This is xnu-8019. See this file in:
Directory listing for xnu-8019//bsd/dev/i386
conf.c
cons.c
cpu_copy_in_cksum.s
cpu_memcmp_mask.s
dis_tables.c
dtrace_isa.c
dtrace_subr_x86.c
fasttrap_isa.c
fasttrap_regset.h
fbt_x86.c
instr_size.c
kern_machdep.c
km.c
sdt_x86.c
stubs.c
sysctl.c
systemcalls.c
unix_signal.c