linux-kernel - Re: printk format "%4.4s"

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Date:	Mon, 17 Sep 2007 10:16:42 +0200
From:	Benny Halevy <bhalevy@...asas.com>
To:	shinkoi2005a <shinkoi2005a@...il.com>
CC:	linux-kernel@...r.kernel.org
Subject: Re: printk format "%4.4s"

On Sep 17, 2007, 2:57 +0200, shinkoi2005a <shinkoi2005a@...il.com> wrote:
> Hi, all
> 
> I have a question about printk format.
> 
> Can printk format use "%4.4s"?

Yes it can.
The precision part of the format determines the max number
of characters to copy from the string.
The 4 byte signature array might not null terminated
so you must use the .4 in the format otherwise vsnprintf
might look over the buffer for the terminating '\0'.

> This format is used following source.
> 
> #############
> drivers/acpi/tables/tbinstal.c
>                 ACPI_ERROR((AE_INFO,
>                             "Table has invalid signature [%4.4s], must be SSDT, PSDT or OEMx",
>                             table_desc->pointer->signature));
> 
> ##############
> At least, my dmesg is buggy output like that..

Hmm, looks like you should believe the error messages
rather than blaming the code for buggy output ;-)

Like it says, the table seems corrupt, has invalid signature
and checksum.

> 
> ##############
> $ dmesg
> (snip)
> ACPI Warning (tbutils-0158): Incorrect checksum in table [  ^E礑 -  00, should b
> e F6 [20070126]
> ACPI Error (tbinstal-0134): Table has invalid signature [  ^E礑, must be SSDT, P
> SDT or OEMx [20070126]
> (snip)
> ##############
> 
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