linux-kernel - Re: [RFC PATCH v2 1/6] fprobe: Use fprobe

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Message-ID: <20230811131001.7b22a17d@gandalf.local.home>
Date:   Fri, 11 Aug 2023 13:10:01 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
Cc:     Florent Revest <revest@...omium.org>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        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: [RFC PATCH v2 1/6] fprobe: Use fprobe_regs in fprobe entry
 handler

On Thu, 10 Aug 2023 07:13:30 +0900
Masami Hiramatsu (Google) <mhiramat@...nel.org> wrote:

> > 
> > I hope that makes my thoughts clearer? It's a hairy topic ahah  
> 
> Ah, I see your point.
> 
> static void fprobe_init(struct fprobe *fp)
> {
>         fp->nmissed = 0;
>         if (fprobe_shared_with_kprobes(fp))
>                 fp->ops.func = fprobe_kprobe_handler;
>         else
>                 fp->ops.func = fprobe_handler;
>         fp->ops.flags |= FTRACE_OPS_FL_SAVE_REGS; <---- This flag!
> }
> 
> So it should be FTRACE_OPS_FL_ARGS. Let me fix that.

Yes, this was the concern that I was bringing up, where I did not see an
advantage of fprobes over kprobes using ftrace, because they both were
saving all registers.

-- Steve