linux-kernel - Re: [PATCH] lib/vsprintf.c: increase the size of the field

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Date:	Wed, 09 Sep 2015 09:33:52 -0700
From:	Joe Perches <joe@...ches.com>
To:	Maurizio Lombardi <mlombard@...hat.com>
Cc:	akpm@...ux-foundation.org, linux@...musvillemoes.dk, tj@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] lib/vsprintf.c: increase the size of the field_width
 variable

On Wed, 2015-09-09 at 12:13 +0200, Maurizio Lombardi wrote:
> When printing a bitmap using the "%*pb[l]" printk format
> a 16 bit variable (field_width) is used to store the size of the bitmap.
> In some cases 16 bits are not sufficient, the variable overflows and
> printk does not work as expected.

If more than 16 bits are necessary, it couldn't work
as a single printk is limited to 1024 bytes.

> 3. Bitmap should be set, but still empty
> # cat /sys/bus/pseudo/drivers/scsi_debug/map
[]
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
[]
> @@ -384,8 +384,8 @@ struct printf_spec {
>  	u8	flags;		/* flags to number() */
>  	u8	base;		/* number base, 8, 10 or 16 only */
>  	u8	qualifier;	/* number qualifier, one of 'hHlLtzZ' */
> -	s16	field_width;	/* width of output field */
>  	s16	precision;	/* # of digits/chars */
> +	s32	field_width;	/* width of output field */
>  };
>  
>  static noinline_for_stack

And this makes the sizeof struct printf_spec more than
8 bytes which isn't desireable on x86-32.

%*pb is meant for smallish bitmaps, not big ones.


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