linux-kernel - Re: [RFC PATCH -next v2 3/4] arm64/ftrace: support dynamically allocated trampolines

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Date:   Wed, 25 May 2022 09:43:07 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Mark Rutland <mark.rutland@....com>
Cc:     Masami Hiramatsu <mhiramat@...nel.org>,
        Wang ShaoBo <bobo.shaobowang@...wei.com>,
        cj.chengjian@...wei.com, huawei.libin@...wei.com,
        xiexiuqi@...wei.com, liwei391@...wei.com,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        catalin.marinas@....com, will@...nel.org, zengshun.wu@...look.com,
        Jiri Olsa <jolsa@...nel.org>
Subject: Re: [RFC PATCH -next v2 3/4] arm64/ftrace: support dynamically
 allocated trampolines

On Wed, 25 May 2022 13:17:30 +0100
Mark Rutland <mark.rutland@....com> wrote:

> For arm64 I'd like to make this static, and have ftrace *always* capture a
> minimal set of ftrace_regs, which would be:
> 
>   X0 to X8 inclusive
>   SP
>   PC
>   LR
>   FP
> 
> Since X0 to X8 + SP is all that we need for arguments and return values (per
> the calling convention we use), and PC+LR+FP gives us everything we need for
> unwinding and live patching.
> 
> I *might* want to add x18 to that when SCS is enabled, but I'm not immediately
> sure.

Does arm64 have HAVE_DYNAMIC_FTRACE_WITH_ARGS enabled? If so, then having
the normal ftrace call back save the above so that all functions have it
available would be useful.

-- Steve