linux-kernel - Re: [PATCH 2/2] ftrace: support for PowerPC

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Date:	Wed, 14 May 2008 22:28:57 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	rostedt@...dmis.org
Cc:	mingo@...e.hu, linux-kernel@...r.kernel.org, pq@....fi,
	proski@....org, sandmann@...hat.com, a.p.zijlstra@...llo.nl,
	linuxppc-dev@...abs.org, paulus@...ba.org,
	benh@...nel.crashing.org, srostedt@...hat.com
Subject: Re: [PATCH 2/2] ftrace: support for PowerPC

From: Steven Rostedt <rostedt@...dmis.org>
Date: Wed, 14 May 2008 23:49:44 -0400

> +#ifdef CONFIG_FTRACE
> +#ifdef CONFIG_DYNAMIC_FTRACE
> +_GLOBAL(mcount)
> +_GLOBAL(_mcount)
> +	stwu	r1,-48(r1)
> +	stw	r3, 12(r1)
> +	stw	r4, 16(r1)
> +	stw	r5, 20(r1)
> +	stw	r6, 24(r1)
> +	mflr	r3
> +	stw	r7, 28(r1)
> +	mfcr	r5
> +	stw	r8, 32(r1)
> +	stw	r9, 36(r1)
> +	stw	r10,40(r1)
> +	stw	r3, 44(r1)
> +	stw	r5, 8(r1)

Yikes, that's really expensive.

Can't you do a tail call and let the function you end
up calling do all the callee-saved register pops onto
the stack?

That's what I did on sparc.
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