linux-kernel - Re: [PATCHv2 1/8] ftrace: add ftrace_init

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Message-ID: <20191104133836.GF45140@lakrids.cambridge.arm.com>
Date:   Mon, 4 Nov 2019 13:38:36 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        amit.kachhap@....com, catalin.marinas@....com, deller@....de,
        duwe@...e.de, James.Bottomley@...senPartnership.com,
        james.morse@....com, jeyu@...nel.org, jpoimboe@...hat.com,
        jthierry@...hat.com, linux-parisc@...r.kernel.org,
        mingo@...hat.com, peterz@...radead.org, svens@...ckframe.org,
        takahiro.akashi@...aro.org, will@...nel.org
Subject: Re: [PATCHv2 1/8] ftrace: add ftrace_init_nop()

On Mon, Nov 04, 2019 at 08:16:20AM -0500, Steven Rostedt wrote:
> On Tue, 29 Oct 2019 16:58:25 +0000
> Mark Rutland <mark.rutland@....com> wrote:
> 
> > Architectures may need to perform special initialization of ftrace
> > callsites, and today they do so by special-casing ftrace_make_nop() when
> > the expected branch address is MCOUNT_ADDR. In some cases (e.g. for
> > patchable-function-entry), we don't have an mcount-like symbol and don't
> > want a synthetic MCOUNT_ADDR, but we may need to perform some
> > initialization of callsites.
> > 
> > To make it possible to separate initialization from runtime
> > modification, and to handle cases without an mcount-like symbol, this
> > patch adds an optional ftrace_init_nop() function that architectures can
> > implement, which does not pass a branch address.
> > 
> > Where an architecture does not provide ftrace_init_nop(), we will fall
> > back to the existing behaviour of calling ftrace_make_nop() with
> > MCOUNT_ADDR.
> > 
> > At the same time, ftrace_code_disable() is renamed to
> > ftrace_nop_initialize() to make it clearer that it is intended to
> > intialize a callsite into a disabled state, and is not for disabling a
> > callsite that has been runtime enabled. The kerneldoc description of rec
> > arguments is updated to cover non-mcount callsites.
> > 
> > Signed-off-by: Mark Rutland <mark.rutland@....com>
> > Reviewed-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
> > Cc: Ingo Molnar <mingo@...hat.com>
> > Cc: Steven Rostedt <rostedt@...dmis.org>
> 
> Reviewed-by: Steven Rostedt (VMware) <rostedt@...dmis.org>

Thanks!

Just to check, are you happy if this were to go via the arm64 tree with
the rest of the patches?

Mark.