linux-kernel - Re: [RFC PATCH] kprobes: arm: enable OPTPROBES for arm 32

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Message-ID: <20140806225719.GW30282@n2100.arm.linux.org.uk>
Date:	Wed, 6 Aug 2014 23:57:19 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	"Jon Medhurst (Tixy)" <tixy@...aro.org>
Cc:	Wang Nan <wangnan0@...wei.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
	davem@...emloft.net,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Will Deacon <will.deacon@....com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Li Zefan <lizefan@...wei.com>, peifeiyue@...wei.com
Subject: Re: [RFC PATCH] kprobes: arm: enable OPTPROBES for arm 32

On Wed, Aug 06, 2014 at 03:23:23PM +0100, Jon Medhurst (Tixy) wrote:
> On Tue, 2014-08-05 at 15:28 +0800, Wang Nan wrote:
> > +static inline int
> > +arm_branch_to_addr(unsigned int *pinst, void *src, void *dest)
> > +{
> > +	unsigned int inst = 0xea000000;
> > +	long offset = (unsigned long)(dest) -
> > +			((unsigned long)(src) + 8);
> > +	if ((offset > 0x3fffffc) || (offset < -0x3fffffc)) {
> > +		printk(KERN_WARNING "Failed to instrument %pS to %pS\n", src, dest);
> > +		return -EINVAL;
> > +	}
> > +
> > +	inst |= (((unsigned long)offset) >> 2) & (0x00ffffffUL);
> > +	*pinst = inst;
> > +	return 0;
> > +}
> > +
> 
> This looks remarkably similar to the code in arch/arm/kernel/insn.c so I
> think you can probably just use the existing arm_gen_branch() function.

Which would be a better idea as the version found in insn.c is not
buggy.

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