linux-kernel - Re: [PATCH] Kprobes: Print details of kretprobe on assertion failure

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Date:	Mon, 2 Apr 2007 14:17:32 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	ananth@...ibm.com
Cc:	lkml <linux-kernel@...r.kernel.org>,
	Prasanna S Panchamukhi <prasanna@...ibm.com>,
	Jim Keniston <jkenisto@...ibm.com>,
	Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
	Maneesh Soni <maneesh@...ibm.com>
Subject: Re: [PATCH] Kprobes: Print details of kretprobe on assertion
 failure

On Mon, 2 Apr 2007 14:56:36 +0530
Ananth N Mavinakayanahalli <ananth@...ibm.com> wrote:

> From: Ananth N Mavinakayanahalli <ananth@...ibm.com>
> 
> In certain cases like when the real return address can't be found or
> when the number of tracked calls to a kretprobed function is less than
> the number of returns, we may not be able to find the correct return
> address after processing a kretprobe. Currently we just do a BUG_ON, but
> no information is provided about the actual failing kretprobe.
> 
> Print out details of the kretprobe before calling BUG().
> 
> Signed-off-by: Ananth N Mavinakayanahalli <ananth@...ibm.com>
> 
> ---
>  arch/i386/kernel/kprobes.c    |    6 +++++-
>  arch/ia64/kernel/kprobes.c    |    7 ++++++-
>  arch/powerpc/kernel/kprobes.c |    7 ++++++-
>  arch/x86_64/kernel/kprobes.c  |    7 ++++++-
>  4 files changed, 23 insertions(+), 4 deletions(-)
> 
> Index: linux-2.6.21-rc5/arch/i386/kernel/kprobes.c
> ===================================================================
> --- linux-2.6.21-rc5.orig/arch/i386/kernel/kprobes.c
> +++ linux-2.6.21-rc5/arch/i386/kernel/kprobes.c
> @@ -440,7 +440,11 @@ fastcall void *__kprobes trampoline_hand
>  			break;
>  	}
>  
> -	BUG_ON(!orig_ret_address || (orig_ret_address == trampoline_address));
> +	if (!orig_ret_address || (orig_ret_address == trampoline_address)) {
> +		printk("kretprobe BUG!: Processing kretprobe %p @ %p\n",
> +				ri->rp, ri->rp->kp.addr);
> +		BUG();
> +	}
>  
>  	spin_unlock_irqrestore(&kretprobe_lock, flags);
>  
> Index: linux-2.6.21-rc5/arch/ia64/kernel/kprobes.c
> ===================================================================
> --- linux-2.6.21-rc5.orig/arch/ia64/kernel/kprobes.c
> +++ linux-2.6.21-rc5/arch/ia64/kernel/kprobes.c
> @@ -444,7 +444,12 @@ int __kprobes trampoline_probe_handler(s
>  			break;
>  	}
>  
> -	BUG_ON(!orig_ret_address || (orig_ret_address == trampoline_address));
> +	if (!orig_ret_address || (orig_ret_address == trampoline_address)) {
> +		printk("kretprobe BUG!: Processing kretprobe %p @ %p\n",
> +				ri->rp, ri->rp->kp.addr);
> +		BUG();
> +	}
> +
>  	regs->cr_iip = orig_ret_address;
>  
>  	reset_current_kprobe();
> Index: linux-2.6.21-rc5/arch/powerpc/kernel/kprobes.c
> ===================================================================
> --- linux-2.6.21-rc5.orig/arch/powerpc/kernel/kprobes.c
> +++ linux-2.6.21-rc5/arch/powerpc/kernel/kprobes.c
> @@ -293,7 +293,12 @@ int __kprobes trampoline_probe_handler(s
>  			break;
>  	}
>  
> -	BUG_ON(!orig_ret_address || (orig_ret_address == trampoline_address));
> +	if (!orig_ret_address || (orig_ret_address == trampoline_address)) {
> +		printk("kretprobe BUG!: Processing kretprobe %p @ %p\n",
> +				ri->rp, ri->rp->kp.addr);
> +		BUG();
> +	}
> +
>  	regs->nip = orig_ret_address;
>  
>  	reset_current_kprobe();
> Index: linux-2.6.21-rc5/arch/x86_64/kernel/kprobes.c
> ===================================================================
> --- linux-2.6.21-rc5.orig/arch/x86_64/kernel/kprobes.c
> +++ linux-2.6.21-rc5/arch/x86_64/kernel/kprobes.c
> @@ -438,7 +438,12 @@ int __kprobes trampoline_probe_handler(s
>  			break;
>  	}
>  
> -	BUG_ON(!orig_ret_address || (orig_ret_address == trampoline_address));
> +	if (!orig_ret_address || (orig_ret_address == trampoline_address)) {
> +		printk("kretprobe BUG!: Processing kretprobe %p @ %p\n",
> +				ri->rp, ri->rp->kp.addr);
> +		BUG();
> +	}
> +
>  	regs->rip = orig_ret_address;
>  

A lot of copying-and-pasting there.  Would it be better if this assertion
was performed in a library function in kernel/kprobes.c?


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