linux-kernel - Re: printk %0*X is broken.

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Date:	Wed, 06 May 2009 16:27:41 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	Vegard Nossum <vegard.nossum@...il.com>
CC:	Ingo Molnar <mingo@...e.hu>, Yinghai Lu <yinghai@...nel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Zhaolei <zhaolei@...fujitsu.com>, Li Zefan <lizf@...fujitsu.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: printk %0*X is broken.

Vegard Nossum wrote:
> 2009/5/6 Ingo Molnar <mingo@...e.hu>:
>> Cc:-ed more folks who modified lib/vsprintf.c recently.
>>
>>        Ingo
>>
>> * Yinghai Lu <yinghai@...nel.org> wrote:
>>
>>> it seems someone broke
>>>
>>> printk(   "%0*X\n", width, x);
>>>
>>> looks like 0 is dumped.
> 
> After %, we look for flags. The problem is that when a flag is found, we
> don't advance in the format string. And thus we start looking for the
> precision, which is read as 0, because we are still at the 0. I think
> this patch should fix it.
> 
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> index 7536ace..ae7d4b2 100644
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -800,14 +800,15 @@ static int format_decode(const char *fmt, struct printf_spec *spec)
>  	if (fmt != start || !*fmt)
>  		return fmt - start;
>  
> +	/* this skips the first '%' */
> +	++fmt;
> +
>  	/* Process flags */
>  	spec->flags = 0;
>  
> -	while (1) { /* this also skips first '%' */
> +	while (1) {
>  		bool found = true;
>  
> -		++fmt;
> -
>  		switch (*fmt) {
>  		case '-': spec->flags |= LEFT;    break;
>  		case '+': spec->flags |= PLUS;    break;
> @@ -819,6 +820,8 @@ static int format_decode(const char *fmt, struct printf_spec *spec)
>  
>  		if (!found)
>  			break;
> +
> +		++fmt;
>  	}
>

It seems that your patch does not change anything.
The code logic is still the same as before.

Lai

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