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

From: Sven Schnelle
Date: Mon Sep 09 2024 - 04:22:57 EST


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