linux-kernel - Re: [PATCH v4 4/9] fprobe: rethook: Use ftrace

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Message-ID: <CABRcYmLCDTMCQMViP56eT13YEW247acDqQUmXY=pf4qTS_4aUw@mail.gmail.com>
Date:   Fri, 25 Aug 2023 18:12:01 +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 4/9] fprobe: rethook: Use ftrace_regs in fprobe exit
 handler and rethook

On Wed, Aug 23, 2023 at 5:16 PM Masami Hiramatsu (Google)
<mhiramat@...nel.org> wrote:
>
> From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
>
> Change the fprobe exit handler and rethook to use ftrace_regs data structure
> instead of pt_regs. This also introduce HAVE_PT_REGS_TO_FTRACE_REGS_CAST
> which means the ftrace_regs's memory layout is equal to the pt_regs so
> that those are able to cast. Only if it is enabled, kretprobe will use
> rethook since kretprobe requires pt_regs for backward compatibility.
>
> This means the archs which currently implement rethook for kretprobes needs to
> set that flag and it must ensure struct ftrace_regs is same as pt_regs.
> If not, it must be either disabling kretprobe or implementing kretprobe
> trampoline separately from rethook trampoline.
>
> Signed-off-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>

Acked-by: Florent Revest <revest@...omium.org>