tsan: fix epoll_pwait2 interceptor

[dvyukov]

Summary

epoll_pwait2 is new and may not be present in libc and/or kernel.
Since we effectively add it to libc (as will be probed by the program
using dlsym or a weak function pointer) we need to handle the case
when it's not present in the actual libc.

[melver]

compiler-rt/lib/tsan/rtl/tsan_interceptors_posix.cpp

1954

sanitizer_posix.cpp already includes things like errno.h - can we include errno.h and use ENOSYS?

Also is this return value correct?

On success, epoll_wait() returns the number of file descriptors
ready for the requested I/O, or zero if no file descriptor became
ready during the requested timeout milliseconds.  On failure,
epoll_wait() returns -1 and errno is set to indicate the error.

https://man7.org/linux/man-pages/man2/epoll_wait.2.html

[dvyukov]

fixed return value

[dvyukov]

Also is this return value correct?

Good point!

Somehow the internal test I was using to check this passed...

sanitizer_posix.cpp already includes things like errno.h - can we include errno.h and use ENOSYS?

We avoided including any system headers to avoid conflicts in definitions and redefinitions. I would do it differently (with asm aliases), but that's how we do it now.
I see there is already sanitizer_common/sanitizer_errno_codes.h, so I extended it.

PTAL

compiler-rt/lib/sanitizer_common/sanitizer_errno_codes.h

 #define SANITIZER_ERRNO_CODES_H
 
 namespace __sanitizer {
 
 #define errno_ENOMEM 12
 #define errno_EBUSY 16
 #define errno_EINVAL 22
 #define errno_ENAMETOOLONG 36
+#define errno_ENOSYS 38
 
 // Those might not present or their value differ on different platforms.
 extern const int errno_EOWNERDEAD;
 
 }  // namespace __sanitizer
 
 #endif  // SANITIZER_ERRNO_CODES_H

compiler-rt/lib/tsan/rtl/tsan_interceptors_posix.cpp

TSAN_INTERCEPTOR(int, epoll_pwait, int epfd, void *ev, int cnt, int timeout,
   int res = BLOCK_REAL(epoll_pwait)(epfd, ev, cnt, timeout, sigmask);
   if (res > 0 && epfd >= 0)
     FdAcquire(thr, pc, epfd);
   return res;
 }
 
 TSAN_INTERCEPTOR(int, epoll_pwait2, int epfd, void *ev, int cnt, void *timeout,
                  void *sigmask) {
-  SCOPED_TSAN_INTERCEPTOR(epoll_pwait2, epfd, ev, cnt, timeout, sigmask);
+  SCOPED_INTERCEPTOR_RAW(epoll_pwait2, epfd, ev, cnt, timeout, sigmask);
+  // This function is new and may not be present in libc and/or kernel.
+  // Since we effectively add it to libc (as will be probed by the program
+  // using dlsym or a weak function pointer) we need to handle the case
+  // when it's not present in the actual libc.
+  if (!REAL(epoll_pwait2)) {
+    errno = errno_ENOSYS;
+    return -1;
+  }
+  if (MustIgnoreInterceptor(thr))
+    REAL(epoll_pwait2)(epfd, ev, cnt, timeout, sigmask);
   if (epfd >= 0)
     FdAccess(thr, pc, epfd);
   int res = BLOCK_REAL(epoll_pwait2)(epfd, ev, cnt, timeout, sigmask);
   if (res > 0 && epfd >= 0)
     FdAcquire(thr, pc, epfd);
   return res;
 }