Here is the traceback up to the first user source file. The user call was to copyfile(3). Looking in /usr/include/sys/syscall.h this syscall (unix:216) is open_dprotected_np

--36893-- WARNING: unhandled amd64-darwin syscall: unix:216
--36893-- You may be able to write your own handler.
--36893-- Read the file README_MISSING_SYSCALL_OR_IOCTL.
--36893-- Nevertheless we consider this a bug.  Please report
--36893-- it at http://valgrind.org/support/bug_reports.html.
--36893-- UNKNOWN mach_msg unhandled MACH_SEND_TRAILER option (repeated 16 times)
==36893== Syscall param mach_msg("rcv_name") contains uninitialised byte(s)
==36893==    at 0x10169B34A: mach_msg_trap (in /usr/lib/system/libsystem_kernel.dylib)
==36893==    by 0x10169A796: mach_msg (in /usr/lib/system/libsystem_kernel.dylib)
==36893==    by 0x1018373F2: _os_trace_prefs_and_mode_refresh_slow (in /usr/lib/system/libsystem_trace.dylib)
==36893==    by 0x10183A4D3: os_log_shim_enabled (in /usr/lib/system/libsystem_trace.dylib)
==36893==    by 0x10153CEAC: syslog (in /usr/lib/system/libsystem_asl.dylib)
==36893==    by 0x1013DB774: copyfile (in /usr/lib/system/libcopyfile.dylib)
==36893==    by 0x110CDB9E6: uv__fs_work (fs.c:797)