Re: [Buildroot] [PATCH] package/linux-tools: perf: build with libtraceevent support when it is selected

[Luca Ceresoli via buildroot <buildroot@buildroot.org>]

Hi Alexis,

On Wed, 25 Jun 2025 22:54:01 +0200
Alexis Lothoré <alexis.lothore@bootlin.com> wrote:

> When trying to perform a custom uprobe recording on a target with perf
> built by buildroot, the recording step fails as perf can not record
> uprobes without libtraceevent support:
> 
>   $ perf probe -x linked_list insert_name index
>   Target program is compiled without optimization. Skipping prologue.
>   Probe on address 0x808 to force probing at the function entry.
> 
>   Added new event:
>     probe_linked_list:insert_name (on insert_name in /root/gdb/linked_list with index)
> 
>   perf is not linked with libtraceevent, to use the new probe you can use tracefs:
> 
>           cd /sys/kernel/tracing/
>           echo 1 > events/probe_linked_list/insert_name/enable
>           echo 1 > tracing_on
>           cat trace_pipe
>           Before removing the probe, echo 0 > events/probe_linked_list/insert_name/enable
>   $ perf record -e probe_linked_list:insert_name ./linked_list
>   event syntax error: 'probe_linked_list:insert_name'
>                        \___ unsupported tracepoint
> 
>   libtraceevent is necessary for tracepoint support
>   Run 'perf list' for a list of valid events
> 
>    Usage: perf record [<options>] [<command>]
>       or: perf record [<options>] -- <command> [<options>]
> 
>       -e, --event <event>   event selector. use 'perf list' to list available events
> 
> libtraceevent support for perf has been disabled with commit
> b4ab45a5c1db ("package/linux-tools: disable libtracevent detection")
> because there was no libtraceevent package in buildroot to replace the
> former libtraceevent removed from the kernel sources. Since then, commit
> 1474f1b34b17 ("package/libtraceevent: new package") has introduced a
> libtraceevent package. We can then expose again the possibility to build
> perf with libtraceevent support.
> 
> Make buildroot perf makefile detect if libtraceevent package has been
> enabled, and if so, allow to build perf with libtraceevent support.
> 
> Signed-off-by: Alexis Lothoré <alexis.lothore@bootlin.com>
> ---
> To: buildroot@buildroot.org
> Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
> Cc: Luca Ceresoli <luca.ceresoli@bootlin.com>
> Cc: Olivier Benjamin <olivier.benjamin@bootlin.com>
> ---
> It is worth noting that there is a bug in perf makefile kernel that
> affects many kernel versions (up to 6.10) and that prevents perf from
> building correctly when enabling libtraceevent support (see 440cf77625e3
> ("perf: build: Setup PKG_CONFIG_LIBDIR for cross compilation") in
> linux).

Thanks for the research!

And apparently the mentioned commit was applied in 6.11 and not
backported to 6.10 and previous stable releases.

Shouldn't it be backported? This looks like a fix, doesn't it?

> Should the libtraceevent then be explicitely enabled by the
> user, rather than automatically enabling it when libtraceevent package
> is selected ?

Should the fix be backported to the currently-supported stable kernel
versions, I'd say we can automatically enable libtraceevent support.
Otherwise I'm not sure... Mentioning the issue and pointing to the fix
commit in the Kconfig help text is another option.

Luca

-- 
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com
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