zero-cost SDT probes

[Oliver Pinter]

On 11/22/15, Simon J. Gerraty <sjg at juniper.net> wrote:
> Mark Johnston <markj at freebsd.org> wrote:
>> For the past while I've been experimenting with various ways to
>> implement "zero-cost" SDT DTrace probes. Basically, at the moment an SDT
>> probe site expands to this:
>
> Would it be feasible to compile the probes into the kernel
> as active calls to a registrar function?
> That would eliminate all the complexity of finding PC's
> though you'd probably need to pass extra args to convey the point of the
> probe?
>
> It would hurt boot time a little too - each probe point would make a
> call to register itself (and get overwritten with nops as a reward) but
> very simple?

In opBSD I have already a similar mechanism for SMAP:
https://github.com/opntr/opBSD/commits/op/gsoc2014/master .

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