package/linux-tools: perf: build with libtraceevent support when it is selected

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). Should the libtraceevent then be explicitely enabled by the
user, rather than automatically enabling it when libtraceevent package
is selected ?
---
 package/linux-tools/linux-tool-perf.mk.in | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)


---
base-commit: f28f34e200bbadf0aea32110c72f7199e65fb0b9
change-id: 20250625-perf_libtraceevent-17e46ee28f90

Best regards,

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

Hi Luca,

>> 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

Yes, you are right, my mistake.

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

Indeed. The original author on kernel side did not bring any Fixes tag so
it may have slipped through the stable kernels, but I can try to submit it
for current stable/LTS kernels.

>> 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.

Mentioning the kernel version fixing the issue in the KConfig help sounds
relevant, but maybe having the exact kernel commit only in the BR commit
description is enough ? If so, I can prepare a v2 with the updated Kconfig.

Thanks

Alexis