[lttng-dev] Ubuntu Package for LTTng-UST Compiled with Debug Logging On By Default

[Simon Marchi]

On 22 October 2015 at 19:35, Brian Robbins <brianrob at microsoft.com> wrote:
> Hello,
>
>
>
> The Linux build of CoreCLR now supports tracing using LTTng-UST.  One
> artifact that we noticed when running on Ubuntu 14.04 in our CI is that apps
> running on CoreCLR all have an LTTng warning written to stderr:
>
>
>
> libust[883/883]: Warning: HOME environment variable not set. Disabling
> LTTng-UST per-user tracing. (in setup_local_apps() at lttng-ust-comm.c:305)
>
>
>
> I’ve investigated, and it is true that in the CI, there is no HOME
> environment variable.  However, what I’m more interested in is why this
> message is written in the first place.  Looking in at the latest LTTng-UST
> code, it appears that this message should only be logged when debug logging
> is enabled.  From code inspection, it appears that debug logging can be
> enabled at either compile time (#define LTTNG_UST_DEBUG) or at runtime via
> an environment variable called LTTNG_UST_DEBUG.
>
>
>
> I have confirmed that the environment variable LTTNG_UST_DEBUG is not
> present.  I’ve also looked at the disassembly, and can confirm that the
> ust_loglevel check is not actually performed (the if statement is optimized
> away).  This makes me think that the Ubuntu package was compiled with
> LTTNG_UST_DEBUG defined.
>
>
>
> The package in question is old – LTTng-UST 2.4.  I’m wondering if either
> debug logging was always present in 2.4, or if the package was compiled with
> LTTNG_UST_DEBUG.  I would expect that most customers would want debug
> logging off by default, since it affects the output of the program.
>
>
>
> Your help in figuring this out is greatly appreciated.
>
>
>
> Thank you.
>
> -Brian


Hi Brian,

This warning used to appear regardless of the definition of LTTNG_UST_DEBUG.

Bisecting shows that it has been fixed in commit
7bdd21a41092a59207958911666cbd458f93a319, which is part of version
2.7.

Here it is: http://git.lttng.org/?p=lttng-ust.git;a=commit;h=7bdd21a41092a59207958911666cbd458f93a319

Simon