Re: [PATCH 0/11] LTTng-core (basic tracing infrastructure) 0.5.108


* Nicholas Miell <nmiell@xxxxxxxxxxx> wrote:

You're going to want to be able to trace every function in the kernel,
which means they'd all need a __trace -- and in that case, a
-fpad-functions-for-tracing gcc option would make more sense then
per-function attributes.

the __trace attribute would be a _specific_ replacement for a _specific_
static markup at the entry of a function. So no, we would not want to
add __trace to _every_ function in the kernel: only those which get
commonly traced. And note that SystemTap can trace the rest too, just
with slighly higher overhead.

In that sense __trace is not an enabling infrastructure, it's a
performance tuning infrastructure.

The option could also insert NOPs before RETs, not just before the
prologue so that function returns are equally easy to trace. (It might
also inhibit tail calls, assuming being able to trace all function
returns is more important than that optimization.)

yeah. __trace_entry and __trace_exit [or both] attributes. Makes sense.

And SystemTap can already hook into sock_sendmsg() (or any other
function) and examine it's arguments -- all of this GCC extension talk
is just performance enhancement.

yes, yes, yes, exactly!!! Finally someone reads my mails and understands
my points. There's hope! ;)

Ingo
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