[lttng-dev] LTTng 32 bits on 64 bits systems - kernel events... but no user-event

MONTET Julien julien.montet at reseau.eseo.fr
Fri Jun 4 09:09:53 EDT 2021

Hi LTTng team,

I am currently trying to add lttng 32bits on a 64bits system with a custom kernel 4.19.177+ x86_64 (Debian 10.9)
My former attempt only with only a 100% arm32 bits was successful (raspberry).
I am facing now a strange issue : I can record kernel event but not userspace event... but I can see these user-event (see below)!
(tuto : https://lttng.org/docs/#doc-instrumenting-32-bit-app-on-64-bit-system)

I followed two times the tutorial : on lttng 2.12 and lttng 2.10.
I am on lttng (LTTng Trace Control) 2.10.11 - KeKriek now
All installation seemed to install without any error.
The only thing I added is at the very end where I did a : ln -s /usr/local/bin/lttng /usr/bin/lttng (to directly call commands like "lttng start")

Here some interesting outputs, I am using this projet as an example : https://lttng.org/docs/#doc-tracing-your-own-user-application
lttng list -u : OK Ubuntu Pastebin<https://paste.ubuntu.com/p/hZptnNzySw/>
LTTNG_UST_DEBUG=1 ./hello : seems OK : Ubuntu Pastebin<https://paste.ubuntu.com/p/w6xHrJsWJ9/>
kernel-event output : Ubuntu Pastebin<https://paste.ubuntu.com/p/5KfyS8wVdb/>
user-event ouput : none - the output folder stated with lttng create my-user-session --output=/tmp/my-user-session doesn't even appear
apt-file search lttng : Ubuntu Pastebin<https://paste.ubuntu.com/p/xMcCc7bqwk/>
lsmod | grep lttng : Ubuntu Pastebin<https://paste.ubuntu.com/p/7YNkNsh9Fr/>

Note : file /usr/local/bin/lttng (the exe I am using) gives :
/usr/local/bin/lttng: ELF 64-bit LSB pie executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, for GNU/Linux 3.2.0, BuildID[sha1]=542a108c40e386c17027c2c8f8fcb30e278b7748, with debug_info, not stripped

I am wondering if the installation didn't pick a 64bits RCU and analyses programms only on this.
However, I have currently absolutely no idea how to debug this.

Could you advise me some methods ?

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