/usr/include/xenomai/asm-blackfin/ is in libxenomai-dev 2.6.4+dfsg-0.2.
This file is owned by root:root, with mode 0o755.
..
/usr/include/xenomai/asm-blackfin/arith.h
/usr/include/xenomai/asm-blackfin/atomic.h
/usr/include/xenomai/asm-blackfin/atomic_asm.h
/usr/include/xenomai/asm-blackfin/bits/
/usr/include/xenomai/asm-blackfin/bits/bind.h
/usr/include/xenomai/asm-blackfin/bits/heap.h
/usr/include/xenomai/asm-blackfin/bits/init.h
/usr/include/xenomai/asm-blackfin/bits/intr.h
/usr/include/xenomai/asm-blackfin/bits/pod.h
/usr/include/xenomai/asm-blackfin/bits/sched.h
/usr/include/xenomai/asm-blackfin/bits/shadow.h
/usr/include/xenomai/asm-blackfin/bits/thread.h
/usr/include/xenomai/asm-blackfin/bits/timer.h
/usr/include/xenomai/asm-blackfin/calibration.h
/usr/include/xenomai/asm-blackfin/features.h
/usr/include/xenomai/asm-blackfin/fptest.h
/usr/include/xenomai/asm-blackfin/hal.h
/usr/include/xenomai/asm-blackfin/syscall.h
/usr/include/xenomai/asm-blackfin/system.h
/usr/include/xenomai/asm-blackfin/tsc.h
/usr/include/xenomai/asm-blackfin/wrappers.h