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Date:   Mon, 6 Nov 2023 22:06:17 -0500
From:   Steven Rostedt <rostedt@goodmis.org>
To:     "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Alexei Starovoitov <alexei.starovoitov@gmail.com>,
        Florent Revest <revest@chromium.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>,
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        Mark Rutland <mark.rutland@arm.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Guo Ren <guoren@kernel.org>
Subject: Re: [RFC PATCH 24/32] x86/ftrace: Enable HAVE_FUNCTION_GRAPH_FREGS
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On Tue, 7 Nov 2023 09:42:58 +0900
Masami Hiramatsu (Google) <mhiramat@kernel.org> wrote:

> Got it. So does ftrace_regs need a placeholder for direct trampoline?
> (Or, can we use a register to pass it?)
> I think we don't need to clear it for return_to_handler() but if
> `ftrace_regs` spec requires it, it is better to do so.

It's per arch defined. I think I wrote somewhere that it just needs to pass
back something that can tell if the handler is to return to a direct
trampoline or not. It could be a unused register, or something else.

It's only needed if an architecture supports direct trampolines.

-- Steve