'\" t

.\"     Title: lttng-ust-dl

.\"    Author: [see the "AUTHORS" section]

.\" Generator: DocBook XSL Stylesheets v1.78.1 <http://docbook.sf.net/>

.\"      Date: 06/05/2016

.\"    Manual: LTTng Manual

.\"    Source: LTTng 2.9.0-pre

.\"  Language: English

.\"

.TH "LTTNG\-UST\-DL" "3" "06/05/2016" "LTTng 2\&.9\&.0\-pre" "LTTng Manual"

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.SH "NAME"

lttng-ust-cyg-profile \- Function tracing (LTTng\-UST helper)

.SH "SYNOPSIS"

.sp

Compile your application with compiler option \fB-finstrument-functions\fR\&.

.sp

Launch your application by preloading \fBliblttng-ust-cyg-profile-fast.so\fR for fast function tracing:

.sp

.nf

\fBLD_PRELOAD=liblttng\-ust\-cyg\-profile\-fast\&.so\fR my\-app

.fi

.sp

Launch your application by preloading \fBliblttng-ust-cyg-profile.so\fR for slower, more verbose function tracing:

.sp

.nf

\fBLD_PRELOAD=liblttng\-ust\-cyg\-profile\&.so\fR my\-app

.fi

.SH "DESCRIPTION"

.sp

When the \fBliblttng-ust-cyg-profile.so\fR or the \fBliblttng-ust-cyg-profile-fast.so\fR library is preloaded before a given application starts, all function entry and return points are traced by LTTng\-UST (see \fBlttng-ust\fR(3)), provided said application was compiled with the \fB-finstrument-functions\fR compiler option\&.

.sp

See \fBlttng\fR(1) to learn more about how to control LTTng tracing sessions\&.

.sp

Function tracing with LTTng\-UST comes in two flavors, each one providing a different trade\-off between performance and robustness:

.PP

\fBliblttng-ust-cyg-profile-fast.so\fR

.RS 4

This is a lightweight variant that should only be used where it can be

\fIguaranteed\fR

that the complete event stream is recorded without any missing events\&. Any kind of duplicate information is left out\&.

.sp

At each function entry, the address of the called function is recorded in an LTTng\-UST event\&. Function exits are recorded as another, empty LTTng\-UST event\&.

.sp

See the

\fIFast function tracing\fR

section below for the complete list of emitted events and their fields\&.

.RE

.PP

\fBliblttng-ust-cyg-profile.so\fR

.RS 4

This is a more robust variant which also works for use cases where events might get discarded, or not recorded from application startup\&. In these cases, the trace analyzer needs extra information to be able to reconstruct the program flow\&.

.sp

At each function entry

\fIand\fR

exit, the address of the called function

\fIand\fR

the call site address are recorded in an LTTng\-UST event\&.

.sp

See the

\fIVerbose function tracing\fR

section below for the complete list of emitted events and their fields\&.

.RE

.SS "Usage"

.sp

To use LTTng\-UST function tracing, you need to make sure the sources of your application are compiled with the \fB-finstrument-functions\fR compiler option\&.

.sp

It might be necessary to limit the number of source files where this option is used to prevent excessive amount of trace data to be generated at run time\&. Usually, there are additional compiler flags that allow you to specify a more fine\-grained selection of function instrumentation\&.

.sp

For each instrumented function, the executable will contain calls to profiling function hooks (after function entry, named \fB__cyg_profile_func_enter()\fR, and just before function exit, named \fB__cyg_profile_func_exit()\fR)\&.

.sp

By preloading (using the \fBLD_PRELOAD\fR environment variable) one of the provided shared libraries, these profiling hooks get defined to emit LTTng events (as described below)\&.

.if n \{\

.sp

.\}

.RS 4

.it 1 an-trap

.nr an-no-space-flag 1

.nr an-break-flag 1

.br

.ps +1

\fBNote\fR

.ps -1

.br

.sp

Using this feature can result in a \fBmassive amount\fR of trace data to be generated by the instrumented application\&. Application run time is also considerably affected\&. Be careful on systems with limited resources\&.

.sp .5v

.RE

.SS "Fast function tracing"

.sp

The following LTTng\-UST events are available when using \fBliblttng-ust-cyg-profile-fast.so\fR\&. Their log level is set to \fBTRACE_DEBUG_FUNCTION\fR\&.

.PP

\fBlttng_ust_cyg_profile_fast:func_entry\fR

.RS 4

Emitted when an application function is entered, or more specifically, when

\fB__cyg_profile_func_enter()\fR

is called\&.

.sp

Fields:

.TS

allbox tab(:);

ltB ltB.

T{

Field name

T}:T{

Description

T}

.T&

lt lt.

T{

\fBfunc_addr\fR

T}:T{

Function address

T}

.TE

.sp 1

.RE

.PP

\fBlttng_ust_cyg_profile_fast:func_exit\fR

.RS 4

Emitted when an application function returns, or more specifically, when

\fB__cyg_profile_func_exit()\fR

is called\&.

.sp

This event has no fields\&. Since the

\fBliblttng-ust-cyg-profile-fast.so\fR

library should only be used when it can be guaranteed that the complete event stream is recorded without any missing events, a per\-thread, stack\-based approach can be used on the trace analyzer side to match function entry and return events\&.

.RE

.SS "Verbose function tracing"

.sp

The following LTTng\-UST events are available when using \fBliblttng-ust-cyg-profile.so\fR\&. Their log level is set to \fBTRACE_DEBUG_FUNCTION\fR\&.

.PP

\fBlttng_ust_cyg_profile:func_entry\fR

.RS 4

Emitted when an application function is entered, or more specifically, when

\fB__cyg_profile_func_enter()\fR

is called\&.

.sp

Fields:

.TS

allbox tab(:);

ltB ltB.

T{

Field name

T}:T{

Description

T}

.T&

lt lt

lt lt.

T{

\fBfunc_addr\fR

T}:T{

Function address

T}

T{

\fBcall_site\fR

T}:T{

Address from which this function was called

T}

.TE

.sp 1

.RE

.PP

\fBlttng_ust_cyg_profile:func_exit\fR

.RS 4

Emitted when an application function returns, or more specifically, when

\fB__cyg_profile_func_exit()\fR

is called\&.

.sp

Fields:

.TS

allbox tab(:);

ltB ltB.

T{

Field name

T}:T{

Description

T}

.T&

lt lt

lt lt.

T{

\fBfunc_addr\fR

T}:T{

Function address

T}

T{

\fBcall_site\fR

T}:T{

Address from which this function was called

T}

.TE

.sp 1

.RE

.SH "BUGS"

.sp

If you encounter any issue or usability problem, please report it on the LTTng bug tracker <https://bugs.lttng.org/projects/lttng-ust>\&.

.SH "RESOURCES"

.sp

.RS 4

.ie n \{\

\h'-04'\(bu\h'+03'\c

.\}

.el \{\

.sp -1

.IP \(bu 2.3

.\}

LTTng project website <http://lttng.org>

.RE

.sp

.RS 4

.ie n \{\

\h'-04'\(bu\h'+03'\c

.\}

.el \{\

.sp -1

.IP \(bu 2.3

.\}

LTTng documentation <http://lttng.org/docs>

.RE

.sp

.RS 4

.ie n \{\

\h'-04'\(bu\h'+03'\c

.\}

.el \{\

.sp -1

.IP \(bu 2.3

.\}

Git repositories <http://git.lttng.org>

.RE

.sp

.RS 4

.ie n \{\

\h'-04'\(bu\h'+03'\c

.\}

.el \{\

.sp -1

.IP \(bu 2.3

.\}

GitHub organization <http://github.com/lttng>

.RE

.sp

.RS 4

.ie n \{\

\h'-04'\(bu\h'+03'\c

.\}

.el \{\

.sp -1

.IP \(bu 2.3

.\}

Continuous integration <http://ci.lttng.org/>

.RE

.sp

.RS 4

.ie n \{\

\h'-04'\(bu\h'+03'\c

.\}

.el \{\

.sp -1

.IP \(bu 2.3

.\}

Mailing list <http://lists.lttng.org>

for support and development:

\fBlttng-dev@lists.lttng.org\fR

.RE

.sp

.RS 4

.ie n \{\

\h'-04'\(bu\h'+03'\c

.\}

.el \{\

.sp -1

.IP \(bu 2.3

.\}

IRC channel <irc://irc.oftc.net/lttng>:

\fB#lttng\fR

on

\fBirc.oftc.net\fR

.RE

.SH "COPYRIGHTS"

.sp

This library is part of the LTTng\-UST project\&.

.sp

This library is distributed under the GNU Lesser General Public License, version 2\&.1 <http://www.gnu.org/licenses/old-licenses/lgpl-2.1.en.html>\&. See the \fBCOPYING\fR <https://github.com/lttng/lttng-ust/blob/master/COPYING> file for more details\&.

.SH "THANKS"

.sp

Thanks to Ericsson for funding this work, providing real\-life use cases, and testing\&.

.sp

Special thanks to Michel Dagenais and the DORSAL laboratory <http://www.dorsal.polymtl.ca/> at \('Ecole Polytechnique de Montr\('eal for the LTTng journey\&.

.SH "AUTHORS"

.sp

LTTng\-UST was originally written by Mathieu Desnoyers, with additional contributions from various other people\&. It is currently maintained by Mathieu Desnoyers <mailto:mathieu.desnoyers@efficios.com>\&.

.SH "SEE ALSO"

.sp

\fBlttng-ust\fR(3), \fBlttng\fR(1), \fBgcc\fR(1), \fBld.so\fR(8)