linux-kernel - Re: [PATCH v4 1/3] arm64: implement ftrace with regs

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Message-ID: <20181031185800.6aa17c91@blackhole>
Date:   Wed, 31 Oct 2018 18:58:00 +0100
From:   Torsten Duwe <duwe@....de>
To:     Mark Rutland <mark.rutland@....com>
Cc:     Jiri Kosina <jikos@...nel.org>, Will Deacon <will.deacon@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Julien Thierry <julien.thierry@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        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>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        live-patching@...r.kernel.org, kristina.martsenko@....com
Subject: Re: [PATCH v4 1/3] arm64: implement ftrace with regs

On Wed, 31 Oct 2018 14:18:19 +0000
Mark Rutland <mark.rutland@....com> wrote:

> On Wed, Oct 31, 2018 at 02:19:07PM +0100, Jiri Kosina wrote:

> > Other architectures do rely on that. That's exactly for example why
> > on x86 we use '-pg -mfentry', to make sure we hook the function
> > *before* prologue.  
> 
> Ah, I'd missed -mfentry for x86. I now see that's also the case with
> __gnu_mcount_nc on arch/arm, so that covers my confusion.

Yes, fentry used to be the prerequisite, but it's everything but
portable. PPC64 already had the profile-kernel switch, which was
becoming just usable as we got at live patching.

I'm hoping that the patchable-function-entry will become the future
de-facto standard.

	Torsten