If you only wish to send a short value to the kernel, I’d suggest using a sysctl (adding a syscall is a much trickier task and probably not necessary in your situation). It’s pretty simple to register one in a kext (but would also work in your own version of the kernel). Amit Singh’s "Mac OS X Internals” book has a very good section explaining how to do that but you can also find all you need in bsd/sys/sysctl.h.

From user space, you can use the `syscl` and `sysctlbyname` functions to set or get the value.

Thanks, Damien

On Dec 28, 2015, at 3:18 PM, Gordo Cath <ds@y23.org> wrote:

Hi, I have my own instance of darwin kernel. I'd like to add a one way function to the kernel where from user space a user function can push a short value to kernel. I don't need to get any data back from the kernel.

What steps do I need to do to accomplish this feat. I tried going through the obvious steps by mimicking the obvious of looking at the pattern of another push pattern api and the linker on the user side wasn't able to see the kernel's side api.

when I re-examined the differences I discovered there are additional files

there is a .def file and a task_codes file

the def file appears to specify some sort of prototype

the task_codes file has some sort of hex number and the api name in it.

what do these two files do?

Is there any sort of documentation that defines what needs to be done to add an api to the kernel?

Alternatively, is there a generic way to post a message to the kernel where I can respond to it in the kernel and act accordingly?

Thanks,

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