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From:   Florent Revest <revest@chromium.org>
Date:   Wed, 9 Aug 2023 12:31:00 +0200
Message-ID: <CABRcYm+8-zYRGjKSPtWQ8_Vq2649=vi71fGvFx2aWM1tnOMYQQ@mail.gmail.com>
Subject: Re: [RFC PATCH v2 4/6] tracing/fprobe: Enable fprobe events with CONFIG_DYNAMIC_FTRACE_WITH_ARGS
To:     "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Cc:     Alexei Starovoitov <alexei.starovoitov@gmail.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        linux-trace-kernel@vger.kernel.org,
        LKML <linux-kernel@vger.kernel.org>,
        Martin KaFai Lau <martin.lau@linux.dev>,
        bpf <bpf@vger.kernel.org>, Sven Schnelle <svens@linux.ibm.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Jiri Olsa <jolsa@kernel.org>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Alan Maguire <alan.maguire@oracle.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>
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On Mon, Aug 7, 2023 at 8:49=E2=80=AFAM Masami Hiramatsu (Google)
<mhiramat@kernel.org> wrote:
>
> From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
>
> Allow fprobe events to be enabled with CONFIG_DYNAMIC_FTRACE_WITH_ARGS.
> With this change, fprobe events mostly use ftrace_regs instead of pt_regs=
.
> Note that if the arch doesn't enable HAVE_PT_REGS_COMPAT_FTRACE_REGS,
> fprobe events will not be able to use from perf.

nit: "to be used from perf" ?

> --- a/kernel/trace/trace_fprobe.c
> +++ b/kernel/trace/trace_fprobe.c
> @@ -132,25 +132,30 @@ static int
>  process_fetch_insn(struct fetch_insn *code, void *rec, void *dest,
>                    void *base)
>  {
> -       struct pt_regs *regs =3D rec;
> -       unsigned long val;
> +       struct ftrace_regs *fregs =3D rec;
> +       unsigned long val, *stackp;
>         int ret;
>
>  retry:
>         /* 1st stage: get value from context */
>         switch (code->op) {
>         case FETCH_OP_STACK:
> -               val =3D regs_get_kernel_stack_nth(regs, code->param);
> +               stackp =3D (unsigned long *)ftrace_regs_get_stack_pointer=
(fregs);
> +               if (((unsigned long)(stackp + code->param) & ~(THREAD_SIZ=
E - 1)) =3D=3D
> +                   ((unsigned long)stackp & ~(THREAD_SIZE - 1)))

Maybe it'd be worth extracting a local
"ftrace_regs_get_kernel_stack_nth_addr" helper function and/or
"ftrace_regs_within_kernel_stack" ?