/usr/include/xenomai/asm-x86/ is in libxenomai-dev 2.5.5.2-1ubuntu2.
This file is owned by root:root, with mode 0o755.
..
/usr/include/xenomai/asm-x86/arith.h
/usr/include/xenomai/asm-x86/arith_32.h
/usr/include/xenomai/asm-x86/arith_64.h
/usr/include/xenomai/asm-x86/atomic.h
/usr/include/xenomai/asm-x86/bits/
/usr/include/xenomai/asm-x86/bits/bind.h
/usr/include/xenomai/asm-x86/bits/heap.h
/usr/include/xenomai/asm-x86/bits/init.h
/usr/include/xenomai/asm-x86/bits/init_32.h
/usr/include/xenomai/asm-x86/bits/init_64.h
/usr/include/xenomai/asm-x86/bits/intr.h
/usr/include/xenomai/asm-x86/bits/pod.h
/usr/include/xenomai/asm-x86/bits/pod_32.h
/usr/include/xenomai/asm-x86/bits/pod_64.h
/usr/include/xenomai/asm-x86/bits/sched.h
/usr/include/xenomai/asm-x86/bits/sched_32.h
/usr/include/xenomai/asm-x86/bits/sched_64.h
/usr/include/xenomai/asm-x86/bits/shadow.h
/usr/include/xenomai/asm-x86/bits/shadow_32.h
/usr/include/xenomai/asm-x86/bits/shadow_64.h
/usr/include/xenomai/asm-x86/bits/thread.h
/usr/include/xenomai/asm-x86/bits/thread_32.h
/usr/include/xenomai/asm-x86/bits/thread_64.h
/usr/include/xenomai/asm-x86/bits/timer.h
/usr/include/xenomai/asm-x86/calibration.h
/usr/include/xenomai/asm-x86/features.h
/usr/include/xenomai/asm-x86/features_32.h
/usr/include/xenomai/asm-x86/features_64.h
/usr/include/xenomai/asm-x86/fptest.h
/usr/include/xenomai/asm-x86/hal.h
/usr/include/xenomai/asm-x86/hal_32.h
/usr/include/xenomai/asm-x86/hal_64.h
/usr/include/xenomai/asm-x86/smi.h
/usr/include/xenomai/asm-x86/switch.h
/usr/include/xenomai/asm-x86/switch_32.h
/usr/include/xenomai/asm-x86/switch_64.h
/usr/include/xenomai/asm-x86/syscall.h
/usr/include/xenomai/asm-x86/system.h
/usr/include/xenomai/asm-x86/system_32.h
/usr/include/xenomai/asm-x86/system_64.h
/usr/include/xenomai/asm-x86/wrappers.h
/usr/include/xenomai/asm-x86/wrappers_32.h
/usr/include/xenomai/asm-x86/wrappers_64.h
/usr/include/xenomai/asm-x86/xenomai