linux-kernel - Re: [PATCHv2 7/8] arm64: implement ftrace with regs

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Message-ID: <20191104135155.GG45140@lakrids.cambridge.arm.com>
Date:   Mon, 4 Nov 2019 13:51:56 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Amit Daniel Kachhap <amit.kachhap@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        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, rostedt@...dmis.org, svens@...ckframe.org,
        takahiro.akashi@...aro.org, will@...nel.org,
        Torsten Duwe <duwe@....de>
Subject: Re: [PATCHv2 7/8] arm64: implement ftrace with regs

On Sat, Nov 02, 2019 at 05:51:46PM +0530, Amit Daniel Kachhap wrote:
> On 10/29/19 10:28 PM, Mark Rutland wrote:
> > +/*
> > + * Due to -fpatchable-function-entry=2, the compiler has placed two NOPs before
> > + * the regular function prologue. For an enabled callsite, ftrace_init_nop() and
> > + * ftrace_make_call() have patched those NOPs to:
> > + *
> > + * 	MOV	X9, LR
> > + * 	BL	<entry>
> > + *
> > + * ... where <entry> is either ftrace_caller or ftrace_regs_caller.
> > + *
> > + * Each instrumented function follows the AAPCS, so here x0-x8 and x19-x30 are
> > + * live, and x9-x18 are safe to clobber.
> > + *
> > + * We save the callsite's context into a pt_regs before invoking and ftrace

> s/invoking and ftrace callbacks/invoking the ftrace callbacks

Whoops, that was meant to be 'any'. I've fixed that up locally.

Thanks,
Mark.