[tsan] Add __cxa_guard_acquire hooks to support cooperative scheduling

[krytarowski]

Is this Linux-only?

[dvyukov]

compiler-rt/lib/tsan/rtl/tsan_interceptors.cc

234 ↗

(On Diff #174500)

I think it will be better to call these annotations in a more generic way. Later we may need to use for other functions as well, e.g. phtread_mutex_lock. Internally we call them potentially_blocking_region_begin/end, so if we don't have better naming ideas we could just copy that.

880 ↗

(On Diff #174500)

For my education, why can't at_scope_exit call the function 2 or 3 times? Can't it create 2 or 3 copies of RunOnDestruction, each of which will call the function?

[dvyukov]

compiler-rt/lib/tsan/rtl/tsan_interceptors.cc

880 ↗

(On Diff #174500)

Don't we need to define move constructor for RunOnDestruction, delete copy constructor and all that stuff?

[vitalybuka]

renamed

[vitalybuka]

In D54664#1302072, @krytarowski wrote:

Is this Linux-only?

Should apply to anything with __cxa_guard_acquire interceptor.

compiler-rt/lib/tsan/rtl/tsan_interceptors.cc

880 ↗

(On Diff #174500)

That's https://en.cppreference.com/w/cpp/language/copy_elision
If I read this correctly "required" section applies to this case.

lib/tsan/rtl/tsan_interceptors.cc

for (uptr i = 0; i < n; i++) {
     if (0 == internal_strcmp(s->type, kSuppressionLib))
       libignore()->AddIgnoredLibrary(s->templ);
   }
   if (flags()->ignore_noninstrumented_modules)
     libignore()->IgnoreNoninstrumentedModules(true);
   libignore()->OnLibraryLoaded(0);
 }
 
+// The following two hooks can be used by for cooperative scheduling when
+// locking.
+#ifdef TSAN_EXTERNAL_HOOKS
+void OnPotentiallyBlockingRegionBegin();
+void OnPotentiallyBlockingRegionEnd();
+#else
+SANITIZER_WEAK_CXX_DEFAULT_IMPL void OnPotentiallyBlockingRegionBegin() {}
+SANITIZER_WEAK_CXX_DEFAULT_IMPL void OnPotentiallyBlockingRegionEnd() {}
+#endif
+
 }  // namespace __tsan
 
 static ThreadSignalContext *SigCtx(ThreadState *thr) {
   ThreadSignalContext *ctx = (ThreadSignalContext*)thr->signal_ctx;
   if (ctx == 0 && !thr->is_dead) {
     ctx = (ThreadSignalContext*)MmapOrDie(sizeof(*ctx), "ThreadSignalContext");
     MemoryResetRange(thr, (uptr)&SigCtx, (uptr)ctx, sizeof(*ctx));
     thr->signal_ctx = ctx;

 #else
 #define STDCXX_INTERCEPTOR(rettype, name, ...) \
   extern "C" rettype INTERFACE_ATTRIBUTE name(__VA_ARGS__)
 #endif
 
 // Used in thread-safe function static initialization.
 STDCXX_INTERCEPTOR(int, __cxa_guard_acquire, atomic_uint32_t *g) {
   SCOPED_INTERCEPTOR_RAW(__cxa_guard_acquire, g);
+  OnPotentiallyBlockingRegionBegin();
+  auto on_exit = at_scope_exit(&OnPotentiallyBlockingRegionEnd);
   for (;;) {
     u32 cmp = atomic_load(g, memory_order_acquire);
     if (cmp == 0) {
       if (atomic_compare_exchange_strong(g, &cmp, 1<<16, memory_order_relaxed))
         return 1;
     } else if (cmp == 1) {
       Acquire(thr, pc, (uptr)g);
       return 0;

test/tsan/cxa_guard_acquire.cc

+// RUN: %clangxx_tsan -O1 %s -o %t && %run %t 2>&1 | FileCheck %s
+
+#include <stdio.h>
+
+namespace __tsan {
+
+void OnPotentiallyBlockingRegionBegin() {
+  printf("Enter __cxa_guard_acquire\n");
+}
+
+void OnPotentiallyBlockingRegionEnd() { printf("Exit __cxa_guard_acquire\n"); }
+
+} // namespace __tsan
+
+int main(int argc, char **argv) {
+  // CHECK: Enter main
+  printf("Enter main\n");
+  // CHECK-NEXT: Enter __cxa_guard_acquire
+  // CHECK-NEXT: Exit __cxa_guard_acquire
+  static int s = argc;
+  (void)s;
+  // CHECK-NEXT: Exit main
+  printf("Exit main\n");
+  return 0;
+}