Introducing a function to flush the shadow memory from third-party libraries

[simoatze]

Summary

As discussed with Dmitry (https://goo.gl/SA4izd), I would like to introduce a function to be called from a third-party library to flush the shadow memory.
In particular, we ran some experiments with our tool Archer (an OpenMP data race detector based on Tsan, https://github.com/PRUNER/archer) and flushing the memory at the end of an outer parallel region, slightly increase the runtime overhead, but reduce the memory overhead of about 30%. This feature would come very handy in case of very large OpenMP applications that may cause an "out of memory" exception when checked with Tsan.

[dvyukov]

Submitted in r291346.
Thanks

lib/tsan/rtl/tsan.syms.extra

 __tsan_init
+__tsan_flush_memory
 __tsan_read*
 __tsan_write*
 __tsan_vptr*
 __tsan_func*
 __tsan_atomic*
 __tsan_java*
 __tsan_unaligned*
 __tsan_release
 __tsan_acquire
 __ubsan_*
 Annotate*
 WTFAnnotate*
 RunningOnValgrind
 ValgrindSlowdown

lib/tsan/rtl/tsan_interface.h

 #endif
 
 #if !SANITIZER_GO
 
 // This function should be called at the very beginning of the process,
 // before any instrumented code is executed and before any call to malloc.
 SANITIZER_INTERFACE_ATTRIBUTE void __tsan_init();
 
+SANITIZER_INTERFACE_ATTRIBUTE void __tsan_flush_memory();
+
 SANITIZER_INTERFACE_ATTRIBUTE void __tsan_read1(void *addr);
 SANITIZER_INTERFACE_ATTRIBUTE void __tsan_read2(void *addr);
 SANITIZER_INTERFACE_ATTRIBUTE void __tsan_read4(void *addr);
 SANITIZER_INTERFACE_ATTRIBUTE void __tsan_read8(void *addr);
 SANITIZER_INTERFACE_ATTRIBUTE void __tsan_read16(void *addr);
 
 SANITIZER_INTERFACE_ATTRIBUTE void __tsan_write1(void *addr);
 SANITIZER_INTERFACE_ATTRIBUTE void __tsan_write2(void *addr);

lib/tsan/rtl/tsan_interface.cc

 typedef u16 uint16_t;
 typedef u32 uint32_t;
 typedef u64 uint64_t;
 
 void __tsan_init() {
   Initialize(cur_thread());
 }
 
+void __tsan_flush_memory() {
+  FlushShadowMemory();
+}
+
 void __tsan_read16(void *addr) {
   MemoryRead(cur_thread(), CALLERPC, (uptr)addr, kSizeLog8);
   MemoryRead(cur_thread(), CALLERPC, (uptr)addr + 8, kSizeLog8);
 }
 
 void __tsan_write16(void *addr) {
   MemoryWrite(cur_thread(), CALLERPC, (uptr)addr, kSizeLog8);
   MemoryWrite(cur_thread(), CALLERPC, (uptr)addr + 8, kSizeLog8);