Normally a syscall would check the current privilege level and then
decide to go to _impl_<syscall> directly or go through a
_handler_<syscall>.
__ZEPHYR_SUPERVISOR__ is a compiler optimization flag which will
make all the system calls from the driver files directly link
to the _impl_<syscall>. Thereby reducing the overhead of checking the
privileges.
In the previous implementation all the source files would be compiled
by zephyr_source() rule. This means that zephyr_* is a catchall CMake
library for source files that can be built purely with the include
paths, defines, and other compiler flags that all zephyr source
files uses. This states that adding one extra compiler flag for only
one complete directory would fail.
This limitation can be overcome by using zephyr_libray* APIs. This
creates a library for the required directories and it also supports
directory level properties.
Hence we use zephyr_library* to create a new library with
macro _ZEPHYR_SUPERVISOR_ for the optimization.
Signed-off-by: Adithya Baglody <adithya.nagaraj.baglody@intel.com>
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