linux-kernel - Re: [RFC][PATCH 0/2] ftrace: Add access to function arguments for all callbacks

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Message-ID: <20201028191616.0268d32a@oasis.local.home>
Date:   Wed, 28 Oct 2020 19:16:16 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     linux-kernel@...r.kernel.org,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jiri Olsa <jolsa@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>
Subject: Re: [RFC][PATCH 0/2] ftrace: Add access to function arguments for
 all callbacks

On Wed, 28 Oct 2020 16:03:05 -0700
Alexei Starovoitov <alexei.starovoitov@...il.com> wrote:

> I don't understand what you're trying to say.
> Are we still discussing your patch or something else?
> If your patch then, I said, I'm not against it. I just don't see
> a value in it. Since you're agree that regs_get_kernel_argument()
> is misleading then what's the point of the patch?

I agree that it can be meaningless, but it can also be useful for
debugging purposes. It works just fine on x86_32 (even when you access
4 or more arguments). One just needs to understand the arch (as a long
long will be broken up across "two" arguments). But even that is really
useful for finding out what's going on.

> To make mini-SAVE_REGS version? For what kind of use case?

If the types of the arguments are known, and you have a mini-SAVE_REGS,
can't you still get the true arguments?

-- Steve