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SubjectRe: [RFC][PATCH] Make ftrace able to trace function return

* Steven Rostedt <rostedt@goodmis.org> wrote:

> gcc -c -finstrument-functions traceme.c

> This is not 5 extra bytes but 27 extra bytes for a total of 32 bytes
> at every function. Also note that this also adds these calls to
> inline functions as well. We could easly stop that by adding
> "notrace" to the inline define (which I've done).
>
> But this would make the patching a bit more difficult (not
> impossible). But it will bloat the image quite a bit.

yeah, i too knew it was expensive, but didnt realize it's this bloaty.
It's a non-starter really.

How reliable can we make Frederic's trampoline approach? Especially
with the opt-in function filters of dyn-ftrace, there's real value in
the trampoline approach IMO (we could display real function cost,
etc.), and the runtime cost should be OK as long we dont probe a ton
of functions all the time. (and it's optional anyway)

Ingo


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