linux-kernel - Re: [PATCH v7 2/3] arm64: implement ftrace with regs

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Message-ID: <20190403083019.29f5fd9b@gandalf.local.home>
Date:   Wed, 3 Apr 2019 08:30:19 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Mark Rutland <mark.rutland@....com>
Cc:     Torsten Duwe <duwe@....de>, Will Deacon <will.deacon@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Julien Thierry <julien.thierry@....com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Arnd Bergmann <arnd@...db.de>,
        AKASHI Takahiro <takahiro.akashi@...aro.org>,
        Amit Daniel Kachhap <amit.kachhap@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        live-patching@...r.kernel.org
Subject: Re: [PATCH v7 2/3] arm64: implement ftrace with regs

On Wed, 3 Apr 2019 03:48:43 +0100
Mark Rutland <mark.rutland@....com> wrote:

> We currently have:
> 
> ftrace_make_nop(mod, rec, addr)
> ftrace_make_call(rec, addr)
> ftrace_modify_call(rec, old_addr, new_addr)
> 
> ... whereas we could have:
> 
> ftrace_call_init(mod, rec)
> ftrace_call_enable(rec, addr)
> ftrace_call_disable(rec, addr)
> ftrace_call_modify(rec, old_addr, new_addr)
> 
> ... so we wouldn't need to special-case anything for initialization (and
> don't need MCOUNT_ADDR at all), and it would be clearer as to what was
> happening at each stage.

Just a note. I would be OK if someone wants to work in changing the
ftrace interface to be this. I'll review the code, but I don't have the
cycles to implement such a change.

-- Steve