linux-kernel - Re: [PATCHv3] arm: ftrace: Adds support for CONFIG_DYNAMIC_FTRACE_WITH

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Message-ID: <20170209154913.GG27312@n2100.armlinux.org.uk>
Date:   Thu, 9 Feb 2017 15:49:13 +0000
From:   Russell King - ARM Linux <linux@...linux.org.uk>
To:     Jean-Jacques Hiblot <jjhiblot@...phandler.com>
Cc:     Abel Vesa <abelvesa@...ux.com>,
        Steven Rostedt <rostedt@...dmis.org>, mingo@...hat.com,
        viro@...iv.linux.org.uk,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Petr Mladek <pmladek@...e.com>, robin.murphy@....com,
        zhouchengming1@...wei.com
Subject: Re: [PATCHv3] arm: ftrace: Adds support for
 CONFIG_DYNAMIC_FTRACE_WITH_REGS

On Thu, Feb 09, 2017 at 04:38:32PM +0100, Jean-Jacques Hiblot wrote:
> 2017-02-07 23:57 GMT+01:00 Abel Vesa <abelvesa@...ux.com>:
> > +#ifdef CONFIG_FUNCTION_GRAPH_TRACER
> > +.macro __ftrace_graph_regs_caller
> > +
> > +       sub     r0, fp, #4              @ lr of instrumented routine (parent)
> > +
> > +       @ called from __ftrace_regs_caller
> > +       ldr     r1, [sp, #56]           @ instrumented routine (func)
> > +       mcount_adjust_addr      r1, r1
> > +
> > +       sub     r2, r0, #4              @ frame pointer
> why not mov r2, fp  ?

	r0 = fp - 4
	r2 = r0 - 4

therefore

	r2 = (fp - 4) - 4
	r2 = fp - 8, not r2 = fp

-- 
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