[tsan] Fix warnings in tsan_interceptors.cc from expansion of variadic macros

[xiaobai]

Summary

C99 technically requires the rest arguments to be used in C variadic macros. This presents a
problem with the macro SCOPED_TSAN_INTERCEPTOR when func takes no arguments.
This happens with the function pause. Like other void argument functions, we pass in a fake argument to avoid this warning.

[fjricci]

lib/sanitizer_common/sanitizer_common_defs.h

16 ↗

(On Diff #119732)

I think this should go in sanitizer_internal_defs.h

lib/tsan/rtl/tsan_interceptors.h

59 ↗

(On Diff #119732)

Is it possible to solve this with ##__VA_ARGS__ instead? Not super familiar with how all of this stuff works though.

[xiaobai]

lib/tsan/rtl/tsan_interceptors.h

59 ↗

(On Diff #119732)

Yes, that is one way to solve this. Unfortunately, that is a GNU extension, and is not considered portable. My solution should work on any platform correctly.

[xiaobai]

Moving STRINGIFY macro to sanitier_internal_defs.h

[fjricci]

lib/tsan/rtl/tsan_interceptors.h

59 ↗

(On Diff #119732)

Looks like clang supports it, and I believe that we don't support tsan on windows (so don't need to worry about MSVC). But I'll defer to other reviewers on the best way.

[xiaobai]

lib/tsan/rtl/tsan_interceptors.h

59 ↗

(On Diff #119732)

Sure, I think it's totally fine to use the GNU extension. However, if supporting tsan on windows is something people want, this solution will probably be better.

[dvyukov]

Does the same requirement present in C++11?

This fix for a warning looks too complex to me.
I have hard time understanding how it works. I afraid if I even need to modify this code. It seems to be very subtly different from what we have now because ARGS_ZERO still expands to nothing.
I would prefer if we just do what we do for all other void interceptors -- append 'int fake' argument.

[xiaobai]

Pass a fake argument instead of crafting complex variadic macros

[xiaobai]

I'm not sure if the same requirement is present in C++11.

I tried what you suggested based off of the other void argument functions that use a fake argument, which seems to work well here too. Much better than the complex macros! :)

[dvyukov]

I will commit this later today. Thanks.

[dvyukov]

Landed in http://llvm.org/viewvc/llvm-project?view=revision&revision=316558

lib/tsan/rtl/tsan_interceptors.cc

 
 TSAN_INTERCEPTOR(int, nanosleep, void *req, void *rem) {
   SCOPED_TSAN_INTERCEPTOR(nanosleep, req, rem);
   int res = BLOCK_REAL(nanosleep)(req, rem);
   AfterSleep(thr, pc);
   return res;
 }
 
-TSAN_INTERCEPTOR(int, pause) {
-  SCOPED_TSAN_INTERCEPTOR(pause);
-  return BLOCK_REAL(pause)();
+TSAN_INTERCEPTOR(int, pause, int fake) {
+  SCOPED_TSAN_INTERCEPTOR(pause, fake);
+  return BLOCK_REAL(pause)(fake);
 }
 
 // The sole reason tsan wraps atexit callbacks is to establish synchronization
 // between callback setup and callback execution.
 struct AtExitCtx {
   void (*f)();
   void *arg;
 };