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

[Mathieu Desnoyers]

----- On Jun 4, 2021, at 9:09 AM, lttng-dev lttng-dev at lists.lttng.org wrote:

> 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
> | 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 |
> https://lttng.org/docs/#doc-tracing-your-own-user-application ]
> lttng list -u : OK [ https://paste.ubuntu.com/p/hZptnNzySw/ | Ubuntu Pastebin ]
> LTTNG_UST_DEBUG=1 ./hello : seems OK : [ https://paste.ubuntu.com/p/w6xHrJsWJ9/
> | Ubuntu Pastebin ]
> kernel-event output : [ https://paste.ubuntu.com/p/5KfyS8wVdb/ | Ubuntu Pastebin
> ]
> 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 : [ https://paste.ubuntu.com/p/xMcCc7bqwk/ | Ubuntu
> Pastebin ]
> lsmod | grep lttng : [ https://paste.ubuntu.com/p/7YNkNsh9Fr/ | Ubuntu Pastebin
> ]

> 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 ?

Did you follow this section of the documentation ? 

https://lttng.org/docs/#doc-instrumenting-32-bit-app-on-64-bit-system 

Thanks, 

Mathieu 

> Regards,

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> lttng-dev at lists.lttng.org
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-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com