Re: gcc plugin for instrumenting individual functions

Re: gcc plugin for instrumenting individual functions

[Jonathan Rajotte-Julien]

Hi,

For those at home wondering why this would be relevant to lttng,
lttng-ust comes with a utility shared object allowing you to leverage the
-finstrument-function sites to hook lttng tracepoints [1].

[1] https://lttng.org/man/3/lttng-ust-cyg-profile/v2.10/

Thanks Christophe for this contribution.

Do you know why GCC does not support this out of the box? Is this something that
could be presented to the GCC community?

Cheers

On Mon, Jul 29, 2019 at 08:56:15PM +0200, Christophe Bédard wrote:
> Hi,
> 
> Sharing this just in case it can help someone!
> 
> gcc only lets you disable instrumentation, using the
> `no_instrument_function` attribute, or by matching file names. It does not
> let you explicitly choose the individual functions you want to instrument.
> 
> I've searched many times for a way to do it, but never found anything for
> some reason, so I wrote this plugin:
> https://github.com/christophebedard/instrument-attribute-gcc-plugin
> 
> It simply enables instrumentation for functions with the
> `instrument_function` attribute, and disables instrumentation for all other
> functions.
> 
> 
> Christophe

> _______________________________________________
> lttng-dev mailing list
> lttng-dev@lists.lttng.org
> https://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev


-- 
Jonathan Rajotte-Julien
EfficiOS

Re: gcc plugin for instrumenting individual functions

[Christophe Bédard]

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Hi,

On Mon, 29 Jul 2019 at 21:23, Jonathan Rajotte-Julien <
jonathan.rajotte-julien@efficios.com> wrote:

> Hi,
>
> For those at home wondering why this would be relevant to lttng,
> lttng-ust comes with a utility shared object allowing you to leverage the
> -finstrument-function sites to hook lttng tracepoints [1].
>
> [1] https://lttng.org/man/3/lttng-ust-cyg-profile/v2.10/
>
>
Thank you for providing some context!


> Thanks Christophe for this contribution.
>
> Do you know why GCC does not support this out of the box?
>

I'm not sure. I looked at the the relevant parts of the gcc codebase, and
came to the conclusion that it just wasn't written with this feature in
mind (which is why the plugin uses a sort of workaround).

Is this something that
> could be presented to the GCC community?


If people think it should be presented!


Christophe

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gcc plugin for instrumenting individual functions

[Christophe Bédard]

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Hi,

Sharing this just in case it can help someone!

gcc only lets you disable instrumentation, using the
`no_instrument_function` attribute, or by matching file names. It does not
let you explicitly choose the individual functions you want to instrument.

I've searched many times for a way to do it, but never found anything for
some reason, so I wrote this plugin:
https://github.com/christophebedard/instrument-attribute-gcc-plugin

It simply enables instrumentation for functions with the
`instrument_function` attribute, and disables instrumentation for all other
functions.


Christophe

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