linux-kernel - Re: [patch] s390 kprobe fix instruction length calculation

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Message-ID: <20070815224147.GB8741@osiris.ibm.com>
Date:	Thu, 16 Aug 2007 00:41:47 +0200
From:	Heiko Carstens <heiko.carstens@...ibm.com>
To:	David Wilder <dwilder@...ibm.com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	martin.schwidefsky@...ibm.com
Subject: Re: [patch] s390 kprobe fix instruction length calculation

On Wed, Aug 15, 2007 at 02:31:40PM -0700, David Wilder wrote:
> Placing a kprobe on "bc" instruction (s390/s390x) can cause an oops.
> The instruction length is encoded into the first two bits of the s390 
> instruction.  Kprobe is incorrectly computing the instruction length.
> The instruction length is used for determining what type of "fix-up" is 
> needed for conditional branch instruction.  The problem can bee seen by 
> placing a kprobe on a  "bc" instruction that will not branch.   The results 
> is that  Kprobe incorrectly computes the  new instruction pointer 
> (psw.addr) after single stepping the instruction.   The problem is 
> corrected with this patch.
>
>  	/* save the instruction length (pop 5-5) in bytes */
> -	switch (*(__u8 *) (ainsn->insn) >> 4) {
> +	switch (*(__u8 *) (ainsn->insn) >> 6) {
>  	case 0:

Added to the s390 patch queue. Thanks! :)
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