linux-kernel - Re: [patch] i386: add option to show more code in oops reports

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Message-Id: <20070125145504.c8c0a98a.akpm@osdl.org>
Date:	Thu, 25 Jan 2007 14:55:04 -0800
From:	Andrew Morton <akpm@...l.org>
To:	Chuck Ebbert <cebbert@...hat.com>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	Andi Kleen <ak@...e.de>
Subject: Re: [patch] i386: add option to show more code in oops reports

On Wed, 24 Jan 2007 15:22:49 -0500
Chuck Ebbert <cebbert@...hat.com> wrote:

> Sometimes we may need to see more code than the default in an oops,
> so add an option for that.

spose so, but some more justification would be nice.  As would an x86_64
version?

> Signed-off-by: Chuck Ebbert <cebbert@...hat.com>

ooh, congrats.

> --- 2.6.20-rc5-32.orig/arch/i386/kernel/traps.c
> +++ 2.6.20-rc5-32/arch/i386/kernel/traps.c
> @@ -94,6 +94,7 @@ asmlinkage void spurious_interrupt_bug(v
>  asmlinkage void machine_check(void);
>  
>  int kstack_depth_to_print = 24;
> +int code_bytes = 64;

static scope, please.  And I think it should be unsigned.

>  ATOMIC_NOTIFIER_HEAD(i386die_chain);
>  
>  int register_die_notifier(struct notifier_block *nb)
> @@ -324,7 +325,7 @@ void show_registers(struct pt_regs *regs
>  	 */
>  	if (in_kernel) {
>  		u8 *eip;
> -		int code_bytes = 64;
> +		int code_prologue = code_bytes * 43 / 64;
>  		unsigned char c;
>  
>  		printk("\n" KERN_EMERG "Stack: ");
> @@ -332,7 +333,7 @@ void show_registers(struct pt_regs *regs
>  
>  		printk(KERN_EMERG "Code: ");
>  
> -		eip = (u8 *)regs->eip - 43;
> +		eip = (u8 *)regs->eip - code_prologue;
>  		if (eip < (u8 *)PAGE_OFFSET ||
>  			probe_kernel_address(eip, c)) {
>  			/* try starting at EIP */

You missed this bit:

		if (eip < (u8 *)PAGE_OFFSET ||
			probe_kernel_address(eip, c)) {
			/* try starting at EIP */
			eip = (u8 *)regs->eip;
			code_bytes = 32;
		}

Do we really want to be modifying the global variable here?

> @@ -1191,3 +1192,15 @@ static int __init kstack_setup(char *s)
>  	return 1;
>  }
>  __setup("kstack=", kstack_setup);
> +
> +static int __init code_bytes_setup(char *s)
> +{
> +	code_bytes = simple_strtoul(s, NULL, 0);
> +	if (code_bytes < 64)
> +		code_bytes = 64;
> +	if (code_bytes > 1024)
> +		code_bytes = 1024;
> +
> +	return 1;
> +}
> +__setup("code_bytes=", code_bytes_setup);

I'm OK with the upper limit, but I'd sugegst that we remove the lower
limit: someone might _want_ to be able to set code_bytes=0, who knows?

And if code_bytes is unsigned, the single comparison with 1024 will suffice.

OTOH, why have any checks at all in there?  If the user sets
code_bytes=0xfffffff0 and things break, he gets to own both pieces...

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