-linux-autoconf/build/tsan_debug_build/./bin/clang  --driver-mode=g++ -fsanitize=thread -Wall  -m64   -gline-tables-only -I/b/sanitizer-x86_64-linux-autoconf/build/llvm-project/compiler-rt/test/tsan/../ -std=c++11 -I/b/sanitizer-x86_64-linux-autoconf/build/llvm-project/compiler-rt/test/tsan/../ -nostdinc++ -I/b/sanitizer-x86_64-linux-autoconf/build/tsan_debug_build/tools/clang/runtime/compiler-rt-bins/lib/tsan/libcxx_tsan_x86_64/include/c++/v1 -O1 /b/sanitizer-x86_64-linux-autoconf/build/llvm-project/compiler-rt/test/tsan/stack_race3.cpp -o /b/sanitizer-x86_64-linux-autoconf/build/tsan_debug_build/tools/clang/runtime/compiler-rt-bins/test/tsan/X86_64Config/Output/stack_race3.cpp.tmp && /b/sanitizer-x86_64-linux-autoconf/build/llvm-project/compiler-rt/test/tsan/deflake.bash 10  /b/sanitizer-x86_64-linux-autoconf/build/tsan_debug_build/tools/clang/runtime/compiler-rt-bins/test/tsan/X86_64Config/Output/stack_race3.cpp.tmp | FileCheck /b/sanitizer-x86_64-linux-autoconf/build/llvm-project/compiler-rt/test/tsan/stack_race3.cpp
--
Exit Code: 2
Command Output (stderr):
--
FileCheck error: '<stdin>' is empty.
FileCheck command line:  FileCheck /b/sanitizer-x86_64-linux-autoconf/build/llvm-project/compiler-rt/test/tsan/stack_race3.cpp
--
********************
Testing:  0.. 10.. 20.. 30.. 40.. 50.. 60.. 70.. 80.. 90.. 
********************
Failed Tests (1):
  ThreadSanitizer-x86_64 :: stack_race3.cpp

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) {

compiler-rt/test/tsan/stack_race3.cpp

+// RUN: %clangxx_tsan -O1 %s -o %t && %deflake %run %t | FileCheck %s
+
+// Race with initial stack initialization:
+// there is no explicit second write,
+// but the stack variable is published unsafely.
+#include "test.h"
+
+long *P;
+
+void *Thread(void *a) {
+  long X;
+  __atomic_store_n(&P, &X, __ATOMIC_RELAXED);
+  barrier_wait(&barrier);
+  barrier_wait(&barrier);
+  return 0;
+}
+
+int main() {
+  barrier_init(&barrier, 2);
+  pthread_t t;
+  pthread_create(&t, NULL, Thread, NULL);
+  barrier_wait(&barrier);
+  long *p = __atomic_load_n(&P, __ATOMIC_RELAXED);
+  *p = 42;
+  barrier_wait(&barrier);
+  pthread_join(t, 0);
+}
+
+// CHECK: WARNING: ThreadSanitizer: data race
+// CHECK:   Write of size 8 at {{.*}} by main thread:
+// CHECK:     #0 main
+// CHECK:   Previous write of size 8 at {{.*}} by thread T1:
+// CHECK:     #0 __tsan_stack_initialization
+// CHECK:   Location is stack of thread T1