[lttng-dev] Capturing User-Level Function Calls/Returns

[Mathieu Desnoyers]

----- On Jul 15, 2020, at 2:28 PM, rostedt rostedt at goodmis.org wrote:

> On Wed, 15 Jul 2020 20:37:16 +0430
> ahmadkhorrami <ahmadkhorrami at ut.ac.ir> wrote:
> 
>> Hi,
>> What is the most efficient way to capture occurrence of a function
>> call/return of a binary program in userspace?
>> It seems the answer is Uprobes. 1) Am I right?
>> But Uprobes use "int" instruction which leads to a switch into kernel
>> mode. 2) Wouldn't it be better to avoid this transition?
>> I'm looking forward to your reply and will be happy to read your
>> opinions.
>> Regards.
> 
> 
> Hi, I believe LTTng has utilities that can help you trace user space
> programs.

Indeed, it is documented here:

https://lttng.org/docs/#doc-liblttng-ust-cyg-profile

If your program is generating function entry/exit at a very
high rate (which goes beyond your available I/O throughput and
lasts longer than the memory you have available for ring buffers),
you will also probably want to use the "blocking-timeout" option
documented at:

https://lttng.org/docs/#doc-enabling-disabling-channels

Thanks,

Mathieu

> 
> I think there's also a users ftrace like utility that Namhyung was
> working on. But I don't know where in the development that is.
> 
> -- Steve

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com