linux-kernel - Re: [PATCH v3 2/8] fprobe: Use fprobe

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Message-Id: <20230818195645.6d5b71f339b71c4f217c9a8c@kernel.org>
Date:   Fri, 18 Aug 2023 19:56:45 +0900
From:   Masami Hiramatsu (Google) <mhiramat@...nel.org>
To:     Florent Revest <revest@...omium.org>
Cc:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-trace-kernel@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        bpf <bpf@...r.kernel.org>, Sven Schnelle <svens@...ux.ibm.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Alan Maguire <alan.maguire@...cle.com>,
        Mark Rutland <mark.rutland@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v3 2/8] fprobe: Use fprobe_regs in fprobe entry handler

On Thu, 17 Aug 2023 10:57:26 +0200
Florent Revest <revest@...omium.org> wrote:

> On Sat, Aug 12, 2023 at 7:37 AM Masami Hiramatsu (Google)
> <mhiramat@...nel.org> wrote:
> > --- a/kernel/trace/bpf_trace.c
> > +++ b/kernel/trace/bpf_trace.c
> > @@ -2467,7 +2467,7 @@ static int __init bpf_event_init(void)
> >  fs_initcall(bpf_event_init);
> >  #endif /* CONFIG_MODULES */
> >
> > -#ifdef CONFIG_FPROBE
> > +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
> 
> Shouldn't this be #if defined(CONFIG_FPROBE) &&
> defined(CONFIG_DYNAMIC_FTRACE_WITH_REGS) ?

Oops, that's right!

> 
> I believe one could build a kernel with FTRACE_WITH_REGS and without
> FPROBE and then this code would have undefined references to fprobe
> functions, wouldn't it ?

Yeah, ftrace with regs doesn't mean fprobe is enabled.

> 
> And then patch 7 should be "Enable kprobe_multi feature even if
> FTRACE_WITH_REGS is disabled"

OK.

Thank you!


-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>