Re: [lttng-dev] getting lttng-modules to work on archlinux? - Milian Wolff via lttng-dev

From: Milian Wolff via lttng-dev <lttng-dev@lists.lttng.org>
To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: lttng-dev <lttng-dev@lists.lttng.org>
Subject: Re: [lttng-dev] getting lttng-modules to work on archlinux?
Date: Fri, 18 Mar 2022 16:17:37 +0100	[thread overview]
Message-ID: <2277326.HLNEk0qn7D@milian-workstation> (raw)
In-Reply-To: <881325190.163218.1647615600126.JavaMail.zimbra@efficios.com>

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On Freitag, 18. März 2022 16:00:00 CET Mathieu Desnoyers wrote:
> ----- On Mar 18, 2022, at 10:34 AM, lttng-dev lttng-dev@lists.lttng.org 
wrote:
> > Hey all,
> > 
> > in the past lttng-modules used to work on archlinux. But with a current
> > kernel, I cannot get it to work anymore. Has anyone an idea what is going
> > on here?
> > 
> > I compiled and installed lttng-modules from the latest git, which works
> > fine.
> > 
> > ```
> > 
> >    make
> >    sudo make modules_install
> >    sudo depmod -a
> > 
> > ```
> > 
> > But loading the kernel modules then fails like this:
> > 
> > ```
> > lttng-sessiond
> > Error: Unable to load required module lttng-ring-buffer-client-discard
> > Warning: No kernel tracer available
> > ```
> > 
> > In dmesg I see the following output then, and I wonder if I'm doing
> > something obviously wrong?
> > 
> > ```
> > [16245.772646] Spectre V2 : System may be vulnerable to spectre v2
> > [16245.772653] lttng_uprobes: loading module not compiled with retpoline
> > compiler.
> 
> Hi Milian,

Hey Mathieu!

> I suspect you need to use the same compiler (a compiler that supports
> retpoline Spectre v2 mitigation) to compile lttng-modules as was used to
> compile your kernel.
> 
> I suspect the kernel rejects those modules because they are compiled with a
> different compiler than your Linux kernel.

Indeed, that seems to have been it. I wasn't deliberately using a different 
compiler (normal system GCC) but something seems to have influenced it. Using 
a clean environment without any of my normal overwrites has fixed the issue 
and now it works as expected.

Thanks for making me try this once more!

Cheers
-- 
Milian Wolff | milian.wolff@kdab.com | Senior Software Engineer
KDAB (Deutschland) GmbH, a KDAB Group company
Tel: +49-30-521325470
KDAB - The Qt, C++ and OpenGL Experts

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