Cyril Bur [off-list ref] writes:

Its messy but I think the accepted solution for kselftests is to do:

#include "../../../../../usr/include/linux/elf.h"

which I believe will get the headers generated for the target by `make
headers_install` and therefore should match that for which the
kselftests are being compiled.

Don't put the path in the include line though, add it to CFLAGS.

See eg. tools/testing/selftests/powerpc/tm/Makefile:

tm-syscall: CFLAGS += -I../../../../../usr/include


cheers