Re: [PATCH 5/7] tracing: add config option for print arguments in ftrace

[Sven Schnelle]

Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx> writes:

> On Fri, 6 Sep 2024 11:36:11 +0800
> Zheng Yejian <zhengyejian@xxxxxxxxxxxxxxx> wrote:
>
>> On 2024/9/4 14:58, Sven Schnelle wrote:
>> > Add a config option to disable/enable function argument
>> > printing support during runtime.
>> > 
>> > Signed-off-by: Sven Schnelle <svens@xxxxxxxxxxxxx>
>> > ---
>> >   kernel/trace/Kconfig | 12 ++++++++++++
>> >   1 file changed, 12 insertions(+)
>> > 
>> > diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
>> > index 721c3b221048..8b9b6cdf39ac 100644
>> > --- a/kernel/trace/Kconfig
>> > +++ b/kernel/trace/Kconfig
>> > @@ -242,6 +242,18 @@ config FUNCTION_GRAPH_RETVAL
>> >   	  enable it via the trace option funcgraph-retval.
>> >   	  See Documentation/trace/ftrace.rst
>> >   
>> > +config FUNCTION_TRACE_ARGS
>> > +	bool "Kernel Function Tracer Arguments"
>> > +	depends on HAVE_FUNCTION_ARG_ACCESS_API
>> > +	depends on DEBUG_INFO_BTF && BPF_SYSCALL
>> 
>> Nice feature!
>> 
>> Just a nit, DEBUG_INFO_BTF currently depends on BPF_SYSCALL,
>> so BPF_SYSCALL may not be necessary here. This feature
>> also doesn't seem to depend on bpf.
>
> Indeed. Sven, you can check the PROBE_EVENTS_BTF_ARGS as
> an example.
>
> config PROBE_EVENTS_BTF_ARGS
>         depends on HAVE_FUNCTION_ARG_ACCESS_API
>         depends on FPROBE_EVENTS || KPROBE_EVENTS
>         depends on DEBUG_INFO_BTF && BPF_SYSCALL
>         bool "Support BTF function arguments for probe events"

Now i'm confused - Zheng wrote that DEBUG_INFO_BTF depends on
BPF_SYSCALL. I just verified that. So i could just remove BPF_SYSCALL
from the dependencies - but your example also has BPF_SYSCALL listed.

Regards
Sven