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Date: Wed, 6 May 2009 10:12:21 +0200
From: Vegard Nossum <vegard.nossum@gmail.com>
To: Ingo Molnar <mingo@elte.hu>
Cc: Yinghai Lu <yinghai@kernel.org>, Frederic Weisbecker <fweisbec@gmail.com>,
       Jeremy Fitzhardinge <jeremy@goop.org>, Zhaolei <zhaolei@cn.fujitsu.com>,
       Li Zefan <lizf@cn.fujitsu.com>, Steven Rostedt <rostedt@goodmis.org>,
       Andrew Morton <akpm@linux-foundation.org>,
       "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: printk %0*X is broken.
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2009/5/6 Ingo Molnar <mingo@elte.hu>:
>
> Cc:-ed more folks who modified lib/vsprintf.c recently.
>
>        Ingo
>
> * Yinghai Lu <yinghai@kernel.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;
 	}
 
 	/* get field width */