linux-kernel - Re: [PATCH v4 0/9] bpf: fprobe: rethook: Use ftrace_regs instead of pt

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Date:   Fri, 25 Aug 2023 18:11:49 +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 v4 0/9] bpf: fprobe: rethook: Use ftrace_regs instead of pt_regs

On Wed, Aug 23, 2023 at 5:15 PM Masami Hiramatsu (Google)
<mhiramat@...nel.org> wrote:
>
> Hi,
>
> Here is the 4th version of the series to use ftrace_regs instead of pt_regs
> in fprobe.
> The previous version is here;
>
> https://lore.kernel.org/all/169181859570.505132.10136520092011157898.stgit@devnote2/
>
> This version fixes the issues pointed in the previous series; fix document
> description, keep CONFIG_FPROBE dependency for multi-kprobe, add
> static_assert check for ftrace_regs size, reorder the ftrace_partial_regs()
> patch for perf fprobe event support, introduce per-cpu pt_regs stack for
> perf fprobe event and add Florent's Ack (Thanks!). Also this adds a new
> documentation patch to clarify that the $argN and $retval is best effort.
>
>  - Document fix for the current fprobe callback prototype
>  - Simply replace pt_regs in fprobe_entry_handler with ftrace_regs.
>  - Expose ftrace_regs even if CONFIG_FUNCTION_TRACER=n.
>  - Introduce ftrace_partial_regs(). (This changes ARM64 which needs a custom
>    implementation)
>  - Replace pt_regs in rethook and fprobe_exit_handler with ftrace_regs. This
>    introduce a new HAVE_PT_REGS_TO_FTRACE_REGS_CAST which means ftrace_regs is
>    just a wrapper of pt_regs (except for arm64, other architectures do this)
>  - Update fprobe-events to use ftrace_regs natively.
>  - Update bpf multi-kprobe handler use ftrace_partial_regs().
>  - Update document for new fprobe callbacks.
>  - Add notes for the $argN and $retval.
>
> This series can be applied against the probes/core branch on linux-trace tree.
>
> This series can also be found below branch.
>
> https://git.kernel.org/pub/scm/linux/kernel/git/mhiramat/linux.git/log/?h=topic/fprobe-ftrace-regs
>
> Thank you,

FWIW, I verified that I could implement BPF multi_kprobe on arm64 on
top of this series so the BPF multi_kprobe usecase is tested but I
haven't tested the "trace_fprobe" or perf use cases.