Re: Reserving a syscall number

[Chris Wright <chrisw@osdl.org>]

* John Richard Moser (nigelenki@comcast.net) wrote:
> How would one go about having a specific syscall number reserved in
> entry.S?  I'm exploring doing a kill inside the kernel from a detection
> done in userspace, which would allow the executable header of the binary
> to indicate whether the task should be killed or not; if it works, the
> changes will likely not go into mainline, but will still require a
> non-changing syscall index (assuming I understood the syscall manpage
> properly).

To reserve a syscall there needs to be some users and some eventual hope
of merging.  The idea, btw, means anyone can specify the value in the
binary, so it could just as easily be done via prctl or something
similar that makes the out of tree patch easier to maintain.  Although,
I don't actually see the value with the description above.

> On a side note, if a syscall doesn't exist, how would that be detected
> in userspace?

ENOSYS error.

thanks,
-chris
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