linux-kernel - Re: [PATCH v3 0/8] bpf: fprobe: rethook: Use ftrace_regs instead of pt

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Message-ID: <CABRcYmJLbb0_fs2beiNA2QE468JkxB9nHnmQcQW4dt63pPBoFA@mail.gmail.com>
Date:   Thu, 17 Aug 2023 10:57:13 +0200
From:   Florent Revest <revest@...omium.org>
To:     "Masami Hiramatsu (Google)" <mhiramat@...nel.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 0/8] bpf: fprobe: rethook: Use ftrace_regs instead of pt_regs

On Sat, Aug 12, 2023 at 7:36 AM Masami Hiramatsu (Google)
<mhiramat@...nel.org> wrote:
>
> Hi,
>
> Here is the 3rd version of RFC series to use ftrace_regs instead of pt_regs.
> The previous version is here;
>
> https://lore.kernel.org/all/169139090386.324433.6412259486776991296.stgit@devnote2/
>
> This also includes the generic part and minimum modifications of arch
> dependent code. (e.g. not including rethook for arm64.)

I think that one aspect that's missing from the discussion (and maybe
the series) so far is plans to actually save partial registers in the
existing rethook trampolines.

For now the series makes everything called by the rethook trampolines
handle the possibility of having a sparse ftrace_regs but the rethook
trampolines still save full ftrace_regs. I think that to rip the full
benefits of this series, we should have the rethook trampolines save
the equivalent ftrace_regs as the light "args" version of the ftrace
trampoline.