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

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Message-ID: <4A014BA9.9020201@cn.fujitsu.com>
Date:	Wed, 06 May 2009 16:34:49 +0800
From:	Li Zefan <lizf@...fujitsu.com>
To:	Vegard Nossum <vegard.nossum@...il.com>
CC:	Lai Jiangshan <laijs@...fujitsu.com>, Ingo Molnar <mingo@...e.hu>,
	Yinghai Lu <yinghai@...nel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Zhaolei <zhaolei@...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.

Lai Jiangshan wrote:
> 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.
>>

No, we break out of the while loop when we can't find a flag,
So we are at '*' after we found '0'.

>> 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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