Re: [RESEND] BTF is not generated for gcc-built kernel with the latest pahole

[Jiri Olsa <olsajiri@gmail.com>]

On Wed, Jul 26, 2023 at 10:25:34AM +0900, Masami Hiramatsu wrote:
> Hello,
> (I resend this because kconfig was too big)
> 
> I found that BTF is not generated for gcc-built kernel with that latest
> pahole (v1.25).

hi,
I can't reproduce on my setup with your .config

does 'bpftool btf dump file ./vmlinux' show any error?

is there any error in the kernel build output?

> When I'm using the distro origin pahole (v1.22) it works. (I also checked
> v1.23 and v1.24, both partially generated BTF)
> 
> e.g.
> 
> # echo 'f kfree $arg*' >> /sys/kernel/tracing/dynamic_events
> sh: write error: Invalid argument
> 
> # cat /sys/kernel/tracing/error_log 
> [   21.595724] trace_fprobe: error: BTF is not available or not supported
>   Command: f kfree $arg*
>                    ^
> [   21.596032] trace_fprobe: error: Invalid $-valiable specified
>   Command: f kfree $arg*
>                    ^
> 
> / # strings /sys/kernel/btf/vmlinux | grep kfree

hm, if you have this file present, you have BTF in

> kfree_on_online
> maybe_kfree_parameter
> trace_event_raw_rcu_invoke_kfree_bulk_callback
> trace_event_data_offsets_rcu_invoke_kfree_bulk_callback
> btf_trace_rcu_invoke_kfree_bulk_callback
> early_boot_kfree_rcu
> __bpf_trace_rcu_invoke_kfree_bulk_callback
> perf_trace_rcu_invoke_kfree_bulk_callback
> trace_event_raw_event_rcu_invoke_kfree_bulk_callback
> trace_raw_output_rcu_invoke_kfree_bulk_callback
> __probestub_rcu_invoke_kfree_bulk_callback
> __traceiter_rcu_invoke_kfree_bulk_callback
> kfree_rcu_cpu_work
> kfree_rcu_cpu
> kfree_rcu_batch_init
> kfree_rcu_scheduler_running
> kfree_rcu_shrink_scan
> kfree_rcu_shrink_count
> kfree_rcu_monitor
> kfree_rcu_work
> 
> 
> Here is the gcc version which I'm using.
> 
> gcc version 11.3.0 (Ubuntu 11.3.0-1ubuntu1~22.04.1)

I tried with gcc (GCC) 13.1.1 20230614 (Red Hat 13.1.1-4)
and latest pahole (master branch)

> 
> I also attached the kernel config file.
> 
> What is the recommended combination of the tools?
> Should I use Clang to build the kernel for BTF?

should work fine with both gcc and clang

jirka

> 
> Thank you,
> 
> -- 
> Masami Hiramatsu (Google) <mhiramat@kernel.org>